Displays

TS7.4

The Alpine-Himalayan orogenic belt is one of the largest and most prominent suture zones on Earth. The belt ranges from the Mediterranean in the west to Indonesia in the east. It results from the subduction and closing of different branches of the Tethyan Oceanic Realm and the subsequent collision of the African, Arabian and Indian continental plates with Eurasia. Its long-lasting geological record of complex interactions among major and smaller plates, featuring the presence of subduction zones at different evolutionary stages, has progressively grown as a comprehensive test site to investigate fundamental plate tectonics and geodynamic processes with multi-disciplinary studies. Advances in a variety of geophysical and geological fields provide a rich and growing set of constraints on the crust-lithosphere and mantle structure, as well as tectonics and geodynamic evolution of the entire mountain belt

We welcome contributions presenting new insights and observations derived from different perspectives like geology (stratigraphy, petrology, geochronology, geochemistry, tectonics and geomorphology), geophysics (seismicity, seismic imaging, seismic anisotropy, gravity), geodesy (GPS, InSAR), modelling (numerical and analogue), risk assessment (earthquake, volcanism), as well as from multi-disciplinary studies.

Keynote presentation by Boris Kaus (University of Mainz)

Public information:
The discussion during the chat sessions will follow an order based on location (from East to West), and divide the abstracts such that in the first block we will go from the Himalaya region to Turkey-Anatolia-Cyprus and the East Mediterranean Basin, and in the second block, we will cover the Mediterranean from the Western side of the Black Sea (i.e. Bulgaria) to the Westernmost Mediterranean. The preliminary order (hoping that authors upload their display) is:
14:00-15:45
1· Jatupohnkhongchai et al.
2· Bai et al.
3· Chen et al.

4· Knight et al.
5· Stoner et al.
6· Wei Li et al.

7· Barbero et al.
8 Lom et al.
9· Simmonds et al.
10· Mahleqa Rezaei et al.

11· Sağlam et al.
12· Mueller et al.
13· Gürer et al.
14· Nirrengarten et al.

BREAK (30 minutes)

16:15-18:00
1· de Leeuw et al.
2· Balkanska and Georgiev (?)

3· Faucher et al.
4· Molnár et al.
5· Stanković et al.

6· Schneider and Balen
7· Chang et al.
8· Kaus et al.
9· El-Sharkawy et al.
10· Agostini et al.

11· Gimeno et al.
12· de la Peña et al.
13· Negredo et al.
14· Jiménez-Munt et al.
15· Kumar et al.

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Co-organized by GD7/GMPV11/SM2
Convener: Ágnes KirályECSECS | Co-conveners: Derya GürerECSECS, Marc Hässig, Claudia Piromallo
Displays
| Attendance Fri, 08 May, 14:00–15:45 (CEST), Attendance Fri, 08 May, 16:15–18:00 (CEST)

Files for download

Session materials Download all presentations (216MB)

Chat time: Friday, 8 May 2020, 14:00–15:45

Chairperson: Derya Gürer, Marc Hässig, Claudia Piromallo, Ágnes Király
D1045 |
EGU2020-18224
Simone Agostini, Simon Otto, John Watson, and Roy Howgate

The tectonic evolution of the Mediterranean is well studied, but the models often cover a limited period of geological time and are not always placed in a wider context. Its evolution is linked to the surrounding African and Eurasian continents and their relative movements.

A new fully deformable tectonic model of the Mediterranean has been created as part of a proprietary plate model. This work has led to the identification of key global tectonic events influencing the development of the Mediterranean from the Early Permian to the present day. This first fully-deformable plate model of the Mediterranean enables to account for the shortening and extension that occurred in the area at a temporal resolution of 1 Ma. In most available plate models, plates are rigidly rotated back to their paleo-position, meaning they preserve their present-day size and shape. In some recent papers, the extent of deformation has been illustrated for selected time-slices, but these models cannot be considered to be ‘deformable’ because the deformation is not modelled in a continuous manner.

Following Hercynian orogenesis and until the break-up of Pangea, the Mediterranean was dominated by extensional tectonics along its southern margin, as a series small continental blocks rifted from the northern margin of Gondwana. The opening of the Central Atlantic in the Late Triassic-Early Jurassic led to displacement between Eurasia and Africa south of Iberia and the development of the Alpine Tethys, as the Atlantic initially propagated northwards to the east of Iberia. Rotation of Africa caused by the opening of the South Atlantic in the Late Jurassic-Early Cretaceous led to a ‘jump’ in spreading to the west, at the Iberia-Newfoundland margin. These larger scale plate motions overprinted the more local impacts of continued extension along the northern margin of Africa (e.g. Pindos Ocean). Opening of the North Atlantic once again changed the relative motion of Eurasia and Africa, and initiated a period of oceanic subduction and collision that culminated in the Alpine orogeny. Crucial to this story is the paleo-position of Apulia/Adria, which remained attached to Africa and was able to act as an indenter into Eurasia during the Alpine compression. Evidence for this connection will be presented and discussed.

 

 

How to cite: Agostini, S., Otto, S., Watson, J., and Howgate, R.: Tectonic evolution of the Mediterranean region from a global plate kinematics perspective: insights from a new deformable tectonic model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18224, https://doi.org/10.5194/egusphere-egu2020-18224, 2020

D1046 |
EGU2020-4929
Ivone Jiménez-Munt, Montserrat Torne, Manel Fernàndez, Jaume Vergés, Ajay Kumar, Alberto Carballo, and Daniel Garcia-Castellanos

The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present-day density and compositional structure of the lithosphere along a transect running from S Iberia to N Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African-Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self-consistent geophysical-petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere-asthenosphere boundary (LAB). We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modelled P- and S-wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics-Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains. This work has been supported by Spanish Ministry by the projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100).

How to cite: Jiménez-Munt, I., Torne, M., Fernàndez, M., Vergés, J., Kumar, A., Carballo, A., and Garcia-Castellanos, D.: Deep seated density anomalies across the Iberia-Africa plate boundary and its topographic response, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4929, https://doi.org/10.5194/egusphere-egu2020-4929, 2020

D1047 |
EGU2020-5332
Ajay Kumar, Manel Fernàndez, Jaume Vergés, Montserrat Torne, and Ivone Jimenez-Munt

We present a comparison of the present-day crust to upper-mantle structure in the Western Mediterranean along two NW-SE oriented geo-transects in the Alboran and Algerian basins. The Alboran domain geo-transect traverses the Iberian Massif, the Betics, the Alboran Basin and ends in the northern margin of Africa between the Tell and Rif mountains. The Algerian domain geo-transect traverses the Catalan Coast Ranges, the Valencia Trough, the Balearic Promontory, the Algerian basin, the Greater Kabylies and ends in the Tell-Atlas Mountains in the northern margin of Africa. We model the thermal, density (i.e. compositional) and seismic velocity structure by integrating geophysical and geochemical dataset in a self-consistent thermodynamic framework. The crustal structure is constrained by seismic experiments and geological cross-sections, whereas seismic tomography models and mantle xenoliths constrain the upper mantle structure and composition. The Algerian Basin lithosphere shows a typical oceanic lithosphere composition, whereas the Alboran Basin lithosphere is slightly fertile. The lithospheric mantle beneath the Betics and Greater Kabylies are also fertile compared to the Iberian and African lithospheres showing the involvement of the fertile sublithosphere mantle during the later stages of subduction. In the Valencia Trough, the lithosphere is fertile in comparison to the Balearic Promontory lithosphere, which is similar to Iberian lithosphere. A lithosphere-scale thickening is observed in the Betics, and the Greater Kabylies, and thinning follows towards the Alboran and Algerian back-arc basins. Detached slabs with anomalous temperature of-320 oC, with oceanic lithosphere composition beneath the Greater Kabylies, and Iberian lithosphere composition beneath the Betics, are required to fit the geoid height. Our results impose important constraints for the geodynamic evolution models of the Western Mediterranean.

This work has been supported by SUBTETIS (PIE-201830E039) project, EU Marie Curie Initial Training Network ‘SUBITOP’ (674899-SUBITOP-H2020-MSCA-ITN-2015), the Agencia Estatal de Investigación through projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100), and the Agency for Management of University and Research Grants of Catalonia (AGAUR-2017-SGR-847).

How to cite: Kumar, A., Fernàndez, M., Vergés, J., Torne, M., and Jimenez-Munt, I.: Comparison of the crust and upper mantle structure of the Alboran and Algerian domains (Western Mediterranean): Tectonic significance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5332, https://doi.org/10.5194/egusphere-egu2020-5332, 2020

D1048 |
EGU2020-9535
Laura Gómez de la Peña, César Ranero, Eulàlia Gràcia, and Guillermo Booth-Rea

The Alboran Basin is the westernmost of the Mediterranean basins. It is composed of different sub-basins and connects toward the east with the Algero-Balearic Basin. Regional studies of these basins are mainly from the ´90s, but the restricted seismic coverage and generally low quality (old acquisition and processing methods) of the seismic profiles were not enough to perform a detailed analysis of the entire sediment infill. More recent works characterize in detail a particular area, but the correlation between the different sub-basins remained beyond the scope of those works. Furthermore, these recent works are usually focused only on the Messinian and younger stratigraphy. Thus, the correlation of the sediment history across the entire region and its integration with the regional tectonic evolution has not been achieved. This results in a bunch of models, different for each sub-basin and not always coherent among them, which makes difficult the understanding of the geodynamic evolution of the region

Based on ~4500 km of new and reprocessed multichannel seismic profiles, together with well and dredge data, we are able to review the westernmost Mediterranean stratigraphy at a regional scale. We have correlated the sediment units deposited since the beginning of the formation of the different sub-basins, and we present for the first time a coherent stratigraphy and large-scale tectonic evolution of the whole region. The results provide the information to test and refine models of the geodynamic evolution of the westernmost Mediterranean.

The main objectives are: (i) To define a seismostratigraphy framework for the entire region, integrating previous interpretations and correlating the sedimentary units among depocentres; (ii) To propose an evolutionary model for each sub-basin; and (iii) To integrate all sub-basins results in an updated general kinematic model for the westernmost Mediterranean region.

Main results shed light on the particular evolution of each sub-basin as well as in the entire basin evolution. The Late Oligocene - Miocene represents the formation stage of the basins, controlled by the evolution of the Gibraltar subduction system. During this period, each sub-basin shows different sedimentary units, supporting differences in their evolution. The Plio-Quaternary corresponds to the deformation stage, driven by the Eurasian-African plates convergence. The Plio-Quaternary sediments are covering the entire area, instead of being restricted to the sub-basins. This latter period is characterized by contractional and strike-slip deformation, accommodated mainly by re-activation of pre-existing crustal structures.

How to cite: Gómez de la Peña, L., Ranero, C., Gràcia, E., and Booth-Rea, G.: The Westernmost Mediterranean evolution: A review of the Alboran and Algero-Balearic basins stratigraphy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9535, https://doi.org/10.5194/egusphere-egu2020-9535, 2020

D1049 |
EGU2020-448
Ruihong Chang, Franz Neubauer, Johann Genser, Yongjiang Liu, and Sihua Yuan

A-type subduction is considered to occur at the final stage of continent-continent collision. In many cases, the UHP/HP metamorphic conditions are well known but data on the type of subducted continental crust is lacking. In terms of end members, the type of subducted crust is either (1) normal thick continental crust or (2) the crust from the center of a rift zone, which is influenced by strong extension, high-temperature metamorphism due to thinning of even the continental mantle lithosphere and strong magmatism. To resolve these alternative scenarios, we investigated the southernmost part of the Eclogite-Gneiss Unit (EGU) of Cretaceous metamorphic age exposed in the Pohorje Mountains in Eastern Alps. There, UHP eclogites and ultramafic mantle rocks are exposed in a matrix of paragneiss and hitherto undated granitic orthogneises (Kirst et al., 2010). This study presents, for the first time, geochronological and geochemical data from newly discovered Permian granitic orthogneisses in this area. LA-ICP-MS zircon U–Pb ages of the orthogneisses are 255±2.2 Ma and 260±0.81 Ma, which are interpreted as the age of zircon crystallization in a magma. In contrast, all rounded zircons from paragneissic rocks give Cretaceous ages (89.34±0.69 Ma and 90.8±1.2 Ma), considered as the age of UHP/HP metamorphism. These zircons overgrew older zircons of Permian and rare older ages tentatively indicating that the metasedimentary could be not older than latest Permian. Zircon εHf(t) values of the four ortho- and paragneisses with (176Hf/177Hf) initial from 0.282201 to 0.282562, TDM2 are Proterozoic (1390~1970 Ma). The granitic orthogneisses show the geochemical features (high (La/Lu) N ratios (160.3–307.3), strong negative Eu anomalies) of an evolved granite molten from continental crust. This type of orthogneisses could be considered as the source magma of seemingly rootless Late Permian to Triassic pegmatites (Knoll et al., 2018) widespread within the EGU further to the north. The paragneisses are heterogeneously composed and are associated with eclogites and ultramafic cumulates of oceanic affinity (De Hoog et al., 2011). We argue that the Permian granitic orthogneisses might be derived from partial melting of lower crust in a rift zone. We consider, therefore, this segment of the EGU as part of the distal Late Permian rift zone, which finally led to the opening of the Meliata Ocean during Middle Triassic times. If true, the new data also imply that the stretched continental crust was potentially not much wider than ca. 100 km, was subducted and then rapidly exhumed during early Late Cretaceous times.

 

References

De Hoog, J.C.M., Janák, M., Vrabec, M., Hatton, K.H., 2011. In: Dobrzhinetskaya, L., Faryad, S.W., Wallis, S., Cuthbert, S. (Eds.), Ultrahigh-pressure Metamorphism: 25 Years After the Discovery of Coesite and Diamond. Elsevier Insights, pp. 399–439.

Janák, M., Froitzheim, N., Yoshida, K., Sasinková, V., Nosko, M., Kobayashi, T., Hirajima, T., Vrabec, M., 2015. Journal of Metamorphic Geology 33, 495–512.

Kirst, F., Sandmann. S., Nagel. T., et al. 2010. Geologica Carpathica 61(6), 451-461.

Knoll, T., Schuster, R., Huet, B., Mali, H., Onuk, P., Horschinegg, M., Ertl, A., Giester, G., 2018. Canadian Mineralogist 56, 489-528.

How to cite: Chang, R., Neubauer, F., Genser, J., Liu, Y., and Yuan, S.: Subduction of a rifted passive continental margin: the Pohorje case of Eastern Alps - constraints from geochronology and geochemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-448, https://doi.org/10.5194/egusphere-egu2020-448, 2019

D1050 |
EGU2020-11134
| Highlight
Boris Kaus, Eline Le Breton, Georg Reuber, and Christian Schuler

Using geological and geophysical data, it is possible to reconstruct the past motion of tectonic plates involved in the Alpine orogeny and propose possible scenarios for their geological evolution. However, those scenarios have not yet been tested for geodynamic consistency.

Here, we perform 3D thermomechanical geodynamic simulations of the Mediterranean-Alpine area starting with a plate tectonic reconstruction at 20 Ma based on the work of Le Breton et al. (2017). The models include viscoelastoplastic rheologies and a free surface, and thus simulate the spontaneous occurrence of shear zones as well as the development of topography. Whereas some aspects of the tectonic reconstruction are well constrained (i.e. past position of the plates and subduction-collision fronts), many details such as the dip and length of the subducted plates, their thermal structure as well as their rheology, are unknown. The models are run forward in time to see to which extent they are consistent with the kinematic reconstructions. Perhaps unsurprisingly, our initial modelling attempts show a wide variety of behavior, including slab break off events and slab rollbacks in the wrong directions. Yet, in all cases tested so far, the model evolution does not reproduce the present-day geological setting, with Adria frequently moving too far towards the east and breaking apart internally, frequently no Alpine chain forming and in some cases new subduction zones developing within the Western Mediterranean that swallow Sardinia and Corsica.

Reproducing geological scenarios with thermomechanical geodynamic modelling thus requires substantial additional work, both from the modelling side (testing the effect of uncertain parameters on the behaviour of plates and subduction zones), as well as from the plate reconstruction side (assessing which parameters are well constrained and need to be reproduced).  Nevertheless, interesting insights can already be obtained from our models, and in our presentation, we will highlight some of the links between interacting subducting plates and plate motion.

Le Breton E, Handy MR, Molli G, Ustaszewski K (2017) Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling. Tectonics 36:3135–3154. doi: 10.1002/2016TC004443

 

How to cite: Kaus, B., Le Breton, E., Reuber, G., and Schuler, C.: Using geodynamic modeling to test plate tectonic scenarios of the Mediterranean-Alpine area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11134, https://doi.org/10.5194/egusphere-egu2020-11134, 2020

D1051 |
EGU2020-20638
Arjan de Leeuw, Stephen Vincent, Anton Matoshko, Andrei Matoshko, Marius Stoica, and Igor Nicoara

The Carpathian orogen is part of the Alpine-Himalayan collision zone and formed as the result of the collision of the Tisza-Dacia and ALCAPA mega-units with the European southern margin, following a protracted phase of subduction, slab roll-back and accretionary wedge formation. The foreland basin of the East Carpathians is 800 km long and stretches out across Poland, Ukraine, Moldova and Romania. We use the results of our intensive field research to unravel the sedimentary architecture of this basin and reveal how it responded to the final phases of foreland vergent thrusting, continental collision and subsequent slab detachment. We discuss the asymmetry in the basins evolution and eventual inversion and relate this to the diachronous evolution of the Carpathian orogen. We also address the impact of changing subsidence patterns and base-level changes on connectivity with the Central and Eastern Paratethys, important for faunal exchange and patterns of endemism. We finally show that continental collision led to the establishment of a Late Miocene NW-SE prograding axial drainage system in the foreland supplying abundant sediment to the NW Black Sea, thus triggering large-scale shelf edge progradation.

How to cite: de Leeuw, A., Vincent, S., Matoshko, A., Matoshko, A., Stoica, M., and Nicoara, I.: Geodynamic evolution of the East Carpathian Foreland Basin since the Middle Miocene: Implications for sediment supply to the Black Sea and Dacian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20638, https://doi.org/10.5194/egusphere-egu2020-20638, 2020

D1052 |
EGU2020-7531
Jan Pleuger, Zlatka Cherneva, Linus Klug, Elis Hoffmann, Michael Schmidtke, Nikolaus Froitzheim, Neven Georgiev, Kalin Naydenov, Kristoph Stegmann, Alexandra Pohl, Marisa Germer, Alexander Borchert, and Martina Menneken

Following a tectonic scheme proposed by Janák et al. (2011; Journal of Metamorphic Geology 29, 317-332) and Pleuger et al. (2011; Zeitschrift der Deutschen Gesellschaft für Geowissenschaften 162, 171-192), the Rhodopes are composed of four nappe complexes, from bottom to top the Lower, Middle, and Upper Allochthon and the Circum-Rhodope Belt. Rocks derived from Adria and/or Pelagonia (Lower Allochthon) are separated from rocks of European origin (Upper Allochthon) by lithologically variegated thrust sheets containing sporadic occurrences of ophiolites (Middle Allochthon). These ophiolites typically yield magmatic protolith ages of c. 160 Ma and were metamorphosed under amphibolite- to eclogite-facies conditions. They represent Neotethyan lithosphere subducted below Europe in the Late Cretaceous to Palaeogene whereas the Circum-Rhodope Belt contains ophiolites of the same protolith age but with lower metamorphic grade (greenschist facies at most) and was obducted onto the former European margin in the Jurassic. We present LA-ICP-MS U-Pb zircon and additional geochemical data from the Luda Reka Unit in the Bulgarian Eastern Rhodopes. This unit consists mostly of amphibolite, metagabbro, and metadiorite that yielded two protolith ages of 163.5±2.6 Ma and 154.2±1.0 Ma. The trace element patterns resemble those of typical back-arc basalts and lower oceanic crustal cumulates. Initial epsilon Nd values of six samples calculated to 154 Ma were +10.8 ±0.8 (2σ; n = 6), in agreement with average basalts derived from depleted ambient mantle. A pegmatite crosscutting the Luda Reka Unit yielded a magmatic age of 52.04±1.1 Ma. Such pegmatites are widespread in the Luda Reka Unit (Middle Allochthon) suggesting that emplacement of this unit over the Bjala Reka Orthogneiss Unit (Lower Allochthon) where such pegmatites are lacking happened only after c. 52 Ma. The Bjala Reka Orthogneiss Unit forms the footwall of the top-to-the-SSW Bjala Reka Detachment that became active in the Late Eocene. Where the Luda Reka Unit is lacking, the Bjala Reka Orthogneiss Unit is overlain by rocks that were collectively described as “Low-grade Mesozoic Unit” (e.g. Bonev & Stampfli 2008; Lithos 100, 210-233). Based on peak temperatures determined by Raman spectroscopy of organic matter, two tectonic units can be distinguished in the “Low-grade Mesozoic Unit”. The temperature peak was at c. 530 °C in the Mandrica Unit below and at c. 285 °C in the Maglenica Unit above. For the Mandrica Unit, minimum peak pressures of c. 1.4 GPa were obtained by Raman spectroscopy of quartz inclusions in garnet, indicating that this unit underwent subduction-related metamorphism. Because of this marked difference in peak metamorphic grade, we attribute only the anchimetamorphic Maglenica Unit to the Circum-Rhodope Belt while the high-pressure Mandrica Unit probably represents the Upper Allochthon. Both units are presently separated by the top-to-the-NW Mandrica Detachment that was active before the Bjala Reka Detachment. Our new findings show that the easternmost Rhodopes expose a condensed section through all four nappe complexes, notably including the Neotethys suture.

How to cite: Pleuger, J., Cherneva, Z., Klug, L., Hoffmann, E., Schmidtke, M., Froitzheim, N., Georgiev, N., Naydenov, K., Stegmann, K., Pohl, A., Germer, M., Borchert, A., and Menneken, M.: The Neotethys suture in the eastern Bulgarian Rhodopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7531, https://doi.org/10.5194/egusphere-egu2020-7531, 2020

D1053 |
EGU2020-7529
Agathe Faucher, Christel Tiberi, Frédéric Gueydan, and Alexandrine Gesret

Aegean plate is marked since Eocene by widespread NE-SW extension induced by the African slab roll-back. In Miocene times, E-W shortening created by the westward Anatolian extrusion overlays the extension, with the formation of Miocene dextral strike slip faults in addition to normal faults. We propose to quantify the role of large dextral strike slip faults in accommodating Aegean extension, using receiver functions to image Moho geometry.

Aegean extension is particularly evidenced by a topographic difference between the emerged continental Greece and the submerged Cyclades. In this study we characterize the associated Moho geometry with a particular focus on the transition between these two domains. From a geological point of view, the transition between continental Greece and the Cyclades is marked by two dextral strike slip faults: the Pelagonian fault (onshore) and the South Evvia fault (offshore). Our objective is also to show a potential Moho signature of these strike slip faults.  We processed receiver functions (RF) from the MEDUSA stations located in Attic and Evvia.

Our results show that the Moho is deeper beneath continental Greece (~27km) than beneath the Cyclades (~25km). A detailed azimuthal study of RF distribution shows a flat Moho underneath Continental Greece. The crustal thickness is also almost constant inside the Cyclades, as already suggested by previous studies. However, the transition between the Cyclades and Continental Greece is not continuous. These two crustal blocks are separated by the Pelagonian and the South Evvia strike slip faults in a narrow transition zone (~75km). In this zone (South Evvia/Attica), dip and strike of the Moho vary and suggest a crustal signature of the strike slip structures observed at the surface. These strike slip faults therefore accommodate in a narrow zone the inferred variations in crustal thicknesses between the Cyclades and Continental Greece.

Our data show that differences in topography between Continental Greece and the Cyclades are isostatically compensated, reflecting various amount of crustal thinning larger in the Cyclades than in Continental Greece. Inside these two crustal blocks, we imaged a flat Moho, suggesting a wide rift extension process associated with the formation of numerous Miocene and Plio-Quaternary basins.  The dextral strike slip faults at the edges of the continental blocks (Continental Greece and Cyclades) accommodated the inferred variations in the amount of crustal thinning, suggesting that they act as continental transfer zones at crustal-scale during Miocene Aegean Extension.

How to cite: Faucher, A., Tiberi, C., Gueydan, F., and Gesret, A.: Role of dextral strike slip faulting in the distribution of Aegean extension since Miocene times inferred from receiver function analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7529, https://doi.org/10.5194/egusphere-egu2020-7529, 2020

D1054 |
EGU2020-7260
Guohui Chen and Alastair Robertson

Field, geochemical and geochronological research on Late Cretaceous and Early Cenozoic volcanic rocks in Kyrenia Range provide constraints on the tectono-magmatic evolution of the northerly, active continental margin of the Southern Neotethys. Field mapping in the western Kyrenia Range demonstrates that frontal (southerly) thrust sheets are dominated by felsic volcanogenic rocks. U-Pb zircon dating indicates that the felsic volcanics erupted at 72.9 ± 1.0 Ma (Late Campanian). These volcanics are interpreted as the products of sub-aqueous continental margin arc volcanism based on geochemical evidence. The exposed arc volcanics are somewhat younger than arc-derived volcaniclastic sediments in W Cyprus (80.1 ± 1.1 Ma), and are also younger than arc-related granitic rocks (88-82 Ma) cutting the Tauride active continental margin (Malatya-Keban platform) in SE Turkey. Structurally higher (more northerly) imbricate thrust sheets include Late Cretaceous (Maastrichtian) and Early Cenozoic basalts that are underlain by a Mesozoic continental carbonate platform (metamorphosed), and interbedded with pelagic and redeposited carbonates that formed in an active continental margin setting. The basalts have within-plate geochemical characteristics, although with a variable subduction influence in some areas (e.g., western Kyrenia Range) that could be either be contemporaneous or inherited from Late Cretaceous (c. 70-80 Ma) subduction. Modern and ancient comparisons (e.g., Tyrrhenian Sea) suggest that the basaltic rocks represent incipient, extensional marginal basin formation. Integration with comparable evidence of continental margin arc magmatism in SE Turkey and elsewhere provides a picture of arc magmatism and marginal basin formation along an active continental margin, prior to collision during the Miocene.

How to cite: Chen, G. and Robertson, A.: Formation of a Late Cretaceous continental margin arc and an Early Cenozoic back-arc basin in the Kyrenia Range, northern Cyprus related to S-Neotethyan subduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7260, https://doi.org/10.5194/egusphere-egu2020-7260, 2020

D1055 |
EGU2020-8898
| Highlight
Amr El-Sharkawy, Thomas Meier, Sergei Lebedev, Jan Behrmann, Mona Hamada, Luigia Cristiano, Christian Weidle, and Daniel Köhn

The fascinatingly complex tectonic make-up of the Mediterranean region comprises small, strongly-curved retreating subduction zones, associated back-arc basins, and the continental collisions along the northern and eastern margins of the Adriatic microplate. It remains a challenge to resolve the geometry of the subducted slabs in the Mediterranean upper mantle. Here, we present new evidence for the location and lateral and vertical extent of slab segments from a new, high-resolution, Rayleigh-wave tomography. The tomographic model spans the depth range from the crust down to 300 km and is complemented by intermediate-deep seismicity data in the circum-Mediterranean region.

An automated procedure to measure inter-station Rayleigh wave phase velocities is applied to a large, heterogeneous dataset from all publically available stations around the Mediterranean in the time period from 1990 to 2015. Furthermore, for the first time, data from the Egyptian National Seismological Network (ENSN) are used regional seismic tomography. The resulting large set of about 200,000 inter-station phase velocity measurements is inverted for a set of phase-velocity maps spanning a very broad period range (8 - 350 s). The maps are then inverted, point by point, for a 3D, S-velocity model using a stochastic, particle-swarm-optimization inversion.

We distinguish between attached slab segments reaching down to the bottom of the model and shallow slabs of shorter length or detached slab segments resulting both from horizontal tearing. We discuss evidence for continental subduction east of Cyprus, for continuous NE-dipping subduction in the Antalyan region and NW dipping subduction in the SE Aegean in the area of Rhodes. An attached slab is imaged beneath the Hellenides reaching down to at least 300 km depth whereas beneath the Dinarides a short slab is found down to about 150 km depth above a slab tear. The slab in the southern Carpathians seems to be partly detached. A south-dipping slab is imaged in the central Alps but shallow bivergent subduction is favoured in the eastern Alps. In the western Alps, a shallow slab east-dipping Eurasian slab segment is in close proximity to the nearly vertically dipping attached slab segment beneath the northern Apennines and the southern Po plain. In the central Apennines a slab gap is found whereas the NE-dipping Calabrian Slab seems to partly detached along the northern Sicilian coast. The Kabylides Slab that appears to be attached along the North African coast but detached along the margin of the shelf in the Sicily Channel, is clearly separated from the Calabrian Slab in the NE and the Alboran-Betics Slab in the west. According to our model, the latter slab consists of two segments: a shallow Alboran one and a detached Betics slab segment. We summarize our interpretations in a map of the Mediterranean slab segments and indicate open questions.

How to cite: El-Sharkawy, A., Meier, T., Lebedev, S., Behrmann, J., Hamada, M., Cristiano, L., Weidle, C., and Köhn, D.: The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8898, https://doi.org/10.5194/egusphere-egu2020-8898, 2020

D1056 |
EGU2020-189
Megan Mueller, Alexis Licht, Faruk Ocakoğlu, Clay Campbell, Mustafa Kaya, Begüm Kurtoğlu, Gui Akşit, Michael Taylor, Grégoire Métais, Pauline Coster, and K. Christopher Beard

The 1,700-km-long Izmir-Ankara-Erzincan suture (IAES) in Anatolia (Turkey) marks where Gondwanan and Laurasian microcontinents collided during the Cretaceous and Paleogene. The timing and dynamics of subduction and collision along the IAES are poorly constrained resulting in competitive paleogeographic scenarios requiring unique geodynamic and biogeographic reconstructions of the Mediterranean domain and broader Alpine-Zagros-Himalayan orogen. In western Anatolia, orogenic development following subduction initiation has been poorly documented. The timing of collision is debated: sometime in the Late Cretaceous to Early Eocene. Eocene slab breakoff is inferred from geochemical data but is either not supported or unresolved in mantle tomography and has not been tested using other techniques. 

We use the Saricakaya and Central Sakarya Basins in western Anatolia to appraise models of subduction initiation, intercontinental collision and slab breakoff in northwest Turkey and to discuss the implications of our results for geodynamic evolution of the IAES. From measured sections, volcanic zircon geochronology, and sedimentary provenance proxies, we demonstrate that there was little topographic development associated with early subduction stages. We refine the age of intercontinental collision to the Maastrichtian-middle Paleocene. We challenge the interpretation of Eocene slab breakoff and provide a new model of syncollisional evolution in western Anatolia in which convergence, underthrusting, and accommodation space creation dominate during the early Eocene. 

Finally, we compare results in western Anatolia to central Anatolia to determine that there was a synchronous magmatic history and onset of deformation along the IAES, thus supporting synchronous collision models of the IAES. The location, chronology and style of deformation and topographic development in western Anatolia is an important counterpoint to popular orogenic cyclicity models.

How to cite: Mueller, M., Licht, A., Ocakoğlu, F., Campbell, C., Kaya, M., Kurtoğlu, B., Akşit, G., Taylor, M., Métais, G., Coster, P., and Beard, K. C.: Western Anatolian Record of Subduction Initiation through Collision, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-189, https://doi.org/10.5194/egusphere-egu2020-189, 2019

D1057 |
EGU2020-322
Vartan Simmonds, Mohssen Moazzen, Gültekin Topuz, and Ali Mohammadi

The Qaradagh batholith in northwest Iran mainly comprises granodioritic rocks, which makes more than 50% of the batholith. This lithology is the first intrusive pulse within this batholith and the oldest Tertiary magmatism in the region, though other younger pulses of granite, diorite, quartz-diorite, syenite, quartz-syenite, monzonite, quartz-monzonite, quartz monzodiorite, monzogranite and gabbro intruded the main body. These magmatic rocks have intruded the Upper Cretaceous and Paleogene sedimentary, volcano-sedimentary and igneous rocks.

The Qaradagh batholith hosts vein-type and some local stock-work type Cu–Au–Mo mineralization, especially in its central parts, while skarn-type deposits have been formed at its contacts with peripheral carbonate rocks. Its extension towards the north into the neighboring south Armenia (which is part of the South Armenian Block) is known as the Meghri–Ordubad pluton (MOP), which hosts several large porphyry Cu–Mo deposits and other precious and base metal mineralizations. U–Pb geochronology on the zircons separated from the granodioritic unit yielded a weighted 206Pb/238U mean age of 43.81 ± 0.18 (MSWD=1.38) and a Pb*/U concordia age of 44.04 ± 1.00 Ma (MSWD= 24), which correspond to Middle Eocene.

Since the Qaradagh batholith and especially its earliest magmatic phase are considered as the oldest plutonic event of the Cenozoic age in northwest Iran, thus this investigation testifies to the fact that intrusive activities of Tertiary in this region has commenced in Middle Eocene, contrary to the opinion of the majority of authors who believe that plutonism in this region occurred during Oligocene.

However, this age is much older than the molybdenite Re–Os ages of quartz-sulfide veins hosted by granodioritic rocks (25.19 ± 0.19 to 31.22 ± 0.28 Ma), indicating that mineralization in this batholith is related to another much younger intrusive phase, and even to several phases, as the published ages of molybdenites from various veins and mineralized zones show a large interval. Comparing the obtained age with those from the MOP in southern Armenia indicate that southern part of the MOP is almost coeval with the emplacement of the granodioritic rocks in Qaradagh batholith.

The U and Th contents of the zircons range from 17.1 to 1534.0 and from 4.9 to 641.0 ppm, respectively, with Th/U ratios between 0.66 and 5.82 (mean of 1.26), indicating a magmatic source. Meanwhile, the εHf(t) values of the zircons range from 8.7 to 11.1 with the mean of 9.5, which are plotted between the CHUR and the Depleted Mantle evolution lines, indicating a juvenile and homogeneous magmatic source and the predominance of mantle-derived magmas with limited crustal assimilation.

How to cite: Simmonds, V., Moazzen, M., Topuz, G., and Mohammadi, A.: Geochronology and Lu-Hf isotopic study of the granodioritic pulse in the Qaradagh batholith (NW Iran), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-322, https://doi.org/10.5194/egusphere-egu2020-322, 2019

D1058 |
EGU2020-3709
Axel Schmitt, Jalil Ghalamghash, Razieh Chaharlang, Jamshid Hassanzadeh, and Seyed Mousavi

Post-collisional magmatism of Neogene-Quaternary age is manifested in a long but disjointed belt of volcanoes broadly paralleling the Arabia-Eurasia suture zone. Volcanic compositions in this belt share geochemical characteristics with subduction-related magmas, yet they postdate subduction and formed in the wake of continental collision. Potential mechanisms for melt generation in the absence of subduction include slab break-off, lithospheric mantle delamination, or incorporation of fusible crustal rocks or sediment into the mantle through subduction or collision, leading to volcanism seemingly randomly distributed in time and space. In northwestern Iran, the two largest post-collisional volcanic centers are Sahand and Sabalan stratocones, which are located at distances of 150 and 300 km on a line perpendicular to the strike of the suture zone, where they overlie rocks of the Eocene-Oligocene Urumieh-Dokhtar magmatic arc. Here, we present U-Pb zircon ages for intermediate lavas and pyroclastic rocks from Sabalan volcano which complement published data for the Sahand and Sabalan systems [1, 2]. In both sample suites, inherited zircon from the basement is scarce and restricted to Cretaceous and Eocene-Oligocene ages for Sahand, and Archean, late Proterozoic and Oligocene-Miocene ages for Sabalan. Individual samples display coherent young populations that likely crystallized shortly before eruption. In addition, many samples show evidence of antecrystic zircon, indicating a long-lived subvolcanic reservoir where older intrusive rocks became recycled. Because of this recycling, the overall zircon age distribution of each volcano better represents the duration of magmatic activity than a compilation of eruption ages would. Based on the oldest antecrystic zircon ages, the onset of magmatism is constrained to ca. 10 Ma for Sahand, and ca. 5 Ma for Sabalan. This age difference shows a progression in the onset of magmatism that is consistent with plate tectonic velocities of ~30 mm/a. This rate and the northeastward direction of the volcanic migration also matches the reconstructed convergence of the Neotethyan oceanic lithosphere towards Eurasia. Apparent pulses in zircon production for both, Sahand and Sabalan, as well as a tailing off in the frequency of older ages are likely due to sampling bias of the volcanic stratigraphy, where younger eruptive products may have destroyed or obscured older units. Regardless of this bias, U-Pb and U-Th disequilibrium zircon ages from both volcanoes consistently indicate late Pleistocene eruptions as young as <173 ka and <110 ka for Sahand and Sabalan, respectively. The systematic younging of the onset of volcanism for these two volumetric dominant volcanic centers in northwestern Iran suggests that passage of a detached oceanic slab following closure of the Neotethys is a viable mechanism for post-collisional magmatism in the region.

[1] Ghalamghash, J., Schmitt, A. K., & Chaharlang, R. (2019), Lithos, 344, 265-279.

[2] Ghalamghash, J., Mousavi, S. Z., Hassanzadeh, J., & Schmitt, A. K. (2016), J Volc Geotherm Res, 327, 192-207.

How to cite: Schmitt, A., Ghalamghash, J., Chaharlang, R., Hassanzadeh, J., and Mousavi, S.: Migration of post-collisional volcanism in northwestern Iran at plate tectonic velocities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3709, https://doi.org/10.5194/egusphere-egu2020-3709, 2020

D1059 |
EGU2020-304
Edoardo Barbero, Morteza Delavari, Asghar Dolati, Luca Pandolfi, Emilio Saccani, Michele Marroni, Marco Chiari, Valeria Luciani, and Rita Catanzariti

The Makran Accretionary Prism (SE of Iran) represents the less known segment of the Alpine-Himalayan orogenic system. It results from the Cretaceous to present-day convergence between the Arabian and Eurasian plates that was accommodated by the northward subduction of the Neotethys Ocean below the southern margin of Eurasia. As a peculiar feature, the Makran is the only segment of the Alpine-Himalayan orogenic system, in which subduction is still active. The North Makran is the innermost structural domain of the accretionary wedge. It consists of distinct complexes and tectonic units representing remnants of the Cretaceous-Paleocene accretionary-subduction phases. Among these, the Durkan Complex consists of several tectonic units, which include deformed Early Cretaceous-Paleocene carbonatic and volcanic successions, as well as rare Carboniferous, Permian and Jurassic slices of platform limestones. The Durkan Complex is commonly interpreted as representing the disrupted sedimentary cover of the passive margin of a micro-continent known in literature as the Bajgan-Durkan Complex. However, its stratigraphic succession, as well as the age and geochemistry of the volcanic rocks are still poorly known. Nevertheless, such data are fundamental for constraining its meaning for the pre-Eocene geodynamic evolution of the Makran Accretionary Prism. For this reason, we present new stratigraphic and petrological data on the westernmost sector of the Durkan Complex.

Our data show that the Durkan Complex includes distinct tectonic slices showing both slightly metamorphic and non-metamorphic highly-deformed stratigraphic successions. Stratigraphic data allow us to recognize three main types of successions. Type I consists of an alternation of pillow lavas and Albian-Cenomanian pelagic shales and radiolarites. Type II consists of pillow and massive lavas with minor volcaniclastic arenites grading up to an alternation of volcanic and volcaniclastic rocks and Cenomanian pelagic limestones and shales. Local intercalations of mass-transport deposits are common, particularly in the upper part of the sequence. Type III consists of pillow lava flows, volcanic breccia, and volcaniclastic sandstone overlain by an Albian-Cenomanian carbonatic platform. All these successions are stratigraphically overlain by a post-Cenomanian pelagic and hemipelagic sequence. Ages were determined by foraminifera and radiolarian biostratigraphy. The volcanic rocks in the distinct successions show similar geochemical features. They consist of basalt and minor trachybasalt showing alkaline affinity with high Nb/Y ratios (0.62 – 4.4), as well as marked LREE/HREE enrichment. The overall geochemical features of the rocks are comparable with those of alkaline oceanic within-plate basalts and plume-type MORBs.

In summary, our data show that the rock assemblages of the Durkan Complex represent the remnants of a seamount rather than remnants of continental margin successions, as it was previously described. The distinct successions of the Durkan Complex show tectono-stratigraphic features that can be reconciled to the cap (Type III), the slope (Type II), and the foothill (Type I) of a typical seamount environment. Finally, our new findings and regional-scale comparisons suggest that the Late Cretaceous alkaline magmatic pulse recorded in the Durkan Complex was likely related to mantle plume activity in the Makran sector of the Neotethys.

How to cite: Barbero, E., Delavari, M., Dolati, A., Pandolfi, L., Saccani, E., Marroni, M., Chiari, M., Luciani, V., and Catanzariti, R.: The Durkan Complex in the western Makran Accretionary Prism (SE Iran): Evidence for a Late Cretaceous tectonically disrupted oceanic seamount, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-304, https://doi.org/10.5194/egusphere-egu2020-304, 2019

D1060 |
EGU2020-7360
Bernard Guest

The left-lateral Doruneh Fault System (DFS) bounds the north margin of the Central Iranian microplate, and has played an important role in the structural evolution of the Turkish-Iranian Plateau and of Afghanistan. The western termination of the DFS is a sinistral synthetic branch fault array that shows clear kinematic evidence of having undergone recent slip sense inversion from a dextral array to a sinistral array in the latest Neogene or earliest Quaternary. Similarly, kinematic evidence from the Anarak Metamorphic complex at the southwestern most branch of the DFS terminal fault array suggests that this core complex formed at a transpressive left stepping termination and that it was inverted in the latest Neogene to a transtensional fault termination. The recognition that the DFS and possibly other faults in NE Iran were inverted from dextral to sinistral strike slip in the latest Neogene, and the likely connection between the DFS and the Herat Fault of Afghanistan suggests that the evolutions of Afghanistan and the Indo-Asian collisional system are linked to the tectonic evolution of the Turkish-Iranian Plateau. This speculative model explains the Late Neogene tectonic realignment of the Arabia-Eurasia collision zone in terms of the interaction between the Afghan blocks that were extruding west from the Indo-Asian collision and the Turkish Iranian collision zone that was evolving to the east as Arabia sutured diachronously with Eurasia. The collision of the Afghan blocks with East Iran effectively locked the respective eastern and western free boundaries for the Arabia-Eurasia, and Indo-Asian collisional belts and forced them to diverge away from one another. If confirmed, this explains the Late Miocene to Pliocene tectonic reorganization that is recognized across the Middle East and has implications for geologic process models across the region. Regional tectonic reorganization and/or inversion may (1) invert and possibly breach older Cenozoic structures while forming a younger generation of post-Miocene structures, (2) reorganize drainage and sediment supply networks, and sealing and obscuring older structural and stratigraphic bodies under younger sediments, (3) rejuvenate existing structures and trigger secondary fluid migration, and (4) increase exhumation, sediment supply, and subsidence in late Neogene basins across the region.

How to cite: Guest, B.: Slip-sense inversion in Iran: Implications for Eurasian tectonics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7360, https://doi.org/10.5194/egusphere-egu2020-7360, 2020

D1061 |
EGU2020-4012
Supriyo Mitra, Swati Sharma, Debarchan Powali, Keith Priestley, and Sunil Wanchoo

We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty two stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya to model the seismic velocity structures of the crust and the uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across the major Himalayan thrust systems and litho-tectonic units. We perform Vp/Vs-Depth stacking of P-RF and joint inversion with surface wave dispersion data. Our analysis show that the underthrust Indian crust, beneath the Jammu-Kishtwar Himalaya, has an average thickness of ~40 km and dips northward at ~7-9º. The overlying Himalayan wedge increases in thickness northward from the Shiwalik Himalaya (~8–10 km) to the Tethyan Himalaya (~25–30 km). The underthrust Indian crust Moho is marked by a large positive impedance contrast and lies at a depth of ~45 km beneath the Shiwalik Himalaya and ~65 km beneath the Higher Himalaya, deepening northward beneath the Tethyan Himalaya. We observe Moho flexure across the Mandli-Kishanpur Thrust (MKT), in the Shiwalik Himalaya, and beneath the Kishtwar window. Each time to Moho deepens by ~10 km, from ~45 km to ~55 km, and from ~55 km to ~65 km, respectively. The Moho is remarkably flat at ~56 km beneath the Pir Panjal Ranges, from its southern foothills to the northern flank in the Kashmir Valley. North of the Kashmir Valley the Moho dips steeply underneath the Zanskar Ranges from ~56 km to ~62 km. Along the Jammu-Kishtwar common conversion point (CCP) profile the Main Himalayan Thrust (MHT) is highlighted by the low velocity layer (LVL) at a depth of ~8 km beneath the Shiwalik Himalaya to ~25 km beneath the Higher Himalaya. The average dip on the MHT is ~9º and has a frontal ramp beneath the Kishtwar window. The MKT, MBT and MCT are marked by LVLs which splays updip from the MHT. Average crustal Vp/Vs shows that beneath the Shiwalik Himalaya, west of the MFT anticline the crust is mafic in nature while towards the east the crust is felsic in nature. Beneath the Lesser Himalaya the crust is largely felsic, while beneath the Pir Panjal range the crust is intermediate to mafic. North of the Kashmir Valley, beneath the Zanskar range the crust is felsic to intermediate in nature. We compare the source mechanism of the 2013 Kishtwar earthquake (Mw 5.7) and hypocentral location of small-to-moderate earthquake beneath Kishtwar region with the CCP profile. Our results show that these earthquakes occurred on or above the MHT in the unlocking zone, between the frictionally locked shallow segment and deeper creeping segment of the MHT. This marks the zone of stress build-up on the MHT in the interseismic period and is possibly the zone of megathrust initiation.

How to cite: Mitra, S., Sharma, S., Powali, D., Priestley, K., and Wanchoo, S.: Crustal Structure and Earthquakes beneath the Jammu and Kashmir Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4012, https://doi.org/10.5194/egusphere-egu2020-4012, 2020

D1062 |
EGU2020-22472
Ryan Stoner, Mark Behn, and Bradley Hacker

Geochronological and thermobarometric data from a lower crustal xenolith suite in the Pamir offer a unique record of the transport of lower crust to mantle depths after an episode of slab breakoff. We compare petrologically constrained pressure-temperature-time paths from the xenoliths to pressure-temperature-time (P-T-t) paths of tracked markers in 2-D numerical geodynamic models of density foundering with thermodynamically calculated densities. We investigate whether gravitational “drip” instabilities or the peeling back of a dense layer—delamination—can reproduce the P-T-t paths seen in the xenoliths, with the ancillary goal of capturing the positive feedback between mechanical thickening and densification of the lower crust. Key thermobarometric observations from the xenoliths we try to match in our numerical study are: (1) initial heating at near-constant pressure followed by (2) a sharp increase in pressure with continued heating. We find that thick crustal sections develop P-T-t paths in numerical models of delamination that match the observations from xenoliths: the lower crust initially heats due to return flow from upwelling asthenosphere, and then foundering mantle lithosphere and crust show a marked increase in pressure with additional heating. Initial gravitational drip instabilities founder with relatively little heating yet may thin the mantle lithosphere sufficiently to allow for subsequent delamination or asymmetric drips to nucleate in the region of hotter, thinner mantle lithosphere. Such subsequent asymmetric drips or delamination entrain crust that closely follows the P-T-t path from xenoliths. This suggests that the xenoliths were not derived from an initial drip instability, but instead from later instabilities or delamination enabled by thinning of the lithosphere. In all models where density foundering occurs, the positive feedback between contraction and densification of the lower crust leads to the loss of initially positively buoyant lower crust. The combination of geological and numerical methods constrains the geometry and triggers of lower crustal foundering during collision. Contraction alone does not match the record of foundering; the lithosphere must have also been asymmetrically thinned.

 

How to cite: Stoner, R., Behn, M., and Hacker, B.: Lower crustal recycling: Reconciling Petrological and Numerical Constraints from the Pamir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22472, https://doi.org/10.5194/egusphere-egu2020-22472, 2020

D1063 |
EGU2020-16977
Xiaoshuang Chen and Haijin Xu

Alkaline magmatism is commonly generated in extensional settings, playing an important role in constraining the timing of slab breakoff. Eocene post-collisional magmatism is widely distributed along the Gangdese belt of southern Tibet. However, few Eocene post-collisional alkaline magmatism has been identified. Here, we present a comprehensive study of whole-rock geochemistry, zircon U-Pb ages and Sr-Nd-Hf isotopes of the Mayum alkaline complex from the Southern Lhasa Subterrane, providing an insight into the timing of breakoff of the Neo-Tethyan slab. The alkaline complex is composed of amphibolite syenite, quartz syenite and alkaline granite. The mafic microgranular enclaves are ubiquitous in the syenites. Zircon U-Pb analyses indicates that the alkaline rocks were generated in Early Eocene (ca. 53-50 Ma). These ages suggest that the alkaline rocks emplaced shortly (10-15Ma) after the continental collision between the Indian and Eurasian plates. The alkaline rocks have high SiO2 (64.32-77.36 wt.%), Na2O + K2O (6.63-9.03 wt.%) contents, low MgO (0.14-2.52 wt.%) contents. These rocks show obvious arc-like geochemical features in trace elements, i.e., enrichment in LILEs (e.g., Rb, K), LREEs, Th and U, and depletion in HFSEs (e.g., Nb, Ta, Ti), HREEs with strongly to moderately negative Eu anomalies (δEu=0.28–0.72). These features together with high FeOT/MgO, Ga/Al, Ce/Nb and Y/Nb values, and low Ba, Sr contents, suggesting that the Mayum alkaline rocks belong to an A2-type granitoids. Besides, the alkaline rocks have homogeneous initial 87Sr/86Sr ratios (0.7052-0.7059) and negative εNd(t) values (-2.1 to -0.9) for whole-rock, and positive zircon εHf(t) values (+0.73 to +11.16). Nd-Hf isotope decoupling suggests that the alkaline was likely produced by mixing of mantle- and crust-derived magmas under a post-collisional extensional setting. Combined with previous published results, we propose that the slab breakoff of the subducting Neo-Tethyan oceanic lithosphere at least prior to Early Eocene (ca. 53Ma). The Eocene Mayum alkaline complex might be related to asthenosphere upwelling trigged by the slab breakoff.

How to cite: Chen, X. and Xu, H.: Eocene post-collisional magmatism in Himalaya orogenic belt: evidence from petrography, zircon U-Pb age and Sr-Nd-Hf isotope of the Mayum alkaline complex, southern Lhasa subterrane, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16977, https://doi.org/10.5194/egusphere-egu2020-16977, 2020

D1064 |
EGU2020-904
Ben S. Knight, Fabio A. Capitanio, and Roberto F. Weinberg

The collision of India and Eurasia since ~50 Ma has resulted in a broad range of deformation along the Himalaya-Tibetan orogeny, accommodating >2700 km of convergence. The region is characterised by the Tibetan Plateau, the Himalayan internal units and fold-and-thrust belt from North to South. These formed as a consequence of a convergence history characterised by a progressive decrease in velocity, from ~10 cm/yr 50 Ma, to ~8 cm/yr 42.5 Ma and to present-day values of ~4 cm/yr around 20 Ma. Here, we test the controls of such a convergence velocity history on the orogeny of a viscoplastic wedge during collision, above a subducting continental lithosphere. We compare numerical models simulating India-Asia plate convergence and collision, comparing the structures observed throughout the evolution with those observed in the Himalayan-Tibetan region. The models display distinct phases of growth and structural style evolution in the Himalayan-Tibetan region that are a result of the change in convergence velocity and long-term collision. After an initial stacking, the high convergence velocity forces deformation migration towards the upper plate, where a plateau forms, while late stage slowdown of collision favours the formation of the Himalayan fold-and-thrust belt. While the latter is in agreement with the structuring of the southermost domains and the South Tibetan Detachment (STD) fault, the former provide constraints to the initial uplift of the Tibetan Plateau.

How to cite: Knight, B. S., Capitanio, F. A., and Weinberg, R. F.: Reconciling plate convergence and orogeny: The influence of India-Asia convergence rate on the formation of the Himalayas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-904, https://doi.org/10.5194/egusphere-egu2020-904, 2019

D1065 |
EGU2020-14987
Han-Ao Li, in-Gen Dai, Le-Tian Zhang, Ya-Lin Li, Guang-Hao Ha, and Cheng-Shan Wang

The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology1. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data2. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau3. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.

Key words: N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow

References:

1Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).

2Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.

3Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).

Acknowledgements:

We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang,Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.

How to cite: Li, H.-A., Dai, I.-G., Zhang, L.-T., Li, Y.-L., Ha, G.-H., and Wang, C.-S.: The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14987, https://doi.org/10.5194/egusphere-egu2020-14987, 2020

D1066 |
EGU2020-18249
Oriol Gimeno, Dominique Frizon de Lamotte, Rémi Leprêtre, Faouziya Haissen, Achraf Atouabat, and Geoffroy Mohn

The Rif Belt (Northern Morocco) forms the western edge of the Alpine-Himalayan orogenic system developed during the convergence between the Africa and Eurasia plates. Compared to other mountains belts, the External Rif, which preserves remnants of the North African paleo-margin, presents two unusual features: (1) the presence of metamorphic massifs [External Metamorphic Massifs (EMMs)] and (2) the existence of large allochthonous thrust-sheets that travelled far away [the Higher Nappes]. In this contribution, we combined structural, stratigraphic and metamorphic data, complemented by new field observation and thermochronology results, to revisit the structure of the External Rif and to review its Cenozoic evolution. The External Rif was the site of a poly-phased tectonic evolution recorded before and after of a major unconformity: the so-called “Mesorif Unconformity” postdating an important Midde-Late Eocene deformation. This tectonic event is well-preserved in the North-African paleo-margin because of its under-thrusting (“subduction”) below the Maghrebian Tethys, the former oceanic domain separating Iberia from Africa. The MP-LT metamorphism, recorded in the EMMs (Temsamane Units in Morocco), is a direct vestige of this process.  By contrast, traces of this event are absent in the oceanic units of the Intrarif Domain, element of the Maghrebian Tethys. After the “Mesorif Unconformity”, i.e. during the Miocene, the regional geodynamics is dominated by the westward translation of the Alboran Domain and the coeval deformation of the Ketama Unit (Intrarif) in front of it. This process results directly from the subduction of the Maghrebian Tethys, which happened at that time. The docking of the Ketama Unit against the already exhumed EMMs allowed an uplift and the subsequent detachment of the top of its lithostratigraphic pile, individualizing the Higher Nappes. During their gravity-driven travel towards the foredeep basin, they dragged at their floor the already exhumed Senhadja Nappes, inherited from the distal-most part of the NW African margin. All these elements are integrated in a coherent model integrating the External Rif in the geodynamics of the West Mediterranean.

How to cite: Gimeno, O., Frizon de Lamotte, D., Leprêtre, R., Haissen, F., Atouabat, A., and Mohn, G.: The structure of the Central-Eastern Rif (Morocco) and the disregarded subduction of the North-West African paleo-margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18249, https://doi.org/10.5194/egusphere-egu2020-18249, 2020

D1067 |
EGU2020-7704
Kristóf Porkoláb, Jasper Hupkes, Liviu Matenco, Ernst Willingshofer, and Jan Wijbrans

The Sierra de los Filabres mountain range in the Betics system of SE Spain is one of the best natural laboratory to investigate processes associated with nappe stacking and subsequent exhumation of metamorphic rocks during the orogenic evolution. Existing research separates the Iberia-derived high-pressure, amphibolite facies Nevado-Fillabrides complex in a lower tectonic plate position from the lower grade ALCAPECA microcontinent-derived Alpujárride complex in an upper tectonic plate position. Their nappe-stack contact is also defined as an extensional detachment that controls the exhumation of the higher grade Nevado-Fillabrides complex. We have tested this model with a detailed (micro-)structural and lithological analysis complemented by 40Ar/39Ar white mica dating of key shear zones. We aim to define key shear zones that separate different tectonic units, to determine the kinematics and timing of main deformation phases, and to understand the interplay between burial and exhumation structures. The results show that shearing related to the subduction burial up to the amphibolite facies is ~ top-NW in present-day coordinates. Three amphibolite facies nappe units are distinguished, which may correspond to proximal and more distal parts of the former hyper-extended Iberian margin. The bottom and top nappes consist of continental material, while the middle nappe is largely made of mafic and ultramafic rocks. Top-NW shearing was coeval with the isoclinal and tight asymmetric folding of the formations. These structures were overprinted by upright folds and greenschist facies shear zones that still developed under compression. These contractional structures are cross-cut by ~ top-W shear zones associated with exhumation that show evidences of gradually decreasing P-T conditions during extension from ductile shearing to normal faulting. We show that the same protolith can be followed in amphibolite grade below and in low greenschists grade above the main extensional detachment. This demonstrates that the extensional detachment did not follow and reactivate exactly the former nappe contact between the Nevado-Fillabrides and Alpujárride complexes. Our single grain fusion 40Ar/39Ar ages on white micas show a range of 10 to 20 Ma in case of nappe contacts or extensional shear zones, while yield a significantly older, 25-40 Ma age cluster in case of a sample far away from the main shear zones in the core of the Nevado-Fillabrides dome. This age cluster could either represent excess Ar in the sample, or resetting due to a distinct tectono-metamorphic event that occurred prior to the Early Miocene subduction of the Nevado-Fillabrides complex. The latter case would require the reconsideration of recent tectonic reconstructions of the region.

How to cite: Porkoláb, K., Hupkes, J., Matenco, L., Willingshofer, E., and Wijbrans, J.: Superposition of nappe stacking and extensional exhumation in the Sierra de los Filabres (Southeast Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7704, https://doi.org/10.5194/egusphere-egu2020-7704, 2020

D1068 |
EGU2020-10358
Ana M. Negredo, Flor de Lis Mancilla, Carlos Clemente, Jose Morales, and Javier Fullea

The Gibraltar arc subduction system is the result of the fast westward roll-back of the Alboran slab at the westernmost end of the Mediterranean Sea. This westward motion is controlled, at its northern edge, by slab tearing along a so called STEP (Subduction-Transform-Edge-Propagator) fault under the Betics orogen. The Alboran subduction process is in its last evolutionary stage, where the oceanic lithosphere has been fully consumed and the continental lithosphere attached to it collides with the overriding plate. In this situation the continued slow convergence between Iberia and Africa could lead to a short stage of continental subduction. However, the particular setup after slab tearing, characterized by a sharp lateral contrast between the orogenic Betic lithosphere and the adjacent thinned lithosphere of the overriding Alboran domain, is also prone to trigger continental delamination, i.e. the detachment between the crust and the lithospheric mantle. Several lines of evidence indicate that northwards mantle delamination is likely occurring in the central Betics. The fast average topographic uplift during the last 8 Ma together with the lack of spatial correspondence between the highest topography (Sierra Nevada Mountains) and the thickest crust indicate that the topography could be partly supported by asthenospheric upwelling due to continental delamination. In this study we take advantage of an unprecedented resolution seismic receiver functions lithospheric mapping in the Betic orogen to investigate the conditions for, and consequences of, edge delamination in the Iberian margin after slab tearing. We show that given a weak enough Iberian lower crust the delaminated lithospheric mantle peels off the crust and adopts a geometry consistent with the imaged southward dipping Iberian lithosphere in the central Betics. In contrast, the thinned lower crust beneath the Iberian margin in the eastern Betics prevented mantle delamination via asthenospheric inflow into the lower crust.

How to cite: Negredo, A. M., Mancilla, F. D. L., Clemente, C., Morales, J., and Fullea, J.: Late stage of the Gibraltar arc subduction system (western Mediterranean): from slab-tearing to continental-edge delamination , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10358, https://doi.org/10.5194/egusphere-egu2020-10358, 2020

D1069 |
EGU2020-9221
Marine Larrey, Frédéric Mouthereau, Emmanuel Masini, Sylvain Calassou, Aurélien Virgone, Eric Gaucher, Damien Huyghe, and Nicolas Beaudoin

Since Miocene times, the crustal thinning in eastern Betics and the Alboran region associated with westward slab retreat led to the formation and exhumation of metamorphic domes and EW-directed narrow basins.

The Tabernas basin preserves a sedimentary records of the last stages of metamorphic domes exhumation (14 to 8 Ma). Structural constraints from fault patterns and sedimentary archives show evidence in the field for E-W strike-slip faults that developed close to dome-basin contacts. The evolution of strike-slip faulting and extensional basins reveals strain partitioning during the late Miocene that is consistent with the present-day regional NNW-directed compression and WSW-directed/orogen-parallel extension that result from the NW-SE Africa-Europe plate convergence. A regional cross-section further emphasizes the role of crustal-scale strike-slip faulting and slab detachment and delamination under the Alboran domain.

Calcite veins that developed during the orogen-parallel extension in the metamorphic basement and the Tortonian sedimentary rocks show a wide variety of stable isotopes ratios. Calcite cements have δ18O values ranging from -17.23‰ to -5.30‰ for, and from -15.77‰ to -1.6‰ for δ13C isotopic ratios. This patterns is interpreted to reflect the increase of freshwater input buffered by the composition of host carbonate rocks.

Continental carbonates of Quaternary ages are widespread in the Tabernas basin. Travertines show a close structural relationship with N170 and N50 normal faults, implying tectonically-controlled Ca/CO2 leakages. Their δ13C values are compatible with a hydrothermal origin from a deep-seated carbon source (δ18O median of -7.5‰, δ13C median of 2.1‰). Degassing associated with regional volcanism from the Serravallian until the Tortonian-Messinian ages is likely to be also the main vector of recent CO2 storages in rocks. The U-Th ages of travertines, ranging from 8ka ± 0.2 to 354ka ±76, further outline interactions with captive aquifer from 350ka and subsequent Ca/CO2 leakages due to geodynamic changes.

How to cite: Larrey, M., Mouthereau, F., Masini, E., Calassou, S., Virgone, A., Gaucher, E., Huyghe, D., and Beaudoin, N.: Neogene-to-Quaternary post-orogenic tectonic evolution and CaCO3-rich fluids from the Tabernas basin (eastern Betics, Spain) reveal control by deep-seated processes in the mantle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9221, https://doi.org/10.5194/egusphere-egu2020-9221, 2020

D1070 |
EGU2020-10520
Flor de Lis Mancilla, Jose Morales, Antonio Molina-Aguilera, Daniel Stich, Jose Miguel Azañon, Teresa Teixido, Benjamin Heit, and Xiaohui Yuan

We obtain P-wave receiver functions from recordings at a dense seismic broadband transect, deployed along 170 km across the eastern Betic orogen in south Spain. Migrated images show the crustal structure of the orogen in detail. In particular, they reveal the situation of the subducted Iberian paleomargin, with full preservation of the proximal domain and the ~50 km wide necking domain. Crustal thinning affects the lower continental crust. The Variscan crust of the Tethys margin is bending downward beneath the Betics, reaching ~45 km depth, and terminates abruptly at a major slab tear fault. The distal domain of the paleomargin cannot be reconstructed, but the migrated section suggests that material has been exhumed through the subduction channel and integrated into the Betic Orogene. This supports an origin of the HP-LT Nevado-Filabride units from subducted, hyperextended Variscan crust.

How to cite: Mancilla, F. D. L., Morales, J., Molina-Aguilera, A., Stich, D., Azañon, J. M., Teixido, T., Heit, B., and Yuan, X.: Image of the Iberian Tethys paleomargin beneath the eastern Betic mountain range, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10520, https://doi.org/10.5194/egusphere-egu2020-10520, 2020

Chat time: Friday, 8 May 2020, 16:15–18:00

Chairperson: Ágnes Király, Claudia Piromallo, Derya Gürer, Marc Hässig
D1071 |
EGU2020-10681
Giulia Innamorati, Simone Fabbi, and Massimo Santantonio

The Meso/Cenozoic geodynamic evolution of the Calabria Peloritani Arc (CPA) has been, and is still, hotly debated, this sector of the Apennine chain being an exotic continental ribbon scraped off from its original position (European Plate) during the south-eastward migration of the Apenninic slab.

The Southern sector of the Arc (Peloritani Mts.) has been analysed using a multidisciplinary approach. An analysis of pre-, syn- and late-orogenic siliciclastic deposits (Militello Fm, Frazzanò Flysh, Capo d’Orlando Fm) is essential for our understanding of how orogenic phases developed through the Late Cretaceous and Palaeogene. Biostratigraphical constraints reveal a multi-step compressive history, with discrete events (Alpine phase – Balearic phase – Apenninic phase)

The Northern sector of the Arc is conversely less well known, namely with regards to its pre-Serravallian history, due to the lack of continuous exposures of the Meso/Cenozoic sedimentary cover. One remarkable exception is the Longobucco Basin (Sila Greca, CS), where a Meso/Cenozoic succession covers unconformably the igneous and metamorphic Hercynian basement.  A geological mapping project of the Longobucco Basin is proving instrumental in constraining the Cenozoic dynamics of this sector of the Arc. In particular, the Paludi Fm has been analysed. This is a multifaceted lithostratigraphic unit, made of conglomerates/breccias, reddish marls and arenaceous turbidites, whose composition testifies the dismantling of an orogen. This unit is in turn crosscut and deformed by north eastward verging thrusts dated as Burdigalian by Vignaroli and co-authors (2014), therefore it also apparently predates a younger tectonic phase (see the Frazzanò Flysch in Southern CPA for an analogy).

Despite the regional importance of this Unit, its age is highly debated in the literature, ranging from the Late Cretaceous to the Aquitanian, according to different Authors. In this light, a biostratigraphic study of this unit ( nannoplancton, micro- and macroforaminifer)a, has been performed.

Field mapping has revealed a wealth of sedimentary structures ascribable to ductile and or/brittle-ductile deformation, typical of mass transport deposits (i.e. slumps, non-tectonic thrusts, pseudo sigma structures, asymmetric rootless folds and ductile shear zones). The occurrence of olistostromes, with evidence of syn-emplacement deformation, has been mapped. These plastically deformed bodies are Late Cretaceous in age (Aptian to Maastrichtian). They document lost parts of the succession, eroded during the uplift phases and cannibalized within a younger part of the succession, which must therefore be post-Cretaceous.

Being the age obtained from micropaleontological data comprised between the Eocene and the Oligocene, we must preliminarily ascribe the emplacement stage to an alpine phase. The Burdigalian thrusting event predates the opening of the Tyrrhenian sea and the detachment of the CPA from the Corsica-Sardinia block. It cannot therefore be ascribed to an Apenninic s.s. phase. We attribute this thrusting event to an earlier phase (Balearic phase) related to the Corsica-Sardinia block rotation.     

Vignaroli G., Minelli L., Rossetti F., Balestrieri M.L. & Faccenna C. (2012) - Tectonophysics, 538, 105-119.

How to cite: Innamorati, G., Fabbi, S., and Santantonio, M.: Cenozoic multiphase orogenic deformations in Northern Calabria Arc: hints from geological mapping in the Longobucco Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10681, https://doi.org/10.5194/egusphere-egu2020-10681, 2020

D1072 |
EGU2020-10088
Petra Schneider and Dražen Balen

The Late Cretaceous magmatic rocks within the southwestern part of the Pannonian Basin basement (Croatia) occur in two areas: Voćin volcanic mass (VVM) at the northwestern part of Mt. Papuk (near town of Voćin, covering the area of ~10km2) and volcanic mass of Mt. Požeška Gora (PVM, area of ~30 km2). Both volcanic masses consist of basalts and rhyolites, and in lesser extent of pyroclastic material. Granite can be found it the PVM. Interconnection of this two masses and Late Cretaceous ages have been proposed based on the petrography and mineralogical features of previously studied samples and rather arguable data: K-Ar dating on basalts from VVM (~73−52 Ma) and Rb-Sr isochron age on granite and rhyolite from PVM (~72 Ma). The age has been recently refined with the zircon LA-ICP-MS age dating (~82 Ma), but the magma source of this bimodal formation, geotectonic position, setting and its regional importance still have not been explained in detail.

In order to conduct preliminary research, two localities with acid effusive rocks were sampled from the VVM (Rupnica geosite and Trešnjevica quarry), and three more from PVM (near the village of Vesela, Pakao Creek and the granite from quarry near the village of Gradski Vrhovci).

Acid rocks are characterized by a highly siliceous composition (up to 75 wt.% SiO2), enrichment in alkalies (high-K calc-alkaline towards to shoshonite series) and aluminium (peraluminous affinity), followed by high FeOT/(FeOT+MgO) ratios matching ferroan magmas. They classify as rhyolites or alkali-rhyolites/granite. Microelements including REE show that studied rocks have characteristics of A2-type of post-collisional/post-orogenic acid rocks, most common A-type of rocks formed during rifting caused by extension and thinning of continental crust. According to geotectonic classification diagrams, rocks from PVM show geochemical signature of volcanic arc, while VVM shows signature of within plate environment.

External zircon morphology seems to be uniform with prevailing J3−J5-type for rhyolites and D-type for granite and with average ratio of 2.2:1. Those types are characteristic for the high-temperature magmas (confirmed with the calculated Zr-saturation temperature of 850−930°C) originating from the lower crust or even upper mantle. Inclusions of hematite, F-apatite and anatase have been detected with Raman spectrometry in zircon from all samples, with the most significant findings of kumdykolite and kokchetavite inclusions detected in samples from Vesela and Gradski Vrhovci. Latter inclusions are metastable phases crystallized from enclosed melt and are indicators of a rapid cooling of the host magma.

According to the results presented here, acid rocks show rather uniform geochemistry, which speaks in favor of the early ideas of the unique magmatic complex, although today at the surface they are separated by ~35 km in distance. Those rocks show potential to be of great regional importance bearing new information about the evolution in the Late Cretaceous in the area of Sava Zone, a suture zone between Tisia Mega-Unit (European plate) and Adria microplate, which spatially and temporally marks the closure of the Neotethys Ocean.

Support by the Croatian Science Foundation (IP-2014-09-9541) is acknowledged.

How to cite: Schneider, P. and Balen, D.: High-temperature acid magmatic rocks from the Late Cretaceous suture zone between European plate and Adria microplate (Croatia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10088, https://doi.org/10.5194/egusphere-egu2020-10088, 2020

D1073 |
EGU2020-5919
Nikola Stanković, Vesna Cvetkov, and Vladica Cvetković

In this study we report interim results of our ongoing research that involves the application of numerical modeling for constraining the geodynamic conditions associated with the closure of the Vardar branch of the Tethys Ocean. The study is aimed at better understanding the ultimate fate of the Balkan ophiolites, namely at addressing the question whether these ophiolites represent relicts of an ocean that completely closed during Upper Jurassic/lowermost Cretaceous time (Vardar Tethys) or they also contain remnants of the ocean floor of a Late Cretaceous oceanic realm (Sava – Vardar) [Schmid et al., 2008].

In our numerical models we try to simulate a single intraoceanic subduction that commences in the Lower/Mid Jurassic and ends in the Lower Cretaceous, transitioning into oceanic closure processes and subsequent collision between Adria and Eurasia plates. These convergent-collision events should have led to the formation of ophiolite-like igneous rocks of the so-called Sava - Vardar zone.

A series of numerical simulations were performed with varying parameters. In the scope of our numerical simulations, the set of equations is solved: the continuity equation, the Navier-Stokes equations and the temperature equation. Marker in cell method was incorporated in solving this system with finite difference discretization of the equations on a staggered grid. To utilize this numerical method a thermo-mechanical code I2VIS [Gerya et al., 2000; Gerya & Yuen, 2003] was used for obtaining the final results. 

Our actual 2D thermo-mechanical models cover the crust and the upper portion of the mantle with varying starting widths of the Vardar Ocean in the Lower Jurassic. The ocean is modeled with two segments: the western subducting slab and the eastern overriding slab. Slabs with different ages and thicknesses were used and the convergence rate is varied. The intraoceanic subduction is assumed to have been initiated along the mid oceanic ridge. Two continents (i.e. Adria and Eurasia) with different thicknesses of the continental lithosphere and crust are also modeled adjacent to a single oceanic realm between them.

The parameter study is in function of defining conditions under which the hypothesized scenario occurs. So far, we have succeeded in reproducing westward obduction onto the Adriatic margin, which is in accordance with the geological observations, i.e., with the top-west emplaced West Vardar ophiolites [see Schmid et al., 2008 for references]. However, our model is yet to produce sufficient amounts of back-arc extension along the Eurasian active margin and that is crucial for explaining the formation of the igneous provinces occurring within the Late Cretaceous Sava – Vardar zone and the Timok Magmatic Complex.

How to cite: Stanković, N., Cvetkov, V., and Cvetković, V.: 2D Numerical Simulation of Intraoceanic Subduction during the Upper Jurassic Closure of the Vardar Tethys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5919, https://doi.org/10.5194/egusphere-egu2020-5919, 2020

D1074 |
EGU2020-13101
Kata Molnár, Stéphane Dibacto, Pierre Lahitte, Marjan Temovski, Samuele Agostini, Zsolt Benkó, Artur Ionescu, Ivica Milevski, and László Palcsu

Late Miocene to Pleistocene volcanism within the Vardar zone (North Macedonia) covers a large area, has a wide range in composition and it is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. The scattered potassic to ultrapotassic volcanism developed south from the Scutari-Peć fault zone since 6.57 Ma [1]. The focus of this study is on three volcanic centers located on deep structures or thrust faults along the western part of the Vardar zone, for which there is none to very little geochronological and geochemical data available. Pakoševo and Debrište localities are represented as small remnants of lava flows cropping out at the southern edge of Skopje basin and at the western edge of Tikveš basin, respectively. Šumovit Greben center is considered as part of the Kožuf-Kozjak/Voras massif (6.5-1.8 Ma [1]), and it is located on its westernmost side, at the southern edge of Mariovo basin, which is largely comprised of volcanoclastic sediments. Here we present new eruption ages applying the unspiked Cassignol-Gillot K-Ar technique on groundmass, petrological and geochemical data, supplemented with Sr and Nd isotopes to complement and better understand the Neogene-Quaternary volcanism in the region. Obtaining the eruption ages of these volcanic centers could also help to better constrain the evolution of the sedimentary basins. All of the three centers belong to the shoshonitic series based on their elevated K-content. The oldest center amongst these three localities, as well as other Late Miocene centers within the region, is the trachyandesitic Debrište, which formed at ca. 8.1 Ma, and exhibits the highest Nd isotopic ratios (0.512441-0.512535). The trachybasaltic Pakoševo center formed at ca. 3.8 Ma and, based on its Nd isotopic ratio (0.512260), represents the strongest sign of crustal contamination. The rhyolitic Šumovit Greben center is a composite volcanic structure formed at ca. 3.0-2.7 Ma. Its youngest eruption unit has a slightly larger Nd isotopic ratio (0.512382), representing a less evolved magma at the end of its activity.

This research was funded by the GINOP-2.3.2-15-2016-00009 ‘ICER’ project, the French-Hungarian Cooperation Program TÉT-FR-2018-00018 and the HORIZON 2020 grant N 676564.

References:

[1] Yanev et al., 2008 – Mineralogy and Petrology, 94(1-2), 45-60.

How to cite: Molnár, K., Dibacto, S., Lahitte, P., Temovski, M., Agostini, S., Benkó, Z., Ionescu, A., Milevski, I., and Palcsu, L.: The westernmost Late Miocene-Pliocene volcanic activity in the Vardar Zone (North Macedonia) – geochronology, petrology and geochemistry of Pakoševo, Debrište and Šumovit Greben volcanic centers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13101, https://doi.org/10.5194/egusphere-egu2020-13101, 2020

D1075 |
EGU2020-9122
Nikolay Bonev, Petyo Filipov, Raya Raycheva, and Robert Moritz

In the Aegean sector of the Alpine orogen of the Eastern Mediterranean, the Sakar-Strandzha Zone (SSZ) represents a major tectonic unit that straddles the territories of Bulgaria and Turkey. The westernmost part of the SSZ in Bulgaria includes the area along the Maritsa river valley and the St. Iliya Heights, both connected through several small outcrop areas under the Cenozoic sedimentary cover. In Bulgaria, the Triassic felsic magmatism along the Maritsa river valley was inferred by Chatalov (1961) on the basis of the stratigraphy, but only a single U-Pb zircon age revealed Early Triassic (ca. 249 Ma) felsic magmatism in the SSZ of Turkey (Aysal et al., 2018). Here, we constrain the timing of Triassic magmatism using U-Pb LA-ICP-MS zircon geochronology of felsic magmatic bodies in the western part of the SSZ in Bulgaria.

A sample from a (meta) rhyolite body yielded a concordant age of 237.8 ± 3.4 Ma, which confirmed a crystallization likely concomitant with the deposition of the Triassic clastic rocks in the northern Maritsa river valley. To the east along the valley, a leucocratic granite body located south of the Permian Sakar batholith (ca. 295-296 Ma, Bonev et al., 2019), yielded a concordant age of 242.1 ± 1.8 Ma for the crystallization, having crosscutting relationships with the high-grade metamorphic basement. A leucocratic and K-feldspar porphyric meta-granite bodies yielded concordant ages of 243.3 ± 5.8 Ma and 240.6 ± 2.3 Ma, respectively, for the crystallization within the so-called Harmanli block to the south along the valley. At St. Iliya Heights a sample from the Prochorovo Formation (meta) rhyolite body yielded a concordant age of 245.4 ± 1.5 Ma for the crystallization, which implies an Early Triassic age of the clastic rocks with which it inter-fingers. In the area between the Maritsa river valley and the St. Iliya Heights at the village of Svetlina a leucocratic meta-granite body yielded a concordant age of 229.6 ± 2.4 Ma. The concordantly dated zircons that yielded Triassic ages of the igneous/meta-igneous protoliths all have Th/U ratios compatible with the magmatic process. The major elements of the dated samples reveal calc-alkaline to high-K-alkaline peraluminous felsic compositions similar to the adjacent Late Carboniferous-Permian igneous/meta-igneous rocks of the SSZ.

The U-Pb zircon ages reveal Early-Middle Triassic magmatic phase (ca. 245-230 Ma) in the western SSZ of Bulgaria. These age data provide a regional-scale temporal link for the Triassic magmatism extending to the easternmost extremity of the SSZ in Turkey. The Triassic continental type felsic magmatism in the western SSZ is interpreted to result from the ongoing Paleotethyan subduction under the Eurasian plate, which magmatism follows the development of a Late Carboniferous-Permian continental magmatic arc of the SSZ (Bonev et al., 2019).

References

Aysal, N., Şahin, S.Y., Güngör, Y., Peytcheva, I., Öngen, S., 2018. Journ. Asian Earth Sci., 164, 83-103.

Bonev, N., Filipov, P., Raicheva, R., Moritz, R., 2019. Int. Geol. Rev., 61, 1957-1979.

Chatalov, G., 1961. Compt. Rend. Acad. Bulg. Sci., 14, 503-506.

Acknowledgements: The study was supported by the NSF Bulgaria DN04/6 contract.

How to cite: Bonev, N., Filipov, P., Raycheva, R., and Moritz, R.: Triassic magmatism along the Eurasian margin of the Palaeotethys: U-Pb zircon age constraints from the western part of the Sakar-Strandzha Zone, Bulgaria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9122, https://doi.org/10.5194/egusphere-egu2020-9122, 2020

D1076 |
EGU2020-7790
Eleonora Balkanska and Stoyan Georgiev

The Panagyurishte strip of Central Srednogorie zone, Bulgaria is part of the peri-Tethyan Upper Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic arc belt and it is famous for its rich copper-porphyry and epithermal systems. The magmatic events related to the formation of the known ore systems are dated in the interval of 93–85 Ma and were followed by a period of deposition of carbonate and sandy turbidites during the latest stages of the Cretaceous and Paleocene. The main deformational event of the Central Srednogorie zone occurred after the Maastrichtian due to the closure of the arc basin and affected not only the Upper Cretaceous sequences (including the ore systems) but also the fragments of the Early Alpine edifice.

The present study is focused on the structural analysis of several regional faults that affected the Mesozoic (Triassic and Late Cretaceous) sequences in different parts of the Panagyurishte strip. The study of the post-ore deformations is important to reveal the history and current position of the ore bodies and their host rocks.

Most of the documented faults follow the main NW-SE to W-E orientation of the Panagyurishte strip. They do not represent single discrete fault surfaces but usually are segmented and the fault zones are several tens to hundreds of meters wide, often complicated by the presence of imbricate structures. Some of the faults involve rocks from the crystalline basement but most of the documented structures juxtapose different parts of the Mesozoic sequences. The deformation is brittle in almost all lithological varieties to brittle-ductile in some of the clayey limestones and turbidites at macroscopic view. Both evidence for compressional and dextral strike-slip tectonics are documented as slickenside fibres, geometry of Riedel shears and folds, lithological markers. It is difficult to distinguish them in time as no stratigraphic reference units, overprinting relationships or structural interferences between them are observed. In the different parts of the basin, either compression or strike-slip deformation are dominant. This fact, as well as the echelon configuration of the faults support the idea for their synchronous development in dextral transpressional setting and reactivation in time of the older transtenssional structures that controlled the opening of the Late Cretaceous basin.

 

Acknowledgements. The study is supported by the grant DN 04/9 funded by the National Science Fund, Ministry of Education and Science, Bulgaria.

 

How to cite: Balkanska, E. and Georgiev, S.: Structural analysis of faults related to the Late Cretaceous and Paleocene evolution of the Central Srednogorie zone, Bulgaria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7790, https://doi.org/10.5194/egusphere-egu2020-7790, 2020

D1077 |
EGU2020-122
Felix Camenzuli, Hartwig E. Frimmel, and Adam Wooldridge

The future search for mineral deposits will focus more and more on discoveries under cover. Indirect methods, such as prospective mapping, help in the early stages of exploration programmes to delineate potential target areas and thus reduce costs. On the Balkan peninsula, copper and gold ores have been mined for thousands of years and it hosts Europe’s highest concentration of large porphyry Cu (-Au) deposits. Over the last decades, the region’s mining history was strongly influenced by state-controlled mining under the previous communist regimes and the sudden demise of this mining activity after the collapse of the Union of Soviet Socialist Republics (USSR) in 1991. Following the shutdown of the mining industry and political, social and ethnic tensions in the years thereafter, the region remained comparatively poorly explored and thus holds a high potential for modern brown- and greenfield exploration. This is exemplified by several new discoveries of porphyry Cu (-Au) deposits, e.g. Kiseljak (Serbia) and Skourries (Greece).

Here we report on a regional-scale prospectivity mapping approach applied to the Balkan peninsula, covering Bosnia and Herzegovina, Serbia, Montenegro, Albania, Kosovo, Macedonia, Bulgaria and Greece. The area of interest (AOI) has an acreage of >1 Mill. km2. We modelled the distribution of both porphyry and related epithermal Cu-Au deposits, ophiolite-hosted volcanogenic massive sulphide (VMS) and sediment-hosted stratiform Cu (SSC) deposits with the help of ESRI ArcGIS. The models used were knowledge-driven and mainly based on Fuzzy overlays using Gamma operator and µ-value of 0.975. Areas favourable for porphyry and epithermal Cu-Au deposits follow magmatic arcs that are of Cretaceous and Tertiary age. While the Cretaceous arc has long been known for its fertility, our results suggest that the Tertiary arc is at least as promising. The results were validated by both the magmatic arcs, recommended porphyry Cu tracts and known deposits or occurrences. Our areas of high probability explain 67 % of the 72 existing deposits/occurrences if the location of the latter is considered with a 5 km radius. As the examined VMS deposits are ophiolite-hosted, they are distributed along the ophiolite-bearing tectonic units. Prediction of so-far undefined ophiolites based on lithology lead to a better comparability of prospective areas for VMS deposits throughout the AOI. By validation with locations of existing mines within a radius of 2.5 km, 50% of 16 known deposits lie in areas with a probability of ≥0.5. So far no SSC deposits, which constitute the globally second most important source of Cu, have been discovered in the AOI. Our results suggest that areas favourable for SSC deposits might exist in parts of Bosnia and Herzegovina, where the critical geological prerequisites for SSC formation were found in close vicinity. Whether this close spatial relationship, some of which is most likely tectonic, was realized at the right times remains to be investigated.

How to cite: Camenzuli, F., Frimmel, H. E., and Wooldridge, A.: Predicted spatial distribution of major copper deposits types in southeastern Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-122, https://doi.org/10.5194/egusphere-egu2020-122, 2019

D1078 |
EGU2020-21708
Konstantinos Soukis, Katerina Andropoulou, Bernhard Grasemann, Varvara Antoniou, and Stelios Lozios

Mapping metamorphic rocks in areas with complex tectonometamoprhic history and multi-phase syn-metamorphic isoclinal folding, usually means not having safe stratigraphic evidence such as biomarkers or marker layers to make correlations between formations and units or to assign ages. Novel analytical techniques can be very useful but raise the cost and they do depend on meticulous field work. Therefore, traditional methods such as detailed geological mapping may be the only way to reach to valid correlations.

The Cycladic Islands in the Aegean domain is an area where rocks present a complex history of subduction, accretion and subsequent syn-and post-orogenic exhumation along crustal scale detachments. Fossils are very rarely preserved and lithologies are quite similar throughout the column. Serifos Island is the area where the top-to-S West Cycladic Detachment System (WCDS) was firstly identified and mapped in detail. The detachment is exposed at the northernmost (Platys Ghialos) and the southernmost (Megalo Livadi, Cape Avessalos) part of the Island, having Cycladic Blueschist Unit rocks in the footwall and Upper Unit rocks in the hanging wall. The geometry of the fault resulted from late stage doming on the island scale.

At Platys Ghialos, the structurally highest part of the WCDS footwall, a very distinct lithological sequence is observed exactly below the ultramylonitic marble of the Detachment zone. This sequence includes a marble metaconglomerate, which serves as the main index layer, blue-gray marble, schist, metaconglomerate and metabasite layers. Detailed mapping of the western part of Serifos in 1:5.000 scale, shows that this succession is traced all the way from Platys Ghialos to Megalo Livadi. Also, it revealed meso- to macroscopic scale isoclinal refolding. The overall pattern proves the footwall has a periclinal geometry which follows the doming of the detachment.

How to cite: Soukis, K., Andropoulou, K., Grasemann, B., Antoniou, V., and Lozios, S.: Tracing marker horizons in the Serifos Island metamorphic core complex (Cyclades, Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21708, https://doi.org/10.5194/egusphere-egu2020-21708, 2020

D1079 |
EGU2020-10753
David Schneider, Bernhard Grasemann, Kostis Soukis, Benjamin Huet, Anna Rogowitz, Hugh Rice, Karolina Linder, Johannes Loisl, Stelios Lozios, Vasilis Anastasopoulos, and Nicholas Lemonnier

The timing and kinematics of low-angle normal faulting in the Cyclades (Aegean region, Greece) has been a matter of debate, mainly because the detachments arch over the islands and only remnants of the fault systems and small klippen of hanging-wall rocks are preserved. The small (4.3 km2) island of Agios Georgios, 20 km south of the Attica Peninsula, lies structurally above the West Cycladic Detachment System (WCDS). The island consists of metavolcanic greenschists and grey pelitic schists defined by an Ms+Chl+Ep/Czo+Ab±blue Amp assemblage. Zoned blue amphiboles occur both within albite porphyroclasts and the matrix in greenschists, and in pelitic schists. A locally strongly deformed granitoid dominates the east end of the island, which also contains zoned amphiboles (partly relict magmatic?), actinolite often replacing hornblende and two generations of white mica. The granitoid yields a zircon U-Pb date of 248.2 ± 1.0 Ma (MSWD: 0.83) with Variscan inheritance. Dynamically recrystallized feldspar in both the granitoid and host rocks suggests upper greenschist to amphibolite facies conditions. The white mica in the host rock forms bundles that define an anastomosing foliation, and although strongly deformed in many parts, stretching lineations and shear-sense indicators show variable orientations. New 40Ar/39Ar geochronology on the mica yields c. 60-47 Ma dates, and new zircon (U-Th)/He dates indicate cooling <200°C at c. 21 Ma. The new geochronology and lack of a strong top-to-SW directed deformation, diagnostic of the WCDS, indicates that the island lies well above the detachment system.

Thirty km to the NNE, along a section perpendicular to the strike of the WCDS, lies the small (18.5 km2) island of Makronisos, where the WCDS and the footwall are exposed. The island consists of greenschists and pelitic/graphitic schists with quartzites and blue-grey mylonitic marbles, and metabasites containing blue amphiboles. The structurally highest level consists of white to pale grey/reddish ultramylonites up to 40 m thick lying on the central ridge of the island and along the NE and NW coasts. Strongly clustered stretching lineations and macro-/microscopic shear-criteria indicate a top-to-SSW shear sense. Deformation mechanisms in quartz (LT-bulging) and calcite (recrystallization) indicate deformation at ~300°C. Albite porphyroclasts may preserve an older foliation and an earlier, higher grade metamorphism. This record is consistent with cooling during top-to-SSW deformation. New 40Ar/39Ar analyses on white mica yield ages of 22-15 Ma, markedly younger than the ages from Ag. Georgios. Published zircon (U-Th)/He dates from the Western Cyclades footwall record cooling at 14-9 Ma. The relict status of the HP-mineral assemblages suggests Makronisos is part of the Lower Cycladic Blueschist Nappe (i.e. below the Trans Cycladic Thrust) and hence the ultramylonites are interpreted as the footwall of the early ductile high strain zone forming the WCDS. The older dates and distinctly different structural styles on Ag. Georgios indicate that as the hanging wall to the WCDS it is comparable to the Vari Unit on Syros, likely an extensional allochthon of the Pelagonian block.

How to cite: Schneider, D., Grasemann, B., Soukis, K., Huet, B., Rogowitz, A., Rice, H., Linder, K., Loisl, J., Lozios, S., Anastasopoulos, V., and Lemonnier, N.: The Vari Unit in the hanging wall of the West Cycladic Detachment System (Agios Georgios, Greece): A small island with a big message, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10753, https://doi.org/10.5194/egusphere-egu2020-10753, 2020

D1080 |
EGU2020-19426
Christina Stouraiti, Stelios Lozios, Konstantinos Soukis, Hilary Downes, and Andy Carter

Triassic geodynamic phenomena in the Aegean area are largely controlled by subduction of the Paleotethys ocean and opening of the Neotethys oceans. Triassic volcanosedimentary sequences have a complex composition in many cases, reflecting both subduction and rifting setting.

Detailed mapping of NE Attica (Penteli Mt., Marathonas, Varnavas) revealed the existence of a structurally lower meta-volcanosedimentary sequence, which, comprises quartzofeldspathic rocks, schists, quartzite, metabasite and acid meta-volcanics This sequence is isoclinally folded in the macro-scale with marble layers and the axial plane foliation displays greenschist facies assemblages, whereas earlier HP minerals are mostly preserved as inclusions in albite porphyroblasts. The sequence of rocks has been investigated for their geochemical composition and their field relationships. Two assemblages of volcanic rocks are distinguished based on geochemical criteria: (a) a predominant subalkaline andesite-rhyolite series with a significant proportion of meta-tuffs in the stratigraphic sequence and (b) minor alkali basalts. Lenses of felsic meta-volcanic rocks alternate with siliciclastic layers showing sedimentary banding and allow for an interpretation of a volcano-sedimentary succession.

The geochemical characteristics of the alkali basalts are typical of rift settings (positive anomalies in Nb, Ta, Ti and P) and plot in the field of within plate basalts in the tectonic discrimination diagrams.  The trace element and Rare Earth Element characteristics of the andesites and rhyolites in the subalkaline group show many characteristics of subduction zone melts e.g. negative Nb and Ta anomalies, positive Pb anomaly and LREE-enriched suggesting that a metasomatized mantle wedge source played an important role in the formation of the calcalkaline magmas. A geodynamic model of rift formation in the active continental margin of Pelagonia is proposed to explain the transition from a subduction- to an extension-related magmatic activity in the Late Permian/Triassic time in the broader NE Attica-central Evvia region.

How to cite: Stouraiti, C., Lozios, S., Soukis, K., Downes, H., and Carter, A.: Geochemical and geological evidence for a Triassic transition from subduction- to rift-related volcanic activity in the Cycladic Blueschist Unit in Attica (Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19426, https://doi.org/10.5194/egusphere-egu2020-19426, 2020

D1081 |
EGU2020-19863
Dimitrios Baroutsos, Konstantinos Soukis, Erich Draganits, David A Schneider, Bernhard Grasemann, and Stelios Lozios

Numerous studies throughout the world have focused on the structure and evolution of metamorphic core complexes and the exhumation of subducted rocks in back-arc areas of orogenic belts. The Cycladic Islands (central Aegean Sea, Greece) are key areas for studying mechanisms of high-pressure rock exhumation. In that domain, the highly attenuated upper plate is preserved only as sparse extensional allochthons in the hanging wall of crustal-scale detachments. Several detachment systems have been identified on a number of islands indicating overall bivergent extension during the late Oligocene–Miocene. The island of Antiparos is situated at the center of the Cyclades, SW of the larger Paros Island where the top-to-N Paros-Naxos Detachment has exhumed pre-Alpine basement and metamorphosed Permian-Mesozoic rocks of the Cycladic Blueschist Unit (CBU). The tectonostratigraphic relationship of an enigmatic element, the Dryos Unit, remains unclear.

Detailed mapping in Antiparos revealed the existence of a sub-horizontal normal fault along the eastern coast of the island. This fault juxtaposes CBU in the footwall against the Dryos Unit and scarce (?)late Miocene clastic sediments in the hanging wall.

The CBU occupies most of the island and consists of marble alternating with schists and gneiss layers. The earlier HP assemblages are totally overprinted by mainly amphibolite facies metamorphism. An axial plane foliation to NE-SW isoclinal folds is accompanied by NE-SW stretching lineation. As indicated by recrystallization of feldspars and high-grade deformation mechanisms these structures formed under amphibolite facies conditions. Towards the detachment the foliation is reworked by a brittle-ductile mylonitic foliation and a brittle-ductile S -C’ fabric can be observed.

Numerous kinematic indicators such as σ- and δ-clasts, Riedel shears, flanking structures S-C’ fabric, observed within the ultramylonitic rocks of the footwall and the mylonites/cataclasites of the hanging wall indicate top-to-NE sense of shear, comparable to the sense of shear in the Paros-Naxos detachment.

The Dryos Unit is observed only along the central eastern coast of Antiparos, above the low-angle detachment and comprises lower grade (greenschist facies) metabasite, calc-phyllite and pink marble. Deformation in the structurally upper part is characterized by intense refolding and a steep axial plane foliation. At the structurally lower part a strong mylonitic foliation prevails, overprinted by intense cataclastic deformation. The stretching lineation is mostly NW-SE but in the lower part and towards the detachment it rotates to NE-SW. The late Miocene sediments are found adjacent to the Dryos rocks in two localities, comprising mainly sandstone, mudstone and conglomerate in which, large blueschist clasts are abundant.

The new data presented in this study combined with existing data from Paros Island substantially add to the continuation and structure of the complex Paros-Naxos detachment system, domed at an island scale. Furthermore, it suggests that most probably the Dryos Unit is not an upper part of the Cycladic Blueschist Unit but belongs to a different unit, possibly of Pelagonian origin.

How to cite: Baroutsos, D., Soukis, K., Draganits, E., Schneider, D. A., Grasemann, B., and Lozios, S.: A new Miocene detachment from Antiparos Island (Cyclades, Greece), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19863, https://doi.org/10.5194/egusphere-egu2020-19863, 2020

D1082 |
EGU2020-7157
Michael Nirrengarten, Geoffroy Mohn, François Sapin, Jon Teasdale, Charlotte Nielsen, Julie Tugend, and Dominique Frizon de Lamotte

At the transition between the Atlantic and the Tethys oceanic systems, the plate kinematic configuration of the East Mediterranean domain during the early Mesozoic is still poorly understood. Several factors like the Messinian salt, the different compressional events, the thick carbonate platforms and Cenozoic deltaic deposits combine to blur the imaging of Eastern Mediterranean rifted margins. This has led to distinct and often markedly contrasting interpretations of the timing of opening (ranging from Carboniferous to Cretaceous), structural evolution (divergent to transform segments) and kinematics (N-S to WNW-ESE extension).

To address this long-standing problem, we gathered disparate geological observations from the margins surrounding the Eastern Mediterranean Sea to integrate them in a global plate model. Distinct, end-member plate kinematic scenarios were tested, challenged and iterated by observations from the Eastern Mediterranean rifted margins.

The N-African and NW-Arabian margins of the Eastern Mediterranean Sea are relatively weakly reactivated by the different compressional events and were chosen as the starting point of our integrative tectonic study. Legacy plate models for the area mostly show N-S to NNE-SSW opening of the Eastern Mediterranean of pre-Jurassic age. We have integrated dense industrial seismic data, deep boreholes and dredge data, as well as enhanced satellite gravity images that strongly suggests WNW-ESE oriented lithospheric extension and sea floor spreading during the Late Triassic to Early Jurassic.

Our approach starts by the mapping of the main extensional and compressional structures, the different crustal domains and the pre-rift facies distribution. We investigate the potential conjugate margins now located and imbricated in the Dinarides, Hellenides and Taurides on the northern side of the East Mediterranean Sea by looking at the drowning ages of the Mesozoic carbonate platform and the related rift structures. We refine the full fit and initial spreading of the Atlantic Ocean using crustal thickness and features observed on both sides of the system to calibrate the motion of Eurasia and Africa, which determine the space available to develop the Eastern Mediterranean Sea. Initial tests on the evolution of the main tectonic plates highlight an insufficient eastward motion of Africa relative to Eurasia (Iberia) to accommodate the extension of Eastern Mediterranean during the Jurassic with a purely WNW-ESE direction of extension. Further hypotheses remain to be tested. However, for now, a scenario involving poly-phased and poly-directional motion of the conjugate continent “Greater Adria” during Jurassic is favoured to model the Eastern Mediterranean plate evolution in relation with the closure of the Neo-Tethys further north.

How to cite: Nirrengarten, M., Mohn, G., Sapin, F., Teasdale, J., Nielsen, C., Tugend, J., and Frizon de Lamotte, D.: Testing the Mesozoic plate configuration of the Eastern Mediterranean domain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7157, https://doi.org/10.5194/egusphere-egu2020-7157, 2020

D1083 |
EGU2020-12184
Derya Gürer, Douwe J J van Hinsbergen, Douwe van der Meer, and Wim Spakman

A current frontier in paleogeographic and geodynamic research is the reconstruction of the plate tectonic evolution of deep-time ocean basins. However, deep-time plate reconstructions of now-subducted ocean basins are challenging and often result in competing tectonic models, particularly when the upper plate was oceanic and is only preserved as ophiolitic relics. Correlations between paleogeography and tomographically imaged slab remnants has unlocked Earth’s modern mantle structure as an archive for the analysis of such deep-time geological processes. The geology of the western Tethyan realm from Greece to Oman in northeastern Arabia, holds records of the subsequent closure of the Paleo- and Neotethyan oceanic realms and of plates and microcontinents therein due to subduction since the Permian. Kinematic restorations reveal that the western Tethys contained at least three discrete plate systems bounded by transform faults, similar to the Atlantic Ocean today. Previous tomography-geology studies have interpreted the upper and lower mantle structure in terms of subduction history for the Aegean and Arabian segments, but particularly lower mantle structure of the Anatolian segment has not been resolved in detail before. In this segment, kinematic restorations have suggested that at least four subduction zones were responsible for the consumption of oceanic lithosphere, two consuming the Paleotethys, and two consuming the Neotethys. For the Neotethys system, slab segmentation may have led to more than two slab segments in the final mantle architecture. We here interpret the upper, and for the first-time, the lower mantle structure associated with the Anatolian segment, thereby unraveling western Tethys oceanic lithosphere lost to subduction since the Early Triassic, and link this to mantle structure and subduction evolution of the Aegean and Arabian segments. The modern mantle structure as imaged in the tomographic P-wave speed model UU-P07, tested against multi-model vote maps, provides means to find the relics of the complex subduction history and to discern between existing tectonic models. The tomographic  model reveals ten major positive wave speed anomalies interpreted as slab remnants: the previously identified Aegean, Algerian, Emporios, Antalya, Egypt (which is part of the Arabian slabs), Cyprus, Mesopotamia, Al Jawf, and Zagros slabs, and the newly identified Pontide and Herodotus slabs, partly in the upper, but mostly in the lower mantle. We compare the dimensions, locations, and orientations of these slabs with the kinematically-restored subducted area of the Neotethys, and identify the deepest lower mantle anomalies (Emposios, Herodotus, Al Jawf) as remnants of Paleotethys subduction of the three segments, and the remaining anomalies as the expression of complex Neotethys subduction, consistent with recent kinematic restorations of Eastern Mediterranean and Arabian orogenic history. Moreover, we confirm recent findings that the orientation of slabs influences their net sinking rate, with vertical slabs subducted at mantle-stationary trenches sinking faster than flat-lying slabs that once draped the mantle transition zone due to roll-back or trench advance.

How to cite: Gürer, D., van Hinsbergen, D. J. J., van der Meer, D., and Spakman, W.: Western Tethys subduction history constrained through upper and lower mantle structure coupled to kinematic reconstruction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12184, https://doi.org/10.5194/egusphere-egu2020-12184, 2020

D1084 |
EGU2020-8519
Ezgi Sağlam, Turgut Duzman, and Aral I. Okay

The Pontide Upper Cretaceous magmatic arc can be traced for over 1000 km along the southern Black Sea coast from Georgia to Bulgaria.  The arc extrusive sequence is well-exposed in the İğneada region in Thrace close to the Bulgarian border. The Upper Cretaceous sequence in İğneada region overlies the schists and phyllites of Strandja Massif with an unconformity. It  has a thickness of over 700 meters and consists at the base of Cenomanian shallow marine sandy limestone, which pass up into pelagic limestone, marn and volcanogenic siltstone with Turonian planktonic foraminifera, including Marginotruncana pseudolinneana, Marginotruncana marginata, Whitenella sp., Whitenella praehelvetica, Muricohedbergella sp.  This indicates that the arc volcanism in the region started in the Turonian. The pelagic limestone, marl, and calcareous siltstone series passes up into a volcanic-volcaniclastic sequence of andesitic tuff, lapillistone, agglomerate, andesitic and basaltic-andesitic lava flows. The volcaniclastic rocks are intercalated with lava flows and with rare pelagic limestone and shale beds. Although it is disrupted by several faults, the volcanic sequence can be traced from older to younger along the coast of İğneada. The sequence starts with andesitic volcaniclastic rocks and lava flows, and changes to basaltic-andesitic and then, again to andesitic rocks. The ocean floor alteration, which is found in all volcaniclastic and volcanic rock samples, and the intercalated pelagic limestones show that the rocks were deposited in deep submarine conditions in an intra-arc to fore-arc environment. Campanian (80.6 ±1.5 Ma) U-Pb zircon ages, which are obtained from the andesitic tuffs at the base of the volcanic-volcaniclastic sequence, indicate a continued magmatism from Turonian to Campanian.

How to cite: Sağlam, E., Duzman, T., and Okay, A. I.: Upper Cretaceous Stratigraphy and Volcanism in the İğneada region, Pontides, NW Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8519, https://doi.org/10.5194/egusphere-egu2020-8519, 2020

D1085 |
EGU2020-12776
Vahid Teknik, Hans Thybo, and Irina Artemieva

Maps of depth to magnetic basement and crustal average susceptibility for the Anatolian plateau and adjacent regions are calculated by applying a spectral method to the magnetic data. The first map provides information on the shape of the sedimentary basins and the latter map is used for tracking magmatic arcs and ophiolite belts, which are covered by sediment and/or overprinted by different phases of magmatism and ophiolite emplacement. This is possible because magmatic and ophiolite rocks generally have the highest magnetic susceptibility values, and the huge contrast to sedimentary rocks makes magnetic data very useful.

The results shows a heterogeneous pattern associated with a mosaic of the many continental blocks, Tethyside sutures, magmatism and former subduction systems in Anatolia. Major basins such as northern part of the Arabian plateau, Black Sea basin, Mediterranean Sea basin and central Anatolian micro-basins are highlighted by very deep magnetic basement. Shallow magnetic basement is generally prominent in eastern Anatolia, and may represent that large amounts of magmatic rocks were emplacement during the convergence and compression of the Arabian plate, whereas a sporadic and asymmetric pattern of sedimentary basins in western Anatolia may have developed in the frame of the extensional regime. The average susceptibility map reveals extension of the Pontide magmatic arc in the north of Anatolia, following the coastline of the Black Sea. The average susceptibility indicates magmatism or ophiolite emplacement around the Kirşehır block. A 400 km long NW–SE elongated average susceptibility anomaly extends from south to NW of the Kirşehır beneath the Quaternary sediments, while the depth to magnetic basement indicate more than 6 km sediments. We speculate that this anomaly indicates a covered magnetic arc or a trapped part of oceanic crust. The westeward extension of the Urima-Dokhtar magmatic arc (UDMA) from the Iranian plateau fades away towards to Central Anatolian plateau. It suggest a geological boundary around the border between Iran and Turkey, which caused different magmatism between the two sides. A near zero magnetic anomaly in the Menderes massif region in the southwest of Turkey indirectly suggests a high geothermal gradient and hydrothermal activity that reduce the susceptibility of the rocks. This observation is in agreement with the crustal thinning and many geothermal fields of the Menderes massif.

How to cite: Teknik, V., Thybo, H., and Artemieva, I.: Magmatic arcs, ophiolite belts and sedimentary basins in Anatolia interpreted from magnetic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12776, https://doi.org/10.5194/egusphere-egu2020-12776, 2020

D1086 |
EGU2020-17835
Alexandre Boutoux, Arthur Briaud, Claudio Faccenna, Paolo Ballato, Federico Rossetti, Francesca Funicello, and Eric Jean-Philippe Blanc
  • To unravel the Neotethys subduction history and the evolution of the slab morphology at depth since the mid-Cretaceous, we produced a synthesis of the main events affecting the Persian domain. This synthesis is focused on the upper and lower plates (i.e. the Persian and the Neotethys ocean, respectively) of the subduction system and is based on the compilation of available structural, geochemical and geochronological data. Overall, this compilation allows exploring the structural evolution of the Persian domain and the Neotethys oceanic lithosphere on map view and along selected cross-sections.
  • Furthermore, we performed a 2D single-sided numerical model where we explored the slab behavior at depth and its influence on upper plate deformation. The model suggests that episodic deformation is driven by the folding slab behavior at the mantle transition zone. We combine our data and numerical model into a conceptual scenario to overcome the complexity of the kinematics of the Neotethys slab since the Early Cretaceous. Our modeling approach shows that back-arcs opening and associated extensional deformation are driven by the roll-back of the folded slab into the mantle transition zone. In contrast, back-arc closure and upper plate shortening are triggered by the roll-over of the folding slab. Finally, we associate the widespread, upper plate, Early Miocene marine flooding event to the Neotethys slab avalanche into the lower mantle.

How to cite: Boutoux, A., Briaud, A., Faccenna, C., Ballato, P., Rossetti, F., Funicello, F., and Blanc, E. J.-P.: Deep Slab folding and the deformation of the Persian domain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17835, https://doi.org/10.5194/egusphere-egu2020-17835, 2020

D1087 |
EGU2020-21232
Mahleqa Rezaei, Mohssen Moazzen, and Tian-Nan Yang

The Neo-Tethys-related Chaldoran ophiolite in NW Iran and at the Turkish border is a part of the larger Khoy ophiolite. Cumulate and isotropic gabbro along with serpentinized peridotite, pillow basalt, pelagic limestone, rare radiolarites, and volcano-sedimentary units are the main rock types in the area. The gabbros occur as lenses with ultramafic rocks, or as relatively large exposures with fault contact with ultramafic rocks. In this study, we provide new whole-rock geochemistry, mineral chemistry and zircon U/Pb age for the cumulate gabbros from the Chaldoran area. Gabbros have tholeiitic composition and are highly depleted. Chondrite normalized rare earth elements (REE) pattern for gabbros are comparative with REE patterns for N-MORB, but overall with more depleted features. The N-MORB normalized multi-elements pattern shows high depletion in HREE and HFSE and enrichment in some LREE and LILEs. Negative anomaly for some HFSE relative to N-MORB, along with enrichment in LILE for the samples indicates the source region as subduction influenced mantle. The cumulated gabbro whole rock and Clinopyroxenes geochemistry indicate an intra-oceanic forearc setting for the studied samples. They also have many similarities to boninite in mineral and whole rock geochemistry. U-Pb zircon dating of the gabbro samples indicates 95.3-114.1 Ma ages for the generation of the gabbros parent magma. The original magma was related to the later stages of the forearc setting in the subduction initiation (SI) stage. This ‘SI’ related Albian-Cenomanian the Chaldoran depleted gabbro likely are the continuation of Taurus SI related late Cretaceous ophiolite complexes in Turkey.

How to cite: Rezaei, M., Moazzen, M., and Yang, T.-N.: Geochemistry of Cretaceous subduction initiation related cumulate gabbros in a forearc setting from Chaldoran ophiolite, NW Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21232, https://doi.org/10.5194/egusphere-egu2020-21232, 2020

D1088 |
EGU2020-1334
Leila Rezaei, Martin J. Timmerman, Mohssen Moazzen, and Masafumi Sudo

Metamorphic rocks in the Alborz Mountains are mainly known from the HP-LT Asalem-Shanderman Complex, the Gasht Complex, Gorgan Schists, and the Fariman Schists near Mashad. Recent argon ages are limited to eclogites and blueschists of the Asalem-Shanderman Complex, where phengites yielded c. 350 Ma step-heating ages that reflect cooling, following peak metamorphism related to subduction of the Palaeotethys Ocean (Rosetti et al. 2016).

The Gasht Complex in the Gasht-Masuleh area comprises metasediments and metabasic rocks metamorphosed at amphibolite-facies peak metamorphic conditions (c. 630°C and 8.6 kbar, Razaghi et al., 2018). The metamorphism is most probably related to the accretion of Cimmerian terranes to the Turan Terrane in the late Triassic following closure of the Palaeotethys Ocean and resulting in the Cimmerian Orogeny.

Micas from metapelites, amphibole from an amphibolite and magmatic white mica from deformed granite from the Gasht Complex yield very similar 40Ar/39Ar step-heating plateau ages between 175.1 ± 0.5 Ma and 177.0 ± 0.4 Ma (2 sigma) that are independent of grain size and nominal closure temperatures. In addition, clearly retrograde white mica replacing andalusite porphyroblasts in a metapelite yielded a similar plateau age of 176.1 ± 0.5 Ma.

In the Gasht-Masuleh area the contact between basement and the cover rocks is largely tectonic due to later faulting, but the Gasht Complex must have formed the depositional basement to the late Triassic- Middle Jurassic Shemshak Group. Sedimentation started in the Carnian above the regionally developed Eo-Cimmerian unconformity in the central and eastern Alborz and continued until the mid-Bajocian.

Notably, within the Shemshak Gp. a distinct, regional scale unconformity developed in the mid-Bajocian (c. 170 Ma) recognized by rapid coarsening in sediment grain size. Only locally, in the eastern Alborz Mountains, it developed as an angular unconformity related to block rotation. This Mid-Cimmerian unconformity formed as a result of tectonic movements causing rapid uplift and erosion.

Our c. 175 – 177 Ma mica and amphibole plateau ages for the Gasht Complex are unlikely to reflect slow cooling following the (Carboniferous? Late Triassic?) metamorphism, as this would result in increasingly younger ages for amphibole, white mica and biotite. Instead, the indistinguishable ages for peak metamorphic and retrograde minerals must be due to very rapid cooling at the Toarcian-Aalian boundary (c. 174 Ma) that resulted from rapid basement uplift and at the surface caused the mid-Bajocian Mid-Cimmerian unconformity. Thus, the c. 175 – 177 Ma 40Ar/39Ar ages document the thermal response of the basement below the Shemshak Group to a mid-Jurassic extensional tectonic event.

From a regional perspective, the Mid-Cimmerian unconformity may represent the break-up unconformity of back-arc rift basins that formed due to northward Neotethys subduction to the south of the Alborz Mountains (Wilmsen et al. 2009) and/or the onset of sea-floor spreading within the South Caspian Basin to the north (Fürsich et al. 2009).

Fürsich et al. 2009, Geol. Soc., London, Spec. Publ. 312, 189-203. Razaghi et al., 2018, Geosciences 27, 269-280. Rosetti et al. 2016, J. Geol. Soc. London 174, 741-758. Wilmsen et al. 2009, Terra Nova 21, 211–218.

How to cite: Rezaei, L., Timmerman, M. J., Moazzen, M., and Sudo, M.: Latest Toarcian (c. 175-177 Ma) 40Ar/39Ar mineral ages for amphibolite-facies basement rocks of the Gasht Complex, Alborz Mountains, North Iran: deep crustal response to mid-Jurassic rifting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1334, https://doi.org/10.5194/egusphere-egu2020-1334, 2019

D1089 |
EGU2020-22380
Nalan Lom, Abdul Qayyum, and Douwe J.J. van Hinsbergen

Iran is a mosaic of continental blocks that are surrounded by Palaeo-Tethyan and Neo-Tethyan oceanic relics. Remnants of the ophiolitic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The Present-day “ring” distribution of the Iranian ophiolites is not straightforwardly explained by a simple subduction zone architecture. One of the key features to solve the Iranian puzzle is the CIM which is surrounded by Sabzevar ophiolites in the north (99-77 Ma), Birjand-Nehbandan ophiolites in the east (~110 Ma) and Inner Zagros ophiolites in south-southwest (~103-94 Ma). The CIM consists of three major fault bounded sub-blocks, from east to west, Lut, Tabas, and Yazd. They represent an Atlantic-type continental margin that began rifting in Permo-Triassic as a result of opening of Neotethys Ocean. Subsequent convergence in Cretaceous to Paleogene time close the ocean basins around the CIM and emplaced the ophiolites onto the passive margins. Neogene Arabia-Eurasia collision induced replacement structures e.g., strike‐slip reactivation of normal faults that were associated with major block rotations.

We aim to kinematically restore the opening and closure history of the ocean basins found as ophiolitic relics around the CIM. Key in our analysis is the Doruneh and Great Kavir faults of Central Iran that continues into northern Afghanistan as the Herat Fault. Present-day GPS velocity vector measurements and deformation pattern show a NE-SW orientated shortening in Iran. Structural analysis of the Doruneh Fault indicates slip sense inversion before ~5 Ma. This observation is consistent with the deactivation of the dextral Herat Fault. Pre-Pliocene dextral movement in excess of 500 km along the Doruneh and Great Kavir faults may kinematically accommodate a major counter-clockwise rotation (~65o) of the CIM since the late Jurassic that has been inferred based on previous palaeomagnetic studies. This enables the transport of the Jandaq ophiolite from Aghdarband in the north to Anarak region of Central Iran and, duplication of curved Birjand-Nehbandan ophiolites in Sistan suture. If correct, this may imply that the closure history of the Central Iranian basins is directly connected to the large-scale Cretaceous to Paleogene extrusion tectonics in western Tibet and Hindu Kush regions. This preliminary study shows restoration of the post-Mesozoic deformation is essential to reconstruct the suture zones and pre-collisional setting in Iran, Afghanistan, and Pakistan.

How to cite: Lom, N., Qayyum, A., and van Hinsbergen, D. J. J.: An attempt to reconstruct central and eastern Iranian ophiolite puzzle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22380, https://doi.org/10.5194/egusphere-egu2020-22380, 2020

D1090 |
EGU2020-12873
Wei Li, Yun Chen, Ping Tan, and Xiaohui Yuan

The Pamir plateau, located north of the western syntaxis of the India­–Eurasia collision system, is regarded as one of the most possible places of the ongoing continental deep subduction. Based on a N-S trending linear seismic array across the Pamir plateau, we use the methods of harmonic analysis of receiver functions and the cubic spline interpolation of surface wave dispersions to coordinate their resolutions, and perform a joint inversion of these datasets to construct a 2-D S-wave velocity model of the crust and uppermost mantle. A spatial configuration among the intermediate-depth seismicity, Moho topography, and low-velocity zone(LVZ)s within the crust and upper mantle is revealed. The intermediate-depth seismic zone is enclosed in a mantle LVZ which extends upward to the crustal root and connects with a lower crustal LVZ in the northern Pamir. Just above it, another crustal LVZ is collocated with a Moho uplift. These results not only further confirm the deep subduction of the Asian lower continental crust beneath the Pamir plateau, but also indicate the importance of the metamorphic dehydration of the subducting continental crustal material in the genesis of the intermediate-depth seismicity and crustal deformation.

How to cite: Li, W., Chen, Y., Tan, P., and Yuan, X.: Geodynamic processes of the continental deep subduction: constraints from the fine crustal structure beneath the Pamir Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12873, https://doi.org/10.5194/egusphere-egu2020-12873, 2020

D1091 |
EGU2020-12325
Zhen Zhang, Huai Zhang, and Yaolin Shi

The Qilian Shan orogenic belt, located in the northeastern margin of the Tibetan Plateau, undergoes intensive Cenozoic structural deformation with large lateral growth since the Miocene. The Cenozoic growth of the Qilian Shan is possibly resulted by the passive subduction of the North China Craton due to the far-field effect of the continuous Indo-Asian collision. Thus, the Qilian Shan can be seen as a syntectonic crustal-scale accretionary wedge above a middle intra-crustal weak layer. To date, the detailed Cenozoic crustal deformation manner of the Qilian Shan and its adjacent two basins remains unclear, especially for the southward propagation towards the Qaidam Basin. Whereas, the spatio-temporal characteristics of deformation distribution between the Qilian Shan and the adjacent two basins are critical to fulfill the lateral growth of the Tibetan Plateau. Hence, we conducted a series of high-resolution 2-D numerical models to investigate factors that influence crustal strain distribution. The first series models are thick-skinned models with single décollement, while Series II are two-décollement layer model, regarding the interaction between thick- and thin-skinned tectonics beneath the two adjacent basins. After 150 km of total convergence, model results suggest that the single décollement layer model is not sufficient in depicting the present-day crustal deformation pattern, while strain localization pattern from two-décollement layer model meets well with the geological and geophysical observations. The Hexi Corridor Basin may be involved with deep-crustal thrusting while the dominant deformation is still thin-skinned tectonics. Series III adds the filling-up sedimentation based on the conditions of Series II. We reveal that the differential sedimentation types between the Qaidam Basin and the Hexi Corridor Basin greatly depress fault propagation towards the Qaidam Basin. Note that, how deformation transfers into the Qaidam Basin remains controversial. To date, the above models still need to evolve. However, in summary, our study highlights the crustal deformation of the two margins of northeastern Tibetan Plateau is controlled by the décollements and differential sedimentation styles.

How to cite: Zhang, Z., Zhang, H., and Shi, Y.: The bivergent growth of the Cenozoic Qilian Shan, northeastern Tibetan Plateau: Insights from numerical models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12325, https://doi.org/10.5194/egusphere-egu2020-12325, 2020

D1092 |
EGU2020-13583
Monumoy Ghosh and Supriyo Mitra

We present Love wave group velocity tomography calculated from broadband waveform data from Indian seismograph networks and global dataset downloaded from the IRIS-DMC. We first calculate path average 1-D fundamental mode Love wave group velocity between 10 s and 120 s period of the Transverse component of the seismograms. Then we combine these 1-D path average measurements using linear tomographic inversion, assuming great circular arc propagation, to compute 2-D group velocity map of the region at discrete periods. The region is adaptively parametrized to get high resolution at higher raypath density. We performed checker-board test to ascertain the resolution of the tomography maps and compute ray density map, raypath cross density map, and raypath orientation map to quantitatively analyze the controls of these parameters on the checker board resolution recovery. Tomographic maps at lower period show good correlation to the local geologic structures like low velocity in basins and high velocity in cratons and shields. At mid-period maps high velocity roots of cratons and low velocity in Tibet and Andaman- Burma subduction can be seen. At higher period low velocity in Tibet conforms with previous observations. We will do linear inversion of Love wave group velocity to get 3D SH wave velocity structure of the region.

How to cite: Ghosh, M. and Mitra, S.: Love Wave Group Velocity Tomography of India, Himalaya and Tibet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13583, https://doi.org/10.5194/egusphere-egu2020-13583, 2020

D1093 |
EGU2020-3213
Huiying He, Peter Cawood, and Yuejun Wang

In Southeast Asia, establishing the origin and associated tectonic setting of Late Paleozoic-Early Mesozoic igneous rocks is complicated by structural overprinting and the complex tectonic evolution of the Paleotethyan regime. Hainan Island, located at the south-eastern margin of the Paleotethys, and lacking significant tectonic overprints is a key to understand amalgamation history of the Indochina and South China blocks and to constraining the tectonic evolution of Paleotethys ocean in southeast Asia.

The Late Paleozoic-Early Mesozoic record of igneous rocks on Hainan Island includes the following. 1) ca. 350 Ma island arc andesites and ca. 330 Ma metabasites, the latter with both MORB- and arc-like geochemical affinities, positive εNd(t) values of +5.86 – +9.85 and rare inherited zircons with a zircon age of 1400 Ma inferred to be derived from a MORB source with the input of a slab-derived component. Together with the ~350 Ma island arc andesites, the Carboniferous tectonic environment is supposed to be a continental back-arc basin setting. 2) Late Permian gneiss granitoids (272-252 Ma) characterized by a gneissic foliation and calc-alkaline I-type geochemical affinities with negative Nb-Ta and Ti anomalies, related to metasomatized mantle wedge modified by the sediment-derived component in a continental arc setting. 3) ca. 257 Ma arc-like andesites, which further validate a subduction-related setting. 4) Peraluminious Early-Middle Triassic massive granitoids (251–243 Ma) with slightly high A/CNK ratios, δ18O values (up to 11.75 ‰) and Sr/Y ratios, inferred to have formed in a compressive regime from a mixed source of greywacke and metabasite. 5) Middle-Late Triassic (242–225 Ma) high-K calc-alkaline granitoids with high zircon temperatures (842–867°C) and geochemical signatures of A-type granites. They show slightly low whole-rock εNd(t) and zircon εHf(t) values, suggestive of the derivation from a metabasite–greywacke source in an extensional setting. 6) ca. 240 Ma gabbro-dolerites showing enrichment in LILEs, depletion in HFSEs, negative εNd (t)-εHf (t) values (−8.45 to −1.05 and −5.9 to −2.7, respectively) and crustal-like δ18O values (7.26–8.70‰), it is implied that the Hainan Island entered into post-collisional environment in response to the asthenosphere upwelling shortly after the closure of back-arc basin.

Thus, Hainan Island provides a record of Carboniferous back-arc basin opening, followed by an extended Permian–Triassic history of subduction-related consumption leading to orogenic assembly and extensional collapse between the South China and Indochina blocks. Such a tempo-spatial pattern is consistent with that along the Song Ma–Ailaoshan suture zone rather than the magmatic history of eastern South China and indicates that the Paleotethys extended west to at least Hainan Island in the Late Paleozoic-Early Mesozoic.

How to cite: He, H., Cawood, P., and Wang, Y.: Late Paleozoic- Early Mesozoic tectonics of Hainan Island: Key to understanding Paleotethyan geology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3213, https://doi.org/10.5194/egusphere-egu2020-3213, 2020

D1094 |
EGU2020-7166
Yiming Bai, Yumei He, Xiaohui Yuan, Myo Thant, Kyaing Sein, and Yinshuang Ai

The territory of Myanmar, situated at the eastern flank of the India-Asia collision zone, is characterized by complex tectonic structure and high seismicity. From west to east, this region consists of three nearly NS-trending tectonic units: the Indo-Burma Ranges, the Central Basin and the Shan Plateau. Detailed structure of the crust and uppermost mantle beneath Myanmar can provide crucial constraints on regional tectonics, subduction dynamics as well as seismic hazard assessment. Yet seismic velocity structure beneath this region is poorly determined due to sparse regional seismic networks.

In this study, we utilize seismic data recorded at 80 broadband stations in Myanmar, among which 70 stations were deployed in 2016 under the project of China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO), 9 stations are operated by IRIS and the remaining one is from GEOFON. We measured the Rayleigh-wave phase velocity dispersion from the ambient noise cross-correlations at periods between 5 s and 40 s by using the automatic frequency-time analysis (AFTAN). A fast marching surface wave tomography (FMST) approach was then adopted to invert the 2-D phase velocity maps in the study region. Our preliminary results show variable crustal structure across central Myanmar, with a strong low-velocity zone north of 22°N in the Indo-Burma Ranges. Since Rayleigh-wave dispersion is more sensitive to absolute velocity speed than to velocity contrasts, the ongoing study jointly inverts the dispersion data with P-wave receiver functions to better determine the velocity discontinuities and thus provides tighter constraints on the shear-velocity structure beneath central Myanmar.

How to cite: Bai, Y., He, Y., Yuan, X., Thant, M., Sein, K., and Ai, Y.: Crustal and Uppermost Mantle Structure Across Central Myanmar by Joint Analysis of Receiver Functions and Rayleigh-wave Dispersion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7166, https://doi.org/10.5194/egusphere-egu2020-7166, 2020

D1095 |
EGU2020-19604
Suwijai Jatupohnkhongchai, Sirot Salyapongse, Burapha Phajuy, Daniela Gallhofer, and Christoph Hauzenberger

A series of pyroclastic rocks are mapped as a Silurian-Devonian unit in the Kanchanaburi-Uthai Thani area, Western Thailand, which belongs to the Inthanon Zone. These pyroclastic rocks were discovered and described for the first time in 1977 and mentioned in the 1:250,000 Suphanburi geologic map sheet and report. Since then these rocks were poorly investigated and their formation and geotectonic setting is unclear. As a result, we report petrographic, geochemical and geochronological data of these pyroclastic rocks. Petrographically, the pyroclastic rocks can be described as a meta-quartz-K-feldspar crystal tuff, a meta-quartz crystal tuff, and a meta-lithic tuff. They are made up of mm sized clasts in a finely grained matrix. The clasts consist of potassium feldspar, rounded quartz, embayed quartz, trachytic and metasedimentary rock clasts embedded in a highly altered devitrified fine-ash matrix containing sericite.

The whole-rock composition shows enrichments in SiO2 and K2O and a strong depletion in CaO and Na2O which is related to late alteration of the volcanoclastic rocks. Based on the immobile element classification plot of Pearce 1996, the tuffs can be classified as trachyandesite, trachyte, dacite and rhyolite. Their chondrite-normalized REE patterns display light REE enrichment with nearly flat heavy REE and a negative Eu anomaly, typical for calcalkaline volcanic rocks. Most samples fall in the volcanic arc granites field in the granite discrimination diagrams of Pearce 1984.

Zircons extracted from the tuffs will be used to constrain their crystallization age by U-Pb LA-MCICPMS dating. This allows us to constrain the age of formation and to place this in context with the closure of the Paleotethys.

How to cite: Jatupohnkhongchai, S., Salyapongse, S., Phajuy, B., Gallhofer, D., and Hauzenberger, C.: Pyroclastic rocks from Kanchanaburi and Uthai Thani Province, Inthanon Zone, Western Thailand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19604, https://doi.org/10.5194/egusphere-egu2020-19604, 2020