TS7.4

The eastern Mediterranean Sea preserves crust that was trapped during the collision of Africa with Eurasia and the closure of the Neo-Tethyan Ocean. Thick sedimentary blanketing (10 to 15 km) complicates our ability to assess the nature of the crust, and therefore it has remained one of the least understood regions of the collision belt. In this presentation, I review recent marine geophysical observations (surface and deep-tow magnetics, high-resolution bathymetry and seismic reflection data) and discuss their geodynamic implications. The surface total field and vector magnetic anomalies from the Herodotus Basin reveal a sequence of long-wavelength NE-SW lineated anomalies that straddle the entire basin suggesting a deep two-dimensional magnetic source layer. The magnetic vector data indicate an abrupt transition from a 2D to a 3D magnetic structure along the eastern edge of the Herodotus Basin and west of the Eratosthenes Seamount, where a prominent gravity feature is found. These findings indicate that the Herodotus Basin preserves remnants of oceanic crust accreted along a mid-ocean ridge system that spread in an NW-SE direction. The African Plate's continuous northward and counterclockwise motion during the Paleozoic and Mesozoic allow predicting the crustal remanent magnetization directions, which dictate the shape of the present-day magnetic anomalies. The shape of the Herodotus anomalies best fit Carboniferous magnetization directions. The combination of surface and deep-tow magnetic data, as well as thermal and magnetic forward modeling, suggest that spreading was slow (~25 km/myr half spreading rates) and that the upper oceanic crust has been entirely demagnetized, probably due to the heating effect induced by the thick sedimentary coverage.

The stretched continental crust of the Levant Basin, found east of the Herodotus Basin, preserves a series of horsts and grabens that generally orient in an orthogonal direction relative to the spreading direction, suggesting that they may have formed concurrently with the initial opening of the Herodotus Basin. Earthquake data and long NW-SE bathymetric scars found within the northern edge of the Nile deep-sea fan suggest that an active fault belt transfers the motion from the Gulf of Suez toward the northern convergence boundaries. This fault belt is directed toward, and merges with, the continental-ocean boundary that straddles the eastern Herodotus Basin. This observation may indicate that the mechanical transition from the rather weak and stretched continental crust of the Levant to the relatively strong oceanic Herodotus crust has guided the location of the western boundary of the Sinai Microplate, formed during the Oligocene by the fragmentation of the African Plate.

How to cite: Granot, R.: Trapped remnant of the Tethyan realm: the influence of ancient tectonics on the present-day geodynamics of the eastern Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9408, https://doi.org/10.5194/egusphere-egu22-9408, 2022.

The Black Sea is the largest European back-arc basin connected to the subduction and final closure of the Tethys ocean. Its origin and type of crust are widely debated, with contrasting views suggesting it is either a relic of Paleotethys or a rifted back-arc basin formed within the thick and cold Precambrian lithosphere. To investigate the structure of this atypical intra-continental basin, we constructed the highest resolution seismic tomography of the region using the latest techniques of probabilistic inversion of ambient noise data recorded at seismic stations around the sea. Our results indicate the presence of thinned continental crust beneath the basin, likely of Precambrian lithospheric origin, thus invalidating the existence of either a relic Paleotethys fragment or younger oceanic crust. Extension and rifting probably exploited pre-existing sutures, but the rheologically strong lithosphere resisted transition to seafloor spreading. Seismic anisotropy shows complex paleo-deformational imprints within the crust and upper mantle related to the closure of Tethys. Extension caused by subduction roll-back generated anisotropic lithospheric fabric parallel to the rifting axis within the thinnest sections of the crust in the western basin. The eastern part developed on a distinct lithospheric domain that preserves paleo-extension anisotropy signatures in the form of lower crustal viscous deformation. Further south, anisotropy orients along the Balkanide-Pontide collisional system that records the final stages of Neotethys closure. Our results place key constraints on the type of deformations that occurred throughout the Tethyan realm, with fundamental implications for the development and evolution of back-arc basins and continental break-up. 

How to cite: Petrescu, L., Borleanu, F., and Placinta, A.: Seismic structure of a Tethyan back-arc: transdimensional ambient noise tomography of the Black Sea lithosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2493, https://doi.org/10.5194/egusphere-egu22-2493, 2022.

Middle Permian bimodal volcanic rocks exposed in the Kocaeli Peninsula represent the first igneous event in the entire Paleozoic record of the Istanbul Zone together with coeval acidic intrusions reported from other parts of the zone. These volcanic rocks crop out as intercalations at the lower horizons of Permian-Earliest Triassic fluvial sedimentary rocks and mainly include basalts and rhyolites with subordinate andesites and rhyolitic tuffs. The basalts were derived from 1-3% partial melting of spinel peridotite in the lithospheric mantle; their high Mg-numbers (Mg# = 63-68) along with Ni (85-136 ppm) and Cr (198-240 ppm) concentrations point to derivation from near-primary mantle melts with minor fractionation. These rocks did not undergo low-pressure plagioclase crystallization based on the lack of a Eu anomaly (Eu/Eu* = 0.95-0.99). Their vesicles are filled by secondary calcite, epidote, pumpellyite, albite and chlorite due to hydrothermal alteration under subgreenschist facies conditions whereby temperatures ranged between 250-300°C. The rhyolites are ferroan [FeO*/(FeO*+MgO) = 0.87-0.96], characterized by high Zr concentrations (279-464 ppm) and compositionally similar to A₂-type granitic magmas. Incompatible trace element ratios, rare earth element patterns, initial εNd isotopic data along with temperatures of the rhyolitic melts and absence of inherited zircons in the rhyolites collectively suggest that the rhyolites were derived from fractional crystallization of some basaltic melts in a crustal magma chamber with plagioclase fractionation and minor crustal contamination while the basalts were directly derived from the lithospheric mantle and reached the surface with negligible fractionation. Both volcanic rocks display diagnostic features of subduction-zone melts such as (i) medium- and high-K calc-alkaline affinity and (ii) enrichment in large-ion lithophile elements (LILE) but depletion in high-field strength elements (HFSE) (e.g., Nb-Ta troughs). U-Pb dating of zircon grains extracted from one rhyolite sample yielded a concordia age of 262.7 ± 0.7 Ma (2σ) (Capitanian). The observation that the rhyolites occur near the base of the associated sedimentary rocks places a tight constraint on the age of deposition of these deposits. The bimodal nature of the volcanic rocks, A₂-type signature of the rhyolites, local stratigraphic record and data from regional geology (e.g., possible correlation with Late Permian-Early Triassic A-type rift-related granites in Carpathians and Balkans) all indicate an extensional event in the region which started in Middle Permian and resulted in the deposition of Early Triassic quartz sandstones. This extension seems to have taken place above a subduction zone developed in response to a Late Paleozoic-Triassic ocean floor (Paleo-Tethys) dipping northward beneath Laurasia, as evidenced by Permo-Triassic accretionary melanges restricted to Sakarya Zone. In conclusion, geochronological, geochemical and regional data provide additional evidence that the Paleo-Tethys Ocean was subducting northward beneath Laurasia during Permian time.

How to cite: Babaoğlu, C., Topuz, G., Okay, A., Köksal, S., Wang, J.-M., and Köksal, F.: Middle Permian calc-alkaline basalts and ferroan rhyolites in the Istanbul Zone, NW Turkey: Evidence for Permo-Triassic subduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-65, https://doi.org/10.5194/egusphere-egu22-65, 2022.

The Strandja Massif is a key location for understanding the Paleozoic and Mesozoic tectonic evolution of the Tethyan Realm in the NW Turkey. Some researchers have suggested that the Strandja Massif is a part of the Cimmerian continent, but others consider it as a section of the southern passive continental margin of the Eurasia. Traditionally the massif is divided into two tectono-stratigraphic units: 1) Pre-Permian crystalline basement and 2) Mesozoic sedimentary cover. However, the ages of the lithostratigraphic units have been significantly revised following the recent geochronological studies. Structural relations between these units are not simple and should be re-examined carefully. Our previous studies have shown that the crystallization time of the magmatic rocks and sedimentation ages of the rocks range from late Proterozoic to Permian especially at the east of the Strandja Massif. In this study, the Serves metagreywacke sporadically containing metabasic rocks and Kumlukoy quartz-rich metasandstones are investigated at the north of the Kıyıköy town, in order to check the first studies that assigned them to the Jurassic and Cretaceous cover deposits. These units stretch along the Black Sea coast and reveal significant differences with units that are exposed to the south. Particularly the Serves unit consists of alternation of lithic metasandstones, schists, and phyllites whereas metaconglomerate layers, marble and dolomite bodies are common among Jurassic rocks exposed in the south. Detrital zircon studies carried on the metasandstone reveal that the sedimentation should be younger than Visean-Serpukhovian, because the youngest U-Pb zircon age population obtained are between ~338 and 327 Ma. Considering widespread late Carboniferous magmatism (~312-306 Ma) in the Strandja Massif and bereft of such magmatics constrain deposition of this unit between ~327 and 312 Ma (early-middle Pennsylvanian). In contrast, the Kumlukoy Unit has quartz-rich metasandstones and it has lower metamorphic degree than the Serves Unit. The detrital zircons of these metasandstones, which were considered as Cretaceous in the previous studies, indicate that the sedimentation interval of the unit is younger than latest Permian (~256 Ma). According to the detrital ages obtained the Kumlukoy metasandstone represent a higher stratigraphical position than the Serves metagreywacke. The Kumlukoy metasandstone is most probably the equivalent of the Triassic metaclastics reported in the cover units of the NW Strandja Massif. Whereas the age and petrography of the Serves metagraywacke are similar to the Mahya Complex and Yavuzdere Arc which was interpreted as a paired magmatic arc-accretionary prism unit. Another interpretation is that the Serves Unit predates the Mahya Complex and Yavuzdere Arc and all of them represents a long-lasting subduction and accompanying accretion events in the late Paleozoic history of the Strandja Massif, namely the Silk-road Arc.

How to cite: Akın, A., Sunal, G., Natal'in, B. A., and Aysal, N.: Origin of the metamorphic flysch sequence of the Strandja Massif (NW Turkey) in the Tethyan Realm: insights from new age and structural data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-394, https://doi.org/10.5194/egusphere-egu22-394, 2022.

Orogenic plateaux, the broad high elevation regions of Earth, are mainly formed by plate convergence/shortening and in some cases, there is (hot) mantle support for their formation. Two major examples at present are the Tibetan and Turkish-Iranian plateaux. For instance, Turkish-Iranian plateau, is a consequence of the continental plate collision between Arabia and Eurasia, which began at ~34-25 Ma and continues to the present day. The plateau can be regarded as two distinct entities, with a boundary at roughly the political border between Turkey and Iran. While there have been studies to explain the uplift history, lithospheric/crustal structure and associated magmatism, currently, the mechanisms behind the plateau growth are not well understood. The western region, also known as the East Anatolian Plateau, has a tectonic plate structure with a near-normal crustal thickness (~35-40 km) and a markedly thinned mantle lithosphere (a few 10s of km in thickness). This suggests that, to achieve its regional elevation of ~2 km there is likely considerable support from the underlying hot asthenospheric mantle. In the east, the crust of most of Iran is thicker, up to ~65 km, and it is underlain by a variable but thicker mantle lithosphere (commonly >100 km thick). It is intriguing why these two regions have similar surface elevations (2-3 km on average) and regional geomorphology, despite predicted lithospheric structures. This study will apply new class of geodynamic models to understand how such plateaux form in response to plate collision/convergence and possible mantle upwelling/support. By comparing models with different setups (varying lithospheric thicknesses, strength profiles etc.) suggested by the natural case studies, this study will provide a more general assessment of controls on plateau growth with 2-D and 3-D perspectives in the context of Arabia-Eurasia collision. Further, the study will also help to explain the role of the forces that generate dynamic topography in the evolution of such geologic structures.

How to cite: Çetiner, U., van Hunen, J., Göğüş, O., Allen, M., and Valentine, A.: Arabia-Eurasia Collision and The Geodynamic Models for Plateau Uplift in Turkish-Iranian Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-568, https://doi.org/10.5194/egusphere-egu22-568, 2022.

Situated between Africa and Eurasia in the eastern Mediterranean, the island of Cyprus has developed on the northern margin of the southern Neotethys by the accretion of three terrains, the Mamonia complex, the Troodos ophiolite, and the Kyrenia terrane. The Kyrenia terrane comprises a tectonic stack of Triassic to Eocene rock units interleaved with basic and acid volcanics and minor metamorphic inliers, alongside an Oligocene-Miocene flysch. Our U-Pb-Hf detrital zircon investigation in the Kyrenia Triassic to Eocene section reveals a large amount of Neoproterozoic zircons (950-600 Ma), alongside Silurian (∼430 Ma), Carboniferous (∼300 Ma), Triassic (∼240 Ma), and Upper Cretaceous (∼85 Ma) zircons. The Precambrian age profile of all three studied units resembles that of Paleozoic sandstones of the Tauride Block, as well as that of Paleozoic and Mesozoic sandstones found across North Africa. It is interpreted as reflecting the reworking of Paleozoic sandstone units from the Taurides or other peri-Gondwanan source. The presence of a substantial proportion of ~300 Ma zircons, as early as in Triassic sediments of the Kyrenia, is of significant interest because Carboniferous magmatism is confined to the Paleotethyan realm which is traced north of the Taurides. Deposition of the Kyrenia sequence closer to a Northern Tethyan province would better fit its detrital zircon signal. The detrital signal of the Kyrenia, indicative for Eurasian terranes north of the Mediterranean, also differs significantly from that of the Mamonia Complex (SW Cyprus) in which only Afro-Arabian sources are distinguished. Thus, in view of its unusual detrital zircon content, the Kyrenia sequence stands out in the Eastern Mediterranean as an exotic rock pile that cannot be straightforwardly correlated with its neighboring geologic environment.

How to cite: Glazer, A., Avigad, D., Morag, N., Güngör, T., and Gerdes, A.: Detrital zircon evidence for exotic elements in the southern Neotethys: A provenance study of Triassic-Eocene rock units in the Kyrenia terrane, Northern Cyprus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5391, https://doi.org/10.5194/egusphere-egu22-5391, 2022.

The northern extent of the supercontinent Gondwana in the late Neoproterozoic-Cambrian is not well defined. In most localities the continental margin is covered by thick sedimentary successions, formed following the successive rifting of Tethyan Oceans that episodically detached continental terranes from the edge of the supercontinent. East of the Mediterranean, despite the continental continuity between the Arabian-Nubian-Shield (ANS) and the Tauride block (a Cadomian terrane), the original transition between the two crustal domains is inaccessible and remains obscured. In Israel, investigations of Late Ediacaran, late-stage igneous intrusions of the ANS in the South, together with granulite xenoliths from the lower crust in the North, allow us to probe into the North-Gondwana edge in the late Neoproterozoic and envisage its transition towards the peri-Gondwana Cadomian realm, as well as the evolution of the North Gondwana crust subsequently to the Neoproterozoic. Geochronology and isotopic geochemistry of alkaline intrusions in the Amram massif (southern Israel) as well as doleritic intrusions in the late Neoproterozoic Zenifim Formation (subsurface of south-central Israel) has revealed an igneous and thermal imprint at ca. 550 Ma recorded by the reset of apatite U-Pb ages, together with additional apatite U-Pb dates taken to represent crystallization. Nd and Hf isotopes in apatite, zircon and whole rock also show the ca. 550 Ma intrusions are isotopically distinct from the ANS and resemble Cadomian magmatism in the Taurides. Granulite xenoliths from the lower crust under the lower Galilee (North Israel) contain abundant zircons of distinct U-Pb-Hf properties. These include detrital grains remnant of Neoproterozoic sediment that was subducted and relaminated to the lower crust, late Carboniferous zircons (peaking at 300 Ma) with contrasting εHf_(t) signatures, some of which represent syn-Variscan magmatism, and zircons with the age of the host Pliocene basalt. We demonstrate that the Cadomian (ca. 550 Ma) igneous and thermal imprint on the North ANS may have been driven by proto-Tethys subduction that brought about sediment relamination to the North Gondwana lower crust in the latest Neoproterozoic. The late Carboniferous ages recorded in the xenoliths involve both the reworking of depleted ANS basement as well as the relaminated sediment in the means of metamorphism and minor magmatism. Carboniferous thermal disturbance was associated with the formation of continental scale basin and swell architecture across present-day N Africa, Arabia and Iran, and the development of ‘Hercynian unconformities’ in these areas, that were located at the time south of the passive(?) margin of Paleo-Tethys.

How to cite: Abbo, A., Avigad, D., Gerdes, A., and Morag, N.: The Cadomian and Variscan record of the Gondwana margin in Israel: Protracted Crustal Evolution between the Arabian-Nubian Shield and multiple Tethyan Oceans, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1777, https://doi.org/10.5194/egusphere-egu22-1777, 2022.

The Beni Suef Basin, a rift basin in north-central Egypt, was formed in response to the NeoTethys and Atlantic oceans opening and the associated tectonic motion between Africa and Eurasia during the Early Cretaceous. It is bisected by the Nile Valley into the East and West of the Nile Provinces (EON and WON) and comprises a mixed siliciclastic-carbonate succession ranging from the Albian to the Oligocene.

Burial and thermal history modeling was performed to investigate the subsidence and sedimentation rates in the context of the tectonic evolution of the basin. Tareef-1x well from the EON and Fayoum-1x well from the WON were selected for this study, where the input data and the boundary conditions were incorporated based on the available well reports and literature.

The results show that during the Albian syn-rift phase, sedimentation was initiated slightly later with low burial rates of about 33 m/My in the EON compared with high sedimentation rates of about 210 m/My in the WON. The post-rift phase was characterized by rapid thermal subsidence accompanied by relatively moderate sedimentation rates of around 117 m/My in the EON and 97 m/My in the WON. By the Late Cretaceous, an erosional uplift occurred and culminated through the entire Paleocene resulting in the removal of some parts of the Late Cretaceous Khoman Formation from both sides of the basin. Subsidence had resumed during the Eocene due to extensional tectonics with elevated average sedimentation rates of approximately 145 m/My in the EON compared with relatively low sedimentation rates of approximately 74 m/My in the WON. These phases are interrupted by a hiatus period during the Late Eocene-Oligocene in the EON, while the WON has continued subsiding and resulted in the deposition of the Oligocene Dabaa Formation. The Miocene thermal uplift represents the last tectonic phase, which led to significant erosion from the Eocene Apollonia Formation in the EON and the Oligocene Dabaa Formation in the WON.

The implications on the hydrocarbons potentiality were also investigated through the thermal history modeling, where we found that the Turonian Abu Roash “F” source rock exists in the early oil window with a transformation ratio of about 20 % across the entire basin. While the Lower Kharita shale source rock, which is only deposited in the WON, has reached the late oil window with a transformation ratio of approximately 70 %.

In summary, sedimentation began slightly later in the EON (Middle to Late Albian) compared with the WON (Early Albian), where the paleo basement high has hindered the deposition of the Early Albian Lower Kharita shale in the EON compared with the WON, thus caused a delay at the beginning of the deposition. The different sedimentation rates across the basin could be attributed to various factors such as the amount of sediment supply, climate conditions, different slopes across the basin, and /or lithology, which need to be addressed in further research.

How to cite: Tawfik, A. Y., Ondrak, R., Winterleitner, G., and Mutti, M.: Subsidence and Sedimentation Rates of the Beni Suef Basin, Egypt: Insights From the Burial and Thermal History Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1162, https://doi.org/10.5194/egusphere-egu22-1162, 2022.

The Late Cretaceous Oman Mountains are generally assumed to result from obduction followed by the inversion of the mid-Permian- to Triassic Neotethyan rifted margin. However, the key rift-related crustal features, such as a necking zone or hyper-extended rift domains remain inferred and poorly described so far. In this study, we investigate the tectono-stratigraphic record of the eastern part of the Oman Mountains where the exposed Tonian (Neoproterozoic) crystalline basement outcrops together with the pre- to syn-obduction sedimentary record in the Ja’alan massif area. The description of these units together with subsurface data enables to describe the former Arabian necking zone. The Ja’alan massif itself and the Arabian platform to the southwest represent the former proximal margin domain. It is characterized by the eroded basement sealed by post-obduction continental to shallow marine sediments. In contrast, the north-eastern side of the massif is flanked by Permian-Mesozoic deep marine post-rift sediments (Batain Group) equivalent to the Hawasina thrust sheet in the Oman Mountains. These two endmember paleogeographic units are separated by a major N20 dipping top-to-the-NE normal fault with dip-slip kinematics (slikensides with striae, S/C-fabric). The damage zone of this fault is characterized by a cataclastic and a gouges fault zone, overlain by slope facies with syn-kinematic polymictic mega-breccias reworking the adjacent basement. The breccias are grading finer upwards, contain conglomerate and sandstone interbeds interpreted as to slope-environment turbiditic channel deposits. This exhumation and rift-related record is unconformably covered by the post-obduction sequence affected by a late Cenozoic E/W-directed low-amplitude shortening. The intensity of shortening is increasing toward the NW leading to reactivate the Arabian Necking zone as a ramp for the Hawasina thrust system. Based on these observations, we propose a new geodynamic model showing that the final stage of the obduction result from the inversion of the former Arabian necking zone with significant impacts on the evaluation of (1) the shortening rates accommodated and (2) the former architecture of the Arabian Tethyan rifted margin. As the belt never recorded a mature continent-continent collision, we think that the Oman study case could significantly help to investigate the dynamics of hyper-extended rifted margins inversion at an early orogenic stage.

How to cite: Ducoux, M., Masini, E., Scharf, A., and Calassou, S.: The Neotethyan Arabian necking zone exposed at the SE Oman mountains: field evidence and consequences, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11305, https://doi.org/10.5194/egusphere-egu22-11305, 2022.

The Eocene Lower and Middle members of Rus Formation are exposed at the King Fahd University of Petroleum and Minerals (KFUPM) campus and contain 'odd' structural features. Previously, such structures were overlooked or misinterpreted by other researchers. In this study, we interpret these structures as hydroplastic kinematic indicators in the basal part of the Middle Rus Member. Their occurrence is related to the Rus soft-sediment detachment, a major displacement zone at the boundary/interface between the Lower and Middle Rus. The structures are fist-sized vugs coupled with carrot- or comet-trail imprints (VCT structures), previously translated calcite geodes. VCT structures demonstrate NNW (345°) transport/slip and are found on flat to low-dipping surfaces characterized as Y, R, and P shears according to the Rus detachment orientation. The Andersonian transtension stress regime is indicated by palaeostress analysis, but it was not enough to activate the Rus soft-sediment detachment. The negative effective principal stress σ₃' and the exceptionally low frictional coefficient generated by fluid pressure resulted in detachment activity. Because it reveals the Arabian platform's instability in the larger area of the Dammam Dome during the Late Eocene, the soft-sediment Rus detachment can be considered a 'sensitive stress sensor' for the Zagros collision. The beginning of the Zagros collision, which was previously thought to occur during the Oligocene based on the well-known pre-Neogene unconformity, is credited with this instability.

How to cite: Osman, M. and Tranos, M.: New hydroplastic structures of the Eocene Rus Soft-sediment Detachment (Eastern Saudi Arabia) and their contribution to the dating of the Zagros Collision, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13058, https://doi.org/10.5194/egusphere-egu22-13058, 2022.

The upper crustal volcanic section of the Oman suprasubduction zone ophiolite is divided into an older V1 sequence, overlain by slightly younger V2 lavas and (in places) a final V3 sequence. Paleomagnetic data from the V1 and V2 sequences of the northern massifs of the ophiolite have been used previously to infer that clockwise rotation of the Oman lithosphere began while the upper crust was actively accreting, with V1 lavas apparently more rotated than the overlying V2 units. This inference has been largely accepted by the geological community and has influenced models for the spreading history and geodynamic evolution of the Oman ophiolite.

Here we present new paleomagnetic data from well-exposed and structurally well-constrained volcanic sequences in the Salahi and Fizh massifs of the ophiolite that discredit this interpretation. In contrast to previous studies that employed standard structural tilt corrections, we use a net tectonic rotation approach to determine rotation parameters, taking confidence limits on input variables into account using Monte Carlo modelling. Importantly, we correct the magnetization direction and structural orientation of the older V1 lavas for the effects of the net tectonic rotation of the younger V2 lavas prior to calculating rotation parameters for the older units. Results demonstrate that both massifs rotated ~120° clockwise around steeply-plunging rotation axes after eruption of the V2 lavas. This rotation occurred during roll-back of the Neotethyan subduction zone in response to impingement of the Arabian margin with the trench. Early rotation of the Salahi V1 lavas around shallowly-plunging, broadly ridge-parallel axes indicates only simple tilting between eruption of the V1 and V2 sequences, and no early rotation of the Fizh V1 lavas is required at all. These new constraints on the evolution of the ophiolite therefore provide no evidence of vertical axis rotation during accretion of the Oman volcanic sequences.

How to cite: Morris, A., Di Chiara, A., Anderson, M., MacLeod, C., Koornneef, L., Hepworth, J., and Harris, M.: Coeval volcanism and rotation of Neotethyan oceanic crust in the Oman ophiolite – fact or fiction?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1665, https://doi.org/10.5194/egusphere-egu22-1665, 2022.

The Red Sea rift exhibits two distinct rifting styles: in the north, the rifting is magma-poor, the crust is hyperextended and the lithospheric necking is asymmetric, in the south, rifting rapidly localized atop a symmetric lithospheric necking. One of the long-standing questions is what drives such different lithospheric necking style? We ran 2D high-resolution thermomechanical numerical simulations of lithospheric rifting to address the northern and southern Red Sea extensional end members and validate the models’ deformation patterns by comparing them against 2D data-driven structural models. The modelling investigates (a) the effect of rotational extension by varying extension velocities along the Red Sea, and (b) the thermal structure of the southern Red Sea due to plume impingement, while the analysis of the outcomes focuses on the early rifting stage, which involves normal rifting and dike intrusion. We find that asymmetrical lithospheric necking in the central and northern Red Sea is potentially driven by the velocity boundary conditions and inherited structures, mainly the Sirhan rift. The decoupling between the upper portion of the lithosphere and the asymmetrical lithospheric necking, which plays an essential role in the observed deformation patterns in the Arabian margin, is likely controlled by the lower crustal rheology and thickness. Furthermore, we find that the Afar plume near the southern Red Sea, which introduced in our models in form of thermal anomaly, promotes rifting localization.

How to cite: Aldaajani, T., Khalil, H., Ball, P., Capitanio, F., and Almalki, K.: Asymmetrical lithospheric necking of Red Sea rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9365, https://doi.org/10.5194/egusphere-egu22-9365, 2022.

The magmatic bodies of Jabuka, Brusnik, and Vis Islands of the Adriatic Sea are located in the easternmost part of the Adria Plate (Adriatic Unit according to Slovenec & Šegvić, 2021), close to the External Dinarides (Pamić and Balen, 2005). The magmatic rocks on the islands are, from West to East, intrusive bodies on Jabuka, sub-intrusive on Brusnik, and effusive rocks on Vis.

Feldspar separates from Jabuka and Brusnik Islands yielded mini-plateau ⁴⁰Ar/³⁹Ar ages of 229.0 ± 5.4 Ma and 221.5 ± 2.5 Ma indicating that this magmatism is Carnian-Norian in age. The whole-rock geochemical compositions (major and trace elements, Sr-Nd isotopes) indicate that the magmatic rocks of the Croatian Islands range from tholeiitic to calc-alkaline, yielding a subduction signature. This signature is also shared by coeval magmas from the Adria Plate and may be related to crustal components subducted during the Hercynian orogeny and recycled within the mantle source(s) of this anorogenic magmatism.

How to cite: Velicogna, M., Prasek, M. K., Ziberna, L., De Min, A., Brombin, V., Jourdan, F., Renne, P. R., and Marzoli, A.: The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the evolution of Triassic magmatism in the Adria Plate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11825, https://doi.org/10.5194/egusphere-egu22-11825, 2022.

Despite multiple research efforts since the late 1950’s, many questions regarding the earthquake activity of the Dead Sea Fault (DSF) remain, in particular for its southernmost portion in the Gulf of Aqaba. This is due to its offshore location and little-known interactions with the Red Sea rift system. The emergence of the NEOM city-project in northern Saudi Arabia and the planned King Salman road crossing across the Gulf of Aqaba have made it important to find answers for these questions related to the earthquake hazard of the region. The last major earthquake in the Gulf of Aqaba occurred in 1995 along one of the main strike-slip fault segments in the gulf, bringing both extremities of the fault rupture closer to failure. Studies of the DSF have found that large events along the entire DSF cluster during relatively short active seismic periods lasting about 100-200 years, separated by longer quiescent periods of about 350-400 years. From a tectonic point of view, the time gap between 1995 and the previous major earthquake in AD1588 conforms to this scheme and suggests that the DSF might be ripe for a new earthquake sequence, with the 1995 earthquake as the starter. That said, new results from GPS and InSAR observations have pointed to possible fault creep in the southern part of the gulf, which would significantly decrease the seismic hazard in the area. To explore this possible creep and to test the clustering model, we investigate new sub-bottom profiling data acquired in December 2019 in the Gulf of Aqaba. We aim to map the extent of sand layers present in the different sub-basins of the gulf and to correlate them with seismoturbidite layers found in sediment cores collected in 2018. By looking at the geographic extent of these sand layers, we also aim to define the source of the coarse deposits, or at least, to determine whether they are related to the regular sediment influx or linked to turbidites generated by slope failures during large earthquakes. Our preliminary results indicate that the sub-bottom profiling data allow us to map sand layers up to a depth of about 8 meters. Considering a sedimentation rate in the gulf between 0.2 - 0.4 mm/year, we could be able to gain an overview of the sediment infill of the Gulf of Aqaba over the last 20 ky or more. Even if the resolution of the sub-bottom profiling data is lower than that of the sediment cores, and the assumptions made for the correlation of the sand layers, due to the scattered grid, do not help to constrain properly the source of the deposits, we can still propose a longer-term overview of the earthquake activity and discuss the temporal organization of the large events in the area.

How to cite: Ribot, M., Jónsson, S., Klinger, Y., Avsar, U., and Bektaş, Z.: Mapping the extent of seismoturbidites near the southern Dead Sea Fault in the Gulf of Aqaba, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9219, https://doi.org/10.5194/egusphere-egu22-9219, 2022.

The Schladming Nappe, as a part of the Silvretta-Seckau Nappe System of the Eastern Alps, comprises pre-Alpine remnants of crystalline basement rocks which give important information for reconstructing the Variscan and even pre-Variscan history of the Alps.

The Schladming Nappe mainly consists of paragneisses being intruded by subsequently overprinted granitoids. U-Pb zircon ages were acquired through LA-MC-ICPMS to determine the magmatic emplacement of the metagranitoids and constrain the tectono-metamorphic history of the Schladming Nappe.

Within these meta-granitoids, several intrusive events can be distinguished: (1) a Cambrian event with ²⁰⁶Pb/²³⁸U zircon mean ages between 496±6.5 and 501±7 Ma, (2) a Late Devonian/Early Carboniferous event with zircon mean ages between 350±5 Ma and 371±5 Ma and (3) a Permian event with zircon mean ages between 261±3 Ma and 263±3.5 Ma. The youngest age group is only found in metagranitoids from the southeastern part of the Schladming Nappe. The tectonic contact to the metapelites of the Wölz Nappe system and therefore the affiliation of these Permian granitoids to the Schladming Nappe, however, is still enigmatic.

The various age groups can also be differentiated by their whole rock geochemistry. While all of the metagranitoids are peraluminous, the Cambrian age group exhibits higher SiO₂ values compared to the Late Devonian age group. The Late Devonian age group shows higher contents of CaO, MgO, FeO, Al₂O₃, as well Sr and Ba and can be further divided into two subgroups, with one depicting a distinct negative Eu-anomaly (EuN/Eu*=0.44-0.69) and the other subgroup lacking one (EuN/Eu*=0.82-1.08). The Permian age group often displays high contents of K₂O, Nb and Y.

The Late Cambrian to Early Ordovician metagranitoids can be classified as part of a magmatic arc system, probably belonging to the northern Gondwana margin. The early Variscan granitoids can also be interpreted as part of an active margin. The Permian granitoids show a within plate granite affiliation and can further be interpreted as A-type granitoids, probably related to post-Variscan lithospheric extension.

How to cite: Haas, I., Kurz, W., Gallhofer, D., and Hauzenberger, C.: Implications for the pre-Alpine evolution of the Eastern Alps – a U/Pb zircon study on the Austroalpine Schladming Nappe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4246, https://doi.org/10.5194/egusphere-egu22-4246, 2022.

India-Eurasia convergence velocities have dropped significantly from ~18 cm/yr in the Late Cretaceous-earliest Eocene to ~4-5 cm/yr since ~50 Ma. The mechanisms of convergence deceleration, continued convergence since ~50 Ma, long-term continental subduction and long-term Indian indentation into Eurasia still remain controversial. Many previous studies consider an external driving force for the long-term convergence, continental subduction and Indian indentation, and the initial India-Eurasia collision as the trigger for the deceleration. In this study, we investigate the mechanism(s) of the abrupt deceleration, the continued convergence, the long-term continental subduction and long-term Indian indentation using buoyancy-driven analog experiments. We conduct three large-scale experiments to simulate the subduction and collision process at the convergent boundary with different boundary conditions at the 660-km discontinuity, including an infinite viscosity step (the lower-upper-mantle viscosity ratio (η_LM/η_UM) is infinitely high), no viscosity step (η_M/η_UM =1) and an intermediate viscosity step. The experiment with infinite η_LM/η_UM shows a deceleration when the slab tip reaches the 660-km discontinuity, while the other two experiments show a deceleration at the onset of continental subduction. Our experiments show that a higher η_LM/η_UM favors a lower velocity drop at the onset of continental subduction, lower convergence velocities, reduced continental subduction and a higher indentation amount, and vice versa. Furthermore, our models suggest that in nature, with an intermediate-high η_LM/η_UM, the negative buoyancy force of both upper and lower mantle slab segments is the main driver of long-term convergence, continental subduction and Indian indentation.

How to cite: Xue, K., Schellart, W. P., and Strak, V.: Geodynamics of long-term continental subduction and Indian indentation at the India-Eurasia collision zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7096, https://doi.org/10.5194/egusphere-egu22-7096, 2022.

The study area is situated in the Ulug-Tau and Khaidarkan gold-antimony-mercury deposits in the South Tienshan (STS). Together with Khadamzhai, Chauvai, and Abshyr deposits, they can be grouped into one ore province. The STS consists mainly of middle and late Paleozoic marine sedimentary rocks, which were deposited in the Turkestan Ocean and on the adjacent continental margins. They crop out along with subordinate metamorphic rocks, arc-related and intraplate volcanic suites, and ophiolites. Various lithologies were juxtaposed together in an accretionary prism during the late Carboniferous - early Permian closure of the Turkestan Ocean.

In the investigated area, Late Silurian to Devonian limestones of the Aktur carbonate platform cover both the shales of the Pulgon Formation (Fm.) (Zarhar-Say) and the basalts with gabbro bodies. Gabbro specimens were sampled for absolute age determination by amphibole 40Ar/39Ar geochronology. Volcanic rocks related to the basement of the Silurian-Carboniferous Akturian carbonate platform, part of the regional nappes of Osh-Uratyube, have been studied by Biske et al., (2019) and our group. The nappe sits on top of basaltic rocks of the Chonkoy Fm. and andesites, tuffs, and carbonate rocks of the Dedebulak Fm. In the latter unit, the volcanic suite forms the lower member which is overlain by Cambrian limestone and dolomite with intercalations of radiolarite (upper member). The volcanic rocks at the base of the Aktur carbonate platform succession indicate the Early Paleozoic geodynamic situation in the Turkestan Ocean as well as about the structure of the Khaidarkan and Ulug-Too gold-antimony-mercury deposits. The Ulug-Tau orefield is situated along the mélange zone at the base of the Aktur nappe.

Results of geochemical and geochronologic analyses (in progress) show that the basalts and basaltic andesites of the lower member of the Dedebulak Fm. formed in an island-arc setting. These volcanic rocks confirm the existence of Early Paleozoic island arcs in the Turkestan Ocean. In a later stage, those arcs possibly died out and were overlapped by carbonate platforms. For the Aktur carbonate platform, it can be assumed that it was detached from the Cambrian island arc basement during the Late Carboniferous and was added to the accretionary prism as the Aktur Nappe. The Cambrian island arc basement (Dedebulak Fm.) formed another thrust-sheet unit as part of the accretionary prism. Plastic Silurian shales and other sediments, primarily located between the Aktur carbonate platform sediments and the Cambrian island arc volcanic rocks, were incorporated into the polymictic mélange.

How to cite: Terbishalieva, B., Hnylko, O., Heneralova, L., and Rembe, J.: Paleozoic development of OIB and see-mounts in the Turkestan Ocean within the Khaidarkan and Ulug-Too deposits, South Tianshan (STS), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-322, https://doi.org/10.5194/egusphere-egu22-322, 2022.

Large plutons are common within the Inthanon Zone in Northwestern Thailand. These igneous rocks are also known as Central Granitoids Belt in mainland Southeast Asia. They are interpreted to be part of the suture zone between Sibumasu and Indochina and were emplaced mainly in the Upper Triassic.

Here, we present new petrological and geochemical data for the Central Granitoids Belt.  A geochronological study on selected samples will follow.  The sampled granitoids can be separated into three groups: (1) biotite granite, (2) hornblende granite, (3) syenite/monzonite. The samples consist of various light colored to dark grey granitoids due to the type and amount of mafic minerals (biotite or hornblende) present. The general mineral assemblage of all the intrusive igneous rocks is quartz + plagioclase + K-feldspar + biotite + apatite + zircon ± allanite ± titanite ± ilmenite. The biotite granites are mostly composed of biotite aggregates associated with accessory minerals: zircon, ilmenite, and apatite. The syenite/monzonite group usually contains additional clinopyroxene and hornblende. Plagioclase and hornblende of the syenite/monzonite group commonly exhibit a sieve texture.

The biotite granite group is typically peraluminous and belongs to the high-K calk-alkaline to shoshonitic series. The hornblende granite group is mostly peraluminous and of predominantly shoshonitic affinity. The syenite/monzonites are typically metaluminous but also belong to the shoshonitic series. The chondrite normalized rare earth element (REE) patterns are quite similar for all igneous rocks with elevated LREE, pronounced negative Eu anomaly and a flat HREE segment. The granite tectonic discrimination plots after Pearce et al. (1984) classify most samples as syn-collision granites (syn-COLG) and when using the Batchelor and Bowden (1985) discrimination diagram as syn-, late, and post-collisional.

The intrusive igneous rocks from Northwestern Thailand were presumably emplaced in a syn- to post-collisional setting when the Sibumasu block collided with the Sukhothai terrane and was eventually amalgamated to the Indochina block. This led to the closure of the Palaeotethys along the eastern area of the Sibumasu block.

Batchelor, R.A. and Bowden, P. (1985) Petrogenetic Interpretation of Granitoid Rock Series Using Multicationic Parameters. Chemical Geology, 48, 43-55.

Julian A Pearce, Nigel BW Harris, Andrew G Tindle (1984). Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, 956-983.

How to cite: Santitharangkun, S., Hauzenberger, C., Gallhofer, D., and Skrzypek, E.: Petrology and Geochemistry of intrusive igneous rock from the Inthanon zone, Northwestern Thailand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7993, https://doi.org/10.5194/egusphere-egu22-7993, 2022.

Located in SE Asia in between the Palawan and the Philippine islands, the lozenge-shaped Sulu Sea corresponds to a marginal sea that displays a complex seafloor morphology. The NE-SW trending Cagayan Ridge separates a southeastern deep-water domain, which is bounded by the Sulu Trench towards the east, from a shallower and narrower northwestern domain. Interpretations of low-resolution 2D streamer datasets, ODP Leg 124 drilling results, magnetic, geochemical, and geochronological studies, and gravity inversion results led to distinctive tectonic models, with contrasting basin formation mechanisms, and ages of opening and subsequent contractional reactivation. The debates remain because the structure of most of the Sulu Sea and its along-strike structural variability remain underexplored to date.

We focus on this work on the first detailed analysis of the structure and seismo-stratigraphy of the NW Sulu Sea. Based on the reprocessing, calibration of the Silangan-1 exploration borehole, and interpretation of > 5384 km of 2D seismic data along 19 regional profiles of an irregular grid that covers the whole NW Sulu Sea, we identify, map and interpret the seismo-stratigraphic horizons and units, major structures, and rift-related and syn-orogenic depocenters and structural domains. We define six seismo-stratigraphic units in the NW Sulu Sea, consisting of Quaternary to Paleogene sediments, which developed during an early phase of Paleogene to early Miocene extension, a following early to Middle Miocene phase of contraction, and a late Miocene to Quaternary stage of relative tectonic quiescence. While transpressional faults core uplifted basement areas, strike-slip, high-angle and low-angle oblique extensional faults crosscut continental crystalline basement of variable thickness and bound pull-apart basins, half-grabens and sags respectively. The distribution and trend of rift-related depocenters describe a strong structural segmentation and vary along NW-SE and NE-SW oriented zones. Thrust-cored anticlines, inverted transtensional and transpressional faults and mud diapirs deform the sediment pile and control the geometry of syn-orogenic depocenters distinctively across the NW Sulu Sea.

Normal and oblique trending sets of faults controlled the extension and compartmentalized the NW Sulu Sea. Subsequent contractional reactivation differentiated NE and SW basement and sedimentary domains, separated by the NW Sulu Break Elevation. These domains show a contrasting overall architecture, basement thickness, contractional structures and distribution of rift-related and syn-orogenic depocenters. Rift segmentation, and particularly, basement thickness variations, may have conditioned the type and distribution of contractional deformation.

How to cite: Cadenas, P. and R. Ranero, C.: Formation and contractional reactivation of the NW Sulu Sea (SE Asia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6471, https://doi.org/10.5194/egusphere-egu22-6471, 2022.

Continental collision succeeds long term subduction of oceanic lithosphere into the earth's mantle whereby the negative buoyancy of the downgoing oceanic lithosphere (slab) provides the principal driving force for plate motions. Previous studies have shown that subduction-induced mantle flow could drive overriding plate shortening and orogenesis, and the arrival of the positively buoyant lithosphere at the trench affects the dynamics of the overriding plate and plate motions. The subsequent slab detachment at the subducted continent-ocean margin removes the driving force in the system and eventuates in cessation of subduction (Cloos, 1993)  and plate convergence. The India-Eurasia subduction-collision system has multiple inferred slab break-off episodes (Replumaz et al., 2010), yet convergence is still ongoing. Here, we present 2D-cartesian buoyancy-driven numerical models of continental collision after subduction of a long oceanic plate (~6000 km) in a whole mantle reservoir (2880km), investigating the dynamics of such systems in the presence of detached slabs. These models’ wide aspect ratio (6:1) allows for exploring deep subduction of oceanic slabs and detached slab(s), approximately at the centre of the domain, thereby minimising the effect of free slip sidewalls on obtained slab morphology in the mantle and associated mantle flow. Our results indicate that poloidal mantle flow induced by the sinking of the detached slab sustain long term convergence in collisional settings. Although 2D models lack the 3D components of mantle flow, these models can be used to understand the dynamics of the centre of >4000km wide subductions zones and facilitate interpretation in light of tomographic and plate reconstruction studies.

References:

Cloos, M. (1993). Lithospheric buoyancy and collisional orogenesis: Subduction of oceanic plateaus, continental margins, island arcs, spreading ridges, and seamounts. Geological Society of America Bulletin, 105(6), 715-737.

Replumaz, A., Negredo, A. M., Guillot, S., & Villaseñor, A. (2010). Multiple episodes of continental subduction during India/Asia convergence: Insight from seismic tomography and tectonic reconstruction. Tectonophysics, 483(1-2), 125-134.

How to cite: Laik, A., Schellart, W., and Strak, V.: Convergence at continental collision zones: Insights from long-term 2D geodynamic models buoyancy-driven subduction and collision., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12441, https://doi.org/10.5194/egusphere-egu22-12441, 2022.