The Zagros orogenic belt is a component of the active Arabia-Eurasia collision zone in the Middle Eastern segment of the Alpine-Himalayan system, and it is one of the world's youngest seismically active continental collision zones. The Zagros region, which is one of the most seismically active continental collision zones in Zagros orogenic belt, provides an excellent case study for understanding tectonic processes and their consequences for geological development and seismic hazard assessment. This work presents an overview of the geological significance of the Zagros orogenic belt, with a focus on its function in larger context of the Arabia-Eurasia collision. It investigates the dynamic interaction of tectonic forces that have sculpted the landscape, from the first convergence of the Arabian and Eurasian plates to current deformation and seismic activity. 

Furthermore,  significance of continuing scientific efforts to understand the complexity of the Zagros orogenic region and its implications for seismic risk mitigation and natural resource exploration. Out-of-Sequence thrusts in the Eastern Alps' frontal zone (Levi et al., 2021). Out-of-Sequence thrusting in the Karwendel mountains of the western Northern Calcareous Alp (Kilian and Ortner, 2019). Besides, Out-of-sequence reactivation of older in-sequence thrusts is difficult to quantify. In Vienna Basin area, out of sequence Thrust adjusted to around 2 km at the Early Karpatian (approximately 16.5 Ma). The well Kirchdorf-1 drill explores that Molasse rocks that are exposed in tectonic windows caused by out-of-sequence thrusting at a depth of approximately 800 m above the basal thrust at the Alpine-Carpathian junction (Beidinger and Decker 2014). In-depth examination of the geological significance of the Zagros orogenic belt, focusing on its role within the broader context of the Arabia-Eurasia collision. Mukherjee (2015) docuemented OOS thrust displacement  along the length Himalayan Arc.

Through a detailed analysis of tectonic processes and their consequences for geological development and seismic hazard assessment, this study offers insights into the dynamic evolution of the region. From the initial convergence of the Arabian and Eurasian plates to the ongoing deformation and seismic activity, the landscape of the Zagros orogenic belt bears the imprint of complex tectonic interactions. Furthermore, this study highlights understanding the complexity of the Zagros orogenic region and its implications for seismic risk mitigation and natural resource exploration in neighbouring mountain ranges such as the Eastern Alps and the Northern Calcareous Alps.

References:

• Levi, et al. (2021). Out-of-Sequence thrusts in the Eastern Alps' frontal zone.
• Kilian and Ortner (2019). Out-of-Sequence thrusting in the Karwendel mountains of the western Northern Calcareous Alps.
• Mukherjee,S., (2015).  A reivew of Out-of-sequence thrust in Himalaya
• Beidinger and Decker (2014). Out-of-sequence thrusting in Vienna Basin: Kirchdorf-1 drill. 

How to cite: Ghosh, R.: Discovering Earth's Challenge: Insights of Out-of-Sequence Thrusts in Alpine-Himalayan Orogenic Belt, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-4, https://doi.org/10.5194/egusphere-alpshop2024-4, 2024.

Olivine, a major mineral in the upper mantle with strong intrinsic elastic anisotropy, plays a crucial role in seismic anisotropy in the mantle, primarily through its lattice preferred orientation (LPO). Despite this, the influence of the microstructure of mylonitic rocks on seismic anisotropy remains inadequately understood. Notably, there is a current research gap concerning seismic anisotropy directly inferred from mylonitic peridotite massifs in Korea. In this study, we introduce the deformation microstructure and LPO of olivine in the mantle shear zone. We calculate the characteristics of seismic anisotropy based on the degree of deformation (proto-mylonite, mylonite, ultra-mylonite) and establish correlations between these characteristics. Our findings reveal that the seismic anisotropy resulting from the olivine LPO in the ultra-mylonitic rock appears to be the weakest, whereas the seismic anisotropy resulting from the olivine LPO in the proto-mylonitic rock appears to be the strongest. The results demonstrate a gradual decrease in seismic anisotropy as the fabric strength of olivine LPO diminishes, irrespective of the specific pattern of olivine's LPO. Moreover, all samples exhibit a polarization direction of the fast S-wave aligned subparallel to the lineation. This suggests that seismic anisotropy originating from olivine in mylonitic peridotites is primarily influenced by fabric strength rather than LPO type. Considering these distinctive characteristics of seismic anisotropy is expected to facilitate comparisons and interpretations of the internal mantle structure and seismic data in the Yugu area, Gyeonggi Massif.

How to cite: Park, M.: Relationship between Olivine Fabrics and Seismic Anisotropy in the Yugu Peridotites, Gyeonggi Massif, South Korea, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-1, https://doi.org/10.5194/egusphere-alpshop2024-1, 2024.

Recent ambient noise Vs tomography data at the scale of the Western Alps (Nouibat et al., 2022) highlight the deep structure of the chain. In the European foreland, the seismological model shows a crust of normal thickness, with slow velocities (<3.6 km.s^-1) in the lower part of the crust and the presence of Moho jumps localized below the External Crystalline Massifs (ECMs). In the inner zones to the east of the Pennine Front, crustal geometry is more complex, with the presence of a European continental slab that subducts locally more than 80 km beneath the Adria plate in the SW part of the Alpine arc, and detached beneath the Swiss Alps. This slab is surmounted by a metamorphic orogenic wedge whose lower part shows serpentinized mantle seismic signatures (Vs between 3.8 and 4.3 km.s^-1). Its roof is located at a depth of 10 km below the Dora Maira massif. These data allow to understand the role of crustal geometry in the development of the observed deformation field. Moho morphology is controlled by numerous pre-existing major faults reactivated during the Alpine orogeny. Two mantle indenters located above the subducted European plate at different depths appear to control the locus of active deformation. The rigid nature of Adria mantle explains the localization of brittle deformation that is transferred towards the upper crust. In this context, the strain-field partitioning results in a combination of strike-slip with either shortening or extension controlled by the the displacements imposed by the current NW/SE convergence associated with the anticlockwise rotation of Adria.

REF: Nouibat, A. et al. (2022) Lithospheric transdimensional ambient-noise tomography of W-Europe: implications for crustal-scale geometry of the W-Alps. Geophys. J. Intern. 229(2), 862–879.

How to cite: Schwartz, S., Rolland, Y., Nouibat, A., Sue, C., Dumont, T., Boschetti, L., Bienveignant, D., and Mouthereau, F.: The partitioning of present-day deformation in the W-Alps controlled by mantle indentation, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-54, https://doi.org/10.5194/egusphere-alpshop2024-54, 2024.

In the W-Alpine context, where active deformation is slow and seismicity is moderate, the question of determining and characterizing active faulting remains a scientific challenge. However, previous studies have shown that reliable geodetic strain rates can be assigned to the High-Durance fault (HDF) system, in accordance with the regional seismicity. In this paper, we propose a comparative analysis of two major faults recognized in the W-Alps: the HDF in the Briançon vicinity and the Belledonne fault (BDF) close to Grenoble. The aim is to investigate the constrains that can be brought by GNSS, in slow deformation ranges of 0.1-1 mm/yr, to decipher active faulting, both in terms of localization at the regional scale and quantitative strain rates. We also aim to compare the seismotectonic framework with the geodetic results. Last but not least, these two major faults bear witness of the main kinematics found within the realm of the W-Alps, that is to say extensional mechanism in the internal zone (along the HDF) and strike-slip in the external zone (along the BDF). They can thus be considered as two major fault systems representative of the overall W-Alpine current deformation. From a quantitative viewpoint, the BDF extends over about 50 km along the western side of the Belledonne External Crystalline Massif. Using up to 20 years of data from 22 permanent GNSS stations, approaches exploiting the redundancy between the individual station velocity estimates provide dextral strike-slip kinematics with a rate of 0.2 ± 0.2 mm/yr. This rate is coherent with a unique strain tensor calculated over the 50 km wide local network, evaluating a NNE-SSW extensional axe of 2.0 ± 0.8 nanostrain/yr, with a WNW-ESE shortening axe of 4.7 ± 1.2 nanostrain/yr. Strain calculations by alternative methods on regular grids evaluate a lower total amplitude of strain rate close to the BDF trace, in particular less compression. Comparatively, the HDF is investigated thanks to a dense network of 30 GPS stations covering the Briançon area, which was surveyed during 5 temporary campaigns in 1996, 2006, 2011, 2016, and 2021. The redundancy of the dense network and the long observation interval after the addition of the fifth campaign in 2021 allow to increase the accuracy of the velocity fields. The average horizontal strain rate over the entire network located in the center of the Briançon Seismic Arc has been evaluated at 20 ± 2 nanostrain/yr of E-W extension across the 50 km network, yielding about 0.5 mm/yr of extension across the NS trending HDF. From a seismotectonic viewpoint, the comparison with seismicity highlight the coherency between seismotectonic and geodetic deformation fields, both for the HDF and BDF systems, in terms of style, direction, and amplitude of deformation.

How to cite: Walpersdorf, A., Sue, C., Al Najjar, L., Mathey, M., and Mowbray, V.: Active faulting in the Alps as seen by GNSS: comparative case-studies from the Belledonne and High-Durance fault systems, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-55, https://doi.org/10.5194/egusphere-alpshop2024-55, 2024.

Orogenic arcs result from processes ranging from structural inheritance, to molding around arcuate indenters, and/or oroclinal bending of an initially straight mountain range. Most kinematic models for the formation of the Western Alpine arc (WAA) propose a syn-collisional development under the effect of NW- or Wward Adriatic indentation (Brunsmann et al., 2024, for review). This indentation is sometimes associated with a 25° counter-clockwise rotation of the Adriatic indenter, based on GPS- (e.g. Nocquet, 2012), seismotectonic (Bauve et al., 2014), and paleomagnetic data (e.g. Collombet et al., 2002). Paleogeographic reconstructions based on retro-deformation of collisional shortening imply the existence of a pre-collisional proto-arc (e.g. Bellahsen et al., 2014).

Paleomagnetic analyses allow us to study vertical axis rotations, and to discuss them in the frame of orogenic arc development. We present the analysis of an exhaustive compilation of Alpine paleomagnetic data highlighting that on the 1^st order vertical axis rotations affect the formation of the WAA as follows:

1) in the Adriatic plate (Southern Alps, Istria, Pô plain) paleomagnetic data contradict a post-Miocene counter-clockwise rotation of 20-25° of the indenter, showing that the latter does not undergo significant rotation during Alpine collision (<10°).

2) The orogenic internal, subduction wedge undergoes counterclockwise rotations that increases southward of the arc, following the progressive rotation of the main tectonic structures, striking NE-SW in the north and WNW-ESE in the south. The relation between the direction of the main structures and vertical axis rotations of post-Oligocene age in the Internal Zone suggests that the arc was amplified during collision. However, the rotation of the main tectonic structures is greater than the rotation of the Oligocene paleomagnetic directions, implying the existence of a pre-collisional, proto-arc.

3) There is no significative relation between main tectonic structures of the External Zone and the rotation of the paleomagnetic directions along the WAA, and no rotation is measured in the Permian rocks of the Argentera massif. This implies that the arcuate morphology in the European margin is mainly inherited from a pre-collisional phase.

Vertical axis rotations in the western Alps therefore indicate the collisional amplification of an early arc whose morphology is inherited from the subduction period. It also shows that E-W structures in Ligurian region are controlled by the orocline formation but also by left-lateral shear and Apennine slab retreat.

References

Bauve, V., Plateaux, R., Rolland, Y., Sanchez, G., Bethoux, N., Delouis, B., & Darnault, R. (2014). Tectonophysics, 621, 85-100. https://doi.org/10.1016/j.tecto.2014.02.006

Bellahsen, N., Mouthereau, F., Boutoux, A., Bellanger, M., Lacombe, O., Jolivet, L., & Rolland, Y. (2014). Tectonics, 33(6), 1055-1088. https://doi.org/10.1002/2013TC003453

Brunsmann, Q., Rosenberg, C.L., and Bellahsen, N., (2024). Comptes Rendus. Géoscience, 356, 231-263. https://doi.org/10.5802/crgeos.253

Collombet, M., Thomas, J. C., Chauvin, A., Tricart, P., Bouillin, J. P., & Gratier, J. P. (2002). Tectonics, 21(4), 14-1. https://doi.org/10.1029/2001TC901016

Nocquet, J.-M., 2012. Tectonophysics 579, 220–242. http://dx.doi.org/10.1016/j.tecto.2012.03.037

How to cite: Brunsmann, Q., Rosenberg, C., Bellahsen, N., and Speranza, F.: Kinematics of the Western Alpine arc: insights from paleomagnetic data and vertical axis rotations., 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-58, https://doi.org/10.5194/egusphere-alpshop2024-58, 2024.

Geophysical data from the Liguro-Provençal Basin show prominent margin asymmetry but the nature of the crust, especially in the northeastern part of the basin, remains unclear. The basin formed at the junction of the northern Apennines and the western Alps due to the rollback of the Calabrian-Apennines subduction zone in the Oligo-Miocene. The opening of the basin was accompanied by counter-clockwise rotation of the Corsica-Sardinia block relative to Europe with the basin widening southwestwards. Recent weak compressional earthquakes offshore within the basin suggest possible basin inversion due to the ongoing Africa-Eurasia convergence. An insight into the crustal structure of the basin is therefore the key to understanding these recent processes. To this end, we compiled existing geological and geophysical data, including new data from the German project “Mountain Building Processes in Four Dimensions” (4DMB), to constrain the crustal and sedimentary thicknesses throughout the basin. Moreover, we derived kinematic parameters of extension using regional tectonic reconstructions and used the coupled ASPECT and FastScape geodynamic code to model the opening of the basin in its northeastern (Corsica – Provence) and southwestern (Sardinia – Gulf of Lion) parts. The comparison of the geodynamic models and geophysical data suggests: 1) the extent of oceanic crust in the Liguro-Provençal Basin did not reach as far north as previously presumed; 2) rift-related structures are possibly being reactivated offshore to the northwest of Corsica. We also present new constraints on the lateral extent of rifted continental crust and exhumed mantle and evolution of the basin through time.

How to cite: Jensen, A., Le Breton, E., Brune, S., Dannowski, A., Lange, D., Murray-Bergquist, L., and Kopp, H.: New constraints on the crustal structure and rifting processes of the Liguro-Provençal Basin, Western Mediterranean, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-37, https://doi.org/10.5194/egusphere-alpshop2024-37, 2024.

In the late Eocene, the peripheral portion of the European margin was involved in the Alpine subduction/exhumation processes. Witnesses of this event are the polyphase deformation and the metamorphism registered by slices of continental crust which compose the Lower Units, i.e. a set of tectonic units placed at the lowest structural level of the Alpine Corsica (France). The pressure-temperature-deformation-time (P-T-d-t) path of one of them named Venaco Unit was traced by using an integrated set of data related to the phyllosilicates which dynamically recrystallized in the metagranitoids and metapelites. Different thermobarometric tools were applied to the chlorite and white mica crystals selected in the microdomains of the metapelites of the Venaco Unit. The ⁴⁰Ar/³⁹Ar dating was instead applied on syn-kinematic muscovite sampled from metagranitoids of the Venaco Unit. The results indicates that the Venaco Unit reached the baric peak at ≈ 33 km depth and was exhumed at shallower structural level (i.e., at ≈ 26 km depth) in the middle Priabonian. This retrograde path suggests that the Venaco Unit experienced fast exhumation through the activation of the top-to-W shear zones.

How to cite: Di Rosa, M., Sanità, E., Frassi, C., Lardeaux, J.-M., Corsini, M., Marroni, M., and Pandolfi, L.: The European margin to and from the mantle depth: insights from the Lower Units (Alpine Corsica, France), 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-31, https://doi.org/10.5194/egusphere-alpshop2024-31, 2024.

The Calabrian Arc is the only segment of the Apennine chain that has recorded the entire history of the geological evolution of the Mediterranean. In addition to the first Mesozoic rifts, it recorded Alpine subduction and the subsequent formation of the present Mediterranean basin. The oldest successions, attributable to the opening of the Tyrrhenian Sea, start from the Serravallian stage and fill increasingly recent basins which, in addition to the timing, well record the direction of Tyrrhenian extensions. These data provide the essential elements to outline the dynamics of the opening of the Tyrrhenian Sea and the contemporary formation of the Apennine chain. The main stratigraphic records, regional scale structural maps and the kinematic extension model will be shown to outline the constraints for the dynamics of the Tyrrhenian opening and its correlation with the Calabrian Arc, with the main objective of achieving a more complete knowledge of this portion of the Mediterranean area.

How to cite: Penza, G., Cuturello, G., Martino, A., Muto, F., Pierantoni, P. P., and Turco, E.: The basins of the Calabria Arc, important constraints for the dynamics of the Tyrrhenian opening., 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-39, https://doi.org/10.5194/egusphere-alpshop2024-39, 2024.

A new gravity model was constructed for the composite line, 465 km long, crossing from the Ligurian Sea through the Northern Apennines to the Po Basin as far as Verona province and derived from published cross-sections. Gravity field along the transect varies strongly from high positive values of Bouguer anomalies (160 mGal) offshore to the low-amplitude gravity minima (-160 mGal) above the Po Basin. The structure of the sedimentary succession, basement, and the crystalline crust of the density model were constrained by offshore-onshore WARR (wide-angle reflection and refraction) and reflection seismic profiles. In addition, the European Moho compilation was used as well. We also constrained the upper mantle structure by the S-wave tomography model of Italy. Using the known velocity-density conversion functions for different velocity values and rock types, the velocity model of the crust was transferred into density one, from which the gravity effect was calculated by the GRAV3D software. A stable solution of the modelling was obtained for an oceanic crustal segment, a continental crust, and a transition zone from a thin (18 km) oceanic crust of the Ligurian Sea to ≤ 40 km-thick continental crust with a deep (up to 18 km) meta-sedimentary succession of the Po Basin, which causes the mentioned gravity minimum.

The ocean-continent transition zone, ~100-km wide, including much of the accretionary wedge, is a thinned crust (up to 25 km) with a thick basement (Tuscan metamorphic unit) overlain by Mz carbonate rocks, Oligocene-Miocene foredeep siliciclastic sediments and Ligurian units. A spectacular feature of the transition zone is a underplated sub-Moho high-velocity/density body, which is ~7 km thick and deepens northeastwards, below the Po Basin.  This transition zone is separated from the oceanic crust by a block, ~40 km wide, with subvertical flanks, marked by local magnetic anomaly which we associate to exhumed HP/LT metamorphic rocks. This could be indicative of the complex nature of the transition zone, which was affected by various geodynamic processes during the long-lived history of the Europe and Africa plates and the closure of the Tethys ocean between them since the Late Cretaceous. These processes included the compressional deformation event of the crust (in Eocene times) during the closure of the Piedmont-Ligurian Ocean, between Europe and Adria/Apulia paleocontinent, and the Apenninic subduction. Later (since middle Miocene, ~20-15 Ma), rifting occurred in the area of the modern Ligurian Sea, and it led to formation of the modern Western Mediterranean Basin and southwards opening of the Tyrrhenian Sea which began under the influence of asthenospheric flows. The latters, in the offshore part of our transect, are recorded as low-velocity layers (from S-wave tomography) in the subcrustal region, at a depth of about 30 km, and in the upper mantle. Corresponding zones of low density (up to 3.20-3.25 g/cm³) are present in the upper mantle of the Liguria-Verona density model. The distribution of the high heat flow zones strictly corresponds to the subcrustal astenospheric heterogeneities confirming that these heterogeneities are formed recently in the evolution of the Northern Apennines.

How to cite: Yegorova, T., Murovskaya, A., Artoni, A., Torelli, L., Qadir, A., and Storti, F.: Updated gravity and geophysical model for the crust and upper mantle transectfrom the Ligurian Sea to the Po Basin, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-34, https://doi.org/10.5194/egusphere-alpshop2024-34, 2024.

The Middle Miocene- late Pliocene tectonic evolution of the Tuscan Shelf (northern Tyrrhenian Sea) between Elba Island and Monte Argentario Promontory is re-defined by the re-interpretation of vintage seismic profiles. The location and first evolution of Neogene sedimentary basins in those areas were controlled by structural inheritance since they developed on top of major thrusts before and during the Tyrrhenian Sea formation. Successive minor crustal extension contributed to today's structural setting and basin geometries. Using forward kinematic modeling, the geometrical validation of the seismic transects is presented here. The geometrical validation has been tied to the Martina-1 and Mimosa-1 wells, and the forward models have been successively compared with the geologic constraints derived from the available regional-scale geologic information (geological maps and literature data). Complete forward modeling from the Miocene to the late Pleistocene is forwarded along with an estimation of crustal shortening and extension that may account for the observed geometries of the seismic horizons and the modern basin geometries.

How to cite: Mazzarini, F., Buttinelli, M., Maesano, F. E., Maffucci, R., and Musumeci, G.: The reconstruction of middle Miocene-late Pleistocene Tuscan shelf evolution (Tyrrhenian Sea, Italy) through a re-interpretation and geometrical-kinematic validation of seismic profiles., 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-8, https://doi.org/10.5194/egusphere-alpshop2024-8, 2024.

The Apula plate in the Northern Ionian Sea, is a sliver of continental crust covered by around 8 km of Mesozoic carbonates. It acts as the foreland of two opposite verging chains: the SE-verging Southern Apennine to the southwest, which merges with the Calabrian Arc wedge at the Taranto Gulf and the SW-verging External Hellenides to the northeast. In this work we use deep seismic reflection profiles to illuminate the structures and stratigraphic relationships between the frontal part of the orogenic belts and adjacent foreland, as well as to determine the key tectonic processes that have governed the onset of the region's existing structural architecture. A detailed seismo-stratigraphic study allows us to recognize three major regional unconformities: i) the Jurassic/Cretaceous unconformity which is marked by Cretaceous reflectors that clearly onlap the Jurassic carbonate platform; ii) the Messinian unconformity, related to a regional erosive event linked to the Messinian desiccation of the Mediterranean Sea; and iii) the middle Pliocene unconformity, an erosive and angular unconformity that truncates the Lower Pliocene reflectors. Although the Apula plate is typically thought to be a stable foreland zone, our study shows that it underwent extensive deformation strongly influenced by its interaction with the neighboring Southern Apennine/Calabrian Arc and Hellenic wedges. An active NW-SE-striking extensional fault system is possible due to the Apula plate bending under the stress of the two opposing orogens. Compressive and transpressive structures (e.g., smooth and open folds at the plate contact zone as well as active NE-SW striking positive flower structures) accommodate shortening processes and oblique plate convergence. Transpressive tectonic structures resulted from inherited Mesozoic normal faults that have been reactivated since the middle Pliocene and such compressive/transpressive regime promoted the mobilization and squeezing of Upper Triassic evaporites into teardrop diapirs. These findings make the regional geological setting and the pre-collisional grain of the Apula plate critical aspects in defining the tectonic evolution of the Northern Ionian Sea as well as the position and geometry of tectonic structures located in this area.

How to cite: Chizzini, N., Artoni, A., Torelli, L., Polonia, A., Gasperini, L., and Quadir, A.: The Apula plate's response to the interaction between Calabrian and Hellenic orogens: tectono-stratigraphic evolution and implications on intra-plate deformation (Northern Ionian Sea, Central Mediterranean), 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-57, https://doi.org/10.5194/egusphere-alpshop2024-57, 2024.

The Northern Hellenides are located on the eastern margin of the Adria plate, and represent the central segment of the Dinarides-Hellenides orogenic belt. Situated at the junction between continental subduction to the north and oceanic subduction to the south, the Albanian region offers a prime location for studying the interaction between surface and deep geological processes in the Central Mediterranean area. The coexistence of compressive and extensional tectonic styles over short distances strongly contributes to shaping the landscape (Burchfiel et al., 2008), and it is still reflected in the modern focal mechanisms (D’Agostino et al., 2022). Morphological and seismic evidence indicates intense tectonic activity in this region at least since the late Quaternary, a period that is also characterised by intense climatic variability. In this research, we investigate the landscape's response to tectonics and climate by 1) performing an extensive tectonic, geomorphic and fluvial analysis, and 2) calculating basin-wide denudation rates using cosmogenic nuclides.
Basin-wide denudation rates were calculated using cosmogenic Beryllium nuclides across 19 basins distributed throughout various tectonic and geological domains of the orogenic belt. The presence of different lithologies including limestones, ophiolites, silicates, and metamorphic rocks required the use of the in situ 10Be technique for catchments draining quartz-bearing lithologies, and the new meteoric 10Be/9Be technique for areas dominated by quartz-poor lithologies.
Denudation rates exhibit a significant spatial variability ranging from 0.1 mm/yr to over 1 mm/yr, with higher values concentrated in the central part of Albania, where the transition from compressional to extensional domains occurs. The observed spatial variability in denudation rates likely reflects variations in uplift rates. Geomorphological analysis underscores the transient nature of the Albanian orogen, marked by elevated relict surfaces, non-lithological knickpoints, evidence of recent drainage reorganisation and river terraces, reflecting also Quaternary climatic fluctuations. Projections of rivers draining the relict landscape cluster around three ranges of elevation, possibly recording separate episodes of relative base-level changes due to accelerations in rock uplift rates.
We interpret these findings as the result of the interplay between deep crustal accretion, occurring at the regional scale over long periods (>106 years), and the activity of upper crust normal faults at shallower levels since the Pliocene (Guzmán et al., 2013; Pashko et al., 2020). At the local scale, fault activity seems to influence the observed spatial variation of denudation rates. The consistency of denudation rates with incision rates, calculated from river terraces, and with GNSS vertical rates (Serpelloni et al., 2022) further supports our results, offering new insights into the geodynamic evolution of the Northern Hellenides.

How to cite: Bazzucchi, C., Crosetto, S., Ballato, P., Wittmann, H., Faccenna, C., and Rossetti, F.:  Building topography in the Northern Hellenides: insights from geomorphic analysis and cosmogenic nuclides, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-71, https://doi.org/10.5194/egusphere-alpshop2024-71, 2024.

Located in the central-eastern Mediterranean, the Albanides are a subduction orogen formed by the accretion of slices of continental lithosphere scraped off the upper plate during the eastward subduction of Adria. This subduction has promoted NE-SW shortening that started in the Late Cretaceous and continues to the present. Despite advancements in geophysical studies, aimed at understanding and illuminating the deep structures, the dynamics of crustal accretion within the subduction zone remain challenging. We investigate the recent crustal thickening of the Albanides and explore the relationship between deep-seated structures and surface deformation by employing low-temperature thermochronology and 3D thermokinematic modeling of a seismically constrained crustal section. Our results reveal a latest Miocene-Pliocene rejuvenation of the orogenic system marked by pulses of 3-4 km of exhumation, likely driven by a deep-seated thrust system. These findings provide important insights into the timing and kinematics of orogenic building processes, highlighting the interaction between deep underplating and surface geology in the Albanides, and contributing to our understanding of Mediterranean plate kinematics.

How to cite: Rossetti, F., Fellin, M. G., Ballato, P., Faccenna, C., Balestrieri, M. L., Muceku, B., Rondenay, S., Maesano, F., Crosetto, S., Durmishi, Ç., Bazzucchi, C., and Maden, C.: Building the Albanides by deep underplating: insights from low-temperature thermochronology and 3D thermokinematic modeling, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-72, https://doi.org/10.5194/egusphere-alpshop2024-72, 2024.

The northeast migration of the Oligocene-Pleistocene foreland basins system of the Northern Apennines brought the formation and younging, in the same direction, of wedge-top basins which were moving on top of the Ligurian prism; these basins allow to reconstruct the evolution and propagation of the accretionary prism and orogen growth. A first comparison of the structural and stratigraphic evolution of Northern Apennines and Ukrainian Outer Carpathians foreland basins system shows they are very similar and allow to reveal the occurrence of wedge top basins in the Ukrainian orogenic wedge. Ukrainian Carpathians, now NW-SE trending, are a thin-skinned thrust belt considered to be the Cretaceous-Neogene accretionary prism formed as a result of south-western subduction of the Carpathian  basin, a portion of the Northern Penninic ocean. Neogene Carpathian Foredeep can be divided into the Inner zone, accreted to frontal Boryslav-Pokuttya nappe, and the Outer zone overlaying the European plate.

In 2023-2024, geological-structural and sedimentological field studies were carried out in this frontal part of Ukrainian Carpathians. In Boryslav-Pokuttya nappe frontal zone we identified Early Miocene (23-16 Ma) wedge top basins. They represent NW-SE trending narrow and steep synclines filled with synorogenic deposits grouped in Polyanytsa, Vorotyshcha and Stebnyk Fms. The Polyanytsa and Vorotyshcha Fms start with thick chaotic complex, which lies on the erosional surface above the Oligocene and Eocene turbidites. The chaotic complex consists of matrix-supported debris-flow deposits containing exotic Paleozoic and Riphean fragments of European platform and Carpathian flysch. Specifically, the Polyanytsa Fm is made of gray flysch-like deposits with olistostrome lenses in the inner zones of the studied wedge-top basins. The shallow-water Vorotyshcha Fm is made of gray clays and sandstones and locally conformably overlays the Polyanytsa Fm and, since 21 Ma, evaporitic lenses mark the inception of Inner Foredeep for the more external portion of the Boryslav-Pokuttya nappe. In both wedge-top and Inner Foredeep basins, the Vorotyshcha Fm is followed by shallow-water deposits of the Stebnyk Fm. At the Early-Middle Miocene transition, the sedimentation in the wedge-top basins above the Boryslav-Pokuttya nappe is completed and chaotic complex were deposited in the Inner Foredeep formed to the NE of the Boryslav-Pokuttya nappe. In fact, since 16 Ma, Boryslav-Pokuttya nappe was accreted to the Outer Carpathian prism and became part of the orogenic wedge while the detachments began to advance within the Inner Foredeep which corresponds to the second wedge-top basin identified. The latter is the Middle-Late Miocene wedge-top basin (16-10 Ma), a gently dipping syncline infilled with shallow-water salt-bearing sediments with a thick chaotic complex at the base. In this wedge-top basin the sedimentation ends by 10 Ma with a conglomerate sequence sourced by the Carpathian Flysch.

These newly revealed wedge-top basins in the Ukranian Carpathians and related major tectonic events are (almost) coeval to the lower Miocene, middle Miocene and late Miocene nappe advancement of the Northern Apennines posing the bases for a better comparison between the two orogens

How to cite: Murovska, G., Hnylko, O., Artoni, A., Storti, F., and Bohdanova, M.: Wedge-top basins of the Ukranian Outer Carpathians and the Northern Apennines as tracers of (almost) coeval evolution of accretionary-collisional orogens, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-63, https://doi.org/10.5194/egusphere-alpshop2024-63, 2024.

The supposed Meliata suture divides the Austroalpine-related Central Western Carpathian (CWC) units from the Internal Western Carpathian (IWC) units of the Adria and/or Dinaridic affinity (Transdanubian and Bükk, respectively). The tightly imbricated and dismembered Triassic–Jurassic complexes of the Meliata Unit (Meliaticum) record the subduction/accretionary processes connected with the opening, expansion, subduction and closure of the Neotethyan Meliata Ocean in the southern Western Carpathian zones. The Meliaticum exhibits a lithologically variable composition. In general, three main partial units or complexes can be distinguished: i) the blueschist-facies Bôrka Nappe representing the distal continental margin exhumed from the subduction channel during the Late Jurassic and subsequently thrust over the foreland lower CWC plate; ii) variable chaotic, in part ophiolite-bearing mélange complexes; iii) relatively coherent Jurassic successions of deep-marine hemipelagic and distal flysch deposits with olistostrome bodies which include Triassic carbonate blocks revealing the late Mid-Anisian (Pelsonian) breakup of the Meliata Ocean. This study focuses on the examination of the chaotic complexes of the Meliata Unit at the crucial Čoltovo locality. Due to the poor outcrop conditions caused by soil and debris cover and tectonic reworking typical for the Meliaticum, heavy equipment was used to expose the bedrock and establish the relationships between various components. Based on lithological study and biostratigraphy of radiolarians, the Čoltovo locality represents a chaotic mélange structure of Lower Jurassic clastic pelagic deposits and Middle Jurassic olistostromes with cherty intercalations and blocks of Middle Triassic limestones, terrigenous siltstones and variegated radiolarites, Upper Triassic red radiolarites, siltstones and basic volcanics.

Geochemical analyses were undertaken on various types of sedimentary rocks. Majority of the samples fall within the fields of the pelagic environment affected by terrigenous input from the marginal continental area and a continental slope/rise environment, where they intercalate the radiolaritic shales. In the provenance discrimination diagram, most of the sample's plot fall in the fields of mature quartzose, i.e. continental terrigenous provenance. Basic volcanics plot in the border between the within-plate tholeiites with volcanic arc basalts and MORB. According to primitive mantle normalized REE patterns and other immobile trace elements, samples indicate a typical oceanic crust origin.

Čoltovo locality records gradual spreading and deepening of the Meliata Ocean which was the NW branch of the Neotethys. First phase of deep-water sedimentation is represented by distal terrigenous clastics and radiolarite sedimentation with significant volcanic and tectonic activity during the Middle–Upper Triassic. The second, Jurassic phase, points to the formation of olistostromes in connection to the subduction process. In its current form the Meliatic complexes are fragmented into allochthonous blocks/sheets, comprising the Meliatic Basin and the northern continental margin, together incorporated into subduction–accretion mélanges.

Acknowledgements: The research was supported by following projects: APVV-17-0170, APVV-21-0281 and VEGA 1/0435/21.

How to cite: Molčan Matejová, M., Potočný, T., and Plašienka, D.: Chaotic complexes of the Meliata Unit: biochronology, lithostratigraphy and geochemistry of a mélange near Čoltovo (Western Carpathians, Slovakia), 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-74, https://doi.org/10.5194/egusphere-alpshop2024-74, 2024.

The Eastern European Alps formed during two orogenic cycles, which took place in the Cretaceous and Cenozoic, respectively. In the Ötztal-Stubai Complex – a thrust sheet of Variscan basement and Permo-Mesozoic cover rocks – the record of the first (Eoalpine) orogeny is well preserved, because during the second (Alpine) orogeny the complex remained largely undeformed. We use new zircon (U-Th)/He (ZHe) ages and thermo-kinematic modeling to constrain the cooling and exhumation history of the central part of the Ötztal-Stubai Complex since the Late Cretaceous. The ZHe ages from two elevation profiles increase over a vertical distance of 1500 m from 56±3 to 69±3 Ma (Stubaital) and from 50±2 to 71±4 Ma (Kaunertal), respectively (Hölzer et al., accepted by Lithosphere). These ZHe ages and few published zircon and apatite fission track ages were used for inverse thermo-kinematic modeling. The modeling results show that the age data are well reproduced with a three-phase exhumation history. A first phase with relatively fast exhumation (~250 m/Myr) during the Late Cretaceous ended at ~70 Ma and is interpreted to reflect the erosion of the Eoalpine mountain belt. As Late Cretaceous normal faults occur at the margins of the Ötztal-Stubai Complex, normal faulting may have also contributed to the exhumation of the study area. Subsequently, a long period with slow exhumation (<10 m/Myr) prevailed until ~16 Ma. This long-lasting phase of slow exhumation suggests a rather low topography with little relief in the Ötztal-Stubai Complex until the mid-Miocene, even though the Alpine orogeny had already begun in the Eocene with the subduction of the European continental margin. Accelerated exhumation since the mid-Miocene (~230 m/Myr) is interpreted to reflect the erosion of the mountain belt, due to the development of high topography in front of the Adriatic indenter and repeated glaciations during the Quaternary.

How to cite: Wolff, R., Hölzer, K., Hetzel, R., and Dunkl, I.: The long-lasting exhumation history of the Ötztal-Stubai Complex (Eastern European Alps): New constraints from zircon (U-Th)/He age-elevation profiles and thermo-kinematic modeling, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-76, https://doi.org/10.5194/egusphere-alpshop2024-76, 2024.

Shortening in highly oblique convergent settings often causes strain partitioning into components parallel and orthogonal to the block boundary. Field data collected as part of the 'Progetto CARG della Provincia Autonoma di Bolzano - Foglio Vipiteno scala 1:25.000' provide insight into the structural evolution of the area around Sterzing/Vipiteno (Autonomous Province of South Tyrol, Italy), which is located at a key position in front of the Dolomites Indenter. The southeastern margin of the Ötztal Nappe, with its Permomesozoic cover (Brenner Mesozoic), has been overthrust by garnet mica schist of the Schneeberg Complex. Initially, however, the contact between the Ötztal Nappe and the Schneeberg Complex formed as a thrust during the Eoalpine nappe stacking, with the latter unit being in a footwall position. The garnet mica schist of the Schneeberg Complex shows predominantly E-W trending, subhorizontal fold axes with a subvertical axial plane in the western parts of the study area. These folds are correlated with N-S directed shortening that presumably led to the (?Eocene-Oligocene?) emplacement of the Schneeberg Complex on top of the Ötztal Nappe. Progressive counterclockwise rotation of the fold axes towards the east is interpreted as the result of ongoing shortening combined with left lateral displacement. Brittle-ductile, SE-dipping shear zones and NNE-SSW trending strike-slip faults, comparable to the Passeier or Jaufen faults, accommodate sinistral slip in the study area. Interestingly, a thin layer of garnet mica schist (often misinterpreted as schist of the Raibl Group) is wedged into a cataclastically overprinted dolomitic marble of the Brenner Mesozoic below the Monte Velo. The contact shows top-to-the-W kinematics and N-S trending, subhorizontal fold axes with E-dipping axial planes. The geometry of the Dolomites Indenter results in a highly oblique convergent setting in the study area, therefore, this Monte Velo Thrust is interpreted to accommodate shortening orthogonal to the indenter boundary. NW-SE striking normal faults with top-NE-down kinematics dissect the top-W-thrust plane. These normal faults are considered antithetic faults in the hanging wall of the Brenner Normal Fault and represent the final stage of deformation in the study area. Altogether, the observed structures show good agreement with published results from analogue modeling of highly oblique convergent settings and are consistent with the scenario of strain partitioning in a sinistral transpressional regime. Furthermore, the advance of the Dolomites Indenter had a significant impact on the southeasternmost part of the Ötztal Nappe and its contact with the Schneeberg Complex.

How to cite: Reiser, M.: Strain Partitioning in Front of the Dolomites Indenter: Field Observations in the Austroalpine Nappe Stack, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-62, https://doi.org/10.5194/egusphere-alpshop2024-62, 2024.

The Corsica-Sardinia block (CSB) is set in the middle of western Mediterranean between two highly stretched lithospheric domains, the Balearic and Tyrrhenian basins, that opened because of the progressive eastward migration of the Apennine front and roll-back of the Neotethys slab. The main tectonic features recorded in the CSB are Oligocene-Miocene strike-slip faults with either NE-SW orientation in Corsica and northern Sardinia and NW-SE orientation in southern Sardinia. Several evidence indicate multiple reactivation of these trans-crustal structures over time. The oldest stage of reactivation is testified by voluminous Pliocene-Quaternary anorogenic volcanic activity localized along the strike-slip faults in northern and central Sardinia. Farther to the south, strike-slip faults reactivated as normal faults during the Quaternary accommodating the deposition of more than 1000 m of continental deposits in the Campidano basin. Finally, in several sites strike-slip faults reactivated as normal or oblique faults offsetting upper Pleistocene to Holocene coastal deposits.

In spite of these evidence of recent deformation, the CSB is characterized by vertical aseismic movements in the order of few mm per year and weak seismicity, with earthquakes occurring usually at depth not higher than 10 km and along the main Cenozoic faults. These structures also control the topography of the Corsica and Sardinia islands, supporting a rugged morphology with peaks close to 2000 m in Sardinia and 3000 m in Corsica, deep river incisions and other geomorphic features typical of relief rejuvenation. To investigate the cause of this cryptic neotectonic activity we run a set of Finite Differences numerical models that simulate the CSB as thin elastic plate overlying an inviscid asthenosphere. 

The structure of the model lithosphere is based on available geological and geophysical dataset and is divided into six compositionally homogeneous layers: air or water, sedimentary or volcanic cover, crystalline middle crust, lower crust, lithospheric mantle, and asthenosphere. In the experiments, we change the density and heat production rate of the crustal layers to fit the measured Bouguer gravity anomaly and surface heat flow.

The best fit experiment shows that the CSB crust consists of a relatively low-density lower crust composed by felsic granulites moderately enriched in heat-producing elements, and a standard-density middle crust composed of highly productive granites or migmatites. The results suggest that neotectonic activity can be related to regional uplift driven by a mass deficit localized in the lower crust. In our opinion, the Cenozoic faults accommodate differential vertical displacements of fault-bounded blocks, occasionally triggering low-magnitude earthquakes in the upper crust. This interpretation account also for the peculiar geomorphic features of Sardinia and Corsica, where the landscape is continuously rejuvenated according to the uplift movements.

How to cite: Casini, L., Cocco, F., and Funedda, A.: Neotectonics in the Corsica-Sardinia block: relationships between surface processes and lithospheric structure, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-85, https://doi.org/10.5194/egusphere-alpshop2024-85, 2024.

The Pieniny Klippen Belt (PKB) represents a boundary zone between the Outer and Central Western Carpathians and is interpreted as a separate branch of the north-westernmost Tethyan Ocean (Pieniny Klippen Basin – PKBs). In whole PKBs history at least three phosphatic events took place: (i) Early Bajocian, (ii) Berriasian and (iii) Albian times. The several facies successions accumulated in subtidal/neritic shelf environments of the submarine swell (so-called Czorsztyn Ridge and its southeastern slope), while palaeogeographical orientation of this Czorsztyn Ridge was from NE to SW. These successions can be distinguished, from shallowest zone (Czorsztyn Succession) trough transitional zone (Niedzica and Czertezik successions) up to deepest one (Branisko and Pieniny successions) in the axial part of this basin.

In the late Early Bajocian time (i), just after Czorsztyn Ridge originated by tectonic uplift, sedimentary features recorded condensation episode during start of crinoidal limestones sedimentation (even up to 150m in thickness). The base of the crinoidal limestones are very sharp and directly overlying, with stratigraphical hiatus (ca. 2Ma), the oxygen-depleted dark/black Fleckenkalk/Fleckenmergel-type deposits of Toarcian-lowermost Bajocian in age. This part of crinoidal limestones consists of phosphatic concretions pavements, large phosphatic macrooncoids (up to 8-10cm), light-greenish clasts of micritic limestones, pyrite concretions, and fossils as ammonites, brachiopods and bivalves. Phosphatic concretions (up to 6cm) occur in almost all PKB successions exclusively within lowermost part (first 1.0m above base) of crinoidal beds, which is isochronous event. On the other hand, very rapid change of sedimentation from oxygen-depleted environments (during Toarcian-earliest Bajocian) to carbonate sedimentation is record of rapid vertical tectonic uplift of the Czorsztyn Ridge and adjacent areas and may be also reflect palaeoceanographical changes after this tectonic movements and origin of upwelling currents, for which such condensation and phosphatic structures are typical. The second (ii), Berriasian episode of phosphatisation within PKBs has been connected with post-Tithonian time tectonic uplifting of the Czorsztyn Ridge and surroundings, including Niedzica Succession. The presence of phosphate-rich deposits (phosphorites and microbial phosphate macrooncoids) in this succession, which should be localized in a palinspastic reconstruction near shelf-edge slope boundary, supported idea of upwelling currents as well. In the PKBs this idea is additionally supported by Berriasian brachiopods/crinoids-rich beds of the Czorsztyn Succession and their distribution probably have also been controlled by the upwelling currents, where nutrient-rich oceanic water formed such conditions which caused the proliferation of benthos. The third (iii), Albian episode of phosphatisation of marly deposits on sea-floor occupied by the Czorsztyn Succession zone are represented by phosphatic: stromatolites, lithoclasts and microbialite-coatted bioclasts within beds of different thickness (a few cm up to dozen ones). Usually, these are on the base of Albian marls/marly limestones which covered erosional surfaces of older limestones with several fossil-karst phenomena originated as effect of at least two episodes of tectonic uplift and emersions of the Czorsztyn Ridge/Czorsztyn Succession zone.

How to cite: Krobicki, M.: Palaeoceanographic significance of the Jurassic and Cretaceous phosphatic events in geotectonic history of the Pieniny Klippen Basin (Carpathians), 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-87, https://doi.org/10.5194/egusphere-alpshop2024-87, 2024.