Tethys tectonic system has experienced a long-term evolution history, including multiple Wilson cycles; thus, it is an ideal target for analyzing plate tectonics and geodynamics. Tethyan evolution is typically characterized by a series of continental blocks that separated from the Gondwana in the Southern Hemisphere, drifted northward, and collided and accreted with Laurasia in the Northern Hemisphere. During this process, the successive opening and closing of multistage Tethys oceans (e.g., Proto-Tethys, Paleo-Tethys, and Neo-Tethys) are considered core parts of the Tethyan evolution. Herein, focusing on the life cycle of an oceanic plate, four key geodynamic processes during the Tethyan evolution, namely, continental margin breakup, subduction initiation (SI), Mid-Ocean Ridge (MOR) subduction, and continental collision, were highlighted and dynamically analyzed to gather the following insights. (1) Breakup of the narrow continental margin terranes from the northern Gondwana is probably controlled by plate subduction, particularly the subduction-induced far-field stretching. The breakup of the Indian continent and the subsequent spreading of the Indian Ocean can be attributed to the interactions between multiple mantle plumes and slab drag-induced far-field stretching. (2) Continental margin terrane collision-induced subduction transference/jump is a key factor in progressive Tethyan evolution, which is driven by the combined forces of collision-induced reverse push, far-field ridge push, and mantle flow traction. Moreover, lithospheric weakening plays an important role in the occurrence of SI. (3) MOR subduction is generally accompanied by slab break-off. In case of the considerably reduced or temporary absence of slab pull, mantle flow traction may contribute to the progression of plate subduction. MOR subduction can dynamically influence the overriding and downgoing plates by producing important and diagnostic geological records. (4) The large gravitational potential energy of the Tibetan Plateau indicates that the long-lasting India-Asia continental collision requires other driving forces beyond the far-field ridge push. Further, the mantle flow traction is a good candidate that may considerably contribute to the continuous collision. The possible future SI in the northern Indian Ocean will release the sustained convergent force and cause the collapse of the Tibetan Plateau. Based on the integration of these four key geodynamic processes and their driving forces, a “multiengine-driving” model is proposed for the dynamics of Tethyan evolution, indicating that the multiple stages of Tethys oceanic subduction provide the main driving force for the northward drifting of continental margin terranes. However, the subducting slab pull may be considerably reduced or even lost during tectonic transitional processes, such as terrane collision or MOR subduction. In such stages, the far-field ridge push and mantle flow traction will induce the initiation of new subduction zones, driving the continuous northward convergence of the Tethys tectonic system.

How to cite: Li, Z.-H.: Multiengine-driving Tethyan evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2454, https://doi.org/10.5194/egusphere-egu24-2454, 2024.

The Ediacaran to Cambrian in the northwest Yangtze Block, has long been considered to be formed in a passive margin. Wells and seismic data, however, show that a Lower Cambrian thick siliciclastic rock succession occurs in the northwest Sichuan Basin, the provenance of which has not received attention from previous workers. In this study, we first propose that an Early Cambrian foreland basin was formed in the northwest Yangtze Block. Stratigraphic correlation shows a distinct stratigraphic absence from the Lower Cambrian to Devonian in the Bikou terrane, implying an orogeny might take place from NW to SE. A regional seismic profile shows a wedge stratigraphic geometry of the Lower Cambrian from NW to SE, further indicating a typical structure of a foreland basin. Field outcrops show an overall coarsening-upwards siliciclastic succession of the Lower Cambrian. The petrological analysis of siliciclastic rocks presents an immature feature implying a proximal source. Paleocurrent measurements of siliciclastic rocks point to dominant SE-vergent orientations. The age spectra of detrital zircon U-Pb dating of the Canglangpu Formation show a dominant Early Cambrian age of ca. 530 Ma, together with some positive ɛ_Hf(t) values, indicating that the detrital zircon grains from the Lower Cambrian were derived from a northwest proximal juvenile continental arc and older crust. Therefore, the northwest Yangtze Block experienced a tectonic transition from an Ediacaran passive margin to an Early Cambrian foreland basin. The formation of the Early Cambrian foreland basin appears to have been strongly influenced by an orogenic loading northwestward. Here, this previously-overlooked orogenic event is named as the Motianling orogeny. The origin of the Early Cambrian orogeny may be related to subduction of the Proto-Tethys ocean beneath the northwest Yangtze Block, resulted in continental collision and uplift of northwest microterranes that provided siliciclastic sediments to fill the foreland basin southeastward.

How to cite: Gu, Z., Jian, X., and Watts, A.: Tectonic evolution of an Early Cambrian foreland basin in the northwest Yangtze Block, South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9027, https://doi.org/10.5194/egusphere-egu24-9027, 2024.

The Central Asian Orogenic Belt (CAOB) is one of the largest orogenic collages in the world, and preserves important records of accretionary orogeny and Phanerozoic continental growth. The Yili Block is one microcontinent in southwest of CAOB, with Precambrain basement rocks exposed in the northern and southern margin. The Middle to Late Ordovician arc-type magmatic rocks were identified in the northern margin of the Yili Block with a subduction-related calc-alkaline affinity conclude that the southward subduction of the Junggar Ocran beneath the Yili Block, but the Silurian magmatism is rarely reported.

Mafic dikes preserve a considerable amount of geological information about geodynamics, crustal evolution and transformation of the regional stress field. Multi-period basic dikes, including Neoproterozoic and Carboniferous, are exposed in the northern margin of the Yili Block, which record important information about the transformation process of regional tectonic system. Recently, we have identified early Silurian diabase dikes in the Precambrian metamorphic rocks in the Wustu area, Wenquan County, northern margin of Yili Block. This paper reports zircon U-Pb age and Lu-Hf isotopic compositions, whole-rock geochemistry and Sr-Nd isotopic compositions for the Wustu diabase dikes and its surrounding rocks. One diabase sample yielded a zircon U-Pb age of 442±7 Ma with positive ε_Hf(t) values (+3.0~+9.1), and its surrounding rock sample (leucogranite) yielded a zircon U-Pb age of 901±3 Ma. The diabase samples have high TFe₂O₃ contents (8.34%~9.81%) and K₂O+Na₂O contents (5.72%~6.86%), low MgO contents (3.69%~4.38%) and TiO₂ contents (1.69%~2.00%) and belong to the high-K calc-alkaline series. The samples are enriched in the large ion lithophile elements (LILEs, such as Rb, Th, U and K) and have negative anomalies in the high-field-strength elements (HFSEs, e,g. Nb, Ta and Ti), with low Nb/Th ratios (0.13~1.16), Nb/La ratios (0.42~0.45) and high Zr/Hf ratios (39.6~42.2). They also have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.707369~0.708637) and positive ε_Nd(t) values (+1.9~+3.6). Our results indicate that they were sourced from a metasomatic sub-continental lithospheric mantle, which mainly composed of spinel iherzolite and garnet iherzolite. The trace element contents and its ratios, such as Zr (212×10^-6~242×10^-6), Hf (5.16×10^-6~6.02×10^-6), Nb (6.69×10^-6~9.24×10^-6), Ta (0.60×10^-6~0.81×10^-6), Zr/Y (5.21~6.82) and Hf/Th (0.69~0.91), indicate that the diabase dikes formed in an extensional setting during the early Silurian. Finally, we propose that the extensional tectonic setting maybe relate to the change of the subducted slabs angle or tectonic regime transition induced by the collage of the Aktau-Wenquan continental domain to the Yili Block in the end of Ordovician.

How to cite: Chen, Y., Wang, M., Zhu, S., and Cao, M.: The Early Silurian diabase dikes in the northern margin of the Yili Block, southwestern CAOB: insight into rift-related magmtism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6914, https://doi.org/10.5194/egusphere-egu24-6914, 2024.

Sn wave, a regional seismic phase, propagates horizontally in the uppermost mantle and is sensitive to lateral variations in mantle lid thickness, temperature, and melt. The physical properties of the lithosphere can be indicated by Sn propagation efficiency or attenuation. The inefficient Sn propagation has been typically used to describe the regions with high-temperature anomalies in the uppermost mantle and infer the subduction front of the Indian lithosphere in the north Tibetan plateau. Here we collect 122,481 tangential-component digital seismograms, isolate the geometric spreading and attenuation for SH-type Sn wave, and construct a broadband uppermost mantle shear wave attenuation model in the Tibetan region. Beneath the central and north parts of the Tibetan plateau the Sn waves are strongly attenuated, while relatively weaker attenuation can be observed in the perimeter of the plateau, i.e., the Himalaya mountains in the south, Tarim and Qaidam basins and Eastern Kunlunshan terrain in the north, and Sichuan basin in the east. These weak attenuation regions are likely where the old crustal fragments were deposited during the collision between the Indian and Asian plates. In contrast, strong Sn attenuation likely indicates local lithospheric delamination in central and eastern Tibet. Furthermore, the correlation between strong Sn and Lg attenuation zones reveals the potential mantle upwelling with deep heat sources invading the crust.

How to cite: Zhao, L.-F., Xie, X.-B., He, X., and Yao, Z.-X.: Quantitative Sn-wave Attenuation Beneath the Tibetan Plateau and Lithospheric Rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3712, https://doi.org/10.5194/egusphere-egu24-3712, 2024.

     The collision between the Indian and Eurasian plates in the Cenozoic eras resulted in the formation of the world's largest and highest plateau. The intensive collision, subduction, and related deep dynamic processes led to significant crustal shortening, uplifting, and expansion of the Plateau, accompanied by eastward extrusion of plateau materials. The southeastern Tibetan Plateau (SETP) is one of the most important channels for escaping plateau materials. The widespread existence of crustal weak material flow in the SETP has become widely accepted. However, previous research has mostly been limited to two-dimensional profiles or spaced data measurement points. Therefore, obtaining reliable and high-resolution geophysical models of the lithosphere is crucial for understanding the deformation mechanisms of the plateau.

    Our three-dimensional resistivity model shows unprecedented resolution of the Simao Block of the Indochina Block, offering new insights into the material transport and deformation mechanisms of the SETP. Two consecutive large-scale high-conductivity anomalies observed in the middle-lower crust are speculated to be partial melting associated with crustal flow. The rigid lithosphere separated by significant strike-slip faults on the SETP may be pulled by ductile materials flow, where plastic flows in the middle-lower crust drive the rigid blocks to extrude and escape along the boundary faults, thus dominating the deformation of the lithosphere. The large-scale delamination of the continental lithosphere leads to upwelling of the asthenosphere along mechanically weak areas. Upwelling hot materials continue to heat the entire crust, and the expanding and diffusing lower crust further accelerates partial melting and plastic flow in the middle-lower crust.

How to cite: Ye, G., Sang, W., Wei, W., Jin, S., Lei, Q., and Dong, H.: Preliminary Results of Material Transport Model of Rigid Block Extrusion Driven by Crustal Flow Beneath the SE Tibetan Plateau: insights from high-resolution 3-D Magnetotelluric Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4844, https://doi.org/10.5194/egusphere-egu24-4844, 2024.

The Lhasa Terrane in southern Tibet is widely recognized as having separated from the northern margin of Gondwana with a Precambrian basement and undergoing a protracted and intricate evolution. Abundant Early Cretaceous volcanic rocks are present in the central Lhasa subterrane, Tibet, playing an essential role in models aimed at comprehending the tectonic-magmatic evolution and mantle-crust interaction of this terrane. In this study, we present a well-preserved section of Zenong Group volcano-sedimentary sequence in Eyang, Xainza area within the central Lhasa subterrane. Our new data combined with existing literature data indicate that there was an extensive period of magmatism (approximately 140 Ma to 102 Ma) throughout the Early Cretaceous in the central Lhasa subterrane, reaching its peak around 113 Ma with remarkable compositional diversity.

However, the composition of Early Cretaceous volcanic rocks in the central Lhasa subterrane underwent a temporal transition from high-silica rhyolites to dacites and andesites, exhibiting a reverse cyclicity. Moreover, the intermediate rocks from the upper section display elevated whole rock εNd(t) and zircon εHf(t) values, as well as decreased ⁸⁷Sr/⁸⁶Sr ratios compared to the high-silica rocks from the lower section. These observations collectively suggest: (a) involvement of open-system processes encompassing mantle-derived magmas and ancient crustal-derived materials; (b) an increasing contribution of mantle sources in the magma genesis; (c) variable magma origins with distinct petrogenetic histories rather than a uniform source involving assimilation-fractional crystallization processes.

The high-silica rhyolites from the bottom of the Eyang section display characteristics of fractional crystallization and exhibit varying zircon ε_Hf(t) values (−16.7 to −7.8), negative ε_Nd(t) values (−13.7 to −13.1), highly variable initial Sr isotopic compositions, and radiogenic Pb isotopic signatures, indicating that a combined process of magma mixing (involving crustal-derived felsic melts and mantle-derived mafic melts) followed by fractional crystallization was primarily responsible for their formation. The dacitics from the upper part of the Eyang section show higher ε_Hf(t) values (−9.9 ~ +0.5) and ε_Nd(t) values (−10.6 to −9.5) than the high-silica rhyolites, suggesting that these dacitic rocks were also largely derived from anatexis of ancient crustal material with more involvement of mantle-derived magmas. The andesites exhibit more enriched Sr-Nd-Hf isotopic compositions compared to the contemporaneous dacitics, as well as less radiogenic Pb isotopic compositions, suggesting their likely derivation from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments.

We propose that the high-silica rhyolites in the lower section of the Xainza area (≥ ca. 120 Ma) are associated with slab roll-back, while the dacites and andesites in the upper section (≤ca. 120 Ma) are linked to slab break-off during southward subduction of Bangong-Nujiang Ocean lithosphere. Furthermore, it is evident that the ancient basement of the central Lhasa subterrane underwent localized reworking by mantle-derived melts.

How to cite: Huang, Y., Zhao, Z., and Zhu, D.-C.: Compositional and tectonomagmatic evolution of Early Cretaceous magmatism in the central Lhasa suberrane, Tibet: Implications from the Zenong Group volcanic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4877, https://doi.org/10.5194/egusphere-egu24-4877, 2024.

The Kashmir ‘seismic gap’ in NW Himalaya, between the 1905 Kangra and 2005 Muzaffarabad earthquake rupture zones, has been replete with moderate-to-small earthquakes. GPS geodetic measurements across the Himalayan-arc reveal arc-normal convergence of ~11 mm/yr, which reduces towards the foreland in the India-fixed reference frame. In 2013 the Jammu And Kashmir Seismological NETwork (JAKSNET), and later the Himachal Pradesh Seismological NETwork (HiPSNET) was established to study the seismological characteristics of this ‘seismic gap’. Using continuous waveform data from these networks an earthquake catalog has been created using the Regressive ESTimator (REST) algorithm. Following this, seismic phases were manually picked from ~1100 earthquake records to determine the accurate arrival-times. A subset of these events based on the quality of picked phases are relocated using a probabilistic Non-Linear Location (NLL) method. These earthquakes have magnitudes between 0.5 and 4.5, and are distributed throughout the crust, with the majority concentrating at shallow (<25 km) depth. These shallow earthquakes are concentrated beneath the Higher Himalaya with lateral variations south of the Kishtwar window and to a region to its east. In arc-normal cross-section, the hypocenters lie on and above the MHT and the depth increases hinterlandward. Two distinct clusters of seismicity with increasing depth coincides with the mid-crustal frontal ramp observed in Vs structure beneath the Kishtwar window. The arc-parallel cross-section shows two eastward dipping hypocenter-clusters on and above the MHT. The one west of the Kishtwar window coincides with the lateral ramp observed in the Vs model. We conjecture that the one to the east also illuminates a similar transverse structure within the Himalayan wedge. Comparison of our hypocentral distribution with GPS velocities across this region reveal a frictionally locked shallow segment of the MHT, with the down-dip unlocking-zone highlighted by the across-arc clustering of seismicity beneath the Higher Himalaya. The locked-to-creep transition occurs immediately north of the mid-crustal frontal-ramp. We compute strain-rate from the sparse GPS data which reveals a predominant NE-SW compression and high strain-rates in regions of clustered shallow-seismicity. We are in the process of further refining the hypocentral locations using a double-difference relocation method, results of which will be presented. 

How to cite: Shamim, S., Ghosh, A., Mitra, S., Priestley, K., Sharma, S., and Wanchoo, S. K.: Locked Frontal and Lateral Ramps on the Main Himalayan Thrust beneath NW Himalaya illuminated by precisely located seismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15623, https://doi.org/10.5194/egusphere-egu24-15623, 2024.

Although the arc magmatism before collision has been considered as the main mechanism to the continental crustal growth and vertical geochemical fractionation for many years, the syn-collision magmatism related to the melting of accumulation in the base of arc could be an important contribution to crustal net growth and fractionation. Hence, the syn-collision magmatism could be an ideal object to research the continental crustal maturation and stratification. The arc magmatism could be controlled by the connecting magmatic reservoir in different depth and the experimental data show that the arc magma could be polybaric fractionation. However, the detail fractional phase in different level is not clear. Therefore, we selected the Early Eocene mafic rock series in the Tengchong Block, southwestern extension of Tibet, to reveal the detail magmatic evolution process. The rocks include hornblendite, hornblende (Hb) gabbro and diorite with different mineral assemblages, which is the syn-collision magmatism related to the Indian-Asian continental collision. These rocks have zircon ages of ca. 54Ma, and similar whole rock Sr-Nd and zircon Hf isotopes, indicating they are coeval and congenetic. In contrast to the isotopic composition, the major elements of the suits are variable, such as SiO₂ contents of 48.72-61.49 wt.%, MgO contents of 12.02-2.69wt.%. The clinopyroxene (cpx) is mainly enclosed in the hornblende in the samples and part of the Hb could be the products of the replace reaction associated with cpx and others could be direct crystallization from the magma. The crystallization parameters calculation results show that the clinopyroxenes have high pressures of 2.4-10.7kbar with average of 7.6kbar and temperatures of 1006-1208°C with average of 1154°C. The hornblende crystallized at the pressures of 2.2-7.8kbar with average of 3.8kbar, and temperatures of 776-875°C with average of 827°C. In addition, the plagioclases in the all samples have three types, including high An core, low An rim with overgrowth rim as type I, low An core, high An mantle low An rim with overgrowth rim as type II, low core with overgrowth rim as type III. The homogeneous in-situ Sr isotopes show the compositions variation from the core to rim could be resulted from the process of dissolution and reprecipitation during the batches recharging of homogeneous magma. Therefore it could conclude that the primary magma of the Eocene mafic rocks could be fractionated in the lowermost crust, and the major crystallization phase dominated by clinopyroxene and forming the pyroxenite as the base of the arc. Then the evolution mafic magma emplace and form a mafic reservoir in the middle crust according to the assembly of batches of magma and finally occurring the further fractionation that the hornblende-dominated accumulation forming the hornblendite and the hornblende and plagioclase accumulation forming the Hb-gabbro and diorite. This polybaric fractionation within the continental crust during syn-collision could lead to the melt transition from mafic to granitic and further strengthen the crustal maturation and stratification.

Supported by National Natural Science Foundation of China [Grant Nos. 42272052 and 41902046], Fundamental Research Funds [Grant No. 300102273102]

How to cite: Zhao, S., Wen, T., and Fang, X.: Polybaric and multistage fractionation of syn-collision mafic magma in continental arc: constraints from the Eocene mafic rocks in the Tengchong Block, southeastern extension of Tibet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6939, https://doi.org/10.5194/egusphere-egu24-6939, 2024.

The Tibetan Plateau, Earth's largest and highest plateau, boasts an extraordinarily thick continental crust (60-80 kilometers) and an average elevation exceeding 4000 meters. Unraveling the plateau's uplift history, vital for comprehending Earth's Cenozoic history and its environmental impacts, has long been a subject of debate. While prior studies predominantly attribute the plateau's formation to the India-Asia collision, 45-59 million years ago, its timing and underlying mechanisms remain contentious. Airy isostasy as a response to crustal thickening during the Indian-Asian collision was considered the main factor for the uplift of the Gangdese terrain, the important portion of the Tibetan. Trace elemental ratios, e.g. Sr/Y and (La/Yb)n ratios, of the bulk magmatic rocks were the main geochemical indexes to recover the thickening history. However, the resultant crustal thickness and the consequent geodynamics recovered by different indexes remain controversial. Here, we compile the geochemical data for the volcanic rocks from global young arcs and continental orogens and built a supervised Machine Learning model to estimate crustal thickness. The reliability of this new model was tested, and the crustal thickening history of Gangdese terrain was recovered with it. The results reveal that the Gangdese terrane maintained a global-average thickness during the early stage of the India-Asia collision, which was not sufficient to support the uplift to >3000 m, as revealed by the recent paleoaltimeter data, through Airy isostasy.  This challenges the conventional belief of rapid uplift due to crustal thickening upon the Indian-Asian collision. Instead, our results suggest a protracted uplift process that parallels crustal thickening, reshaping our understanding of this iconic geological feature.

How to cite: Luan, Z., Liu, J., ZhangZhou, J., Xia, Q., and Hanski, E.: Machine Learning unravels the protracted role of India-Eurasia collision in the uplift of the Tibetan plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6941, https://doi.org/10.5194/egusphere-egu24-6941, 2024.

We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on a new thermal-isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady-state lithosphere thermal regime, and assumes that deviations from crustal Airy-type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200–240 km) with a predicted surface heat flow of 40–50 mW/m² typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphere. We identify a “North Tibet anomaly” with thin (<80 km) lithosphere and high surface heat flow (>80–100 mW/m²). We interpret this anomaly as the result of removal of lithospheric mantle and asthenospheric upwelling at the junction of the Indian and Asian slabs with opposite subduction polarities. Other parts of Tibet typically have intermediate lithosphere thickness of 120–160 km and a surface heat flow of 45–60 mW/m², with patchy anomalies in eastern Tibet. While different uplift mechanisms for Tibet predict different lithospheric thermal regimes, our results in terms of a highly variable thermal structure beneath Tibet suggest that topographic uplift is caused by an interplay of several mechanisms.

How to cite: Xia, B.: Strong Variability in the Thermal Structure of Tibetan Lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14740, https://doi.org/10.5194/egusphere-egu24-14740, 2024.

We performed (U-Th-Sm)/He apatite and zircon thermochronology (AHe and ZHe, respectively) on basement rocks from the Central Taurides, southern Turkiye to constrain its Tertiary >2000m surface uplift history. The samples were collected from the Alanya and Antalya units exposing in the southern part of the Central Taurides. The Alanya Massif represent a Late Cretaceous HP/LT eclogite to blueschist facies metamorphic pile whereas the Antalya Unit shows a relatively coherent stratigraphy consisting mainly of Triassic sandstones together with Permian and Jurassic limestones that are exposed as tectonic windows below the Alanya Massif. The AHe ages from the Alanya Massif cluster in with Early Oligocene (ca. 30 Ma), Early Miocene (ca. 20 Ma) and Late Miocene (ca. 8 Ma) ages. Apatites from one of the sandstone samples from the Antalya Unit gave also a Late Miocene age (ca. 9 Ma), consistent with the cooling ages of the tectonically overlying metamorphic rocks. In contrast, apatites from a sandstone sample exposed in the north show old, dispersed ages suggesting that they escaped from tectonic burial during the Eocene nappe stacking. ZHe ages from one of the metamorphic samples gave a ca. 30 Ma age; indistinguishable from its apatite ages. Our new AHe and ZHe age data indicate that, during Late Eocene nappe tectonics, the Alanya Massif and the underlying Antalya Unit was buried enough to reset the AHe and ZHe ages. Following the compressional regime, during the Early Oligocene, the Alanya Massif was subjected to a fast exhumation, possibly through an extensional detachment. This post-contractile-tectonic exhumation continued episodically during the Early Miocene until just prior to the Miocene transgression. The final Late Miocene exhumation ages are noteworthy and overlaps well with the beginning of the surface uplift of the southern margin of the Anatolian plateau. The new thermochronological data from the Central Taurides suggest that the extension of the southern margin of the Anatolian Plateau had already started in the Early Oligocene, predating the Arabia-Anatolia collision. The extension could have been triggered by the roll-back of the until then intact Bitlis-Cyprus-Hellenic slab, which created a widespread Oligo-Miocene extensional regime on the overriding Anatolian margin.

How to cite: Aygül, M., Uysal, I. T., Sobel, E. R., Okay, A. I., and Glodny, J.: New (U-Th-Sm)/He low-temperature apatite and zircon thermochronology ages reveal episodic Tertiary exhumation and uplift of the Central Taurides, southern Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1527, https://doi.org/10.5194/egusphere-egu24-1527, 2024.

During the Late Cretaceous, a 2700 km long magmatic arc extended from the Lesser Caucasus through the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans. We studied the arc volcanic rocks in three regions of the Western Pontides, and compared them to the other arc magmatic rocks from the Lesser Caucasus, Eastern Pontides and Balkans. Prior to the onset of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data indicate that magmatism in the Lesser Caucasus, Pontides and Balkans started during the Turonian (ca. 93 Ma), peaked in the middle Campanian (80–78 Ma), and subsequently became rare and sporadic after the late Campanian (ca. 75 Ma). The arc magmatism, characterized by typical subduction signatures, was mainly of middle to high-K calc-alkaline affinity. Late Cretaceous volcanism occurred in a submarine and extensional environment. Along the whole belt, the arc volcanic rocks are overlain by Maastrichtian to Paleocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The geochemistry of the Maastrichtian volcanic rocks is more diverse compared to the older arc volcanic rocks, including alkaline and calc-alkaline basalts, as well as adakitic dacites. The coeval initiation of arc magmatism along the 2700-km-long magmatic arc is associated with the acceleration of Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of suprasubduction-zone ophiolites and sub-ophiolite metamorphic rocks in Anatolia. The end of the magmatic activity in the arc is associated with a marked decrease in the convergence rate during the Campanian.     

How to cite: Sağlam, E., Duzman, T., Ay, C., Okay, A., Topuz, G., Sunal, G., Özcan, E., Altıner, D., Hakyemez, A., Wang, J.-M., and Kylander-Clark, A. R.: Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8570, https://doi.org/10.5194/egusphere-egu24-8570, 2024.

Magmatic arcs are generally considered to be the direct record of subduction zone. Magmatic activity can start with subduction initiation until the end of oceanic subduction. In the Neo-Tethys tectonic domain, arc magma gaps in Alps and Iran prove that arc magmatism and oceanic subduction are not always coupled.

Unlike the Alps, where arc magmatism is absent, or the Gangdese, where arc magmatism is continuous, Iran exhibits an intermittent arc magma record. Since the subduction of the Neo-Tethys Ocean in the Jurassic, Iran has recorded two phases of magmatic activities: the Middle Jurassic (200-140 Ma, with a peak at ~170 Ma) and the Eocene (55-25 Ma, with a peak at ~40 Ma), which are attested by the age peaks of detrital zircons from Mesozoic-Cenozoic clastic rocks. The Cretaceous magma record is sparse, but Cretaceous detrital zircons are abundant (120-65 Ma, with a peak at ~90 Ma). Regarding this mismatched age record of detrital zircons and magmatic rocks, we choose the Makran forearc basin deposits as the target because it receives thick detritus from Eurasia to form a tens of kilometer thick sedimentary sequence. We conducted a detrital zircon study from the Makran to explore the magmatic evolution of the Iranian Tethys zone.

Euhedral zircon grains, obvious oscillatory zoning, low zircon Th/U>0.1, and trace element geochemistry indicate Cretaceous magmatic zircons sourced from the continental magmatic arcs rather than ophiolites. Positive zircon Hf isotopes excludes the source region of the Gangdese arc which is more depleted. We further used machine learning to confirm our provenance results, that reveal Cretaceous (120-65 Ma) magmatism by the Neo-Tethys Ocean subduction in Iran.

The decreasing trend of Cretaceous zircons U-Pb in Late Cretaceous to Pliocene strata indicates gradual denudation of the Cretaceous magmatic arc from deep to shallow. Cretaceous zircon peaks disappears abruptly in the Pliocene rocks, implying that the Cretaceous magmatic arc was completely denuded. Thus, we confirm that since the subduction initiation, magmatic activity was continuous in Iran but the “missing” was due to the denudation process. This works also highlights the importance of comprehensive analysis before discussing subduction geodynamics based on the record of magmatic outcrops.

How to cite: Lei, Y., Chu, Y., Wan, B., Lin, W., Chen, L., Xin, G., and Talebian, M.: A missing Cretaceous magmatic arc of Neo-Tethys in Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8893, https://doi.org/10.5194/egusphere-egu24-8893, 2024.

The central Tethys realm including Anatolia, Caucasus and Iran is one of the most complex geodynamic settings within the Alpine-Himalayan belt. We calculate the depth to magnetic basement and the average crustal magnetic susceptibility, which is sensitive to the presence of iron-rich minerals, to interpret its present structure and the tecto-magmatic evolution. The data demonstrates that the structural complexity increases from the Iranian plateau into Anatolia.

In Iran, our data reveals the presence of hitherto unknown sedimentary basins and we identify two unknown parallel Magmatic-Ophiolite Arcs hidden by the sedimentary cover in eastern Iran. Based on the width of the magmatic anomalies we find that the paleo-subduction zone at the Urmia-Dokhtar Magmatic Arc (Neo-Tethys subduction structure at Zagros) was steeply dipping (> 60°) in the SE and, in contrast, it had shallow dip(< 20°) in the NW part.

Our results for Anatolia demonstrate exceptional variability of crustal magnetization with smooth, small-amplitude anomalies in the Gondwana realm and short-wavelength high-amplitude variations in the Laurentia realm. Poor correlation between known ophiolites and magnetization anomalies indicates that Tethyan ophiolites are relatively poorly magnetized, which we explain by demagnetization during recent magmatism. We analyze regional magnetic characteristics for mapping previously unknown oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by tectono-magmatic events. By the style of crustal magnetization, we distinguish three types of basins and demonstrate that many small-size basins host large volumes of magmatic rocks within or below the sedimentary cover. We map the width of magmatic arcs to estimate paleo-subduction dip angle and find no systematic variation between the Neo-Tethys and Paleo-Tethys subduction systems, while the Pontides magmatic arc has shallow (∼15°) dip in the east and steep (∼50°–55°) dip in the west. We recognize an unknown, buried 450 km-long magmatic arc along the western margin of the Kırşehir massif formed above steep (55°) subduction. We propose that lithosphere fragmentation associated with Neo-Tethys subduction systems may explain high-amplitude, high-gradient crustal magnetization in the Caucasus Large Igneous Province. Our results challenge conventional regional geological models, such as Neo-Tethyan subduction below the Greater Caucasus, and call for reevaluation of the regional paleotectonics.

References:

Teknik V., Thybo H., Artemieva I.M., Ghods A., 2020, Crustal density structure of NW Iranian Plateau. Tectonophysics, 792, 228588, doi: 10.1016/j.tecto.2020.228588.

Teknik, V., Artemieva, I. M., & Thybo, H. 2023. Geodynamics of the central Tethyan belt revisited: Inferences from crustal magnetization in the Anatolia-Caucasus-Black Sea region. Tectonics, 42, https://doi.org/10.1029/2022TC007282.

How to cite: Teknik, V., Thybo, H., and Artemieva, I.: Crustal Structure in the Central Tethys Realm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11578, https://doi.org/10.5194/egusphere-egu24-11578, 2024.

The Oligocene-to-present tectonic history of the western Mediterranean region is characterized by the ESE-ward roll-back of isolated Alpine and Neo Tethys oceanic slab fragments that determined the spreading of two diachronous back-arc basins: the Liguro-Provencal Basin between 30 and 15 Ma and the Tyrrhenian Sea between 10 and 2 Ma. Such geodynamic events induced the fragmentation and dispersal of the Alpine chain through the formation and migration of microplates and terranes, making the debate on the nature, origin, and evolution of such crustal blocks vivid since the 1970s. For instance, it is commonly accepted that the Corsica-Sardinia microplate rotated counterclockwise (CCW) by at least 50° during Oligo-Miocene and that the Calabro-Peloritan, Kabylies and Alboran blocks drifted hundreds of kms on top of nappe piles ESE-ward, SE-ward and SW-ward, respectively. These blocks, know all together as AlKaPeCa, presently form isolated and enigmatic igneous/metamorphic terranes stacked over the Meso-Cenozoic sedimentary successions of the Apennines and Maghrebides. Besides back-arc basins widths and ages, no other kinds of geologic/geophysical data from Corsica-Sardinia microplate or AlKaPeCa terranes constraining their drift magnitudes exist. On the other hand, drift timing may be properly documented by paleomagnetic vertical-axis rotations obtained from different age rocks, and such data usefully complement ages derived from back-arc basins.

We paleomagnetically sampled the Meso-Cenozoic sedimentary cover of the Calabrian (Longobucco sequence) and Peloritan (Longi-Taormina sequence) terranes and the mid-late Eocene continental Cixerri Formation of SW Sardinia. In addition, we re-evaluated previous paleomagnetic results from the whole Corsica-Sardinia microplate and considered the robust Serravallian-Pleistocene dataset from the Calabrian block. Such data indicate a novel rotation and drift history in the western Mediterranean region (Siravo et al., 2021; 2022). The South Sardinia, Peloritan and Calabrian blocks belonged to the “Greater Iberia plate” before mid-Oligocene (<30 Ma) dispersal, as they all show its characteristic paleomagnetic fingerprint (middle Cretaceous 30°-40° CCW rotation). Rifting of the Liguro-Provencal between 30 and 21 Ma induced 30° CCW rotation of both South Sardinia and Calabria blocks, whereas the Peloritan block, located further south, was passively drifted SE ward at the non-rotation apex of a Paleo Appennine-Maghrebides orogenic salient. South Sardinia plus the adjacent Calabrian block and North Sardinia-Corsica blocks assembled in the early Miocene and rotated 60° CCW as a whole between 21 and 15 Ma. After 10 Ma ago the Calabrian block detached from south Sardinia following the opening of the Tyrrhenian Sea and rotated 20° clockwise (CW), at the apex of a Neo Appennine-Maghrebides Arc. On the other hand, the Peloritan terrane rotated 130° CW on top of the Sicilian Maghrebides, along the southern limb of the orogenic salient.

REFERENCES

Siravo, G., Speranza, F., & Macrì, P. (2022). First Pre‐Miocene Paleomagnetic Data From the Calabrian Block Document a 160 Post‐Late Jurassic CCW Rotation as a Consequence of Left‐Lateral Shear Along Alpine Tethys. Tectonics, 41(7), e2021TC007156.

Siravo, G., Speranza, F., & Mattei, M. (2023). Paleomagnetic evidence for pre‐21 Ma independent drift of South Sardinia from North Sardinia‐Corsica:“Greater Iberia” vs. Europe. Tectonics, e2022TC007705.

How to cite: Siravo, G. and Speranza, F.: Paleomagnetism of the Peloritan, Calabrian and South Sardinia blocks unveils a Greater Iberia plate and its mid Oligocene-early Miocene breakup    , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1733, https://doi.org/10.5194/egusphere-egu24-1733, 2024.

North-East India comprises a part of the eastern extremity of the Alpine-Himalayan Belt and is one of the most rapidly deforming regions owing to its unique geological setup. The tectonics of this region is dominated by oblique convergence between two nearly perpendicular plates and results in a zone of distributed deformation. This region is associated with a large number of intra-plate strike-slip and oblique-slip (thrust) earthquakes which are not related to any of the plate boundaries. In this study we model the source mechanisms of five recent strong-to-moderate earthquakes (5.5≥Mw≤6.0) using teleseismic P and SH waveforms inversion and use source directivity and back-projection of the high-frequency energy from multiple teleseismic arrays for the largest event, to isolate the fault plane from the auxiliary plane. We then combine these mechanisms with results from previous studies of earthquake source and GPS geodetic velocity vectors and the GPS-derived strain field to build a kinematic model for this region. The depth distribution of the earthquakes reveals that they occur in the lower crust of the underthrusting Indian Plate. The oblique-thrust and thrust events are the result of compressive stresses in the inner arc of the flexed Indian Plate. The oblique convergence of the Indian Plate with respect to Tibet and the slab pull force from the subduction of the Indian Plate beneath Burma combined together are responsible for the strike-slip earthquakes. The region north of the Dauki Fault in the vicinity of the Kopili Fault Zone deforms through dextral strike-slip faulting and anti-clockwise rotation of blocks along NW-SE trending transverse structures. The transitional crust of the Bengal Basin has several NE-SW trending paleorifts which manifest sinistral strike-slip motion and clockwise rotation. The GPS velocity vectors and the strain field indicate that throughout most of the region north of the Dauki Fault there is a strong coupling between the surface deformation and the earthquake faulting whereas towards the south in some areas the coupling is weaker. The strike-slip events in the Indo-Burman Ranges probably occur due to a complex interplay between the trench-normal slab pull forces and lateral shear forces set up by the strike parallel components of the interplate coupling resistance and the mantle drag forces.

How to cite: Chaudhuri, D., Banerjee, R., Mahanti, S. S., Kumar, A., and Mitra, S.: Kinematics of Intra-Plate Strike-Slip Earthquakes in an Oblique Convergent Setting  : Insights from the Eastern Himalayan and Indo-Burman Plate Boundary Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9628, https://doi.org/10.5194/egusphere-egu24-9628, 2024.

The powerful earthquake that struck eastern Türkiye on February 6^th 2023 is the most devastating earthquake of the past century in the region. Here we present our first-hand field measurements of the ground offsets and the high resolution (centimeter level) drone-mapped surface ruptures 10 days after the first shock. It is clear that the initial rupture was on the Dead Sea fault zone (DSFZ), yet maximum displacements and energy release (Mw 7.8) occurred 24 sec later when rupture transferred to the East Anatolian fault zone (EAFZ). Seven hours later, a Mw 4.5 aftershock at the junction of the EAFZ with the east-west striking Çardak-Sürgü fault (Ç-SF) triggered the second large (Mw 7.5) earthquake, causing another round of the damage in the region. The maximum ground offsets are around 47.5 kilometers away from the epicenter in this event on the EAFZ. The surface ruptures directly cut young basins and mountains, as well as activating some pre-existing surfaces. Our observation provides important data on surface deformation during large continental strike-slip earthquakes, rupture propagation mechanisms, and how slip may be transferred between complex fault systems. We also provide insight into how slip along linked fault systems accommodates global plate motions.

How to cite: Meng, J., Kusky, T., Mooney, W. D., Bozkurt, E., Bodur, M. N., and Wang, L.: Fault rupture mapping of the February 6, 2023 earthquake sequence, eastern Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21398, https://doi.org/10.5194/egusphere-egu24-21398, 2024.