GD9.1 | The Tethyan Belt, Central Asia, and Circum Pacific margins: Formation, Evolution, Structure, Topography, and Resources
EDI
The Tethyan Belt, Central Asia, and Circum Pacific margins: Formation, Evolution, Structure, Topography, and Resources
Co-organized by ERE1/GMPV10/SM1/TS6, co-sponsored by ILP
Convener: Hans Thybo | Co-conveners: Shaofeng Liu, Lingxiao Gong, Nalan Lom, Johannes RembeECSECS, Bo Wan, Chengfa LinECSECS
Orals
| Fri, 28 Apr, 10:45–12:30 (CEST), 14:00–15:45 (CEST), 16:15–18:00 (CEST)
 
Room D2
Posters on site
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
Hall X2
Posters virtual
| Attendance Fri, 28 Apr, 08:30–10:15 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Fri, 10:45
Fri, 08:30
Fri, 08:30
We invite contributions based on geological, tectonic, geophysical and geodynamic studies of the Tethyan Belt, Central Asia, and the Circum Pacific margins. We particularly invite interdisciplinary studies, which integrate observations and interpretations based on a variety of methods. This session will include a suite of studies of these regions with the aim of providing a comprehensive overview of their formation and evolution, influence of the tectonic features on climate, biodiversity, human habitat, and topographic change.
The Tethyan Belt is the most prominent collisional zone on Earth, covering the vast area between far eastern Asia and Europe. The geological-tectonic evolution of the belt has led to significant along-strike heterogeneity in its various regions, including the SE-Asian subduction-collision system, the Tibetan-Himalayan region, the Iranian Plateau, Anatolia, and the Alpine orogen. The Tethyan Belt is the result of subduction of the Tethyan Oceans, including significant terrane amalgamation, and collisional tectonics along the whole belt. The belt is today strongly affected by the ongoing collision of Eurasia with the African, Arabian and Indian plates and the large-scale geometry of the Cenozoic mountain ranges is often determined by inherited features. The long formation history and the variability of tectonic characteristics and deep structure of the region make it a natural laboratory for understanding the accretion processes that have shaped the Earth through its history and have led to the formation of vast resources in the crust.
The circum-Pacific domain has been undergoing multiple re-orientations in subduction and given rise to basin-mountain systems in both the eastern and western Pacific continental margins since the late Mesozoic. We welcome contributions on (1) the formation/origin and evolution of lithosphere architecture, (2) spatial-temporal evolution of Earth’s surface topography, (3) evolution of basin-mountain systems, and (4) 4-D geodynamic models of eastern and western Pacific continental margins.

Orals: Fri, 28 Apr | Room D2

Chairpersons: Bo Wan, Nalan Lom, Hans Thybo
10:45–10:50
10:50–11:00
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EGU23-17123
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Highlight
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On-site presentation
A.M. Celâl Şengör, Demir Altıner, Cengiz Zabcı, Gürsel Sunal, Nalan Lom, and Tayfun Öner

We have compiled local stratigraphic, structural, palaeobiogeographical and reliable isotopic age data from the remnants of the Cimmerian Continent from western Turkey to Malaysia with a view to understanding its nature and evolution. Our principal conclusions are the following:

1) The entire northwestern margin of Gondwana-Land was an extensional Pacific-type continental margin much like the present-day western Pacific during the Permo-Carboniferous characterised by typical Gondwana-Land biotas.

2) Beginning with the Permian, the Cimmerian Continent began to pull away from the northeastern margin of Gondwana-Land from Turkey in the west to Malaysia in the east, although in Thailand and Malaysia rifting may have started already during the earlierst Carboniferous.

3) Synchronously with this rifting, the Wašer/Rushan-Pshart/ Banggong Co-Nu Jiang ocean, herein called the Maera, began opening in the Permian isolating the Lhasa/Victoria Land block from the rest of the Cimmerian Continent. In fact, the Himalayan sector of the Neo-Tethys may have opened slightly later than the Maeran ocean.

4) Central Iran consisted of two parts: the northest Iranian extensional area and the multi-block Central Iranian Continent consisting of the Yazd, Posht-e Badam, Tabas and the Lut blocks. These blocks were stacked against one another horizontally as a consequence of the Cimmeride collisions in the Pamirs and Afghanistan while Albors was rifted away from the Sanandaj-Sirjan zone, as the latter was also rifting away from Gondwana-Land, stretching northwestern Iran into its present-day triangular shape.

5) Significant arc magmatism characterised the entire Cimmerian continent from one end to the other during the Permian to the Liassic interval.

We thus maintain that the Cimmerian Continent was the site of supra-subduction extension throughout its history until it collided with Laurasia during the medial to late Jurassic. In some areas the collision may have been earlier. The Maeran ocean remained opened until the Aptian. The best analogue for the evolution of the Cimmerian Continent and its attendant small oceans is the present-day southwest Pacific arc/marginal basin systems from the Tonga-Kermadec system in the east as far west as Australia.

How to cite: Şengör, A. M. C., Altıner, D., Zabcı, C., Sunal, G., Lom, N., and Öner, T.: The Nature of the Cimmerian Continent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17123, https://doi.org/10.5194/egusphere-egu23-17123, 2023.

11:00–11:10
11:10–11:20
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EGU23-1665
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On-site presentation
Pietro Sternai

The majestic Himalayan-Tibetan mountains raised due to doubling of the continental crust during the India-Asia collision, which is commonly assumed to occur by under-thrusting of the Indian crust directly below the Asian crust. However, this model implies rheologically weak subducting and upper plate lithospheres and, thus, a collision system that is unable to support a high plateau and whose deformation style is inconsistent with the gross structural and metamorphic architecture of the Himalayan-Tibetan system. Numerical models show that collision between relatively stiffer plates generates strain and metamorphic structures as well as elevations more similar to those observed, but crustal doubling occurs by stacking the subducting crust underneath the rigid upper plate mantle lithosphere. A marked mantellic signature in fluids outflowing the suture zone, the geochemistry of south Tibetan mantle xenoliths, and long wavelength buckling of the Tibetan lithosphere further support the presence of intra-crustal mantle between the Indian and Asian continental crusts. Reconciling the available geophysical evidence with this new model of crustal doubling in the Himalayan-Tibetan range will entail profound implications for our understanding of mountain building during continental subduction and collision.

How to cite: Sternai, P.: Intra-crustal mantle underneath the Himalayan-Tibetan range, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1665, https://doi.org/10.5194/egusphere-egu23-1665, 2023.

11:20–11:30
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EGU23-10233
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ECS
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Highlight
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On-site presentation
Bing Xia, Irina Artemieva, Hans Thybo, and Simon Klemperer

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 the 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., Artemieva, I., Thybo, H., and Klemperer, S.: Strong variability in the thermal structure of Tibetan Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10233, https://doi.org/10.5194/egusphere-egu23-10233, 2023.

11:30–11:40
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EGU23-13642
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ECS
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Highlight
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On-site presentation
Jin Fang, Greg Houseman, Tim Wright, Lynn Evans, Tim Craig, John Elliott, and Andy Hooper

Block versus continuum description of lithospheric deformation in the India-Eurasia collision zone has been hotly debated over many decades. Here we apply the adapted two-dimensional (2-D) Thin Viscous Shell (TVS) approach explicitly accounting for displacement on major faults in Tibet (Altyn Tagh, Haiyuan, Kunlun, Xianshuihe, Sagaing, and Main Pamir Thrust Faults) and investigate the impact of lateral variations in depth-averaged lithospheric strength. We present a suite of dynamic models to explain the key observations from new high-resolution Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) as well as Global Navigation Satellite System (GNSS) velocities. Comparisons between calculated and observed velocity and strain rate fields indicate: (a) internal buoyancy forces from Gravitational Potential Energy (GPE) acting on a relatively weak region of high topography (~2,000 m) contribute to dilatation of high plateau and contraction on the margins; (b) a weak central Tibet (~1021 Pa s relative to far-field depth-averaged effective viscosity of 1022 to 1023 Pa s) yields the observed long-wavelength eastward velocity variation away from major faults; (c) slip resistance on faults produces strain localization and clockwise rotation around the Eastern Himalayan Syntaxis (EHS). We discuss the tectonic implications for rheology of the lithosphere, distribution of geodetic strain, and partitioning of active faulting and seismicity in light of our best-fit geodynamic solutions.

How to cite: Fang, J., Houseman, G., Wright, T., Evans, L., Craig, T., Elliott, J., and Hooper, A.: The Dynamics of the India-Eurasia Collision: A Suite of Faulted Viscous Continuum Models Constrained by New High-Resolution Sentinel-1 InSAR and GNSS Velocities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13642, https://doi.org/10.5194/egusphere-egu23-13642, 2023.

11:40–11:50
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EGU23-16615
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On-site presentation
Supriyo Mitra, Swati Sharma, Debarchan Powali, Keith Priestley, and Sunil Wanchoo

We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya, to model the seismic velocity structures of the crust and uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across major Himalayan thrust systems and litho-tectonic units. We perform depth–Vp /Vs (H-K) stacking of P-RF, common conversion point (CCP) stacking along 2D profiles and joint inversion with surface wave dispersion data. H-K analysis reveals increasing average crustal thickness from the foreland (∼40 km) to the hinterland (∼65 km), with felsic- to-intermediate (Vp /Vs of 1.71–1.80) average crustal composition. In CCPs the Indian crust Moho is marked by a large positive impedance contrast boundary, and the Main Himalayan Thrust (MHT) by a negative phase, indicating a low velocity layer (LVL). The underthrust Indian crust (between the MHT and Moho) has an average thickness of ∼40 km and the Moho dips northward at ∼7–9◦ . Moho flexure (or possible off-set) are observed in across-arc profiles, beneath the Shiwalik Himalaya, Higher Himalaya and the Kishtwar window. The Moho is remarkably flat at ∼55 km beneath the Pir Panjal Ranges and the Kashmir Valley. North of the Kishtwar window (E) and Kashmir Valley (W) the Moho dips steeply underneath the Tethyan Himalaya/Zanskar Ranges from ∼55 km to ∼65 km. The MHT LVL is at a depth of ∼8 km beneath the Shiwalik Himalaya, and dips gradually northeast at ∼7–9◦ , to reach a depth of ∼25 km beneath the Higher Himalaya. The MHT is marked by a frontal ramp beneath the Kishtwar window (E) and north of the Kashmir Valley (W). The MKT, MBT and MCT are marked by LVLs which splay updip from the MHT. To study the 3D variation of the crustal structure, we grid the region into 0.1◦ square grids and jointly model the P-RFs within each grid with Rayleigh wave dispersion data, obtained from regional tomography. The 3D models obtained from this analysis provide variations in Vs and Moho depth. The Kashmir Valley and Zanskar Ranges are underlain by the highest average crustal Vs followed by the Pir-Panjal Ranges. These are also regions of the thickest crust. The Shiwalik Himalaya is underlain by the slowest average Vs , with lateral variations along the MKT, Reasi Thrust and the Kotli Thrust. These are also regions of thinnest crust (~40 km). A remarkable lower Vs region extends SW-NE from Jammu to the Kishtwar window, along the reentrants of the MHT, MBT and MCT. This marks a strong E-W lateral variation in crustal Vs , Moho depth and a possible lateral ramp on the MHT, also highlighted by small-to-moderate earthquake clusters.

How to cite: Mitra, S., Sharma, S., Powali, D., Priestley, K., and Wanchoo, S.: Crustal Structure of the Jammu and Kashmir Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16615, https://doi.org/10.5194/egusphere-egu23-16615, 2023.

11:50–12:00
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EGU23-15394
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Virtual presentation
Zhang Bo

Gneiss dome records the deformation and tectonothermal evolution of orogenic belt and lithosphere, which provides a perfect window for studying of collisional orogenic process and tectonic evolution. The North Himalayan Gneiss Domes, trending East-West, as one of the important tectonic units of the Himalayan orogen, experienced deep materials uplifting and lateral flow. Based on the above observations, we suggest that the RBD experienced 4 periods of tectonothermal evolutions (D1-D4) and 2 stages of tectonic background transformations. (1) D1: Crustal thickening, regional metamorphism and anatexis occurred during plate collision in the Eocene (46.3-40.6 Ma). (2) D2: Partial melting of middle-lower crust result in the development of channel flow which reduced the rheology of the middle-lower crust and led to the onset of the STDS and crustal thinning in the early Miocene (26.1-21.0 Ma). Therefore, the tectonic background transformed from N-S compression to N-S extension (the first tectonic background transformation). (3) D3: The ongoing of the STDS contribute to the decompression melting, small-scale diapirism and accompanied magmatic emplacement. The activity of the NSTRs started at mid-Miocene (12.0-10.2 Ma), the tectonic background shifted from N-S extension to E-W extension (the second tectonic background transformation). (4) D4: +With NSTRs’ activity peaking in the late Miocene (8.7-7.6 Ma), further crustal thinning, decompression melting and leucogranite intrusion occurred under extensional condition, which result in the contact metamorphism, and established the final tectonic framework, geometry, and thermalstructure of the RBD. The tectonothermal evolution of the RBD supports the middle-lower crustal channel flow orogenic model.

Fluid inclusion and oxygen isotope data for quartz veins in the Ramba Dome in the North Himalayan Gneiss Domes show limited variations in individual quartz veins, but δ18Oquartz values vary from 12.07 to 18.16‰ (V-SMOW) among veins. The corresponding δ18Ofluid values range from 7.71 to 13.80‰, based on equilibrium temperatures obtained from fluid inclusions. From the footwall to the detachment zone, δ18Ofluid values exhibit a broadly decreasing trend and indicate that the STDS dominated the fluid flux pathway in the crust, with more contributions of meteoric water in the detachment zone. We further quantified the contribution of meteoric fluids to 8–27% using a binary end-member mixing model. These data imply that the fluids were predominantly metamorphic/ magmatic in origin, and were mixed with infiltrating, isotopically light, meteoric water during extensional detachment shearing of the STDS. Based on the above research, we propose that metamorphic dehydration of lower crust and atmospheric precipitation "stimulate" new activity of Himalayan mountain building.

How to cite: Bo, Z.: The multistage extensional structure and excitation mechanism of Himalayan orogeny, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15394, https://doi.org/10.5194/egusphere-egu23-15394, 2023.

12:00–12:10
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EGU23-2622
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On-site presentation
Yang Chu, Bo Wan, Ling Chen, Wei Lin, Morteza Talebian, Xiaofeng Liang, and Liang Zhao

Plate convergence has continued for over 25 Myr after the Arabia initially collided with the Eurasia, causing vast intracontinental deformation within the Central Iran Block at the southern margin of the Eurasia. During the same period, the Iranian Plateau grew as tectonic stress from continental collision propagated northwards, accompanied by strong deformation, crustal shortening and rapid rock exhumation, but the process of the plateau formation remains less discussed. From west to east, the Talesh-Alborz-Kopet Dagh (TAK) situates at the northern front of the Iranian Plateau and suffers intense folding and thrusting that creates the highest mountain range in Iran, so its tectonic evolution history carries important clues for the building of the current plateau.

To better constrain the spatial and temporal patterns of deformation and exhumation, we carried out comprehensive structural analysis and new geochronology-thermochronology dating for the TAK. As a first order feature of the collision zone, the TAK records an immediate response to the initial collision. Oligocene deformation is well documented but unevenly exhumed different segments of the belt along-strike. The Talesh and westernmost Alborz preserves late Neoproterozoic basement rocks (~570 Ma) and old, Mesozoic zircon U-Th/He ages (150-90 Ma), acting as a relatively rigid part resistant to Oligocene deformation. In contrast, the main part of Alborz was remarkedly shortened by folds and thrusts and exhumed rapidly, while the Kopet Dagh shows a simply folded belt dominated by box folds in deca-kilometer scale. All the TAK experienced enhanced exhumation since 20 Ma, peaked at the Late Miocene, suggesting the deformation was synced around 7 Ma when the internal tectonic organization along the belt and within the Central Iran Block had been much reduced. This Late Miocene switch reflects a reorganization of Arabia-Eurasia plate convergence. The causes could include that elevation increased to a level at which the Iranian Plateau was built and resisted further thickening, or internal heterogeneity was decreased and the whole region began to evolve as a single tectonic unit, causing deformation to be accommodated in other regions. The growth model of Iranian Plateau can also enlighten us on how Tibetan Plateau developed and expanded at its early stage.

How to cite: Chu, Y., Wan, B., Chen, L., Lin, W., Talebian, M., Liang, X., and Zhao, L.: Synced deformation of the Talesh-Alborz-Kopet Dagh belt and formation of the Iranian Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2622, https://doi.org/10.5194/egusphere-egu23-2622, 2023.

12:10–12:20
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EGU23-3799
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On-site presentation
Daniel Pastor-Galán, Tatsuki Tsujimori, Alicia López-Carmona, and Keewook Yi

The Tethyan oceans are the internal sotry-tellers of the amalgamation, tenure and break up of Pangea. All tethyan oceans have been mostly consumend and only remnants of them occur now along the margins of the Atlantic, Mediterranean, Black and Caspian seas, as well as in the Alpine-Himalayan and adjacent orogens. The Rheic (~500 to ~300 ma, some-times Ran or Proto-Tethys) closed during the amalgamation of Pangea and the Neo-Tethys (~270 to ~20 ma) is the main witness of its break-up. The Paleotethys is the ocean that shared an internal position during most of Pangea’s tenure. There is no consensus about its origin, some suggest that opened during the latest stages of Pangea’s amalgamation (Devonian-Carboniferous) whereas others considert it a remnant of the mostly subducted Rheic ocean after Gondwana-Laurussia collision.

We have studied the Shanderman eclogites (NW Iran) and put them into their context within other HP rocks in the area because they a potential candidate to represent the Paleotethys ocean. They are metamorphosed oceanic rocks (protolith oceanic tholeiitic basalt with MORB composition). Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation.

In this contribution we will show the new petrological, geochemical and geochronological results from this eclogites to shed light on the evolution of the tethyan oceans during the Paleozoic. The protolithic oceanic crust of Shanderman crystallized ~350 Ma, metamorphic age suggest that this piece of ocean subducted soon after forming, representing, perhaps, a subduction initiation or a ride-subduction event. We also found a metasomatic event at ~280 ma. Considering its relation with other HP rocks in Iran, we interpret that the Shanderman ophiolites are not a fragment of the Paleotethys but a fragment of the Rheic (Ran/Prototethys) ocean.

How to cite: Pastor-Galán, D., Tsujimori, T., López-Carmona, A., and Yi, K.: NW Iran under pressure: Cristallization and metamorphic ages of the Shanderman eclogites., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3799, https://doi.org/10.5194/egusphere-egu23-3799, 2023.

12:20–12:30
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EGU23-17021
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ECS
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Virtual presentation
Yifan Gao, Ling Chen, Jianfeng Yang, and Kun Wang

The Iranian plateau is at the early stage of plateau development and intracontinental deformation in response to the Arabia-Eurasia collision. Its compressive deformation is concentrated in the northern plateau but skips the central counterpart, challenging the common views envisaging the progressive uplift from the collisional front to the hinterland. Based on three-dimensional, crustal-scale numerical models, we present how the rheological heterogeneities common in continents control the deformation of the young Iranian plateau. The weak northern plateau ensures itself a preferential zone in accommodating continental collision. The N-S strike-slip faults within the non-rigid central plateau, formed along the boundaries between the tectonic units with rheological contrast, suppress the shortening of the central plateau while further accentuating the compressive deformation of the northern plateau. Our results suggest a non-progressive intracontinental deformation pattern where rheological boundaries and mechanically weak zones, not necessarily those close to collisional fronts, preferentially accommodate continental convergence.

How to cite: Gao, Y., Chen, L., Yang, J., and Wang, K.: Rheological heterogeneities control the non-progressive uplift of the young Iranian plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17021, https://doi.org/10.5194/egusphere-egu23-17021, 2023.

Lunch break
Chairpersons: Johannes Rembe, Shaofeng Liu, Jonas Kley
14:00–14:10
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EGU23-349
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ECS
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On-site presentation
Kristijan Sokol, Dejan Prelević, and Ana Radivojević

Кеy words: Upper Cretaceous magmatism, Sava Vardar Zone, Adria, basalts

The complex geodynamic evolution of the northernmost Neotethys is the subject of a long-living controversy. The most perplexing issues are related to the waning stage(s) of the Tethyan ocean(s) in the Balkans and the timing of the Europe-Adria collision. Some authors consider this collision to have occurred in the Late Jurassic, whereas others envisage that have happened at the end of the Cretaceous along the Sava-Vardar Zone. The second model assumes this zone contains a relic suture between Africa- and Europe-derived units.

Late Cretaceous magmatism along the Sava-Vardar Zone includes several centers of small-volume transitional to alkaline Na-basalt (with subordinate rhyolitic rocks) and rare ultrapotassic lavas. This volcanism occurs in both Europe- and Africa- derived units of the collisional zone. The geochemical and isotope compositions of the Late Cretaceous lavas suggest that they are not a part of dismembered ophiolite sequences, but represent intracontinental magmas derived from variably enriched mantle sources. The transitional to alkaline Na-basaltic lavas show a clear “within plate” geochemical signature with typical mantle-like 87Sr/86Sri, 143Nd/144Ndi and 206Pb/204Pbi ratios with relatively high HFSE/LILE ratios, and without orogenic geochemical signatures such as high LILE/HFSE ratios, positive Pb and negative Ti–Nb–Ta anomalies, whereas the ultrapotassic lavas are lamprophyres demonstrating enriched 87Sr/86Sri, 143Nd/144Ndi and 206Pb/204Pbi ratios, LILE enrichment, and orogenic geochemical signatures. A broad range of MREE/HREE ratios in these locations suggests polybaric mantle melting.

Our working melting model is that the mafic melts were generated as a continuum with low-degree melting in the asthenospheric mantle within the garnet stability field and high-degree melting of the freshly metasomatized lithospheric mantle in the spinel stability field. The ultimate trigger of the mantle melting along the Sava-Vardar Zone should be localized extension during transtensional tectonics, in a system of pull-apart basins (Köpping et al., 2019).

Acknowledgments: This research was financed by the Science Fund of the Republic of Serbia through project RECON TETHYS (7744807).

Köopping, J., Peternell, M., Prelevi_c, D., Rutte, D., 2019. Cretaceous tectonic evolution of the Sava-Klepa Massif, Republic of North Macedonia e results from calcite twin based automated paleostress analysis. Tectonophysics 758. https://doi.org/10.1016/j.tecto.2019.03.010.

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How to cite: Sokol, K., Prelević, D., and Radivojević, A.: Cretaceous magmatism from the Sava-Vardar Zone of the Balkans, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-349, https://doi.org/10.5194/egusphere-egu23-349, 2023.

14:10–14:15
14:15–14:25
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EGU23-4091
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ECS
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On-site presentation
Yuling Deng and Changhai Xu

The Late Mesozoic subduction of Izanagi beneath East Asia formed large-scale intraplate magmatism in SE China and subduction mélanges from SW Japan to eastern Taiwan (Müller et al., 2016; Wang et al., 2008; Wakita and Metcalfe, 2005), but the accompanying arc remains uncertain. The East China Sea (ECS) is settled between the intraplate and trench, in which previous studies have found some arc indications (Xu et al., 2017). ECS domains share a unified basement with, or are regarded as an exotic microcontinent of Cathaysia block, which is still up for debate.

Discerning delta facies and litharenite types of sediment samples support a typical proximal environment of Lishui-Jiaojiang sag, SW ECS. As its provenances, nearby Zhemin and Yandang swells provide Late Mesozoic voluminous felsic suites with minor metabasite materials. We conducted LA-ICP-MS U-Pb zircon dating and trace element analyses of proximal sandstones in the SW ECS to track a Jurassic to Cretaceous magmatic arc, which advantages over the use of a few drilled igneous rocks. Newly acquired data reveal an evolved magmatic arc in SW ECS from Jurassic to Cretaceous (200–86 Ma), which developed predominantly in episodes of 150–124 Ma and 124–102 Ma. Arc magmatism exhibits characteristics of low-T and continental zircon types, yielding high Th/U, U/Yb, Sc/Yb, and Th/Nb ratios and low Nb/Yb and Nb/Hf ratios. Trace elements U and Th in arc zircons indicate a decline in subduction fluids addition due to slab rollback and a rise in lower crustal addition owing to fluid-fluxed crustal melting from Jurassic to Cretaceous.

The swells of Yushan, Zhemin, Haijiao, and Hupijiao outline a Late Mesozoic magmatic arc in the West ECS. This magmatic arc, in conjunction with the SE China intraplate, and subduction mélanges, spatially forms a Late Mesozoic trench-arc-intraplate architecture in response to the Izanagi subduction beneath East Asia. Its identified tectonic scenarios mainly include slab strike-slip subduction (200–170 Ma), slab stagnation and intraplate foundering (170–150 Ma), slab rollback and removal of the thickened arc root (150–102 Ma), and trench retreat with arc migration (102–86 Ma). Detrital zircon data suggest that the West ECS and Cathaysia block share a unified basement that formed at ca. 2.44 Ga and ca. 1.85 Ga, which was reworked at ca. 780 Ma, ca. 442 Ma, and ca. 240 Ma. The West ECS magmatic arc evolved on this Cathaysia-type basement.

Keywords: magmatic arc; detrital zircon; Late Mesozoic; Izanagi subduction

 

 

Müller, R.D., et al., 2016. Ocean basin evolution and global-scale plate reorganization events since Pangea breakup. Annual Review of Earth and Planetary Sciences, 44(1), 107138.

Wakita, K., and Metcalfe, I., 2005. Ocean plate stratigraphy in East and Southeast Asia. Journal of Asian Earth Sciences, 24(6), 679–702.

Wang, Y.J., et al., 2008. Sr-Nd-Pb isotopic constraints on multiple mantle domains for Mesozoic mafic rocks beneath the South China Block hinterland. Lithos, 106(3–4), 297–308.

Xu, C.H., et al., 2017. Tracing an Early Jurassic magmatic arc from South to East China Seas. Tectonics, 36, 466–492.

How to cite: Deng, Y. and Xu, C.: Late Mesozoic continental arc in East China Sea: Constraints from detrital zircons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4091, https://doi.org/10.5194/egusphere-egu23-4091, 2023.

14:25–14:35
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EGU23-4597
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On-site presentation
Dickson Cunningham, Haibo Yang, and Jin Zhang

The active deformation field between northern Tibet and central Mongolia is dominated by diffuse sinistral transpressional reactivation of the southern Altaids Phanerozoic terrane collage.   The angular relationship between NE-directed SHmax and pre-existing basement trends is the dominant control on Quaternary fault kinematics.  Along Tibet’s northern margin, the Altyn Tagh system is widening northwards by transpressional duplexing.  The Nanjieshan and Sanweishan comprise sinistral oblique-slip thrust ridges within a regional asymmetric flower structure centered on the Altyn Tagh Fault.  In the southern Beishan, interconnected lensoidal domains of transpressional and transtensional faulting are subtly indicated by Quaternary fault scarps, low-relief rejuvenated landscapes and alluvial sedimentation.  The SE Beishan and western Hexi Corridor region contain numerous Late Quaternary fault systems including the Heishan-Jinta'Nanshan sinistral strike-slip corridor and the Helishan-Longshoushan fault array that connects eastwards with the transtensional grabens of the Yabrai and Langshan in the eastern Alxa Block.  Further north, the Paleozoic terrane collage of the Gobi Corridor was repeatedly reactivated during the Permo-Triassic, Jurassic, Cretaceous and Neogene.  Late Cenozoic reactivation was likely facilitated by thermal weakening of the crust due to Jurassic-Miocene volcanism, and diffuse Cretaceous rifting and crustal thinning.  Although terrane boundaries and other faults are reactivated in many areas, thrust and oblique-slip reactivation of WNW striking shallowly dipping sedimentary bedding and metamorphic fabrics is equally important.  Conversely, modern E-W trending strike-slip faults in the Gobi Altai typically crosscut older basement trends. In the Altai and Gobi Altai, the Late Cenozoic fault array has created a transpressional  basin and range physiographic province.  Coalescence of separate ranges into topographically continuous mountain belts in the Altai, Gobi Altai and easternmost Tien Shan is an important mechanism of transpressional mountain building not predicted by classical plate tectonic models.  Throughout the vast deforming region north of Tibet, tectonic loading is shared amongst a diffuse fault network challenging assumptions about earthquake recurrence intervals and seismic hazard forecasting.

How to cite: Cunningham, D., Yang, H., and Zhang, J.: Late Cenozoic Crustal Reactivation of the North Tibetan Foreland, Western Hexi Corridor, Beishan, and Gobi Corridor: Implications for Intraplate Fault Networks, Mountain Building Processes and Earthquake Hazards in Slowly Deforming Regions of Central Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4597, https://doi.org/10.5194/egusphere-egu23-4597, 2023.

14:35–14:45
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EGU23-7851
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ECS
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On-site presentation
Jérémie Soldner, Yingde Jiang, Pavla Štípská, Karel Schulmann, Chao Yuan, Zongying Huang, and Robert Anczkiewicz

The Dunhuang block in NW China preserves Archean to Paleoproterozoic basement rocks that are exposed alongside Paleozoic magmatic and metamorphic rocks. Although both subduction-accretion and collisional processes have been proposed for the formation of Paleozoic metamorphic rocks, links between their metamorphic ages, P−T evolution and deformational history remains ambiguous. Here we present zircon and in-situ monazite U−Pb geochronology linked to P−T modelling of metapelites from the Hongliuxia belt in the southern Dunhuang block. Oriented inclusion trails in garnet from metapelites reveal rare relics of an S1 fabric. The earliest continuous metamorphic fabric is an originally steep N-S striking foliation S2. This fabric was further reworked by upright folds F3 associated with development of an ubiquitous steep, mainly south-dipping, E-W striking axial planar foliation S3. The Bt−Ms−St−Pl−Qz−Tur−Ilm assemblage forming inclusions in garnet is assigned as the D1-M1a event whereas the foliation S1b in metapelites is associated with Grt–Ky–St–Bt–Ms–Pl–Qz–Rt assemblage. The Grt−Ky−St aligned parallel to the S2 matrix in low-strain domains are considered as remnants of a dismembered M1 assemblage, while the S2 foliation is characterized by the Grt–Sil–Bt–Pl–Qz–Rt–Liq in high-strain domains. The S3 foliation is associated with the Grt–Sil–Bt–Ms–Pl–Qz–Kfs–Chl–Ilm assemblage. Altogether, metapelites record similar clockwise P–T evolution an early prograde (M1a) stage starting at 4.5–5 kbar and 500–550°C, metamorphic peak (M1b) stage at ~8 kbar and 700–725°C, decompressional heating to ~6 kbar and ~750°C (M2) and a retrograde stage to 4.5–5.5 kbar and 500–550°C (M3). Zircon U−Pb geochronological investigations suggest that metapelites from the basement record metamorphic ages of 1847 ± 11 Ma and 404 ± 15 Ma.  In-situ U–Pb dating of monazite combined to monazite trace-element composition analysis further suggest that the rock burial most likely started at c. 410 Ma, peak-P conditions M1b were reached at 400–395 Ma, M2 heating occurred at c. 390 Ma and M3 retrogression occurred between c. 384 and 353 Ma. The D1-M1 burial event reflects either underthrusting of the basement below the supra-subduction active margin system or propagation of the deformation front to the south of the Dunhuang block. The D2-M2 event is a consequence of thermal relaxation following crustal thickening, possibly accompanied by convective lithospheric thinning, whereas D3-M3 reflects exhumation during shortening of the system. Combined with the available regional data, it is suggested that the Devonian multi-stage tectono-metamorphic evolution described in the study area corresponds to a polyphase Andean-type deformation of the active margin of the Dunhuang block. Such a process can be regarded as a response to a progressive relocation of the Dunhuang block alongside with the Tarim-North China Collage in the Devonian.

 

Funding: This research is part of the project No. 2021/43/P/ST10/02996 co-funded by the National Science Centre and the European Union Framework Program for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie grant agreement No. 945339, as well as the President’s International Fellowship Initiative for Postdoctoral Researchers of the Chinese Academy of Sciences, grant No. 2021PC0013.

How to cite: Soldner, J., Jiang, Y., Štípská, P., Schulmann, K., Yuan, C., Huang, Z., and Anczkiewicz, R.: Devonian Andean-type orogeny in the southern Dunhuang block (NW China): Petro-structural, geochronological and metamorphic P−T constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7851, https://doi.org/10.5194/egusphere-egu23-7851, 2023.

14:45–14:55
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EGU23-2521
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Virtual presentation
Meng Wang, Xianzhi Pei, Zuochen Li, Ruibao Li, Lei Pei, Youxin Chen, Chengjun Liu, and Shaowei Zhao

The West Qinling Orogen (WQO), which is bounded by the Qilian Orogenic Belt, Qaidam Block and the Songpan-Ganzi Block, is the western extension of the Qinling Orogenic Belt, and experienced complex tectonic evolution processes, involving the opening, subduction and closure history of the Proto- and Paleo-Tethys Oceans. The WQO features widespread Indosinian magmatic rocks, which are crucial to constrain the tectonic evolution of the WQO. The Indosinian magmatic rocks were formed mainly in two stages, 250 to 240 Ma and 225 to 210 Ma. The Early Indosinian magmatic rocks (250 to 240 Ma) are mainly distributed in the west and middle northern WQO. In comparison, the Late Indosinian magmatic rocks are mainly exposed in the eastern WQO, but also in the western WQO and the Bikou terrane. Controversy has existed for a long time on the petrogenesis and tectonic setting of the Early Indosinian magmatic rocks. We selected four respective plutons, including the Heimahe pluton, the Ren’ai pluton, the Daerzang pluton and the Ganjiagongma pluton. Detailed field investigation, petrology, LA-ICP-MS zircon U-Pb dating, zircon Lu-Hf isotope analyses, whole rock geochemistry and Sr-Nd isotope analyses, and mineral EPMA analyses were conducted for the studied plutons. The studied plutons were emplaced between 246 to 241 Ma according to zircon U-Pb dating results. Based on detailed studies on petrology, geochronology and geochemistry, we emphasis the significance of magma mixing in the petrogenesis of the Early Indosinian granitic rocks. The high Mg# signature of the Early Indosinian granitic rocks were generated by magma mixing between mafic and felsic magmas, but not result of direct fractional crystallization of mafic rocks. The granitic rocks with high Sr/Y values in the WQO, represented by the Ganjiagongma pluton, were not derived from thickened continental crust. No evident continental thickening occurred in the WQO during the Early Indosinian. Combining with regional geological evidence, we propose an alternative tectonic model to explain the evolution history of the WQO during the early Mesozoic. The A’nimaque-Mianlue ocean subducted northward with low angle, then the subducted slab rolled back during the Late Permian to Middle Triassic, and the ocean closured in the Late Triassic. This model can explain the spatial and temporal distribution characteristics of the magmatic rocks and sedimentary rocks, as well as Late Triassic uplift and deformation event in the WQO.

How to cite: Wang, M., Pei, X., Li, Z., Li, R., Pei, L., Chen, Y., Liu, C., and Zhao, S.: Early Indosinian magmatism in the West Qinling orogen and its tectonic implication, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2521, https://doi.org/10.5194/egusphere-egu23-2521, 2023.

14:55–15:05
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EGU23-4201
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ECS
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On-site presentation
Ariuntsetseg Ganbat, Tatsuki Tsujimori, Daniel Pastor-Galán, and Alexander Webb

The Central Asian Orogenic Belt (CAOB) consists of several continental blocks, was assembled during the Phanerozoic, and preserves large volumes of Phanerozoic granitoids with juvenile Nd and Hf isotope characteristics, and thus regarded as the largest site of Phanerozoic continental growth on Earth. Nonetheless, it remains disputed whether the significant crustal additions occurred during the Phanerozoic. We compiled available zircon U–Pb geochronological and Hf-in-zircon isotopic data for granitoids from the orogenic segments of CAOB. Using this data, we estimated the percentage of juvenile versus evolved crustal portions in different Phanerozoic time slices of the CAOB.     

The areal distribution of Hf isotopic information shows a younging trend in the Hf model age and radiogenic Hf values from northeast to southwest. For many orogenic segments of the CAOB, the range of hafnium isotope signatures for the granitoids shifted towards more radiogenic compositions over time. We interpret these findings to indicate that the lower crust and lithospheric mantle beneath the CAOB continental blocks were largely removed during continuous oceanic subduction and replaced by juvenile crust. Melts of this crust display the radiogenic hafnium signature. The juvenile versus evolved crustal portion estimations in different time slices show that the crustal growth has taken place in a steady-state mode, and the rate of the radiogenic crustal generation is close to overall global averaged rates of crust generation. It follows that Phanerozoic net crustal growth in accretionary orogens, as exemplified by the CAOB, may have been overestimated as it has been compensated by crustal destruction.

How to cite: Ganbat, A., Tsujimori, T., Pastor-Galán, D., and Webb, A.: Reassessment of the Phanerozoic net crustal growth: U–Pb and Hf zircon data for the Central Asian Orogenic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4201, https://doi.org/10.5194/egusphere-egu23-4201, 2023.

15:05–15:15
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EGU23-7091
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ECS
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On-site presentation
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Florian Trilsch, Sanaa Reuter, Ratschbacher Lothar, Shadi Ansari Jafari, Raymond Jonckheere, Birk Härtel, Christoph Glotzbach, and Bastian Wauschkuhn

Cenozoic reactivation of the Paleozoic thick-skinned fold-thrust belt of the southwestern Tian Shan has—as the Afghan-Tajik Basin inversion—been interpreted to reflect Indian mantle-lithosphere indentation underneath the Pamir. New low-temperature thermochronologic data, i.e. apatite fission-track (AFT), apatite (AHe), and zircon (ZHe) (U-Th)/He ages, reveal the exhumation history of the SW-Tajik Tian Shan along two N-S-transects. We date the reactivation and explore its temporal and spatial variations. Three domains emerged. In the Central Domain (Zeravshan-Gissar and Vashan), AFT data—aided by Raman-spectroscopic chemical-composition discrimination of detrital apatite samples and vitrinite-reflectance temperature estimates—record a ~10-13 Ma onset of shortening and >4 km exhumation. The Northern Domain, where the N-Zeravshan Fault constitutes a major Cenozoic structural divide reactivating the Paleozoic Zirabulak Suture, exhumed from <4 km, but apatite AHe ages outline a similar reactivation history as in the Central Domain. The synchronous structural reactivation implies rapid shortening propagation from the Pamir indenter across the Afghan-Tajik fold-thrust belt into and across the Tian Shan. In the Southern Domain (Gissar Batholith), ~7‒9 Ma AFT and ~4 Ma AHe ages suggest a southward shortening propagation from the northern Domains and anew thrust generation. In the hanging wall of major thrusts, ~3‒7 Ma-old AFT ages record significant and persistent exhumation but ZHe data limit it to <6 km. Most of the Southern and Central Domains cooled monotonously but temperature-time models indicate northward-decreasing reheating by syn-orogenic deposition, consistent with stratigraphic data.

How to cite: Trilsch, F., Reuter, S., Lothar, R., Ansari Jafari, S., Jonckheere, R., Härtel, B., Glotzbach, C., and Wauschkuhn, B.: Cenozoic Southwestern Tian Shan: Timing of Mountain Building, Intra-montane Basin Inversion, and Relation to Lithospheric Mantle Indentation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7091, https://doi.org/10.5194/egusphere-egu23-7091, 2023.

15:15–15:25
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EGU23-10968
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ECS
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Virtual presentation
Azam Soltani Dehnavi, Reimar Seltmann, and Fereshteh Shabani

 

Several sedimentary basins (out of 15 basins) in Kazakhstan are characterized by the association of sandstone-type uranium and sedimentary-hosted copper mineralization with oil, gas or coal fields. In central Kazakhstan, the Chu-Sarysu basin (along with Syr-Darya basin), both hosting a multicolored clay–gravel–sandstone sequence, are famous for roll-front type uranium deposits. The Chu-Sarysu basin is also the host of the world-class historical giant deposit of Dzhezkazgan (22 million metric tons) sandstone-hosted copper (by-product of rhenium) as well as smaller deposits of Zhaman-Aibat and the Zhilandy group. The Teniz depression, located in the northern Chu-Sarysu basin, is also prospective for the occurrence of sedimentary copper. Both basins share lithological and structural peculiarities significant to mineralization. The Teniz and Chu-Sarysu basins originated during the development of the Altaid Orogen (Wilhelm, et al., 2012). The Chu-Sarysu and Teniz basins are characterized by a continental-marine-continental depositional cycle from Devonian to Permian. The base of basins includes Early to Middle Devonian intermediate volcanic and volcanoclastic rocks grading upward into Late Devonian red beds (Box et al., 2012; Cossette et al., 2014). The Early Carboniferous is marked by the deposition of lagoonal to marginal-marine salt-bearing strata, which is overlain by Late Carboniferous to Permian alluvial-lacustrine red beds, and a shale-limestone sequence. Both Chu-Sarysu and Teniz basins endured the folding of rocks in the Permian, generating dome-and-basin forms. Both basins are marked by parallel strike-slip lineaments likely related to Permian Kazakhstan oroclinal bending, resulting in a back-arc/rift-graben development. The localization of most of the Cu deposits at the Chu-Sarysu basin is adjacent to the intersection of F2 anticlines (N-NW-trending) with the syn-depositional folding F1 anticlines (E-NE-trending) within the zones of sandstone bleaching. The F1 anticlines locally trapped petroleum fluid deposits. These structures are the pathway of the flow of dense ore brines across the petroleum-bearing anticlines, resulting in ore sulfide deposition via two fluids mixed. Satellite images display the same structural pattern in the Teniz basin, which can assist to narrow down the prospecting regions for copper occurrences. Since the sedimentary-hosted copper systems are complicated in terms of the mineralization events, the comparison of the two basins enables to generate valuable information related to depositional patterns and to guide exploration. Also, non-genetic special relationship between uranium and copper can be postulated.

 

References

Box, S. E., Syusyura, B., Seltmann, R., Creaser, R. A., Dolgopolova, A., & Zientek, M. L., 2012, Dzhezkazgan and associated sandstone copper deposits of the Chu-Sarysu Basin, Central Kazakhstan. Econ. Geol. Sp. Publ, 16, p. 303-328.

 

Cossette, P.M., Bookstrom, A.A., Hayes, T.S., Robinson, G.R., Jr., Wallis, J.C., and Zientek, M.L., 2014, Sandstone copper assessment of the Teniz Basin, Kazakhstan: U.S. Geological Survey Scientific Investigations Report 2010–5090–R, 42 p.

 

Wilhem, Caroline, Windley, B.F., and Stampfli, G.M., 2012, The Altaids of Central Asia—A tectonic and evolutionary innovative review: Earth-Science Reviews, v. 113, p. 303– 341.

How to cite: Soltani Dehnavi, A., Seltmann, R., and Shabani, F.: Sedimentary Basins of Kazakhstan and Occurrence of Copper and Uranium: A Geological Overview and Tectonic Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10968, https://doi.org/10.5194/egusphere-egu23-10968, 2023.

15:25–15:45
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EGU23-10720
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solicited
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On-site presentation
Sabin Zahirovic

A range of interpretations of regional geology have led to diverging models describing the elusive predecessor marginal basin to the South China Sea, with significant implications for interpreting regional extrusion tectonics and volcanic episodes. Interpretations contrast between the presence or absence of the Proto South China Sea, while models arguing for a Proto South China Sea also diverge in the geodynamic origin of the marginal sea as either 1) a trapped piece of Cretaceous-age proto Pacific (namely, Izanagi) crust, or 2) sourced from back-arc opening along the east Asian margin.

I will provide a comparison of proposed models for the Proto South China Sea, and I will argue that the existence of a Proto South China Sea, including in the region north of Borneo, is a necessity for reconciling multiple and independent geological and geophysical constraints. First, a back-arc basin along east Asia in the Late Cretaceous helps explain tectonic subsidence curves, the presence of Late Cretaceous ophiolites on Mindoro, and also the abandonment of Andean-style arc volcanism on the South China continental margin. Second, regional basin histories and even the tectonic structure of Luzon Island and northwest Borneo suggest continental or arc fragments from east Asia were accreted in both settings. And finally, the ~50 to 20 Ma subduction-related volcanic history on Borneo, the presence of mapped sutures, evidence of subducted slabs in seismic tomography, requires significant south-dipping subduction of a Proto South China Sea. However, interpretations of a number of features, including the Billiton Depression, the Bentong-Raub Suture, and the West Baram Line on Borneo, and the origin of the Natuna Islands granites continue to provoke continued divergence in models for the region.

I will present an updated plate tectonic reconstruction in GPlates that incorporates recent spatial and temporal constraints, such as the west-east division of Luzon island (South China and Pacific affinity, respectively), and the timing of Proto South China Sea back-arc opening, closure, and accretion events. To test the new model, I show that the model conforms to plate kinematic constraints (such as reasonable convergence rates, and associated arc volcanism). In addition, I present new forward models of mantle flow in CitcomS, and compare the predictions to high-resolution P-wave tomography models (e.g. MIT-P08, UU-P07).

Although more geochronological and geochemical constraints are needed to establish the nature and age of the sutures on northwest Borneo, a clearer tectonic model for this area is essential in guiding mineral exploration – as established models have proposed there has been no subduction in this region since ~100 Ma. The new model presented here argues that subduction ceased much more recently, likely by ~20-15 Ma, coinciding with the arrival of the Dangerous Grounds block in the northern Borneo Trough, choking subduction, triggering the Sabah Orogeny, the eruption of Sintang-area adakites (related to slab break-off), and the abandonment of seafloor spreading in the South China Sea at ~15 Ma. Reconciling these interpretations will improve our understanding of paleogeography, basin evolution, sedimentary provenance, and regional geodynamics.

How to cite: Zahirovic, S.: The geological, tectonic, and geodynamic fingerprint of the elusive Proto South China Sea back-arc basin in northern Borneo, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10720, https://doi.org/10.5194/egusphere-egu23-10720, 2023.

Coffee break
Chairpersons: Shaofeng Liu, Chengfa Lin, Lingxiao Gong
16:15–16:25
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EGU23-12729
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ECS
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Virtual presentation
Sk Shamim, Ayon Ghosh, Supriyo Mitra, Keith Priestley, and Sunil Kumar Wanchoo

Broadband waveform data from the recently established Jammu And Kashmir Seismological NETwork (JAKSNET) has been used to detect and locate earthquakes in the Jammu and Kashmir (J&K) Himalaya. Continuous data recorded by the network between 2015 and 2018 has been used for the analysis. The Coalescence Microseismic Mapping (CMM) algorithm is used to detect and locate hundreds of earthquakes, not reported in regional and global catalogs. These earthquakes are then relocated using a probabilistic relocation method of NonLinLoc (NLL). This produced a subset of earthquakes within 200 km of the network and having spatial uncertainty of less than 10 km. Most of the earthquakes are located beneath the Lesser and Higher Himalaya, with depth less than 25 km. A few earthquakes have depths between 30-60 km and lie across the entire region. The shallow earthquakes occur within the Himalayan wedge and define the locked-to-creep transition (unlocking) zone on the Main Himalayan Thrust. These earthquakes occur in clusters in the Jammu-Kishtwar segment, immediately south of the Kishtwar window, beneath the Kashmir Valley and in the NW Syntaxis, surrounding the 2005 (Mw 7.6) Kashmir earthquake source zone. These events provide the first evidence of the MHT locked segment beneath J&K Himalaya. The deeper events are within the underthrusting Indian crust, which reveal that the entire Indian crust is seismogenic. Double-difference algorithm is being used to improve the relative location of the shallow events to study possible clustering of earthquakes in the MHT.  

How to cite: Shamim, S., Ghosh, A., Mitra, S., Priestley, K., and Wanchoo, S. K.: Detection and (re)location of earthquakes using Jammu And Kashmir Seismological NETwork, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12729, https://doi.org/10.5194/egusphere-egu23-12729, 2023.

16:25–16:35
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EGU23-14296
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ECS
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On-site presentation
Sofia-Katerina Kufner, Lidong Bie, Ya-Jian Gao, Mike Lindner, Hamidullah Waizy, Najibullah Kakar, and Andreas Rietbrock

On June 21th, a Mw6.2 earthquake struck the Afghan-Pakistan-border-region, an area dominated by partitioned deformation related to the India-Asia collision. Despite its moderate size, 1150 deaths were reported, making the event the deadliest earthquake of 2022 so far. We investigate the event’s rupture processes, aiming to understand what made it that fatal. Our InSAR-constrained slip model and regional moment-tensor inversion reveal a sinistral rupture with maximum slip of 1.8 m at 5 km depth on a N20°E striking, sub-vertical fault. Field observations confirm fault location and slip-sense. Based on our analysis and a global comparison, we suggest that not only external factors (e.g. time of the event and building stock) but also fault-specific factors made the event excessively destructive. Surface rupture was favored by the local rock anisotropy (foliation), coinciding with the fault strike. The distribution of Peak Ground Velocity was governed by the sub-vertical fault. The maximum slip was large compared to other events globally and might have resulted in peak-frequencies coinciding with the resonance-frequency of the local one-story buildings. More generally, our study demonstrates the devastating impact of moderate earthquakes, being small enough to be accommodated by many tectonic structures but large enough to cause significant damage.

How to cite: Kufner, S.-K., Bie, L., Gao, Y.-J., Lindner, M., Waizy, H., Kakar, N., and Rietbrock, A.: The devastating 2022 M6.2 Afghanistan earthquake: challenges, processes and implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14296, https://doi.org/10.5194/egusphere-egu23-14296, 2023.

16:35–16:45
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EGU23-4041
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Virtual presentation
Youxin Chen, Meng Wang, and Xianzhi Pei

High-pressure and ultrahigh-pressure minerals tend to be preserved in mafic and ultramafic metamorphic rocks, such as eclogites and garnet amphibolites, rather than felsic rocks. Generally, the garnet amphibolites preserve particular porphyroblastic and corona textures that provide important information of geological processes. Therefore, identification of garnet amphibolite might hint that subduction or collision processes were likely to have occurred.

The Yili Block is one microcontinent in southwest of Central Asian Orogenic Belt, 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 infer that the southward subduction of the Junggar Ocran beneath the Yili Block, but the record of coeval metamorphism is rarely reported. The Toksai garnet amphibolites idientified from the Wenquan Group in the northern margin of Yili Block records a clockwise P-T-t path. Its near isothermal depressive retrogressive metamorphism was typical characteristic of the Western Alps P-T path, recording the process of subduction and collision. The protolith belongs to tholeiite, with high TiO2 and low K2O+Na2O contents (3.10~3.89 wt.%, 0.76~2.01 wt.% respectively), enrichment of large ionic lithophile elements and depletion of high field strength elements, and enrichment of rare earth elements, showing the geochemical characteristics of tholeiite in intra-continental rift setting (Th/Ta=1.70~2.76, Ta/Hf=0.23~0.37). The geochemical characteristics reveal that the magmatic rocks derived from an OIB-like mantle source. The garnet amphibolites also has low contents of MgO (4.82~6.40 wt.%), Cr (70.8~224 ppm), Ni (9.68~65.7 ppm) and low values of Mg# (34.0~41.3), Nb/U (14.3~36.3), Nb/Ta (9.70~16.2), indicating that their protolith are not primitive magma, were formed by separate crystallization of different mineral phases with a small amount of crustal contamination. The zircon U-Pb dating results suggest that the garnet amphibolites protolith was formed in the middle to late Neoproterozoic, and the metamorphic age is end of Late Ordovician (450~440 Ma). The zircon and monazite from surrounding rocks also record the coeval tectonic thermal event. Consequently, it is inferred that the protolith of the garnet amphibolites may have formed in an intraplate rifting setting as a result of the breakup of Rodinia, and indicating that the Yili Block maybe a continental fragment separated from the Tarim Block during the middle to late Neoproterozoic. In the Middle to Late Ordovician, the Wenquan Group as a part of Aktau-Wenquan contineantal domain was involved in the continental–arc collision and continuing accretion in north of the Yili/Kazakhstan Block with the southward subduction of the Junggar–Balkhash oceanic lithosphere, and experience high amphibolite facies metamorphism in the end of Ordovician.

How to cite: Chen, Y., Wang, M., and Pei, X.: Chronology, geochemistry, metamorphic evolution and its tectonic implications of the Toksai garnet amphibolites in the northern margin of Yili Block, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4041, https://doi.org/10.5194/egusphere-egu23-4041, 2023.

16:45–16:55
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EGU23-1933
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ECS
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Highlight
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On-site presentation
EaDz: a web-based, relational database for detrital zircons from East Asia
(withdrawn)
Bo zhang, Shaofeng Liu, and Chenxi Zhang
16:55–17:00
17:00–17:20
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EGU23-9971
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solicited
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Highlight
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Virtual presentation
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Nicolas Flament, Omer Bodur, Simon Williams, Andrew Merdith, Dietmar Muller, John Cannon, Michael Tetley, Xianzhi Cao, and Sabin Zahirovic

Plate tectonics shapes Earth’s surface and is linked to motions within its deep interior. Cold oceanic lithosphere sinks into the mantle, and hot mantle plumes rise from the deep Earth, leading to volcanism. Volcanic eruptions over the past 320 million years have been linked to two large structures at the base of the mantle presently under Africa and the Pacific Ocean. This has led to the hypothesis that these basal mantle structures could have been stationary over geological time, in contrast to observations and models suggesting that tectonic plates, subduction zones, and mantle plumes have been mobile and that basal mantle structures are presently deforming. Here we reconstruct mantle flow from one billion years ago to the present day to show that the history of volcanism is statistically as consistent with mobile basal mantle structures as with fixed ones. In our reconstructions, cold lithosphere sank deep into the African hemisphere between 740 and 500 million years ago, and from 400 million years ago the structure beneath Africa progressively assembled, pushed by peri-Gondwana slabs, to become a coherent structure as recently as 60 million years ago. In contrast, the structure beneath the Pacific Ocean was established between 400 and 200 million years ago. These results confirm the link between basal mantle structures and surface volcanism, and they suggest that basal mantle structures are mobile, and aggregate and disperse over time, similarly to continents at Earth’s surface. This implies that the present-day shape and location of basal mantle structures may not be a suitable reference frame for the motion of tectonic plates.

How to cite: Flament, N., Bodur, O., Williams, S., Merdith, A., Muller, D., Cannon, J., Tetley, M., Cao, X., and Zahirovic, S.: The Pacific basal mantle structure could be older than the African one, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9971, https://doi.org/10.5194/egusphere-egu23-9971, 2023.

17:20–17:30
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EGU23-11327
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ECS
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On-site presentation
Bingxi Liu, Simon Williams, Guochun Zhao, Shan Yu, and Dongchuan Jian

Reconstructing past episodes of mountain building from the geological rock record is one of the main challenges for unravelling the ancient physical geography of Earth’s surface. Mountains and mountain ranges, often situated at convergent plate margins, play a pivotal role in many fields of the Earth, climate, and biological sciences. Established methods for quantifying past elevations traditionally relied on sedimentary rocks, but in recent years, alternative approaches have emerged on the basis that geochemical signatures of magmatic rocks formed in convergent settings correlate with crustal thickness or elevation. These correlations allow for empirical relations of igneous whole-rock ratios such as La/Yb and Sr/Y with Moho depth for modern convergent settings, which can then be used to estimate ancient crustal thickness or paleoelevation. Since a relatively large number of igneous samples are available for pre-Cenozoic times compared to other paleoelevation proxies, these methods have the potential to allow quantitative mapping of past topographic change for times where existing maps are largely based on a qualitative approach.

Here, we investigate the application of paleoelevation estimates derived from geochemistry using the Pacific margin of South America as a case study. We investigate their consistency with independent indicators of past elevations such as stratigraphy, stable isotopes, fossils etc. for Cenozoic samples along the Andean margin. For older times, we compare the estimated paleoelevations with other aspects of the geological record, as well as equivalent values from global paleogeography models widely used in climate modelling studies, to evaluate the extent to which these models are consistent with the igneous geochemical proxies. We derive paleoelevation estimates according to different data filtering schemes, showing that a major consequence of the choice of geochemistry filter is the number of data points left after the filtering. We find that the igneous geochemical proxies yield elevations broadly consistent with traditional results for the Cenozoic, though our results do not resolve some of the rapid uplifts recorded by other proxies. In deeper time, we show that igneous geochemistry quantifies changes in elevation related to documented phases of crustal thickening and thinning, and is thus likely to allow improvements to existing maps of paleotopography. 

How to cite: Liu, B., Williams, S., Zhao, G., Yu, S., and Jian, D.: Paleoelevation Reconstruction of Subduction Zones in Eastern Pacific Continental Margins Quantitatively with Igneous Geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11327, https://doi.org/10.5194/egusphere-egu23-11327, 2023.

17:30–17:40
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EGU23-7625
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On-site presentation
Neng Wan, Shaofeng Liu, and Zhang Bo

The giant Late Triassic Ordos basin, developed along northern Tethyan margin where prolonged terrane amalgamation and accretion occurred, is characterized by rapid subsidence rate along its southwestern margin, but slow and uniform subsidence rate within its interior. Its formation mechanism still remains poorly understood. Here, we use flexural simulation and 4D-geodynamic modeling to explore the potential role of basin adjacent mountain belts and deep mantle processes towards basin subsidence, respectively. Flexural backstripping of stratigraphic record spanning from 245-201 Ma, along two SW-NE trending well sections perpendicular to the southwestern margin of Ordos basin clearly demonstrates that there were long wavelength anomalous subsidence components, here termed residual subsidence, in addition to those induced by thrust loads and sediment loads. From 245-201 Ma, residual subsidence increases from 0 m to ca. 500 m and gradually decreases from southwest towards northeast. Our results indicate that basin adjacent thrust loads could act as the dominant driver for subsidence of foredeep but have limited control towards basin interior. Other mechanism is required to explain the basin-wide anomalous residual subsidence. Long-wavelength nature of residual subsidence and its general agreement, regarding both the magnitude and trend, with dynamic topography predicted by an independently designed geodynamic model suggest that the anomalous subsidence component might be of dynamic origin. We attribute this excess residual subsidence as dynamic subsidence induced by the sinking slab beneath North China plate during and after the oblique closure of Mianlue ocean between North China plate and South China plate. We argue that the Ordos basin is triggered by subduction related mantle processes while modulated by flexural loading along its margin. Our findings may also shed light on formation mechanisms of other giant basins with similar settings in East Asia.

How to cite: Wan, N., Liu, S., and Bo, Z.: Sinking-slab triggered formation of the giant Ordos basin in central China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7625, https://doi.org/10.5194/egusphere-egu23-7625, 2023.

17:40–17:50
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EGU23-10007
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Highlight
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On-site presentation
Jonny Wu, Yi-An Lin, and Lorenzo Colli

The plate tectonic history of the Pacific Ocean and its predecessor ocean, Panthalassa, are challenging regions on Earth to reconstruct during the Mesozoic-Cenozoic eras. More than 95% of Pacific-Panthalassa crust has been subducted into the Earth’s interior since the Jurassic, and this has created extensive (>9000 km length) plate reconstruction gaps between the Pacific and Eurasia/Laurasia. Here we build four contrasted NW Pacific-Panthalassa global plate reconstructions and assimilate their velocity fields into the global geodynamic models using the code TERRA: Andean-style subduction along East Asia following the corrected ‘R’ Matthews et al. (2016); and, three models that include intra-oceanic subduction within Pacific-Panthalassa with increasing tectonic complexity.   We compare our predicted present mantle structure, synthetic geoid and dynamic topography to Earth observations. P-wave tomographic filtering of predicted mantle structures allows for more explicit comparisons to global tomography.

All three plate reconstructions that include NW Pacific-Panthalassa intra-oceanic subduction fit better to the observed long-wavelength geoid and residual topography.  Correlations between modeled and imaged mantle structure do not systematically favor any single model, and this is attributed to limited tomographic resolution within the central Pacific mantle relative to variability in our modeled mantle structures.  Taken together, our results robustly show the likelihood of intra-oceanic subduction within NW Pacific-Panthalassa.  This presents a challenge to popular plate models of Andean-style subduction along East Asia, which are deeply-embedded into most published plate tectonic, geodynamic and geologic studies.  Our geodynamic models predict significant (>2000 km from Mesozoic to present) southeastwards lateral slab advections within the lower mantle that would confound ‘vertical slab sinking’-style restorations of ancient subduction zones.  Plate reconstructions that can better incorporate intra-oceanic subduction within Pacific-Panthalassa may improve our knowledge of past global CO2, mantle flow, and dynamic topography histories.

How to cite: Wu, J., Lin, Y.-A., and Colli, L.: NW Pacific-Panthalassa intra-oceanic subduction during Mesozoic-Cenozoic times from mantle convection and geoid models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10007, https://doi.org/10.5194/egusphere-egu23-10007, 2023.

17:50–18:00
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EGU23-12290
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Virtual presentation
Gleb Smirnov, Reimar Seltmann, and Azam Soltani Dehnavi

The Kalba-Narym Belt is part of the Central Asian Orogenic Belt (CAOB) and formed due to the
continental collision between Kazakhstan and Siberian plates in the Late Paleozoic. Several
plutons comprising the Kalba-Narym granitic batholith are considered post-orogenic. The
commonly accepted theory claims that these intrusive bodies might have been formed due to
the far-spreading influence of the Tarim mantle plume (Khromykh et al., 2019). However, the
volcanic facies, that are normally associated with plume-related activities are present only
sporadically in the Kalba-Narym area, which may imply that the heat source is plume-unrelated
and instead linked to mafic underplating and uplift processes of the crust. Amongst the variable
intrusive rocks formed in this region, highly-fractionated pegmatites are particularly important
but nevertheless remain poorly understood with origin controversially discussed. The
mineralized pegmatites are associated with Phase 1 granites of the Kalba complex, with a
40Ar/ 39Ar age of 297 to 290 Ma (Kotler et al., 2021). The formation of pegmatites, driven either
by the differentiation of granitic melts or by anatectic melting processes, was likely
supplemented by the inputs of volatiles and rare metals with fluids. The rocks of the best-
known pegmatite occurrences located near Asubulak village, such as Yubileynoye and Krasny
Kordon deposits, can be categorized as LCT pegmatites, including three main zones based on
mineralogical and geochemical assemblages of a) microcline-albite with pollucite and petalite
(Ta, Cs, Be, Sn), b) microcline-albite with spodumene (Ta, Nb, Cs, Li, Be, Sn), and c) spodumene-
albite (Li, Ta, Nb, Sn) (D'yachkov et al., 2021).
Apart from the mineralized pegmatites, there are known occurrences of barren pegmatites,
which creates an opportunity for comparison with the mineralized pegmatites specifically via
contrasting geochemical signatures. Aiming at a proper understanding of the pegmatite
genesis, mineralization mechanisms and geochemical approach on a bigger regional scale of the
Greater Altai may open up unique perspectives for the future exploration of the region.
Therefore, this presentation provides an overview and re-evaluation of the detailed geological
characteristics of the Kalba-Narym Belt, continuous into Chinese Altai, and the processes
involved in rare-metal pegmatite mineralization.

References:
D'yachkov, B. A., Bissatova, A. Y., Mizernaya, M. A., Zimanovskaya, N. A., Oitseva, T. A.,
Amralinova, B. B., Aitbayeva, S. S., Kuzmina, O. N., &amp; Orazbekova, G. B. (2021). Specific
Features of Geotectonic Development and Ore Potential in Southern Altai (Eastern
Kazakhstan). Geology of Ore Deposits, 63(5), 383–408.
https://doi.org/10.1134/s1075701521050020


Khromykh, S. V., Oitseva, T. A., Kotler, P. D., D’yachkov, B. A., Smirnov, S. Z., Travin, A. V.,
Vladimirov, A. G., Sokolova, E. N., Kuzmina, O. N., Mizernaya, M. A., &amp; Agaliyeva, B. B.
(2020). Rare-metal Pegmatite Deposits of the Kalba Region, Eastern Kazakhstan: Age,
Composition and Petrogenetic Implications. Minerals, 10(11), 1017.
https://doi.org/10.3390/min10111017

Kotler, P., Khromykh, S., Kruk, N., Sun, M., Li, P., Khubanov, V., Semenova, D., &amp; Vladimirov, A.
(2021). Granitoids of the Kalba Batholith, Eastern Kazakhstan: U–PB Zircon Age,
Petrogenesis and Tectonic Implications. Lithos, 388-389, 106056.
https://doi.org/10.1016/j.lithos.2021.106056

How to cite: Smirnov, G., Seltmann, R., and Soltani Dehnavi, A.: Lithium pegmatites of the Kalba-Narym Belt, East Kazakhstan: Geological overview, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12290, https://doi.org/10.5194/egusphere-egu23-12290, 2023.

Posters on site: Fri, 28 Apr, 08:30–10:15 | Hall X2

Chairpersons: Nalan Lom, Johannes Rembe, Chengfa Lin
X2.129
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EGU23-7701
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ECS
Chengfa Lin and Shaofeng Liu

Since Late Palaeozoic, the North China Block (NCB) experienced a unique tectonic process in which sequential plate subduction and collision took place around this once stable and rigid craton. Due to this multi-direction convergent setting and its small size, the NCB was characterized with intensive intracontinental deformation and associated depositional processes and magmatism during Mesozoic. However, conflicting debates on the timing and kinematics of the intracontinental deformations are still open to the geologist community and hamper the understanding of the driving forces. Our works focus on the syn-tectonic depositions, including syn-tectonic conglomerates and growth strata, in Mesozoic sedimentary basins in the Yanshan belt of northern NCB, and the high-precision zircon U-Pb geochronological data. Previously reported stratigraphic levels of regional unconformities and isotopic ages of igneous rocks in the Yanshan belt were also compiled in this study. Our results suggest that during Middle Triassic-earliest Jurassic (ca. 240-195 Ma), the northern NCB was dominated by nearly N-S compressional regime, leading to formation of large-scale E-W-trending thrust faults and basement-cored buckles. A significant magmatic lull was also witnessed within this period (ca. 210-195 Ma). This N-S crustal shortening was believed to be related with collision between the NCB and the Songliao-Nenjiang terrane along the Solonker suture. During Middle Jurassic-Early Cretaceous (ca. 172-135 Ma), the Yanshan belt underwent strong NW-SE contraction and gave rise to NE-SW-striking thrust faults, asymmetric folds, and reactivation of previous E-W thrust faults with prominent dextral component. Both deformation, deposition, and magmatism showed a westward younging trend in the Yanshan belt during Early Jurassic-Early Cretaceous (ca. 180-140 Ma), indicating their westward migration. However, magmatism turned to migrate toward east after that. All these lines of evidences could be integrated in a tectonic model with westward flat-slab subduction of the Paleo-Pacific/Izanagi plate beneath the East Asian continent. Early Jurassic witnessed an imported and profound transition from closure of the paleo-Asian Ocean to the subduction of the Paleo-Pacific Ocean plate.

How to cite: Lin, C. and Liu, S.: Mesozoic intracontinental deformations of the northern North China Block in a multi-direction convergent setting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7701, https://doi.org/10.5194/egusphere-egu23-7701, 2023.

X2.130
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EGU23-343
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ECS
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Mita Uthaman, Chandrani Singh, Arun Singh, Abhisek Dutta, Arun Kumar Dubey, and Gaurav Kumar

The Himalayas, which formed as a result of the impactful collision of the Indian plate with Eurasian plate, is a tectonically complex and seismically active region. It has been a hotspot for many great earthquakes in the past. The continued collision coupled with the complex structural features has led to the persistent seismic activity of the region. The progressive collision led to the formation of distinct tectonic units bounded by thrust faults. The northeastern state of Sikkim in India, which is sandwiched between Nepal and Bhutan in the Himalayas, has been prone to frequent great earthquakes. The deployment of a dense seismic network consisting of 27 broadband seismometers, across Sikkim Himalayas and the northern part of West Bengal, since April 2019 has enabled us to monitor the seismic activity in the study region.

Here, we present a study which aims at understanding the seismotectonic activity of the study region using local earthquakes (epicentral distance < 200km) recorded by the network between April 2019 and September 2022. The progressively improved relocation of local earthquakes recorded in the study region shows a diffuse cloud of micro-seismicity concentrated along a diagonal region extending from north of Assam in the southeast to south of Tibet in the northwest. From south to north we have observed clusters of earthquakes with a gradual increase in their hypocentral depths.

The upper-crustal earthquakes (~0-25km) are located near the down-dip end of the locked part of the Main Himalayan Thrust (MHT), along which India underplates Tibet. We also observe prominent lower crustal earthquakes at depths greater than 30 km. These earthquakes are possibly originating at the junctions of different blocks in an imbricated crust in response to active shortening. We also observe a mid-crustal seismicity pattern following the DCFZ (Dhubri-Chungthang Fault Zone), supporting observations from earlier studies. Striking variations are observed in the faulting mechanisms and orientation of stress axes along the north-south and east-west profiles, and also with depth. We plan to further investigate if these variations imply the presence of possible segmentation, its depth, extent, surface expression and determine its relation to the geodynamics of the region. Integrating the results obtained from the various studies and interpreting them will help in delineating the seismotectonic activity of the study region. Quality data recorded by the dense network will further complement in enhancing the resolution of the results obtained.

How to cite: Uthaman, M., Singh, C., Singh, A., Dutta, A., Kumar Dubey, A., and Kumar, G.: Seismicity and active tectonics:  New insights from Sikkim Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-343, https://doi.org/10.5194/egusphere-egu23-343, 2023.

X2.131
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EGU23-2259
Chandrani Singh, Ashwani Kant Tiwari, Eric Sandvol, Shirish Bose, Namrata Jaiswal, Niptika Jana, and Arun Kumar Gupta

We have formulated frequency dependent Lg and Pg attenuation tomographic models to investigate the
crustal Q values and its tectonic implications beneath western Tibet. The frequency dependent
behaviour of both Lg and Pg are studied for the frequency bands of 0.2-0.6, 0.6-1.0 and 1.0-1.4 Hz at
central frequencies of 0.4, 0.8, and 1.2 Hz, respectively, implementing both Two-Station Method
(TSM) and Reverse Two-Station Method (RTSM). The amplitudes of both the waves are fundamentally
sensitive to the crustal structures and are controlled by both scattering and intrinsic attenuation. The
frequency dependent characteristics of QLg and QPg are consistent in nature for the region. Moderate to
high Q values evident in the Lhasa terrane could supplement the trace of underthrusting Indian
lithosphere beneath the region. The average Q values for both Lg and Pg increase with increasing
frequency. The frequency dependent parameter η shows quite high values, for both the waves using
TSM and RTSM, which may indicate strong heterogeneities present in the crust. Subsequently, relative
site responses at each station are studied using RTSM for the central frequencies of 0.4, 0.8, and 1.2
Hz. Weak to negative site responses are mostly dominant in western Tibet. Relative site responses are
found to vary with frequency which could be associated with the sampling depth. We found no
correlation of site responses with the elevation.

How to cite: Singh, C., Tiwari, A. K., Sandvol, E., Bose, S., Jaiswal, N., Jana, N., and Gupta, A. K.: Frequency dependent attenuation and relative site response of western Tibet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2259, https://doi.org/10.5194/egusphere-egu23-2259, 2023.

X2.132
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EGU23-2463
Arun Singh, Gaurav Kumar, Chandrani Singh, M. Ravi Kumar, Mita Uthaman, Dipankar Saikia, and Arun Kumar Dubey

  The exact role of subducting Indian continental crust in the formation of Himalaya-Tibet collision zone remains enigmatic. The mass budget estimates describing shortening across the orogen is partly derived from the observations made from seismic imaging of deep earth. Here using data from 38 broadband seismic stations covering Sikkim Himalaya, we produce high resolution seismic images in order to fill the crucial gaps in our understanding of the formation of Himalayan collision zone. We have used 11,594 high quality receiver functions using earthquakes of magnitude >5.5 in the distance range of 30-100°. Our data demonstrates a highly imbricated and heterogeneous crust beneath Sikkim Himalaya. The Main Himalayan thrust responsible for large scale earthquakes in the Himalayan collision zone is not so vivid in the migrated images, but is observed intermittently. The main cluster of earthquakes at shallower depths linked to the Main Himalayan thrust is marked by low amplitude arrivals. Overall trend suggests a gently dipping Moho attaining crustal depths of ∼60 km beneath Higher Himalaya compared to ∼40 km in the Himalayan foredeep. Moho as we see in this segment of Himalaya is with possible offsets and overlapping segments. Imbrication is well reported in the Himalayan orogenic wedge forming upper crust, we also observe this in the lower crust indicating lithospheric imbrication in response to collision. Interestingly, the lower crustal clusters of earthquakes fall at the juncture of offsets in the Moho. The offset positions at lower crustal depths seem more prone to earthquakes in response to active shortening. Seismic images reveal differences in amplitude of receiver functions and presence of conversions at deeper depths in the lithospheric mantle across Dhubri-Chungthang Fault Zone, possibly related to the segmentation of Himalaya.  

How to cite: Singh, A., Kumar, G., Singh, C., Kumar, M. R., Uthaman, M., Saikia, D., and Dubey, A. K.: Seismic constraints on the nature and geometry of the downwelling Indian crust beneath Sikkim Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2463, https://doi.org/10.5194/egusphere-egu23-2463, 2023.

X2.133
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EGU23-3845
Xuexiang Gu, Yongmei Zhang, Zhanlin Ge, Weizhi Chen, and Liqiang Feng

There are many lode gold deposits and occurrences in the Kalamaili area of the East Junggar, Northwestern China. The deposits are confined to a narrow zone between the regional NW- to NWW-trending Kalamaili and Qingshui-Sujiquan shear zones and are structurally controlled by secondary, high-angle faults of the regional shear zones. The orebodies occur in the Middle Devonian and Lower Carboniferous strata that are largely composed of zeolite to lower greenschist facies clastic sedimentary and pyroclastic rocks. Gold mineralization occurs as auriferous quartz-sulfide±tourmaline veins/veinlets and disseminated ores in the immediate altered wall rocks. The ore mineralogy is relatively simple and dominated by quartz with minor to trace amounts of sulfides (pyrite and arsenopyrite, typically <5% in volume), sericite, calcite, and gold. The hydrothermal alteration halos are characterized by a proximal, 0.5–5 m wide zone composed mainly of quartz-sericite (-tourmaline)-sulfide (-gold) and a distal, several to tens of meters wide zone with a calcite-chlorite-epidote assemblage. Hydrothermal processes essentially involve a pre-ore stage of barren quartz, a main-ore stage of quartz-sulfide-gold (±tourmaline), and a post-ore stage of barren quartz-calcite (±sericite).

Fluid inclusion microthermometry, stable isotopes, and hydrothermal zircon U-Pb dating were combined to constrain the nature and source of ore fluids, the timing of mineralization, and the mechanism of gold precipitation. The ore-forming fluid of the main-ore stage is uniformly characterized by a medium to high homogenization temperature (mostly 240° to 330℃), low salinity (typically <6 wt % NaCl equiv), reduced, and CO2-rich-H2O-NaCl±CH4 fluid. The hydrogen and oxygen isotope data (δ18OH2O=+8.4 to +17.3‰, δDH2O=–99 to –62‰) indicate a metamorphic origin for the mineralizing fluid. The majority of δ34S values of the sulfides range between 0 and +10‰ with a mean of +2‰ (n=62), indicative of a largely sedimentary rock reservoir of sulfur in the ore-forming fluids. LA-ICP-MS U-Pb isotope dating of the hydrothermal zircons from auriferous quartz veins yielded a weighted mean 206Pb/238U age of ~313 Ma.

Combined geological and geochemical evidence indicates that the transition from compressional to transcurrent deformation during the late- to post-orogeny in the late Carboniferous played a vital role for the gold-bearing fluid flow along regional shear zones and subsequent channeling into the second- and third-order faults. On a deposit scale, fault-valve behavior during seismic fault activity is a key mechanism that caused episodic changes in fluid pressure and the resultant phase separation of ore fluids and precipitation of gold. Sulfidation of wall rocks due to fluid-rock interaction is another important mechanism for the gold precipitation. Later since the Permian, the N-S compression resulted in uplift and exhumation of the East Junggar terrane and deformation of the orebodies. Target gold exploration in this region is suggested to focus on the northeast side of the Kalamaili fault zone, where there exist suitable faults that connect with the first-order fault zones at depth and lead to focused fluid flux into depositional sites at shallower levels.

How to cite: Gu, X., Zhang, Y., Ge, Z., Chen, W., and Feng, L.: Orogenic Gold Mineralization and its Relationship to Tectonic Evolution of the Kalamaili Area, East Junggar, Northwest China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3845, https://doi.org/10.5194/egusphere-egu23-3845, 2023.

X2.134
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EGU23-4461
Edward Sobel, Jonas Kley, Johannes Rembe, Rasmus Thiede, Johannes Glodny, Lennart Grimm, Maximilian Rometsch, Asil Newigy, Nowrad Ali, Wafaa Altyeb, and Daniela Espinoza Tapia

The Pamir orogen forms the northwest prolongation of the Tibetan plateau. The most important surficial structure bounding the northern and northwestern margin is the Main Pamir Thrust (MPT); however, despite the importance of the structure, surprisingly little is known about the displacement history of the fault. Together with the younger, foreland-oriented Pamir Frontal thrust system (PFT), displacement estimates range from 50 to over 300 km. The larger estimates are based on the estimated Cenozoic northward indentation of the Pamir with respect to Tibet as well as the length of the intracontinental Pamir seismic zone. However, recent work suggests that some of the indentation predates the Cenozoic or is related to an original Paleozoic embayed paleogeography and other studies have suggested that the seismic zone is not related to intracontinental subduction. Shortening estimates in the hanging walls of the MPT and PFT suggest more modest amounts: between 30 and 75 km in the north, with higher values for SE-NW shortening in the Tadjik depression.

Constraining the onset of deformation has proven challenging. Most publications suggest a late Oligo-early Miocene onset age. Cenozoic stratigraphic sequences are unfossiliferous and poorly dated. We have attempted to resolve this question by collecting samples for thermochronologic analysis from many locations along the arcuate margin. In general, zircon (U-Th-Sm)/He (ZHe) samples yield ages between ~60 and 17 Ma. Many are likely to be partially reset. Ages are slightly older in the east, which could reflect an overall westward increase in exhumation. The relatively small amount of exhumation in the north supports our structural interpretation that the MPT there has a low dip angle and might not have produced pronounced topography. Apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) are often much younger; often between <15 and 10 Ma in the MPT hanging wall and < 10 Ma in the footwall. These younger ages may reflect the activation of a second pulse of exhumation linked to motion along the PFT. We are modeling these data sets using QTQt to try to better constrain the exhumation history of the fault system. In turn, these should help constrain shortening estimates.

How to cite: Sobel, E., Kley, J., Rembe, J., Thiede, R., Glodny, J., Grimm, L., Rometsch, M., Newigy, A., Ali, N., Altyeb, W., and Espinoza Tapia, D.: Thermochronologic constraints on exhumation associated with the Main Pamir Thrust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4461, https://doi.org/10.5194/egusphere-egu23-4461, 2023.

X2.135
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EGU23-4737
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ECS
Yuantong Mao, Liang Zhao, Marco Malusà, Stefano Solarino, Silvia Pondrelli, Baolu Sun, Coralie Aubert, Simone Salimbeni, Elena Eva, and Stéphane Guillot

Continental subduction zones are crucial tectonic settings where subducted slabs exchange crustal materials with the mantle, and geochemical changes occur with the participation of fluids at increasing temperatures and pressures. The occurrence of pervasive networks of quartz veins in exhumed sections of the Alpine subduction wedge provides evidence for major silica-rich fluid circulation in the shallowest levels of the subduction zone. However, the occurrence of silica-rich fluids at greater depths above the subduction interface remains speculative.

Rocks involved in the subduction zone experience variable temperature and pressure conditions and show a wide range of densities and seismic velocities that are not necessarily correlated. An integrated analysis of seismic velocities, Vp/Vs ratios and rock densities may provide a viable tool to detect compositional variations in the Earth’s interiors and infer the impact of large-scale fluid flows on the intrinsic physical properties of subducted rocks. We tackle this issue from a geophysical perspective, by applying H-κ stacking, receiver function analysis, and waveform and gravity modelling. We found a belt of high Vp/Vs ratios >1.9 in the rear part of the Alpine subduction wedge, consistent with a partly serpentinized upper-plate mantle, and a belt of unusually low Vp/Vs ratios <1.7 in the frontal part of the subduction wedge that we interpret as the effect of a pervasive network of silica-rich veins above the subduction interface. Laboratory experiment shows that Vp/Vs ratios are generally higher for serpentinite (2.0-2.2), and much lower for quartz (1.46-1.48).

Our results suggest a dominant role of silica-rich fluids in the subduction wedge. These silica-rich fluids rose within the subduction wedge until the change in ambient conditions precipitated the formation of a widespread network of quartz veins, as observed in the field. And this pervasive quartz-vein network changes the physical properties of the subduction-wedge rocks, implying a major impact on rheology favoring crustal deformation during continental subduction.

How to cite: Mao, Y., Zhao, L., Malusà, M., Solarino, S., Pondrelli, S., Sun, B., Aubert, C., Salimbeni, S., Eva, E., and Guillot, S.: Geophysical evidence of large-scale silica-rich fluid flow above the continental subduction interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4737, https://doi.org/10.5194/egusphere-egu23-4737, 2023.

X2.136
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EGU23-5179
Wilfried Bauer, Joachim Jacobs, Ivan Callegari, Andreas Scharf, and Frank Mattern

The Saih Hatat Dome is a tectonic window in northeastern Oman with a NW-SE extension of <95 km and an E-W extension of <50 km, rimmed by the allochthonous Samail Ophiolite and the underlain nappes composed of sedimentary rocks from the Neo-Tethyan Hawasina Basin. Rocks within the window were affected by an upper Cretaceous high- to ultra-high pressure/low-temperature eclogite- and blueschist-facies metamorphism.

Stratigraphically, the Saih Hatat Dome contains a several kilometer thick basal (“Autochthonous A”) sequence from what is believed Cryogenian Hatat schists to the Ediacaran Hiyam dolostone, unconformably overlain by 3400 m Cambro-Ordovician siliciclastics. This basal sequence is separated by a so-called ‘Hercynian’ unconformity from Permian to Jurassic overall shelf carbonates (“Autochthonous B”). In the eastern part of the window, intense Cretaceous deformation and metamorphism makes it difficult to identify this stratigraphic subdivision.

New U-Pb zircon LA-ICP-MS data from a quartzdiorite dyke, intruding the basal part of the Hatat schists gave a crystallization age of 845 +2/-4 Ma. Thus, the basal part of the Hatat schists is Tonian in age and older than the Cryogenian/Ediacaran strata of the nearby Jebel Akhdar Dome and Huqf area, 40 km to the west and 300 km to the south, respectively.

Two blueschist-facies tuffites from eastern Saih Hatat contain concordant detrital zircons, ranging in age between c. 530 and 2872 Ma with age clusters around 750 to 850 Ma and 1010 to 1164 Ma. The latter ages are not known from a source on the Arabian Plate and might be derived from an Indian source.

Based on the new results, we suggest a subdivision of the Saih Hatat stratigraphy with a Tonian accretionary wedge (Hatat schist) which might be coeval with igneous intrusion from the Ja’alab area, an Ediacaran carbonate platform, and a Cambrian sedimentary basin, unconformably overlain by upper Cambrian/Ordovician quartzites.

How to cite: Bauer, W., Jacobs, J., Callegari, I., Scharf, A., and Mattern, F.: New constraints on the geological evolution of the SE corner of the Arabian Plate (NE Oman), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5179, https://doi.org/10.5194/egusphere-egu23-5179, 2023.

X2.137
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EGU23-6614
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ECS
Nalan Lom and A.M. Celal Şengör

The stratigraphy of the southern half of Afghanistan has been studied and the timing of first order events have been established in some detail. By contrast, the structural evolution has not been treated with the same discernment. We here report the existence of a marginal fold and thrust belt within the Logar Syncline (western Afghanistan) that was detached along a décollement surface at the base of the Cambrian, mainly between Zargaran dolomites and polymictic conglomerates filling the underlying depressions. The basement consists of Pan-African magmatic and metamorphic rocks including volcanic tuffs making up the Loy Khwar Series. Some of this material has been worked into the conglomerates of the Loy Khwar. The overlying sedimentary package reaches from the Cambrian to the Permian and has been deformed into concentric folds. Nowhere do these folds expose the underlying Pan-African basement which crops out in the extreme SW, in a kind of root zone wherein the décollement separating the sedimentary package from the basement seems to root. Having a décollement within dolomites seems unexpected due to their presumed strength but a similar case has been reported from the Keystone Thrust of the Sevier Belt in Nevada. This phenomenon seems to be more widespread than previously thought.

How to cite: Lom, N. and Şengör, A. M. C.: The discovery of a Palaeozoic décollement in SW Afghanistan: orogenic events along the Tethyan edge of Gondwana-Land, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6614, https://doi.org/10.5194/egusphere-egu23-6614, 2023.

X2.138
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EGU23-7378
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ECS
Nikola Randjelovic, Liviu Matenco, Maja Maleš, Nemanja Krstekanic, Uros Stojadinovic, Branislav Trivić, and Marinko Toljić

Convergence zones are often characterized by numerous subduction- to collision-related dynamics in many orogenic areas worldwide. Processes such as continental indentation, extrusion and slab roll-back can occur simultaneously along orogens as a consequence of different rates of convergence. Such along-strike variability accross the orogen can lead to migration of deformation from partly detached slab to the still active oceanic or continental subduction. These conditions create slab tearing often followed by rotation, rapid roll-back of the attached slab and/or exhumation of previously buried crust in the upper plate above the already detached slab. The main mechanism that explains transition from slabs with contrasting kinematics to the crustal level strain partitioning is still not fully understood.

One very good example of strain partitioning associated with indentation, slab-detachment and slab-tearing is the junction between the Dinarides and Hellenides in southeastern Europe. Following the Jurassic – Eocene closure of the Neotethys Ocean and subsequent Adria – Europe collision, the Dinarides - Hellenides orogen has recorded a significant extensional deformation. This extension was driven by the Oligocene – early Miocene slab detachment of the Dinarides slab, while the Hellenides segment continued its evolution until the present day.

We have performed a field kinematic and structural study in the less understood area of Montenegro near Dinarides - Hellenides transition to determine the influence of Oligocene – early Miocene deformation on Dinarides composite nappes. The results imply that Oligocene – early Miocene slab detachment followed by slab tearing was accommodated in crustal domain by bi-directional extension associated with the exhumation of mid-crustal levels in the footwall of both orogen-parallel and orogen-perpendicular faults, reactivation of inherited Cretaceous-Paleogene nappe contacts and formation of extensional klippen.

How to cite: Randjelovic, N., Matenco, L., Maleš, M., Krstekanic, N., Stojadinovic, U., Trivić, B., and Toljić, M.: Towards understanding the crustal response of slab tearing and detachment: inferences from the Dinarides-Hellenides transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7378, https://doi.org/10.5194/egusphere-egu23-7378, 2023.

X2.139
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EGU23-8253
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ECS
Zimu Wu, Ling Chen, Haiqiang Lan, Morteza Talebian, Xu Wang, Yifan Gao, Jianyong Zhang, Yinshuang Ai, Mingming Jiang, and Yingjie Yang

The Makran subduction zone (MSZ) is located in between the Zagros mountain belt to the west and Himalayan orogen to the east, forming a transition from oceanic subduction to continental collision on both sides along the Tethyan orogenic belt. The Arabian oceanic plate, a narrow remnant of the Neotethys ocean, is subducting northward beneath the Eurasian plate in Makran. Such a unique tectonic setting makes the MSZ an ideal place to investigate the geodynamic processes in response to subduction-collision transition. Since most of the Neotethys has already dived into the deep mantle and the associated geological records are not always well preserved due to the strong collision, the MSZ also provides a special opportunity to explore the evolution history of the Neotethys in a more direct way.

To better understand the deep dynamics of the subduction-collision transition and evolution of the Neotethys, we investigated the lithospheric structure, especially the depth variation of the lithosphere-asthenosphere boundary (LAB), across the Iranian MSZ by S-wave receiver function (SRF) imaging. The teleseismic data used were acquired from 67 broadband stations that were operational from March 2017 to September 2018 in southeastern Iran. This temporary array constitutes the third phase of seismic observations under the “China-Iran Geological and Geophysical Survey in the Iranian Plateau” project.

Our SRF migration images show clear structural variations of both the upper and lower plates in the MSZ. In the upper plate in the southeastern Iranian plateau, we image a thin lithosphere (70-90 km) with monotonic decrease in LAB depth from the plateau interior to the arc region. This arc-ward thinning is probably caused by the focused thermal and chemical erosion at the LAB by arc magmatism. The LAB of the subducting slab is imaged at ~110-90 km depth near the coast but with an unexpected ~20-km deepening along the trench-parallel direction. Assuming a 25-km-thick accretionary wedge (deduced from active-source data), the observed ~85-65-km-thick slab is consistent with the thermal predictions for a mature oceanic lithosphere. However, the trench-parallel LAB step can hardly be explained by the age difference of the Neotethys but may be a result of the Cretaceous plate-mantle plume interaction. The plume-modified slab could be characterized by low density and high viscosity, and thus play an important role in forming low-angle (<10°) subduction beneath the present-day Makran fore-arc region. Our results also suggest that the thin overriding lithosphere is a persistent feature in both the MSZ and the neighboring continental collision/subduction zone, which favors the idea that the vertical-axis rotation and possible convective thinning dominate the evolution of central-east Iranian microblocks during the late Cenozoic. In addition, we detect an east-dipping structure at 70-90 km depth beneath the Zagros-Makran border, perhaps indicating a relatively sharp contact relationship between the oceanic and continental portions of the Arabian plate. These new observations imply a much more complex tectonic evolution than previously envisaged in the MSZ and adjacent subduction-collision transitional area, which deserves future studies to understand the continuous process from Neotethys subduction to continental collision.

 

How to cite: Wu, Z., Chen, L., Lan, H., Talebian, M., Wang, X., Gao, Y., Zhang, J., Ai, Y., Jiang, M., and Yang, Y.: Seismic imaging of the lithospheric structures in the Iranian Makran subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8253, https://doi.org/10.5194/egusphere-egu23-8253, 2023.

X2.140
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EGU23-13519
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ECS
Luuk van Agtmaal, Attila Balazs, Dave May, and Taras Gerya

Geological and geophysical observations have highlighted the multi-stage deformation history of the continental lithosphere. Such inherited heterogeneities, observed from microscopic to kilometre-scales, lead to important mechanical weakening for the subsequent development of orogens. This strain-weakening may be frictional (fault gauge, filled veins), ductile (banding, recrystallisation, etc) or caused by changes in grain-size, and largely determines the response of the lithosphere to stresses (Bercovici & Ricard, 2014). Representing the microstructural weakening mechanisms with the relatively low resolution of regional and global numerical modelling studies has been a longstanding challenge. Mechanisms are often grouped into an “effective” plastic strain weakening implementation, where the frictional strength decreases with increasing accumulated strain. Alternatively, materials can be modelled to weaken depending on the local strain-rate (Ruh et al., 2014), which is characteristic for e.g. coseismic frictional weakening of faults. Here we show key differences of strain- vs. strain-rate-dependent faults weakening in terms of orogenic strain propagation patterns in numerical models of a corner collision setting, based on the eastern corner of the India-Eurasia collision. The numerical model I3ELVIS (Gerya & Yuen, 2007) consists of a finite-difference, marker-in-cell method coupled to a diffusion-advection-based finite-difference surface process model, FDSPM (Munch et al., 2022). We highlight key differences between the results of a model with strain-rate-dependent weakening, and a model with conventional strain-dependent weakening based on accumulated strain. The former shows significantly sharper shear zones, as well as a higher number of thrust faults that are relatively evenly spaced, which is more realistic in natural collision zones. 

 

Gerya, T. V., & Yuen, D. A. (2007). Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Physics of the Earth and Planetary Interiors, 163(1), 83–105. https://doi.org/10.1016/j.pepi.2007.04.015

Bercovici, D., & Ricard, Y. (2014). Plate tectonics, damage and inheritance. Nature, 508(7497), 513–516. https://doi.org/10.1038/nature13072

Ruh, J. B., Gerya, T., & Burg, J.-P. (2014). 3D effects of strain vs. Velocity weakening on deformation patterns in accretionary wedges. Tectonophysics, 615–616, 122–141. https://doi.org/10.1016/j.tecto.2014.01.003

Munch, J., Ueda, K., Schnydrig, S., May, D. A., & Gerya, T. V. (2022). Contrasting influence of sediments vs surface processes on retreating subduction zones dynamics. Tectonophysics, 836, 229410. https://doi.org/10.1016/j.tecto.2022.229410

 

How to cite: van Agtmaal, L., Balazs, A., May, D., and Gerya, T.: Effects of strain- vs. strain-rate-dependent faults weakening for continental corner collision: insight from 3D thermomechanical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13519, https://doi.org/10.5194/egusphere-egu23-13519, 2023.

X2.141
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EGU23-14406
Jonas Kley, Edward R. Sobel, Thomas Voigt, Johannes Rembe, and Rasmus Thiede

The south-dipping Benioff zone beneath the Pamir mountains marks the youngest, active slab accommodating India-Asia convergence near the western edge of the Indian indenter (75° E). Seismic tomography suggests the existence of two older slabs farther south, both interpreted as Indian lithosphere detached and sinking: the Tethys slab, broken off around 46 Ma concomitant with early collision and the more northerly and shallower Indian slab, detached around 25 Ma at the longitude considered here (Replumaz et al. 2010). The total length of the three slabs is about 1300 km (Tethys 600 km, India 300 km, Pamir 400 km), substantially less than the distance of more than 2000 km that India has moved north since 46 Ma. This discrepancy implies that either the tomographic record of subduction is incomplete or that Indian mantle lithosphere has underthrust (thin?) Asian lithosphere, with the stacked lithospheres unresolvable by tomography. As a consequence, the rate of slab lengthening and the age of slab initiation in the Pamir are poorly constrained. The absence of asthenosphere between the Pamir slab of Asian provenance and supposedly Indian mantle lithosphere above it suggests that India´s leading edge is advancing at the same rate as rollback of the Pamir slab. This rate could be as high as full India-Asia convergence at ca. 35 mm/yr (Kufner et al. 2016) or as low as present-day Pamir-foreland convergence at 15 mm/yr, corresponding to ages of the 300-400 km long slab of 9-12 Ma or 20-27 Ma. The wide range of possible ages makes it difficult to tie slab initiation to specific geologic events during the Pamir orogeny. Other evidence suggests that the direction and rate of India-Asia convergence may be poor predictors of mantle lithospheric motion above the slab: The shortening direction in the Tajik foreland thrust belt is WNW, and foreland shortening decreases northeastward from a maximum of 150 km in the Tajik belt to 75 and 30 km in the Alai Valley and westernmost Tarim. Slab length follows a similar trend, with a steeply east-dipping Benioff zone in the west and a more gently south-dipping one in the north, traced by earthquakes to depths of 250 km and 150 km, respectively. Also, the longest, NE-striking segment of the slab is relatively straight in map view and parallel to the axis of thickest crust (Schneider et al. 2019). These observations are difficult to reconcile with northward convergence. Instead, they suggest overall northwestward convergence during the Pamir orogeny. We speculate that this could be due to westward deflection at depth of an Indian lithosphere promontory interacting with the NW-trending edge of thick Tarim lithosphere.

Kufner, S.-K., et al. (2016). Deep India meets deep Asia: Lithospheric indentation, delamination and break-off under Pamir and Hindu Kush (Central Asia). Earth and Planetary Science Letters 435: 171-184.

Replumaz, A., et al. (2010). Indian continental subduction and slab break-off during Tertiary collision. Terra Nova 22: 290-296.

Schneider, F. M., et al. (2019). The Crust in the Pamir: Insights from Receiver Functions. Journal of Geophysical Research: Solid Earth 124(8): 9313-9331.

How to cite: Kley, J., Sobel, E. R., Voigt, T., Rembe, J., and Thiede, R.: Kinematics of the Pamir orogeny on a lithospheric scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14406, https://doi.org/10.5194/egusphere-egu23-14406, 2023.

Posters virtual: Fri, 28 Apr, 08:30–10:15 | vHall GMPV/G/GD/SM

Chairpersons: Nalan Lom, Johannes Rembe, Chengfa Lin
vGGGS.18
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EGU23-3961
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ECS
Shaghayegh Shafiee, Shojaeddin Niroomand, and Majid Soleymani

Epithermal base and precious veins are typically structurally controlled, and structures are fundamental to fluid flow and mineralization in hydrothermal deposits. In recent mineral explorations in east Kerman, especially in the northeast of the Shahr-e Babak area, it was found that structures play a key role in the mineralization of epithermal gold deposits. Shahr-e Babak epithermal gold deposit is located at 30°27'54.80'' N, 54°31'47'' E in the southeast of the Sanandaj Sirjan Zone, east of Kerman. The lithological outcrops of the Shahr-e Babak deposit area consist of Cretaceous felsic to mafic intrusive and extrusive rocks, Eocene micrite limestone and sandstone intruded by hornblende diorite, granodiorite, and microgranite stocks and dykes. Gold mineralization with an average grade of 1.5 g/t, is associated with anomalous Ag, Mo, Pb, and Sb and is usually concentrated in jasperoids with argillic and silicification alteration halos which are < 120 m in length and average about 10 m in width within east-west trending structures.  

The Shahr-e Babak deposit area is located in a restraining bend of the Shahr-e Babak fault. There is a strike-slip duplex and E-W trending fault lens with an approximate 5×7 kilometers area related to the young movements of the Shahr-e Babak fault. For these reasons, the rocks in the deposit area have been ruptured and crushed which are not associated with extensive hydrothermal alterations. According to measurements, faults can be divided into three main groups. The first group is the main faults with 80–90-degree trending, the second group consists of faults with 100–120-degree trending and the last category is minor faults with NE-SW and NW-SE trending. A combination of field observations, measurements of faults and fractures, and drill core logging indicates that gold-bearing jasperoids are formed along strike-slip faults with a 100–120-degree trend in lens-shaped fault zones that change in thickness with depth. 

The recent discovery of the Shahr-e Babak epithermal gold deposit, located on a restraining bend of the Shahr-e Babak fault, highlights the exploration potential for epithermal gold mineralization in East Kerman. In addition, undiscoverable epithermal gold deposits may be hidden below the regionally extensive Quaternary cover.

How to cite: Shafiee, S., Niroomand, S., and Soleymani, M.: Identifying the Role of Structures in the Mineralization of Shahr-e Babak Epithermal Gold Deposit: Implications for Epithermal Gold Exploration in East Kerman, Southeastern Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3961, https://doi.org/10.5194/egusphere-egu23-3961, 2023.

vGGGS.19
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EGU23-66
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ECS
Hai Zhou, Guochun Zhao, Yigui Han, Donghai Zhang, and Xianzhi Pei

During Carboniferous time, tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt (CAOB), although its origin remains unclear. Our work presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia. These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons, probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north, indicative of a continental arc nature. In addition, they have a main zircon U-Pb age of ca. 370–330 Ma, positive Hf and Nd isotopes, and mafic-intermediate arc affinity, similar to the coeval arc magmatism. Moreover, the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time (ca. 350–370 Ma; Visean and Bashkirian stages) earlier than that in the southern area (mainly ca. 350–315 Ma; Serpukhovian and Bashkirian stages). Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean (PAO) during Carboniferous and Triassic times, we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback. Thus, the juvenile arc volcanism of Mongolia, together with other areas (e.g., Junggar) in the southern CAOB, represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO. This research was financially supported NSFC Project (42102260, 41890831, 42072267, and 41972229), Hong Kong RGC GRF (17307918), and HKU Internal Grants for Member of Chinese Academy of Sciences (102009906) and for Distinguished Research Achievement Award (102010100).

How to cite: Zhou, H., Zhao, G., Han, Y., Zhang, D., and Pei, X.: The time and geodynamics for the final large-scale lateral accretion of the southern Central Asian Orogenic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-66, https://doi.org/10.5194/egusphere-egu23-66, 2023.

vGGGS.20
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EGU23-5946
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ECS
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Mingye Feng, Ling Chen, Shengji Wei, Xin Wang, Xu Wang, and Zimu Wu

Geometry and structure of the subducting plate boundary are key to understanding geodynamic processes of subduction and related geological phenomena. Located between the obliquely converging Indo-Australian and Sunda plates, the Sumatran subduction zone is featured by a strongly deformed slab coupling with the overlying plate, and complicated slab-mantle interactions, leading to frequent occurrence of great megathrust earthquakes (e.g., 2004 Mw9.2 and 2005 Mw8.7 events) and extremely intensive magmatism (e.g., Toba supervolcano). Previous seismic studies reveal a rugged slab surface with seamounts, and slab folding and tearing beneath Sumatra, both of which govern the features of earthquake rupture and magma generation associated with fluid release and mantle wedge hydration. However, the details of the slab geometry (e.g., along-strike variation of dip direction and dip angle) and the “slab dehydration-mantle hydration” process across the subducting plate boundary remain poorly known, due to limited data coverage and resolution of these studies.

To better reveal the geometry of the slab and the feature of “slab dehydration-mantle hydration” during the oblique subduction, in this study, we develop a Dip Direction Searching (DDS) method to constrain the dipping structure of slab and the nature of the slab upper boundary. In this method, we estimate dip directions of velocity discontinuities by grid search based on the back azimuthal variation of radial receiver functions (RFs). DDS is a single-station-based method thus applicable in the areas with sparse seismic instruments. Synthetic tests demonstrate that the DDS method has higher resolution (with uncertainty of several degrees) in dip direction estimation than traditional RF analysis approaches and is applicable to the cases with strong white noise contamination, incomplete/uneven back azimuthal coverage, <5%-10% crustal and mantle anisotropy, and their compound effects. The method also provides constraints on the thickness and depths of dipping layers.

Applying the DDS method, we find a dipping Low Velocity Layer (LVL) commonly beneath the forearc areas and constrain its depths, thickness, and dip directions. The depth and dip direction estimates are highly consistent with the Slab2 model, indicating that the LVL is at the subducting plate boundary. We interpret the lower boundary of the LVL as the subducting oceanic Moho, which is less deformed so its dip direction can represent the dip direction of the whole slab. The slab dip direction gradually increases from 47±5.3˚ in southern Sumatra to 70±10.7˚ in northern Sumatra, indicating an along-strike bending of slab, which is possibly related to the oblique subduction. We find that the dip directions at the upper and lower boundaries of the LVL differ up to 23˚ beneath central Sumatra, indicating the two boundaries are locally unparallel. The thickness of the LVL is estimated to be 10-14 km, larger than those of regular oceanic crusts (~7 km). These observations imply that the LVL is composed by not only the oceanic crust but also a low-velocity serpentinized mantle layer at the top. Therefore, the upper boundary of the LVL represents the serpentinization front, indicating a diffuse plate boundary.

How to cite: Feng, M., Chen, L., Wei, S., Wang, X., Wang, X., and Wu, Z.: Slab geometry and a diffuse plate boundary beneath Sumatra: constrained using a new receiver function analysis method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5946, https://doi.org/10.5194/egusphere-egu23-5946, 2023.

vGGGS.21
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EGU23-8755
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ECS
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Mehmet Çam, İlkay Kuşcu, Nuretdin Kaymakcı, and Mehtap Karcı

Kirazlı porphyry Cu-Au and epitermal Au mineralization is located in Biga peninsula where the region hosts numerious porphyry- and epithermal- style Au mineralizations within the Tethyan orogenic belt. Crustal deformation in the region is resulted by Cretaceous collusion during the closure of northern branch of Neotethys Ocean, related subduction, post-collusion, Cenozoic extension and following dextral strike-slip deformation regime which is emerged during the westward migration of Anatolian plate. The study includes regional fault mapping, slip data collection from regonal and district scale faults for paleostress analysis, oriented surface sampling of vein hosted deformational zones and micro-structural thin section examinations of oriented samples. Paleostress findings and fault orientations indicates two seperate character of deformations as nearly E-W trending extensional fault systems and subsequent NE-SW striking, steeply dipping dextral strike-slip faults with accompanying NNW-SSE trending left-lateral strike slip and ENE-WSW trending dextral strike-slip and oblique-slip faults. Later tectonic phase related with N-E Dextral strike-slip faults establishes the main deformational trend with accompanying district scale  R (synthetic) ENE-WSW trending dextral and NNW-SSE trending R' (antithetic) sinistral strike-slip faults. Slip data related to  E-W and ENE-WSW faults indicate that these faults are subjected to both N-S trending extensional and NE-SW trending dextral strike-slip tectonic regime. The petrographic and textural studies of oriented thin sections resulted in identification of two predominant vein directions as ENE-WSW and NNW-SSE of porphyry mineralization within the project area. ENE-WSW trending syntaxial, streched-blocky quartz bearing veins indicates multiple N-S extension and crack-seal events and postdated by NNW-SSE trending quartz veins. Also the veins with same orientation which were observed during field studies share similar orientations.

This study presents the early results off Ph.D. thesis "Crustal Extension and its Relationship to Porphyry Cu-Au and Epithermal Au Mineralization in the Kirazlı Gold Deposit (Çan, Çanakkale, Türkiye)" and supported by Alamos Gold Inc..

How to cite: Çam, M., Kuşcu, İ., Kaymakcı, N., and Karcı, M.: Crustal Deformation of Biga Peninsula and Structural Controls on Porphyry Cu-Au and Epitermal Au Mineralization in Kirazlı Gold Deposit (Türkiye), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8755, https://doi.org/10.5194/egusphere-egu23-8755, 2023.

vGGGS.22
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EGU23-6117
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ECS
hongxin xing

Abstract:

The development of faults governs the kinematics of continental deformation. The Songliao Basin, located at the central part of late Mesozoic lithospheric thinning province in East Asian region, experienced intense rifting during Early Cretaceous epoch and formed an intricate syn-rift fault system. However, the geometric and kinematic relationships inherent in the fault system have not yet been satisfactorily explained, hampering the understanding of basin formation and related marginal plate tectonic processes. Here, theories for polymodal faulting were applied to evaluate the faulting evolution of the Songliao Basin, based on which a quantitively deformation reconstruction was developed. Our reconstruction shows that the basin formation during the syn-rifting period was subdivided into three main stages: late Valanginian–Barremian(133-118.2Ma) initiation of extension, Aptian(118.2-113.9M) extension climax, and Albian(113.9-100.5Ma) extension wanning and initiation of post-extensional subsidence. The deformation of the Songliao Basin is spatially heterogeneous. Faulting analyses revealed a three-dimensional strain filed with a dominating horizontal ESE-WNW extension, a minor horizontal near N-S extension, and a large vertical shortening in the Northern Songliao Basin (NSL). The 3-D non-plane strain with non-zero intermediated extension(ε2) magnitude controlled the synchronous displacement of a NNE–SSW-striking fault set and a NNW–SSE-striking fault set in orthorhombic pattern to create the characteristic rhomboidal fault geometry. Whereas, the Southern Songliao Basin (SSL) deformed under a 2-D plane strain filed with a horizontal ESE-WNW extension and vertical shortening. The plane strain condition is interpreted as a special case with no intermediated strain(ε2), and produces a pair of near N-S-striking fault sets in conjugate symmetry. Our results illustrate that this particular three-dimensional deformation result in the intricate fault system in the Songliao Basin and that the fault geometry is controlled by the ratios of the principal strains, especially the relative magnitude of the intermediate strain. We argue that the three-dimensional strain field in the NSL reflected the trench retreat in the Paleo-Pacific subduction zone and the gravitational collapse of the thickened lithosphere, and that the extension of the SSL is merely the consequence of the trench retreat.

Keywords:

Songliao Basin, three-dimensional strain, orthorhombic fault, syn-rift deformation, quantitative reconstruction

How to cite: xing, H.: Late Mesozoic rift evolution and deformation reconstruction of the Songliao Basin, northeastern China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6117, https://doi.org/10.5194/egusphere-egu23-6117, 2023.

vGGGS.23
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EGU23-14244
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ECS
Jovid Aminov, Denis Mikhailenko, Sharifjon Odinaev, Mohssen Moazzen, Guillaume Dupont-Nivet, Yunus Mamadjanov, Aleksandr Stepanov, Jovid Yogibekov, and Sohibnazar Ashuraliev

The Pamir orogen, the western extension of the Tibetan plateau, formed and uplifted due to Mesozoic terrane amalgamation and Cenozoic India-Asia collision. The Mesozoic history of the amalgamation of Gondwana-derived Cimmerian terranes to the southern margin of Eurasia that produced the crust of the Pamirs is poorly understood. The birth and demise of an oceanic basin that divided Central and Southern Pamir in the early Mesozoic is an example of a gap in the knowledge of Pamir orogen formation throughout the Mesozoic and Cenozoic eras. Termed Mesotethys, this ocean likely originated in the early Permian when the Cimmerian super-terrane broke from Gondwana's northern limit. Geochemistry of early Permian basalts suggests this rifting event was driven by a plume that generated a seamount or series of seamounts that accreted to the Central Pamir before the Mesotethys closed in the late Triassic. Vestiges of the Mesotethys are preserved in the Rushan - Pshart suture zone.   This zone comprises Permian and Triassic marine sedimentary strata and thick layers of volcanic rocks, including the late Triassic basalts. This volcano-sedimentary sequence is intruded by the late Triassic – early Jurassic granites that have subduction-related affinity marking the closure of the Mesotethys. The current work focuses on the geochemical markers of late Triassic volcanism to evaluate whether a plume-related magmatic activity was responsible for the creation of the Mesotethys Ocean.

Our preliminary geochemical results indicate that the SiO2 content of basalts is low, ranging from 36.5 to 47.7 wt.%, which classifies the rocks as mafic and ultramafic. The rocks' TiO2 concentration is exceptionally high, ranging from 1.9 to 4.4 wt.%, which is not typical of arc-related basalts and instead resembles oceanic island basalts. Concentration of Al2O3 (7.5-18.8 wt.%), Fe2O3 (8.3-16.3 wt.%), MgO (2.7 – 14.9 wt.%) and CaO (2.5 – 12.4 wt.%) likewise fluctuate in a large range. Alkalis also vary across a wide range (K2O: 0.2 – 3.1 wt.%; Na2O: 1.4 – 5.5 wt.%) and add up to values (1.7 – 7 wt.%) that define the majority of the examined samples (11) as alkali basalts, with three samples plotting below the sub-alkaline – alkaline dividing line. The rocks' relatively high P2O5 (0.2 to 0.6 wt.%) may further reflect their OIB affinity. Normalized to the primitive mantle, trace element patterns on spidergrams reveal a small enrichment of Large-Ion Lithophile Elements and depletion of High-Field Strength Elements. However, positive anomalies in Nb (14.3 – 29 ppm) and Ti rule out subduction as the cause of the rocks' formation. Moreover, high ratios of Nb/La (1.1–1.7) and La/Yb (6.9–15) also support the non-subductional origin of the basalts. Thus, our collected geochemical data reveal a striking similarity to the basalts of oceanic islands.

 

How to cite: Aminov, J., Mikhailenko, D., Odinaev, S., Moazzen, M., Dupont-Nivet, G., Mamadjanov, Y., Stepanov, A., Yogibekov, J., and Ashuraliev, S.: The birth of the Mesotethys ocean recorded in the Southern Pamir Triassic basalts , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14244, https://doi.org/10.5194/egusphere-egu23-14244, 2023.

vGGGS.24
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EGU23-14762
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ECS
Huseyin Kocaturk, Mustafa Kumral, Ali Tugcan Unluer, Mustafa Kaya, Merve Sutcu, Zeynep Doner, Huseyin Sendir, and Amr Abdelnasser

Magmatic Suite around Uludag Massif contains some alkaline (A-type or highly fractionated felsic I-type) granites that developed in post-collisional plate tectonic conditions. Their genesis involved by Eocene calc-alkaline and Oligocene strongly peraluminous granite magmatism. Their emplacement is linked to strike-slip shear movements and/or extension that occur after the Neo-Tethys collisional events. These granites are spatially related to the Izmir-Ankara Suture Zone (IASZ). The majority of these alkaline granites are formed by middle or lower crustal anatexis, extracted melt restite of I-type granites. Previously non-melted mafic meta-tonalites are considered to represent their source rocks. The mechanism for the required high melting temperatures will be well explained by our new model. However, models based on partial delamination of the base of the lithosphere or asthenospheric upwelling due to steepening and breaking of the subducted Tethyan oceanic slab are still consistent. As is the case for many well-known post-collisional regimes, transpressional to transtensional and/or moderately extensional tectonism predominates throughout to region. Although crustal thickening does not appear evident as in the notable arcs and microcontinent collisions, uplifting of particular regions associated with post-collisional calc-alkaline granite emplacement is observable. Understanding the nature of post-collisional highly fractionated granites around Uludag will extend the view of how Western Anatolia was affected by Alpine Orogeny in the Tethyan Realm. The challenge is drawing the geochemistry line for the tectono-magmatic setting between post-collision to post-orogenic. Describing the nature of alkaline magmatism through late-stage orogeny to intra-plate setting may need to be more precise because of trace elements' overprinting. However, a holistic view of the magmatism and source rocks points out a synchronous crustal growth and crustal rework. Our new possible geodynamic scenario suggests crust–mantle decoupling combined with slab retreat results in thinning of the lithospheric mantle. The 75-80 km decoupling depth calculated from obducted blueschists of Tavsanlı Zone confirms the plate motions controlled thermal relaxation temperature is enough at the base of the lithosphere for the geotherm-induced magma generation for the Tavsanlı Zone.

How to cite: Kocaturk, H., Kumral, M., Unluer, A. T., Kaya, M., Sutcu, M., Doner, Z., Sendir, H., and Abdelnasser, A.: Understanding Magma Nature of Post-Collisional Alkaline Granites Around Uludag (NW, Turkiye): Implications for New Geodynamic Scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14762, https://doi.org/10.5194/egusphere-egu23-14762, 2023.

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EGU23-17000
Ruibao Li, Xianzhi Pei, Zuochen Li, Lei Pei, Guochao Chen, Zhanqing Liu, Youxin Chen, Chengjun Liu, and Meng Wang

The East Kunlun Orogen on the northern margin of the Tethyan orogenic system records a history of Gondwana dispersal and Laurasian accretion. Based on a synthesis of sedimentary, structural, lithological, geochemical, and geochronological data from the East Kunlun Orogen and adjacent regions, we discusses the spreading and northward consumption of the Paleo-Tethys Ocean during Late Paleozoic-Early Mesozoic times. The main evolutionary stages are: (1) During Carboniferous to Middle Permian, the Paleo-Tethys Ocean (Buqingshan Ocean) was in an ocean spreading stage, as suggested by the occurrence of Carboniferous MORB-, and OIB-type oceanic units and Carboniferous to Middle Permian Passive continental margin deposits; (2) The Buqingshan Ocean subducted northward beneath the East Kunlun Terrane, leading to the development of a large continental magmatic arc (Burhan Budai arc) and forearc basin between ~270-240 Ma; (3) During the late Middle Triassic to early Late Triassic (ca. 240-230 Ma), the Qiangtang terrane collided with the East Kunlun-Qaidam terranes, leading to the final closure of the Buqingshan Ocean and occurrences of minor collision-type magmatism and potentially inception of the Bayan Har foreland basin; (4) Finally, the East Kunlun Orogen evolved into a postcollisional stage and produced major magmatic flare-ups and polymetallic mineral deposits between Late Triassic to Early Jurassic (ca. 230-200 Ma), which is possibly related to asthenospheric mantle upwelling induced by delamination of thickened continental lithosphere and partial melting of the lower crust. Accordingly, we propose that the Wilson cycle-like processes controlled the Late Paleozoic-Early Triassic tectonic evolution of East Kunlun, which provides significant implications for the evolution of Paleo-Tethys Ocean.

How to cite: Li, R., Pei, X., Li, Z., Pei, L., Chen, G., Liu, Z., Chen, Y., Liu, C., and Wang, M.: Paleo-Tethyan ocean evolution in the East Kunlun Orogen, northern Tibetan plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17000, https://doi.org/10.5194/egusphere-egu23-17000, 2023.