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1. Accommodation of India–Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold–thrust belt, northern margin of the Tibetan Plateau

   https://doi.org/10.1144/jgs2020-207  

   Cheng, Feng; Zuza, Andrew V.; Haproff, Peter J.; Wu, Chen; Neudorf, Christina; Chang, Hong; Li, Xiangzhong; Li, Bing (April 2021, Journal of the Geological Society)

   null (Ed.)

   Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a −1 , which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent. Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MN Thematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts 

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2. Connecting subduction, extension and shear localization across the Aegean Sea and Anatolia

   https://doi.org/10.1093/gji/ggab078  

   Barbot, S; Weiss, J R (May 2021, Geophysical Journal International)

   null (Ed.)

   SUMMARY The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geological structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north–south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa–Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm yr–1 in a largely trench-normal direction except near eastern Crete where variably oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy–Pliny–Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation. 

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3. Seismicity and Present‐Day Crustal Deformation in the Southern Puna Plateau

   https://doi.org/10.1029/2024JB028918  

   Mahanti, Sankha_Subhra; Kiser, Eric; Beck, Susan; Hughes, Amanda (December 2024, Journal of Geophysical Research: Solid Earth)

   Abstract The Southern Puna plateau in the central Andes has a complicated tectonic history that includes episodes of distributed shortening and extension, lithospheric delamination, uplift and Quaternary backarc volcanism. In this study, the upper crustal structure and present‐day deformation in this area is investigated using a new regional earthquake catalog derived with a deep‐learning‐based phase picker. Results show abundant strike‐slip seismicity at shallow depths in the eastern Southern Puna plateau that reveals active fault systems in the area and indicates N‐S extension/E‐W compression that changes orientation and relative magnitude from north to south. A broad zone of seismic quiescence in the western plateau may indicate a zone of upper crustal decoupling from large‐scale deformation. The region separating the western and eastern plateau exhibits a complex stress field that can be related to the boundary of east/west oriented middle‐to‐lower crustal flow in the main volcanic arc. Southeast of the plateau in the Sierras Pampeanas, crustal seismicity deepens and is dominated by conjugate reverse faulting structures associated with the direction of plate convergence. Vp and Vs seismic velocity models of the upper crust obtained through local earthquake tomography with the improved seismic catalog show low‐velocity anomalies near intermontane basins, except in the Antofagasta basin where a high‐velocity anomaly possibly represents shallow intrusive component of Quaternary basaltic volcanism. Below the Cerro Galan caldera, an upper crustal 10‐day long earthquake swarm is observed which may indicate local stress perturbations from fluids at the top of the crustal magmatic system that feeds this volcano. 

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4. Heterogenous late Miocene extension in the northern Walker Lane (California-Nevada, USA) demonstrates vertically decoupled crustal extension

   https://doi.org/10.1130/GES02409.1  

   Say, Michael C.; Zuza, Andrew V. (September 2021, Geosphere)

   Abstract The spatial distribution and kinematics of intracontinental deformation provide insight into the dominant mode of continental tectonics: rigid-body motion versus continuum flow. The discrete San Andreas fault defines the western North America plate boundary, but transtensional deformation is distributed hundreds of kilometers eastward across the Walker Lane–Basin and Range provinces. In particular, distributed Basin and Range extension has been encroaching westward onto the relatively stable Sierra Nevada block since the Miocene, but the timing and style of distributed deformation overprinting the stable Sierra Nevada crust remains poorly resolved. Here we bracket the timing, magnitude, and kinematics of overprinting Walker Lane and Basin and Range deformation in the Pine Nut Mountains, Nevada (USA), which are the westernmost structural and topographic expression of the Basin and Range, with new geologic mapping and 40Ar/39Ar geochronology. Structural mapping suggests that north-striking normal faults developed during the initiation of Basin and Range extension and were later reactivated as northeast-striking oblique-slip faults following the onset of Walker Lane transtensional deformation. Conformable volcanic and sedimentary rocks, with new ages spanning ca. 14.2 Ma to 6.8 Ma, were tilted 30°–36° northwest by east-dipping normal faults. This relationship demonstrates that dip-slip deformation initiated after ca. 6.8 Ma. A retrodeformed cross section across the range suggests that the range experienced 14% extension. Subsequently, Walker Lane transtension initiated, and clockwise rotation of the Carson domain may have been accommodated by northeast-striking left-slip faults. Our work better defines strain patterns at the western extent of the Basin and Range province across an approximately 150-km-long east-west transect that reveals domains of low strain (∼15%) in the Carson Range–Pine Nut Mountains and Gillis Range surrounding high-magnitude extension (∼150%–180%) in the Singatse and Wassuk Ranges. There is no evidence for irregular crustal thickness variations across this same transect—either in the Mesozoic, prior to extension, or today—which suggests that strain must be accommodated differently at decoupled crustal levels to result in smooth, homogenous crustal thickness values despite the significantly heterogeneous extensional evolution. This example across an ∼150 km transect demonstrates that the use of upper-crust extension estimates to constrain pre-extension crustal thickness, assuming pure shear as commonly done for the Mesozoic Nevadaplano orogenic plateau, may not be reliable. 

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5. Permian plume-strengthened Tarim lithosphere controls the Cenozoic deformation pattern of the Himalayan-Tibetan orogen

   https://doi.org/10.1130/G47961.1  

   Xu, Xi; Zuza, Andrew V.; Yin, An; Lin, Xiubin; Chen, Hanlin; Yang, Shufeng (September 2020, Geology)

   null (Ed.)

   Abstract The high strength of the Tarim Basin (northwestern China) lithosphere, widely regarded as a Precambrian craton, is evidenced by its resistance to Cenozoic deformation in the Himalayan-Tibetan orogen. However, Neoproterozoic suturing and early Paleozoic shortening within the Tarim Basin suggest that its rigidity is a relatively recent phenomenon with unknown cause. We reprocessed high-resolution magnetic data that show a 300–400-km-diameter radial pattern of linear anomalies emanating from a central region characterized by mixed positive-negative anomalies. We suggest that this pattern was generated by the previously hypothesized Permian (ca. 300–270 Ma) plume beneath the Tarim Basin. Constrained by published geochemical and geochronological data from plume-related igneous rocks, we propose that the ∼30 m.y. Permian plume activity resulted in a more viscous, depleted, thicker, dehydrated, and low-density mantle lithosphere. The resulting stronger lithosphere deflected strain from the Cenozoic India-Asia convergence around Tarim Basin, including Pamir overthrusting to the northwest and Altyn Tagh left-slip displacement to the northeast, thus shaping the geometry of the Himalayan-Tibetan orogen. 

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