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Unravelling early Cenozoic basin development in northern Tibetan Plateau remains crucial to understanding continental deformation mechanisms and to assessing models of plateau growth. We target coarse‐grained red beds from the Cenozoic basal Lulehe Formation in the Qaidam basin by combining conglomerate clast compositions, paleocurrent determinations, sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology to characterize sediment provenance and the relationship between deformation and deposition. The red beds are dominated by matrix‐supported, poorly sorted clastic rocks, implying low compositional and textural maturity and short transport distances. Although most sandstones have high (meta)sedimentary lithic fragment contents and abundant heavy minerals of metamorphic origin (e.g., garnet, epidote and chlorite), spatiotemporal differences in detrital compositions are evident. Detrital zircon grains mainly have Phanerozoic ages (210–280 Ma and 390–480 Ma), but Proterozoic ages (750–1000 Ma, 1700–2000 Ma and 2300–2500 Ma) are also prominent in some samples. Analysed strata display dissimilar (including south‐, north‐ and west‐directed) paleocurrent orientations. These results demonstrate that the Cenozoic basal deposits were derived from localized, spatially diverse sources with small drainage networks. We advocate that initial sedimentary filling in the northern Qaidam basin was fed by parent‐rocks from the North Qaidam‐South Qilian belts and the pre‐Cenozoic basement within the Qaidam terrane interior, rather than southern distant Eastern Kunlun regions. Seismic and drilling well stratigraphic data indicate the presence of paleohighs and syn‐sedimentary reverse faults and noteworthy diversity in sediment thickness of the Lulehe Formation, revealing that the Qaidam terrane exhibited as several isolated depocenters, rather than a coherent basin, in the early stage of the Cenozoic deposition. We suggest the Cenozoic Qaidam basin to have developed in a contractional deformation regime, which supports models with synchronous deformation throughout most of Tibet shortly after the India‐Eurasia collision. [ABSTRACT FROM AUTHOR]

We used an updated data set of 192 GPS-derived surface velocities and 393 earthquake focal mechanisms (Mw > 3.0, hypocenter depths < 30 km) to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the Pamir Plateau and its surrounding regions. The strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional-scale stress inversion (DRSSI) method of Hardebeck and Michael (Journal of Geophysical Research, 10.1029/2005jb004144, 2006). The results show that the crustal stress field around the Pamir Plateau is predominantly characterized by NNW-SSE compression and E-W extension, which is consistent with the principal orientations of the two-dimensional surface strain rate tensor. This agreement supports the notion that the Pamir and southwestern Tien Shan are uniformly strained blocks. In particular, the fan-shaped rotational pattern between Shmax and the strain rate from the western Pamir to the Tajik Basin shows that the counterclockwise rotation of the Shmax orientation is associated with vertical deformation, which is consistent with the idea of Schurr et al. (Tectonics 33(8):2014TC003576, 2014) concerning the gravitational collapse and westward extrusion of the crust in the western Pamir. We propose that such a stress-strain pattern, dominated by NNW-ESE oriented compression and E-W trending extension, originated from a combination of the northward push of the Indian continent and the southward subduction of the Tien Shan. [ABSTRACT FROM AUTHOR]

Active intraplate deformation of the India–Australia Plate is now being captured by far-field global positioning system (GPS) measurements as well as measurements on a few islands located within the deforming zone itself. In this paper, we combine global and regional geodetic solutions with focal mechanisms of earthquakes to derive the present-day strain field of the India–Australia Plate. We first compile an updated catalogue of 131 Indian intraplate earthquakes spanning the period between the two Asian mega earthquakes of Assam 1897 and Sumatra 2004. Using Haines and Holt's numerical approach applied to a fully deformable India–Australia Plate, we show that the use of GPS data only or earthquakes data only has severe drawbacks, related, respectively, to the small number of stations and the incompleteness of the earthquakes catalogue. The combined solution avoids underestimation of the strain inherent to the Kostrov summation of seismic moments and provides details that cannot be reached by pure GPS modelling. We further explore the role of heterogeneity of the India–Australia Plate and find that the best model, in terms of geodetic vectors fit, relative distribution of strain, style and direction of principal strain from earthquakes, is obtained using the surface heat-flow as a proxy for rheological weakness of the oceanic lithosphere. The present-day deformation is distributed around the Afanasy Nikitin Chain in the Central Indian Basin (CIB)—where it is almost pure shortening—and within the Wharton Basin (WB) off Sumatra—where it is almost pure lateral strike-slip. The northern portion of NinetyEast ridge (NyR) appears as a major discontinuity for both strain and velocity. The new velocity field gives an India/Australia rotation pole located at overlapping with previous solutions, with continental India moving eastward at rates ranging from 13 mm yr−1 (southern India) to 26 mm yr−1 (northern India) with respect to Australia. Taking into account the intraplate velocity field in the vicinity of the Sumatra trench, we obtain a convergence rate of 46 mm yr−1 towards N18°E at the epicentre of the 2004 Aceh megaearthquake. The predicted instantaneous shortening in the CIB and WB and extension near Chagos-Laccadive are in good agreement with the finite deformation measured from plate reconstructions and seismic profiles, suggesting a continuum of deformation since the onset of intraplate deformation around 7.5–8 Ma. Since no significant change in India convergence is detected at that time, we suggest that the intraplate deformation started with the trenchward acceleration of Australia detaching from India along a wide left-lateral oceanic shear band activating the NyR line of weakness as well as north–south fracture zones east of it. The predicted total amount of left lateral finite strain along these faults is in the range 110–140 km. [ABSTRACT FROM AUTHOR]

Abstract: A number of previous models have been proposed to explain the formation of the South China Sea, the largest marginal sea basin in Southeast Asia, but no consensus has been reached. In this work, two-dimensional (2D) plan-view models (linear viscous rheology) are constructed to simulate the India–Eurasia collision, its resultant intra-plate deformation and lateral motion along the Red River Fault. We then use 2D cross-section models (a combination of linear viscous rheology and elastic–plastic rheology) to simulate the influence of deep asthenosphere upwelling on lithospheric deformation. The plan-view models show that the India–Eurasia collision can result in extensive east-southeastward tectonic extrusion, consistent with the prediction of the analogue experiments. During extrusion, the modelled Red River Fault first experienced huge left-lateral shearing and then changed to right-lateral shearing (reversal). The style of shearing motion along the Red River Fault is a function of the distance between the fault and the India–Eurasia collision frontier, which decreases with time and controls relative extrusion movement between the South China Block and Indochina Block. Our models also show that the extrusion can generate extension in an approximately N-S direction in the region containing the present-day South China Sea. Our cross-section models further demonstrate that such horizontal extension can only generate limited thinning of the continental lithosphere in the South China Sea region. In contrast, asthenosphere upwelling is much more efficient in generating lithospheric upper mantle thinning but still inefficient for crust thinning. It is the combination of mechanical extension and asthenosphere upwelling that proves to be the most efficient way to thin the entire lithosphere, and that represents the most likely driving mechanism for the opening and spreading of the South China Sea. [Copyright &y& Elsevier]