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Since the Late Cenozoic, tectonic deformation has been intense in the Longxian–Baoji Fault Zone (LBFZ), which is at the intersection of the southwest margin of the Ordos Block, the northeast margin of the Tibet Plateau, and the Qinling Orogenic Belt. To evaluate the relative tectonic activity within the LBFZ and discuss the influence of the northeastward expansion of the Tibetan Plateau on the geomorphological evolution of the LBFZ, we extracted data of the Qianhe, Hengshuihe, and Jinlinghe River Basins from the ASTER GDEM and analyzed the geomorphic indices, including the hypsometric integral (HI), standardized stream length-gradient index (SL/K) and Hack profile, elongation ratio (Re), the drainage basin asymmetry factor (AF) and valley floor width-to-height ratio (VF). Through geomorphic indices and field investigations, we found that the LBFZ has experienced relatively high tectonic activity. Combined with the index of relative active tectonics (IAT), we compared the tectonic activity strengths of the four major faults in the study area. Among them, the tectonic activities of the Longxian-Qishan Fault (LQF) and the Taoyuan-Guichuansi Fault (TGF) are the highest. The morphology and AF values of the drainage basin of the southwest side of the study area indicate the influence of northwest-southeast compressive stress. The northeastward expansion of the Tibetan Plateau affected the LBFZ region, and the stress brought about by it controlled the tectonic deformation in the region and sculpted the modern landscape. This study is of great significance for understanding the impact of the northeastward expansion of the Tibetan Plateau on the geomorphological evolution of the LBFZ. [ABSTRACT FROM AUTHOR]

The Neoproterozoic granitoids in East Kunlun Orogen (EKO) record critical information on the composition and evolution of the early crustal materials, as well as the Precambrian tectonic evolutionary history of the Qaidam Block, northern Tibetan Plateau. Zircon U–Pb geochronology and Hf isotopic compositions of three newly discriminated gneissic granitoids in the Hongshuihe, Dangennaomuru and south Bokalike areas are employed in this study to elucidate the Neoproterozoic tectonics of EKO. Petrological studies reveal that these granitoids are S–type granite with abundant Al–rich minerals like muscovite and garnet in their mineral assemblages. Zircon U–Pb geochronological results show that the Hongshuihe and Dangennaomuru plutons yield weighted mean 206 Pb/ 238 U ages of 914 ± 5 Ma (MSWD = 0.25) and 935 ± 6 Ma (MSWD = 0.56), respectively, indicating their magmatic crystallization ages. And the south Bokalike pluton yields upper and lower intercept ages of 1002 ± 31 Ma and 388 ± 39 Ma (MSWD = 0.63), disclosing its magmatic crystallization age and the time of subsequent Paleozoic metamorphic event, respectively. The ε Hf ( t ) values of zircons in this study are dominated by negative with minor positive values ranging from −7.18 to +2.76. The two–stage Hf model ages of the zircons having negative ε Hf ( t ) values are ca. 1.7–2.0 Ga, whereas those with positive ε Hf ( t ) values are ca. 1.5 Ga. Both the ε Hf ( t ) values and the two–stage Hf model ages indicate that these granitoids were probably derived from the reworking of ancient continental crustal materials with minor mantle contribution. Combined with available data of the granitoids in EKO, central and north Qaidam Block, we propose that the Neoproterozoic granitoids in Qaidam Block have similar crystallization ages of ca. 0.9–1.0 Ga, as well as same or similar geochemical and zircon Hf isotopic compositions revealing the Qaidam Block was involved into the amalgamation of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

Mountain-Basin Coupling systems form during late stages of the collisional orogeny when mountains rise compared to the adjacent sedimentary basins. In this study, we focus on the spatial and temporal pattern of uplift, subsidence and related topographic features of the transtensional Weihe Graben–North Qinling Mountain Coupling system, at the northeastern extension of the Tibetan Plateau. The opening of the Weihe Graben and the ongoing high seismicity in the Weihe Graben result from the lateral extrusion of the Qinling Block away from the Tibetan Plateau. We quantify the influence of uplift gradients on topography and drainage divides by (a) carrying out field surveys, (b) conducting a digital elevation model-based analysis of topographic properties, and (c) compiling and integrating data on exhumation, uplift, subsidence, and denudation of numerous previous studies. Together, these morphological analyses show that the influence of the uplift of the Tibetan Plateau on the study area gradually decreases from the westernmost Taibai Mts. to the easternmost Huashan Mts. We found large χ gradients across the drainage divide of the Huashan Mts. and river piracy implying a southward migration of the drainage divide in the Huashan Mts. We conclude that the initial exhumation of the North Qinling Mts. occurred during the Lower Eocene to Oligocene (cycle 1). As peneplanation surfaces formed, this implies discontinuous exhumation and surface uplift. A second stage of uplift occurred in the Oligocene to Middle Miocene (cycle 2), followed by the third stage from Middle to Upper Miocene (cycle 3). The final period of uplift occurred from latest Miocene to Holocene times (cycle 4). The uppermost Miocene to Holocene geomorphological features imply surface uplift within the westernmost North Qinling Mts. and are controlled by the inflation of a mid-crustal magma layer, prograding from the eastern Tibetan Plateau towards the Taibai Mts., associated with lateral extrusion of the Qinling Block away from the rising Tibetan Plateau. The high seismicity of the Weihe Graben implies ongoing tectonic activity influenced by deep-seated lithospheric motion. • India-Asia convergence is driving the North Qinling–Weihe Graben Coupling system. • Lateral extrusion formed the North Qinling–Weihe Graben Mountain-Basin system. • The Eocene––Recent North Qinling–Weihe Graben pattern is a transtensional system. • Crustal magma inflation explains Pliocene–Quaternary geomorphological features. • S-ward drainage divide migration and river piracy occurs during Pliocene–Quaternary. [ABSTRACT FROM AUTHOR]