A Regionally Evolving Transpressional Duplex Along the Northern Margin of the Altyn Tagh Fault: New Kinematic and Timing Constraints From the Sanweishan and Nanjieshan, China

Abstract

In this study, we document the kinematics and Late Quaternary slip rates of actively developing faults and folds on the northern side of the Altyn Tagh Fault (ATF) that accommodate uplift and lateral expansion of the northern Tibetan Plateau. Field observations and detailed measurements using Unmanned-Aerial-Vehicle Structure-from-Motion high-resolution imagery of offset fan surfaces, gullies, and channel risers coupled with optically stimulated luminescence and 10 Be ages constrain the timing and slip rates of the Sanweishan Fault (SWSF) and Nanjieshan Fault (NJSF) systems. The NE striking SWSF is characterized by sinistral strike slip with a top-to-the-NW thrusting component. Offset geomorphic markers and dating results yield Pleistocene strike slip and vertical uplift rates of 0.06-1.25 mm/a and 0.05-0.08 mm/a, respectively. The E-W trending NJSF is dominated by north and south directed thrusting and km-scale folding with variable components of sinistral strike slip. The calculated total N-S shortening rate across the NJSF is~0.3 mm/a. Low rates of deformation for the SWSF and NJSF account for less than 10% of the total intraplate strain accommodated along the northeasternmost ATF system. Over a 1,000-km length, the northward expansion of the Tibetan Plateau occurs by progressive northeastward growth of a transpressional duplex rooted SE into the ATF. An assumed crustal strength discontinuity along the northeast trending southern margin of the Tarim Craton focuses oblique convergence along the ATF. Oblique-slip thrusting and sinistral strike slip along the ATF and to the north accommodate the oblique convergence, consistent with the ENE directed geodetically derived crustal velocity field driven by India's continued indentation 1,500 km to the south.

Late Miocene to Quaternary Development of the Jiujing Basin, Southern Beishan Block, China: Implications for the Kinematics and Timing of Crustal Reactivation North of Tibet

“…At each site, at least 100 photos were captured by a DJI Phantom 3 Pro drone. The resultant DEMs have a resolution of 3~5 cm/pixel (c.f., Yang et al [13,26]). Printed shaded relief maps with remote sensing interpretations were carried to the field for validation, modification, and as basemaps for further ground study.…”

“…For comparison, pre-60 Ma rapid exhumation and subsequent thermal quiescence of the Nanjieshan east of Dunhuang (Figure 1) is suggested by apatite Helium analysis [8]. However, Neogene and Quaternary faulting and sub-2 km block uplift are well documented in the Nanjieshan by field studies and remote sensing analysis [25,26]. In addition, semiconsolidated Neogene deposits (Kuquan Formation) within the Beishan are widely folded and faulted according to 1 : 200,000 scale geological mapping (and confirmed by satellite image analysis) [21].…”

“…Subsidence of the hanging wall would have produced the accommodation space for alluvial sedimentation derived from the adjacent Xinchang bedrock block on the east side of the basin (c.f., [31]). 26 Al/ 10 Be Simple Burial Dating. Terrestrial cosmogenic nuclides (e.g., 10 Be, 26 Al, and 21 Ne) are produced by the interaction of quartz-bearing minerals in catchmentor hillslope-derived rocks with cosmic ray particles, such as neutrons and μ muons (e.g., [32][33][34]).…”

“…26 Al/ 10 Be Simple Burial Dating. Terrestrial cosmogenic nuclides (e.g., 10 Be, 26 Al, and 21 Ne) are produced by the interaction of quartz-bearing minerals in catchmentor hillslope-derived rocks with cosmic ray particles, such as neutrons and μ muons (e.g., [32][33][34]). The increased nuclide concentration in surface sediments with time can be measured for dating the exposure history with site-dependent nuclide productions.…”

Late Quaternary slip rate of the Aksay segment and its rapidly decreasing gradient along the Altyn Tagh fault

“…The strike-slip structures are mainly large-scale strike-slip faults, such as the Altyn Tagh fault and Haiyuan fault. In contrast, the dip-slip structures are dominated by thrusts in the Qilian Shan, causing series of NW-trending mountain ranges, e.g., the Qilian Shan, Daxue Shan, Danghe Nan Shan, and Qaidam Shan from NE to SW (Meyer et al, 1998;Xu et al, 2005;Allen et al, 2017), and late Cenozoic uplift parallel to the Altyn Tagh fault, observed in the Sanwei Shan and Nanjie Shan to the north (Yang et al, 2020). There is a close interaction between the thrusts in the Qilian Shan and the Altyn Tagh fault.…”