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

Abstract

We present results from a multidisciplinary investigation of the Jiujing fault (JJF) system and adjacent Jiujing Basin in the southern Beishan block, western China. Structural and geomorphological fieldwork involving fault and landform investigations, remote sensing analysis of satellite and drone imagery, analysis of drill-core data, paleoseismological trench studies, and Quaternary dating of alluvial sediments suggest the JJF is a late Pleistocene to Holocene oblique sinistral-slip normal fault. Satellite image analysis indicates that the JJF is a connecting structure between two regional E-W-trending Quaternary left-lateral fault systems. The Jiujing Basin is the largest and best developed of three parallel NE-striking transtensional basins within an evolving sinistral transtensional duplex. Sinistral transtension is compatible with the orientation of inherited basement strike belts, NE-directed SHmax, and the modern E-NE-directed geodetic velocity field. Cosmogenic 26Al/10Be burial dating of the deepest sediments in the Jiujing Basin indicates that the basin began to form at ~5.5 Ma. Our study reveals a previously unreported actively deforming domain of transtensional deformation 100 km north of Tibet in a sector of the Beishan previously considered tectonically quiescent. Recognition of latest Miocene-Recent crustal reactivation in the Jiujing region has important implications for earthquake hazards in the Beishan and western Hexi Corridor/North Tibetan foreland sectors of the Silk Road Economic Belt. Additionally, we compare the timing of latest Miocene-Recent crustal reactivation in the southern Beishan with the documented onset of reactivation in other deforming regions north of Tibet.

New Magnetotelluric Data Reveal Deep Fault Boundaries and Contrasting Late Cenozoic Fault Kinematics Between the Qilian Shan Thrust Wedge and Beishan‐Alxa Block, Western China

“…Thus, the HSF (western part of the NHBF) appears to serve as the present‐day lithospheric‐scale block boundary between the northern Tibet and Beishan‐Alxa crustal domains (Figure 4, Yue & Liou, 1999; Darby et al., 2005; Yang, Li, Cunningham, Yang, et al., 2023). It also separates different deformation regimes, including E‐W extension or transtension in the Ejina basin area further to the NNE as recorded by focal mechanism solutions and field and geophysical data (Figures 1a and Yang, Yang, et al., 2021; Rudersdorf et al., 2013).…”

“…It can be regarded as a rheologically strong crustal block due to its Precambrian crystalline basement, Paleozoic magmatic arc complexes and regionally metamorphosed assemblages (Yuan et al., 2015; Zong et al., 2017). It has been locally reactivated by strike‐slip, transtensional and transpressional fault systems since the late Miocene (Yang, Yang, et al., 2021; Yu et al., 2017). Earthquake focal mechanisms in the Qilian Shan and Beishan‐Alxa areas are dominated by thrusting and strike‐slip displacements, respectively (Figure S4 in Supporting Information , Pan et al., 2020).…”