Northeastward expansion of the Tibetan Plateau: Topographic evidence from the North Qinling Mts.–Weihe Graben Coupling system, Central China

Abstract

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.