Fold-and-thrust deformation of the hinterland of Qilian Shan, northeastern Tibetan Plateau since Mesozoic with implications for the plateau growth

Abstract

The northeastern margin of the Tibetan Plateau (NETP) represents an ideal site to probe the far-field effects and plateau growth in response to the collisions of Eurasia Continent with India Plate and intervening terranes. Here, we investigate the fold-and-thrust deformation of the Shule River region in the hinterland of Qilian Shan, NETP since Mesozoic, based on geological mapping and structural analysis to evaluate the role of multiple-phase deformation in plateau rise and growth. The structural style of the Shule River region is dominated by the foreland-verging Liuhuang Shan fold-and-thrust belt (LHTB) to the southwest and the hinterland-verging Tuolai Nan Shan fold-and-thrust belt (TLTB) to the northeast, separated by the Cenozoic Shule River intermontane basin. Integrated with published thermochronological, sedimentological and structural data, our study reveals four significant deformation phases in the NETP since the Mesozoic. During the Late Triassic to Early Jurassic time, the regional deformation spread in the NETP and produced the Jura-type folds and related thrusts of the LHTB in the study area under the NE-SW-directed compression, and was likely driven by the collision between the Qiangtang and Kunlun terranes. During the late Early Cretaceous, the continuous Lhasa-Qiangtang collision induced reactivation of the LHTB and an extensive exhumation event in the NETP. Since the Early Eocene, the upper crustal shortening and initial uplift of the NETP have accommodated the far-field stress of India-Eurasian collision. Given the widespread Miocene uplift event in the NETP, revealed by previous studies, we attribute the southwestward thrusting of the TLTB and tight-isoclinal syncline of the Oligocene-Miocene Baiyanghe Formation to the significant crustal shortening and topographical growth of NETP during the Early-Middle Miocene. The reactivation of TLTB and newly generated low-angle reverse faults represent gently tilted deformation and plateau growth in response to surface uplift of NETP as a whole since the Late Miocene. Our results imply that the multiple-phase deformation in the NETP since the Late Triassic should have been a first-order control on plateau growth.