Lateral extrusion along the Altyn Tagh Fault, Qilian Shan (NE Tibet): insight from a 3D crustal budget

Abstract

The lithospheric strike-slip Altyn Tagh Fault has accommodated hundreds of kilometres of displacement between the Qaidam and Tarim blocks since its Eocene reactivation. However, the way the deformation is accommodated in the Qilian Shan and further east remains uncertain. Based on 360 km of north-eastward migration of the relatively rigid Qaidam block along the Altyn Tagh Fault and 3D isovolumetric balancing of the crustal deformation within the Altyn Tagh Fault-Qilian Shan system, we demonstrate that 250 AE 28 km (43.8-49.4%) of N20E directed crustal shortening and an additional~250-370 km of eastward motion of the Qilian Shan crust must be accounted for by strikeslip faulting in the Qilian Shan and crustal thickening in the Qinling area, as well as by extension in the adjoining North China block graben systems.

A New Sediment Accumulation Model of Cenozoic Depositional Ages From the Qaidam Basin, Tibetan Plateau

“…To balance the erosion from the surrounding mountain belts with the deposits preserved in the basin, we assume that Qaidam basin has been internally drained basin since initial subsidence of the basin in the Cenozoic. This inference is supported by recent source‐to‐sink studies that reveal that exhumation of the Altyn Tagh Shan, Eastern Kunlun Shan and the Qilian Shan source regions has provided clastic material to the Qaidam basin since the deposition of Lulehe Formation (Bush et al, ; F. Cheng, Fu, et al, ; F. Cheng, Guo, et al, ; F. Cheng, Jolivet, et al, ; F. Cheng, Jolivet, et al, ; L. Li et al, ; L. Li et al, ; W. Wang, Zheng, et al, ; W. Zhu, Wu, Wang, Fang, et al, ; W. Zhu, Wu, Wang, Zhou, et al, ).…”

“…where M erosion is the total mass of the materials eroded from the Altyn Tagh Shan, Qilian Shan, and Eastern Kunlun Shan, M basin fill is the total mass of the deposits preserved in the Qaidam basin, and M escape is the mass of eroded sediment flux from the Qaidam basin. Based on seismic profile interpretation and field investigation (F. Cheng, Guo, et al, ; F. Cheng, Jolivet, et al, ; L. Wang et al, ), a Miocene regional angular unconformity between the upper and lower Xiaganchaigou Formation has been identified. Although this unconformity likely indicates the erosion of the pre‐Miocene strata within the basin during the Miocene, those eroded materials would be transported by local drainage systems and again deposited within the basin given the prevalence of closed‐basin conditions since at least ~30 Ma (Bush et al, ; F. Cheng, Fu, et al, ; W. Wang, Zheng, et al, ) and the late Pliocene to early Pleistocene onset of wind erosion in the basin (Heermance et al, ; Kapp et al, ; Pullen et al, ).…”

“…This petroliferous basin is filled with as much as ~14 km of Cenozoic clastic sedimentary rocks, that preserves an exceptional record of the intraplate response to the India‐Asia collision and postcollision convergence (Meng & Fang, ; Métivier et al, ; Meyer et al, ; Molnar & Tapponnier, ; Rieser et al, ; Xia et al, ; Yin, Dang, Wang, et al, ; Yin, Dang, Zhang, et al, ; Yin et al, ). Investigating the nature of these strata provides constraints on the topographic evolution of northern Tibet and the overall pattern of the Cenozoic plateau growth (Bush et al, ; F. Cheng, Fu, et al, ; F Cheng, Guo, et al, ; F. Cheng, Jolivet, et al, ; Fang et al, ; Ji et al, ; W Wang, Zheng, et al, ; Zhuang et al, ). Nonetheless, the depositional age of these Cenozoic strata remains highly debated.…”

The Cenozoic growth of the Qilian Shan in the northeastern Tibetan Plateau: A sedimentary archive from the Jiuxi Basin

“…Many previous studies have demonstrated that the Cenozoic contractional structures in the Qilian Shan region accommodated sizable left‐lateral displacement along the Altyn Tagh Fault [e.g., Métivier et al ., ; Meyer et al ., ; Tapponnier et al ., ; Yin et al ., , ; Cheng et al ., ]. These studies suggested that the migration of the loci of thrust faulting and crustal shortening was guided by the propagation of the Altyn Tagh Fault and led to the formation of distant, parallel, and narrow ranges.…”

“…The Altyn Tagh Fault zone extends ~2000 km along strike and is a major left‐lateral, strike‐slip fault zone that is thought to accommodate 375–400 km of slip that was imposed by the northeastward extrusion of the Tibetan Plateau during the Cenozoic [ Cowgill et al ., ; Peltzer and Tapponnier , ; Yang et al ., ; Yin et al ., ; Yue et al ., , ]. Slip on the fault has been absorbed by deformation within the western margin of the Qaidam Basin [ Fang et al ., ; Yin et al ., ] and by folds and the south dipping thrust fault system in the Qilian Shan region [ Meyer et al ., ; Wang et al ., ; Cheng et al ., ]. The North Qilian Shan Fault is an active thrust fault in the study region.…”