Geometry and kinematics of the Arlar strike-slip fault, SW Qaidam basin, China: New insights from 3-D seismic data

The right-stepping en-echelon Kunbei fault system, consisting of the Hongliuquan, Arlar, XIII, and Kunbei faults, features importantly in the tectonic evolution of the southwest Qaidam basin. The 3D seismic cross-section interpretation and key horizon similarity attribute analysis show that the NWW-striking Arlar fault is composed of two steeply dipping faults (F1 and F2) in cross-sectional view, and branches eastward into two west-dipping faults (F5 and F6) in map view. The fact that the strata above T-2 (the base of the early Miocene Xiayoushashan Formation) become dramatically thinner toward the high points of the Arlar fault suggests an early Miocene initiation (ca. 22,0 Ma) for this fault. As indicated by the windowed amplitude-related attribute maps, the Arlar fault and F5 (one branch of the Arlar fault) have cumulative sinistral offsets of similar to 8.6-8.7 km and similar to 5.2-5.4 km, respectively. These considerably greater strike-slip components, in conjunction with the respective maximum true dip-slip displacements of <2.2 km and <1.5 km, convincingly demonstrate that the Arlar fault and F5 are two predominantly left-lateral strike-slip faults. The other faults in the Kunbei fault system are similarly of strike-slip types. This means that the southern boundary of the Qaidam basin is not governed by south- or north-directed thrusting but rather strike-slip faulting, implying that the Qaidam basin is not a foreland basin of the Eastern Kunlun Range. Taking the Altyn Tagh fault into account, the Qaidam basin is essentially a strike-slip superimposed basin developing between two large left-lateral strike-slip faults. (C) 2014 Elsevier Ltd. All rights reserved.