A Paleoseismic Record Spanning 2‐Myr Reveals Episodic Late Pliocene Deformation in the Western Qaidam Basin, NE Tibet

Yin Lu,Shmuel Marco,Aurélia Hubert‐Ferrari,Nadav Wetzler,G Ian Alsop,Xiaomin Fang

doi:10.1029/2020gl090530

Abstract

AbstractThe western Qaidam Basin, NE Tibet contains numerous NW‐SE‐trending thrusts that extend over a distance of ∼300 km along the Altyn Tagh Fault and north of the Kunlun Range. However, little is known about the long‐term seismo‐tectonic evolution of this active thrust zone due to the absence of an extended paleoseismic record. We present a 2‐Myr‐long disturbance record established from a core drilled on the crest of a thrust‐cored anticline. Based on detailed sedimentological analysis, the disturbances (micro‐faults, soft‐sediment deformation, slumps, and detachment surfaces) are interpreted as paleoearthquake/tectonic indicators. The core records five seismite clusters which occurred at 3.6‐3.5, 3.4‐3.2, 3.15‐3.1, 3.0‐2.9, and 2.8‐2.75 Ma. This suggests the rate of tectonic strain accommodated by the folds and thrusts in the region varies and thus reveals episodic local deformation. During the clusters, regional deformation is concentrated more in the fold‐and‐thrust system than along regional major strike‐slip faults.

Highlights

The Qaidam Basin is the largest topographic depression on the Tibetan Plateau and was formed since the early Oligocene by the ongoing India-Asia collision (Yin et al, 2008)
The western Qaidam Basin, NE Tibet contains numerous NW-SE-trending thrusts that extend over a distance of ∼300 km along the Altyn Tagh Fault and north of the Kunlun Range
Little is known about the long-term seismo-tectonic evolution of this active thrust zone due to the absence of an extended paleoseismic record

Summary

Introduction

The Qaidam Basin is the largest topographic depression on the Tibetan Plateau and was formed since the early Oligocene by the ongoing India-Asia collision (Yin et al, 2008). It is bound to the northwest by the Altyn Tagh Range, to the south by the Kunlun Range, and the Qilian Range to the northeast (Figure 1) (Tapponnier, 2001; Taylor & Yin, 2009; Yin et al, 2008). The northeastward growth of Tibet during the Oligocene-Quaternary, and the associated propagation of deformation along the Kunlun Fault, formed a series of sub-parallel NW-SE-trending folds over a distance of ∼300 km along the Altyn Tagh Fault, which is the most prominent morphological feature in the Qaidam Basin of NE Tibet (Lu et al, 2018; Métivier et al, 1998; Meyer et al, 1998; Yuan et al, 2013) (Figure 1). The absence of protracted paleoseismic records means that little is known about the long-term rupture behavior of the still active thrust zone.

Objectives

Results

Conclusion