Inherited strike-slip faults as an origin for basement-cored uplifts: Example of the Kungey and Zailiskey ranges, northern Tian Shan

Abstract

Basement-cored uplifts bounded by steeply dipping reverse faults are mechanically difficult to explain. Reactivation of strike-slip faults that aid the formation of new, high-angle reverse faults in the surrounding crust may provide one origin for these structures. This hypothesis is explored by examining the late Miocene to Quaternary evolution of the Kungey and Zailiskey ranges in the northern Tian Shan. These ranges are cored by the Kemin-Chilik fault (KCF), an inherited Paleozoic structure with sinistral separation of basement terranes. Range growth in response to northward propagation of the Tian Shan has taken place along a network of steeply dipping reverse and oblique-slip faults surrounding the KCF. Deformation of a low relief unconformity separating Neogene strata from Paleozoic basement records structural growth in response to fault slip. Deformed river terraces surrounding the ranges are correlated to a well preserved chronosequence in the southern Kungey Range. Cosmogenic 10 Be dating of this chronosequence combined with offset measurements yields slip rates ranging from 0.07 to 0.37 mm/yr for dip-slip faults, and 1.1 to 1.5 mm/yr for strike-slip faults Late Quaternary activity in the Kungey-Zailiskey ranges is consistent with the longer-term, outward stepping pattern of range growth. Based on cross sections constrained from the folded unconformity surface, deformed Neogene strata and Quaternary terraces, faults building the Kungey Range are inferred to steepen at depth and emanate from a shear zone co-located with the reactivated KCF. This geometry is consistent with a slip partitioned system developed by an obliquely slipping reactivated fault at depth. © 2012. American Geophysical Union. All Rights Reserved.