Magnitude of post-Middle Jurassic (Bajocian) displacement on the central Altyn Tagh fault system, northwest China

Abstract

The Altyn Tagh fault system, a key structural feature in the tectonic collage of central Asia, is an active left-lateral strike-slip fault system. However, its age of initiation, kinematic history, and total magnitude of displacement are not well known. Middle Jurassic nonmarine sedimentary rocks that crop out along the central segment of the Altyn Tagh fault were deposited in a contiguous Tarim-Qaidam foreland-style basin that was geodynamically linked to Mesozoic contraction in the Tian Shan, Bei Shan, Qilian Shan, and Kunlun Shan. This study documents the best evidence of a piercing point to date, consisting of an offset lacustrine shoreline demarcated by Aalenian-Bajocian open lacustrine strata to the west and fluvial and alluvial strata of comparable age to the east. Detrital compositions, palynology, paleocurrents, and lithostratigraphy support correlation of these sections. Restoration of this Jurassic facies boundary indicates 400 ± 60 km of post-Bajocian left-lateral separation on the Altyn Tagh fault. Consistent with this result, restoration of the Jurassic shoreline aligns felsic plutons across the western segment of the Altyn Tagh fault system that may have been left-laterally offset by 360 km. These two pairs of offset features suggest that the current best estimate for net magnitude of post-Bajocian left-lateral separation on the Altyn Tagh fault is about 360 km.