Analysis of Slip History on Strike-Slip Faults Using Sedimentary Basins: Examples from the NE Tibetan Plateau

Ritts, Bradley¹, Yongjun Yue², Stephan Graham³ (1) Indiana University, Bloomington, IN (2) Chevron North America Exploration and Production Company, Bakersfield, CA (3) Stanford University, Stanford, CA

Sedimentary basins forming along active strike-slip faults show progressive dislocation from potential sediment source terranes on the opposite wall of the fault and thus provide the opportunity to reconstruct fault slip history through provenance analysis. We have applied this technique, inspired by work of John Crowell in the Ridge basin, to develop an understanding of the timing and distribution of slip on the left-lateral Altyn Tagh fault (ATF) and associated structures that bound the northern margin of the Tibetan Plateau. Piercing points in the Xorkol basin, on the central segment of the ATF, are supported by petrologic and geochronologic matches between sediments and sources and show that the Oligocene Xorkol basin was aligned with the North Qilian Shan, but by early Miocene the basin had been translated to a position adjacent to the Central Qilian Shan, and by the end of the early Miocene the Xorkol basin was opposite the South Qilian-North Qaidam terrane. These offsets indicate large (360±40 km) Oligocene and younger displacement and low (°Ü65 km) post-early Miocene displacement. The small post-early Miocene offset is confirmed by similar relationships in the Mangnai, Xorkol Pass, and Aksay basins, all of which show little or no dislocation from their cross-fault source terranes in upper Miocene and Pliocene conglomerate. In contrast to the ATF, sediment-source matches on the Northern Altyn Tagh fault, a left-reverse oblique slip fault that is sub-parallel to the ATF, indicate that the fault has relatively little strike-slip separation (<30 km) and is dominantly a reverse fault