Rapid Uplift of the Kumkuli Basin Since ~5 Ma as a Consequence of Large-Scale Transpressional Faulting within the Northern Tibetan Plateau
Petr Yakovlev, Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI
Marin Clark, Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI
Hong Chang, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
Jiang Yi, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
The north to northeast convergence of India with Eurasia is accommodated in northern Tibet predominantly by the left-lateral Altyn Tagh and Kunlun strike-slip faults via eastward motion of the Qaidam Basin and north-central plateau, respectively. West of ~91°E, where the east-west trending Kunlun Fault is within ~300 km of the northeast-southwest trending Altyn Tagh, it location becomes ambiguous. The Kumkuli Basin lies immediately to the northwest of this region, and contains Oligo-Pliocene strata that have undergone a minimum of 9 km or ~21 % shortening, and resulted in a ~1 km high range front. Uplift of the Quimen Tagh range along the southern margin of the Qaidam Basin isolated Kumkuli, and marked the beginning of basin infilling, where the stratigraphic sequence is primarily comprised of Oligocene conglomerates and Mio-Pliocene fluvial to lacustrine sediments. Long-term Miocene aridity in the Kumkuli basin is indicated by the presence of distinct 0.2-2 m thick gypsum-rich siltstone beds. South to north paleocurrent directions, and abundant limestone and chert clasts in basin strata indicate sourcing of material from 150 km to the south in the Hoh Xil Basin. A notable coarsening upward sequence from mudstones to conglomerates at the top of the Pliocene section marks the transition from basin infilling to the initiation of deformation, which continues into Quaternary time. We use 36Cl cosmogenic radionuclide dating to estimate the age and erosion rates at the tops of two folded alluvial fan surfaces, and reconstruct their original depositional elevations based on local geomorphology to derive Quaternary vertical uplift rates of 3.5-5.7 mm/yr. Estimated subsurface fold geometries translate vertical uplift into shortening rates of ~ 1.8 mm/yr, which are consistent with a Pliocene initiation age for deformation. The 1997 Mw 7.6 Manyi earthquake focal mechanism and associated aftershocks indicate that strike-slip faulting south of the Kumkuli Basin may begin to run sub-parallel to the Altyn Tagh fault. We link the Manyi seismic zone to the Kunlun fault based on regional seismicity, and a distinct transition from a westerly to a west-southwest trend of the Kunlun Fault as described by the 2001 Mw 7.8 Kokoxili rupture. We interpret shortening within the Kumkuli Basin to be the consequence of large-scale transpressional shear between the Altyn Tagh Fault and the Manyi seismogenic zone, both of which accommodate ~ 10 mm/yr of left-lateral deformation.