Late Quaternary activity and dextral strike-slip movement on the Karakax Fault Zone, northwest Tibet

Field observations and interpretations of satellite images reveal that the westernmost segment of the Altyn Tagh Fault (called Karakax Fault Zone) striking WNW located in the northwestern margin of the Tibetan Plateau has distinctive geomorphic and tectonic features indicative of right-lateral strike-slip fault in the Late Quaternary. South-flowing gullies and N-S-trending ridges are systematically deflected and offset by up to similar to 1250 m, and Late Pleistocene-Holocene alluvial fans and small gullies that incise south-sloping fans record dextral offset up to similar to 150 m along the fault zone. Fault scarps developed on alluvial fans vary in height from 1 to 24 m. Riedel composite fabrics of foliated cataclastic rocks including cataclasite and fault gouge developed in the shear zone indicate a principal right-lateral shear sense with a thrust component. Based on offset Late Quaternary alluvial fans, C-14 ages and composite fabrics of cataclastic fault rocks, it is inferred that the average right-lateral strike-slip rate along the Karakax Fault Zone is similar to 9 mm/a in the Late Quaternary, with a vertical component of similar to 2 mm/a, and that a M 7.5 morphogenic earthquake occurred along this fault in 1902. We suggest that right-lateral slip in the Late Quaternary along the WNW-trending Karakax Fault Zone is caused by escape tectonics that accommodate north-south shortening of the western Tibetan Plateau due to ongoing northward penetration of the Indian plate into the Eurasian plate. (C) 2008 Elsevier B.V. All rights reserved.