HR: 1340h
AN: T23D-1642    [Abstracts]
TI: Cenozoic Right-slip Faulting Along the East Flank of the Pamirs, NW China: Implications for the Kinematic Evolution of a Major Salient in the Northern Margin of the Himalayan-Tibetan Orogen
AU: * Cowgill, E
EM: cowgill@geology.ucdavis.edu
AF: Geology Department, One Shields Ave. University of California, Davis, Davis, CA 95616, United States
AB: The Pamir salient defines the western end of the Himalayan-Tibetan orogen in China, Tajikistan, and Kyrgyzstan. The leading edge of this salient has overthrust the Tarim-Tajik basin to the north by ~300 km along a late Cenozoic, south-dipping intracontinental subduction zone beneath the North Pamir. Its eastern flank trends NW- SE, and lies between north-directed thrust belts in the North Pamir, to the west, and the Western Kunlun Shan, to the east. New 1:100,000-scale geological mapping, detailed structural measurements, and analysis of mesoscale structures along a 40 km-long transect along the east-flowing Yarkand River document the tectonic evolution of the this flank of the Pamir salient. The study area is cut by a set of four, NW-striking, steeply dipping, brittle faults with right-lateral slip, as indicated by brittle microstructures and asymmetric, outcrop- to map-scale folds. Panels of Phanerozoic strata that lie between these faults are deformed by en échelon folds with axes that trend more westerly than the adjacent faults, consistent with dextral transpression. Synthesis of these new results with previous regional geologic mapping suggests that the fault system described here extends for a total of ~350 km along strike, forming a structural system that defines the eastern flank of the Pamir salient and is here called the Kashgar-Yecheng transfer system. Transpressional right-slip along the Kashgar-Yecheng transfer system appears to have accommodated late Cenozoic separation of the North Pamir from the Western Kunlun Shan during south-directed intracontinental subduction beneath the leading edge of the Pamir salient. Correlation of major faults suggests total slip along the Kashgar-Yecheng transfer system of up to ~280 km. When combined with previous sedimentologic, stratigraphic, and thermochronologic data indicating deformation along the east flank of the Pamir started between the Late Eocene to Early Miocene, this offset estimate implies long term slip rates of 7-15 mm/yr along the Kashgar-Yecheng transfer system. Our results imply that the first- order structures on the western and eastern flanks of the Pamir are strongly asymmetric: in contrast to the transpressional right-slip transfer faulting we find on the east side, previous work has shown that deformation in the west was accommodated by northwest-directed radial thrusting and associated anti-clockwise vertical axis rotation of the Pamir over the eastern margin of the Tajik basin.
DE: 7205 Continental crust (1219)
DE: 8012 High strain deformation zones
DE: 8038 Regional crustal structure
DE: 8102 Continental contractional orogenic belts and inversion tectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting