Young, active conjugate strike-slip deformation in West Sichuan: evidence for the stress-strain pattern of the southeastern Tibetan Plateau

摘要

The active kinematics of the eastern Tibetan Plateau are characterized by the southeastward movement of a major tectonic unit, the Chuan-Dian crustal fragment, bounded by the left-lateral Xianshuihe-Xiaojiang fault in the northeast and the right-lateral Red River-Ailao Shan shear zone in the southwest. Our field structural and geomorphic observations define two sets of young, active strike-slip faults within the northern part of the fragment that lie within the SE Tibetan Plateau. One set trends NE-SW with right-lateral displacement and includes the Jiulong, Batang, and Derong faults. The second set trends NW-SE with left-lateral displacement and includes the Xianshuihe, Litang, Xiangcheng, Zhongdian, and Xuebo faults. Strike-slip displacements along these faults were established by the deflection and offset of streams and various lithologic units; these offsets yield an average magnitude of right- and left-lateral displacements of 15-35 km. Using 5.7-3.5 Ma as the time of onset of the late-stage evolution of the Xianshuihe fault and the regional stream incision within this part of the plateau as a proxy for the initiation age of conjugate strike-slip faulting, we have determined an average slip rate of 2.6-9.4 mm/year. These two sets of strike-slip faults intersect at an obtuse angle that ranges from 100° to 140° facing east and west; the fault sets define a conjugate strike-slip pattern that expresses internal E-W shortening in the northern part of the Chuan-Dian crustal fragment. These conjugate faults are interpreted to have experienced clockwise and counterclockwise rotations of up to 20°. The presence of this conjugate fault system demonstrates that this part of the Tibetan Plateau is undergoing not only southward movement, but also E-W shortening and N-S lengthening due to convergence between the Sichuan Basin and the eastern Himalayan syntaxis.View full textDownload full textKeywordsTibetan Plateau, Chuan-Dian crustal fragment, conjugate strike-slip fault system, Wenchuan and Yushu earthquakesRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00206814.2011.583491