The Moho beneath western Tibet: Shear zones and eclogitization in the lower crust
作者单位：Institute of Geology and GeophysicsChinese Academy of Sciences Department of Earth Science and EngineeringImperial College London GFZ German Research Centre for Geosciences
会议名称：《中国科学院地质与地球物理研究所2014年度（第14届）学术年会》
会议日期：2015年
学科分类：070904[理学-构造地质学] 0709[理学-地质学] 07[理学]
基 金：funded by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant XDB03010700) provided by the National Natural Science Foundation of China (Grant nos.41374062,41374063 and 41474111)
关 键 词：Tibetan Plateau Moho segmentation receiver functions crustal thickness eclogitization shear zones
摘 要：The Tibetan Plateau is formed by continuing convergence between Indian and Asian plates since～50 Ma,involving more than 1400 km of crustal shortening. New seismic data from western Tibet(the TW-80 experiment at80°E)reveal segmentation of lower crustal structure by the major sutures,contradicting the idea of a mobile lower crust that flows laterally in response to stress *** changes in crustal structure and Moho depth occur at the mapped major tectonic boundaries, suggesting that zones of localized shear on sub-vertical planes extend through the crust and into the upper *** waves originating at the Moho and at a shallower discontinuity are interpreted to define a partially eclogitized layer that extends 200 km north of the Indus–Yarlung Suture Zone, beneath the entire Lhasa block at depths of between 50 and 70 km. This layer is thinner and shallower to the north of the Shiquanhe Fault which separates the northern Lhasa block from the southern part,and the degree of eclogitization is interpreted to increase northward. The segmentation of the Tibetan crust is compatible with a shortening deformation rather than shear on horizontal planes. Unless the Indianplate mantle lithosphere plunges steeply into the mantle beneath the Indus–Yarlung suture, leaving Indian-plate crust accreted to the southern margin of Tibet,then it too must have experienced a similar shortening deformation.