STRUCTURAL AND GEOCHRONOLOGICAL EVIDENCE FOR MUL-TIPLE EPISODES OF DEFORMATION SINCE PALEOCENE ALONG THE AILAO SHAN-RED RIVER SHEAR ZONE, SOUTHEA STERN ASIA
Zhang Jinjiang1, Zhong Dalai2, Sang Haiqing2, Zhou Yong2
1. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871; 2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029
Structural analyses showed that the Ailao Shan sector, Ailao Shan-Red River shear zone (ASRR SZ) was composed of three different deformational domains. These domains might represent three episodes of left-lateral slip experienced by the ASRR SZ. The first episode of such deformation occurred throughout the eastern high-grade belt of the ASRR SZ under a transtensional regime and produced L tectonites of amphibolite grade. The second episode of left-lateral slip formed high strain zones overprinting the high-grade metamorphic belt. Its deformational mechanism was similar to simple shear and the deformed rocks were L-S mylonites of greenschist grade. The third episode of left-lateral slip took place chiefly in a western lower-grade belt of the ASRR SZ. This deformation occurred in a transpressional regime, formed an overall structure pattern of a sinistral thrust system and produced phyllonites of lower-greenschist grade. The geochronological data indicated that the three episodes of left-lateral slip happened 58~56 Ma ago, at least from ~27 Ma to 22 Ma ago and 13~12 Ma ago respectively. The first episode of slip in the ASRR SZ appeared to correspond to the initial collision of India and Asia about 60 Ma ago. The second episode took place almost at the same time as the most intensive compression and uplift in Tibet. The latest event might represent a further eastward material flow in Tibet 16~13 Ma ago. Thus, the ASRR SZ of southeastern Asia probably experienced three main episodes of left-lateral slip since Paleocene in the course of intracontinental convergence by the India-Asia collision.
Zhang Jinjiang,Zhong Dalai,Sang Haiqing et al. STRUCTURAL AND GEOCHRONOLOGICAL EVIDENCE FOR MUL-TIPLE EPISODES OF DEFORMATION SINCE PALEOCENE ALONG THE AILAO SHAN-RED RIVER SHEAR ZONE, SOUTHEA STERN ASIA[J]. Chinese Journal of Geology, 2006, (2): 291-310.