Structural Evolution Analsis and Zircon U-Pb Dating of the Ailao Shan Metamorphic Belt, Yunnan, SW China

• Main Authors: Huang, Ning-Hsiang, 黃寧祥
• Other Authors: Lee, Tung-Yi
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/60055231653702801264

碩士 === 國立臺灣師範大學 === 地球科學系 === 99 === The Ailao Shan (ALS) metamorphic complex is part of the NW-SE trending Ailao Shan- Red River Shear Zone (ASRR) in SE China. The E-W bending of the ASRR between Yuanjiang and Honghe along the southern section of the ALS was considered due to the clockwise block rotation around the Eastern Himalaya Syntaxes along the Xianshuihe Xiaojiang fault zone. In order to decipher the interaction structural pattern and kinematic relationship between these two fault systems in this region, field, micro-structural and U-Pb zircon geochronology analysis were conducted. Three deformation events of: an oldest isoclinal recumbent fold forming event (Dn-1) with sub-horizontal fold axial planes occurred younger than 185Ma. Dn deformation event is the strongest deformation event forming large-scale upright folds with NW-SE striking sub-vertical fold axial planes (Sn) for gneiss outcrops and S/C shear fabrics along mylonite zones. Since the Sn is parallel to the dominant shear plane with left-lateral sense of shear demonstrating biotite fish, we interpreted the Dn is the left-lateral shear event of the ASRR which occurred between 27~22Ma. Dn+1 deformation event formed upright folds with N-S striking sub-vertical fold axial plane (Sn+1) with right-lateral sense of shear indicators such as: clockwise sigmoid foliations and quartz ribbons. As the Sn+1 fabrics are parallel to the Xianshuihe-Xiaojiang fault zone, we suggest this deformation might be due to the clockwise rotation of crustal fragments around the Eastern Himalaya syntaxis possibly around mid Miocene.