Structural feature and its significance of the northernmost segment of the Tertiary Biluoxueshan-Chongshan shear zone,east of the Eastern Himalayan Syntaxis  

作　　者：ZHANG Bo ZHANG JinJiang ZHONG DaLai WANG XiaoXian QU JunFeng GUO Lei 

机构地区：[1]Key Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China [2]State Key Laboratory of Geological Processes and Mineral Resources, China University ofGeosciences, Beijing 100083, China [3]Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China [4]Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

出　　处：《Science China Earth Sciences》2011年第7期959-974,共16页中国科学（地球科学英文版）

基　　金：supported by National Natural Science Foundation of China for Young Foundation (Grant No. 40802050);China Postdoctoral Science Foundation (Grant No. 20070420065)

摘　　要：Here we describe ductile, ductile-brittle and brittle deformation styles in the northern segment of the Tertiary Biluoxue- shan-Chongshan shear zone lying to the east of the Eastern Himalayan Syntaxis. In the northernmost part of the zone in the vi- cinity of the Eastern Himalayan Syntaxis, it consists of mylonitic gneiss, granite, and schist. Based on field relations and min- eral assemblages, the rocks are classified into gneiss belt in the west limb, including banded gneiss, augen mylonite and mig- matite gneiss, and schist belt in the east limb. Except for the massive granite pluton, the other three tectonites are affected by polystage deformation （D1-D4）. Fold deformation of the first stage D1 is isoclinal to tight pattern with nearly N-S fold axes and steeply axial planar cleavage S 1, which resulted in the local crustal thickening under a contractive setting. D2 overprinted D1 and is characterized by tight folds with steep axes and N-S fold axial planar, which are also characterized by large-scale ductile strike-slip shear foliation $2, parallel to the nearly N-S trending axial planes of D1 and D2. The structural pattern of D2 represents a transpression along the zone. D3 occurred during the late stage of the transpression or post-transpression, produc- ing the NW-SE and NE-SW trending strike-slip faults of the third stage D3. Following the D3 deformation, the zone was ex- humed to shallow crustal level where the various tectonites underwent a brittle transtensional deformation D4, combined with one N-S trending strike-slip component and one normal faulting component. Structures and previous geochronologies pre- sented in the paper suggest that the study area is correlated with those in the adjacent tectonic zones, Ailaoshan-Red River shear zone and Gaoligong shear zone in the western Yunnan. It underwent intensive polyphase deformation, namely, crustal thickening, transpression, and transtension, responding to syn-collision and post-collision of India-Eurasia from 65 Ma to cur- rent period east of theHere we describe ductile,ductile-brittle and brittle deformation styles in the northern segment of the Tertiary Biluoxue-shan-Chongshan shear zone lying to the east of the Eastern Himalayan Syntaxis.In the northernmost part of the zone in the vicinity of the Eastern Himalayan Syntaxis,it consists of mylonitic gneiss,granite,and schist.Based on field relations andmineral assemblages,the rocks are classified into gneiss belt in the west limb,including banded gneiss,augen mylonite and migmatite gneiss,and schist belt in the east limb.Except for the massive granite pluton,the other three tectonites are affected by polystage deformation (D1-D4).Fold deformation of the first stage D1 is isoclinal to tight pattern with nearly N-S fold axes and steeply axial planar cleavage S1,which resulted in the local crustal thickening under a contractive setting.D2 overprinted D1 and is characterized by tight folds with steep axes and N-S fold axial planar,which are also characterized by large-scale ductile strike-slip shear foliation S2,parallel to the nearly N-S trending axial planes of D1 and D2.The structural pattern of D2 represents a transpression along the zone.D3 occurred during the late stage of the transpression or post-transpression,produc-ing the NW-SE and NE-SW trending strike-slip faults of the third stage D3.Following the D3 deformation,the zone was ex-humed to shallow crustal level where the various tectonites underwent a brittle transtensional deformation D4,combined with one N-S trending strike-slip component and one normal faulting component.Structures and previous geochronologies presented in the paper suggest that the study area is correlated with those in the adjacent tectonic zones,Ailaoshan-Red River shear zone and Gaoligong shear zone in the western Yunnan.It underwent intensive polyphase deformation,namely,crustal thickening,transpression,and transtension,responding to syn-collision and post-collision of India-Eurasia from 65 Ma to current period east of the Eastern Himalayan Syntaxis.

关 键 词：Biluoxueshan-Chongshan shear zone TERTIARY structure polystage deformation 

分 类 号：P542.2[天文地球—构造地质学] Q949.751.9[天文地球—地质学]