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 the
ZHANG BoZHANG JinJiangZHONG DaLaiWANG XiaoXianQU JunFengGUO Lei
