KINEMATICS AND GEOCHRONOLOGY OF THE PROTEROZOIC DONGXIANG-SHEXIAN DUCTILE SHEAR ZONE - WITH HP METAMORPHISM AND OPHIOLITIC MELANGE (JIANGNAN REGION, SOUTH CHINA)

A kinematic and geochronological analysis of the 10-20-km-wide northea st-trending Dongxiang-Shexian ductile shear zone, that trends along a length of 250 km in the eastern part of the Jiangnan belt indicates a sinistral strike-slip ductile shear that was formed during the Neo-Pro terozoic. The zone experienced polyphase deformation related to tecton ic collision between the Huaiyu and the Jiuling terranes. Geochronolog ical data and kinematic analysis of macroscopic structures, microscopi c shear indicators and quartz C-axes fabrics shows that a ductile sout heastward thrusting occurred at about 950-900 Ma followed by a sinistr al strike-slip shearing along a northeast trend at about 770 Ma. Coars e clastic sedimentary rocks of Sinian age were deposited unconformably on the entire Jiangnan belt including the Huaiyu and the Jiuling terr anes. This paper emphasizes that the Jiangnan belt in the SE margin of Yangzi plate is a Neo-Proterozoic orogenic belt with HP metamorphism and ophiolitic melange, not a Late Paleozoic-Mesozoic collisional orog en.