剪切指向转换的韧性剪切带——中国大陆科学钻探工程(CCSD)主孔中韧性剪切带(深度2010～2145m)的EBSD特征及运动学研究

Ductile shear zone of changed shear sense:EBSD characteristics and kinematics of ductile shear zone from 2010 to 2145m of the main borehole in Chinese Continental Scientific Drilling(CCSD).

位于苏鲁超高压变质地体南部的中国大陆科学钻探工程(CCSD)主孔深度1596～2038m的榴辉岩段和2038～2500m的片麻岩段之间存在一条厚一百余米的韧性剪切带(深度2010～2145m)。韧性剪切带由糜棱岩化退变榴辉岩、花岗质糜棱岩等强应变岩石组成,韧性剪切带的面理倾向SEE,倾角由上部平均52°向中、下部平均32°转变,拉伸线理产状与面理倾向近一致,是220～200Ma期间折返应变的产物。糜棱岩化退变榴辉岩和花岗质糜棱岩的显微构造与石英晶格优选方位显示了折返阶段早期自SEE向NWW逆冲剪切指向以及后期自NWW向SEE正滑剪切指向转化的应变行为。CCSD主孔2010～2145m韧性剪切带的形成与它位于以榴辉岩为主的岩性-构造单元与其下以片麻岩为主的岩性-构造单元的界线附近有密切联系。第一期超高压阶段南北向韧性剪切作用形成的叶理、拉伸线理产状及相关的岩石类型与第二期、第三期阶段SEE- NWW向折返变形明显不同。

There is a ductile shear zone (2010 similar to 2145m) between eclogite unit (depth 1596 similar to 2038m) and gneiss unit(depth 2038 similar to 2500m) in main borehole of Chinese Continental Scientific Drilling(CCSD) located in southern part of SuLu ultra-highpressure metamorphic terrane. Ductile shear zone is composed of strong deformational rocks of mylonitic retrograde metamorphic eclogite, granitic mylonite et al., foliation of ductile shear zone dip to SEE, dip angle changes from average 52 degrees in upper part to 32 degrees in middle and lower part. Attitude of stretching lineation is basic identical with dip of foliation, ductile shear zone resulted from exhumed deformations in 220 similar to 200Ma. Microstructure and lattice-preferred orientations of quartzs from mylonitic retrograde metamorphic eclogite and granitic mylonite indicate that exhumed early stage have a SEE-NWW thrust shear sense and exhumed later stage have a NWW-SEE normal-slip shear sense. Forming of ductile shear zone(2010 similar to 2145m) in main borehole from CCSD is related with site of ductile shear zone(2010 similar to 2145m) which locate in boundary between eclogite unit and gneiss unit. Attitude of foliation, stretching lineation of the first stage N-S direction ductile shear deformation in ultra-highpressure stage is different from the second, the third stage SEE-NWW direction exhumed deformation.