西藏阿里札达韧性剪切带特征及其X光岩组分析

文中简述了西藏阿里札达盆地的地质背景、区域地层和札达韧性剪切带的基本特征。采用X射线衍射法对札达韧性剪切带中的石英、方解石和白云母等三种矿物,进行了X光岩组分析,确定了韧性变形岩石的组构特征、韧性剪切带的属性和变形岩石的应变类型,以及韧性剪切带形成时的温压条件。研究表明,韧性变形岩石均具不对称组构,反映韧性带属于南盘(下盘)俯冲型韧性剪切带,韧性变形是在高温、高压、低应变速率条件下发生的,处于>10km的地壳深度,岩石应变类型以压扁应变为主。

The characteristics of ductile shear zones and X-ray petrofabrics analyses in Zanda, Ali, Tibet

This paper reports on the geologic settings, regional strata and characteristics of the Zanda ductile shear zone in Tibet. The Zanda ductile shear zone that lies 10 km north of Zanda county town and above pre-Cenozoic folded strata, resulted from late continent-continent collision. This ductile shear fracture accompanied with underthrusting mainly exhibits a wide, north-dipping, penetrative schistosity cleavage belt. The Triassic and Permian rocks in schistosity cleavage belt have experienced green schist metamorphism and deformation. A series of isoclinal folded phyllite schists and sand slates, with fold axis dipping north and plunging south, were overprinted by a group of schists paralleling the fold axial plane. The schist's attitude is 55°∠50° and the lineation points to the east, with dip angle of 30°-40°. The authors have made X-ray petrofabric analyses of quartz, calcite, dolomite and other minerals in the Zanda ductile shear zone by the X-ray diffraction method. In addition, we have determined the fabric characteristics of ductile deformation rocks, the attributes of the ductile shear zone, the mechanism, the slip system and dynamics of ductile shear zone, the strain types of deformation rocks, and the temperature-pressure conditions for the formation of the shear zone. A plane-pole figure and an optical axis figure were drawn from X-ray petrofabrics. This study demonstrates that the ductile deformation rocks have an asymmetric fabric, indicating northward underthrusting of India plate beneath the Eurasian plate. Ductile deformation within the Zanda shear zone occurred under conditions of high-temperature, high-pressure and low strain rate at a depth of more than 10 km. Our study also shows that compressive strain is the main strain type of the rocks we have examined.