商丹断裂南侧糜棱岩的演化及递减变形序列

THE EVOLUTION AND THE DECLINING DEFORMATION SERIES OF MYLONITES ON THE SOUTH SIDE OF THE SHANGDAN FAULT

本文研究的糜棱岩中,矿物的变形行为表现出明显差异。在糜棱岩形成期间,主要矿物依斜长石,钾长石、石英的次序先后从热加工变形状态向冷加工变形状态转化,据此可将糜棱岩的形成划分为4个演化阶段。研究表明,矿物变形行为的转化主要是温度下降引起的。作者将斜长石、钾长石、石英变形行为的依次转化称为递减变形序列。

All the mylonites studied are polycrystalline and consist maily of quartz, Kfeldspar, plagioclase, micas and garnet. The deformation behavior and recrystallization characteristics of these minerals are studied in the paper. The characteristics of deformation and dynamic recrystallization of micas, feldspars and quartz indicate that the ductile shear metamorphism proceeded under the changing conditions of P-T. This kind of metamorphism is thought to begin at about 580℃ and 550 MPa, and end at about 380℃ and 480 MPa.Due to the decrease of temperature and pressure the behaviour of hot working deformation of main minerals is transformed into cold working and brittle deformation behaviour in order of plagioclase, K-feldspar and quartz from the early to the late period. And these changes are accompanied by an increase in heterogeneity of deformation. On the basis of these variations the evolution of the mylonites may be divided into four stages:plagioclase stage,k-feldspar stage,quartz stage,mica stage.A process of lowering P-T is showed from plagioclase stage to mica stage. The characteristics of deformation defined by the main minerale is called the declining deformation series.