新疆西南天山含金红石脉的显微构造变形机制

新疆西南天山变质带是研究有关洋壳型俯冲变质演化的重要地区之一。岩石、矿物的显微构造是其变形、变质等各种地质作用的直观记录。选择含金红石绿辉石脉的变质岩作为样品进行显微构造研究。通过显微镜观察了解脉体中绿辉石的须状增生、晶内裂隙、穿晶张裂隙,金红石的锯齿状颗粒边界和主岩中石榴子石的变斑晶包迹结构,蓝闪石的晶内裂隙和显微分层现象,白云母的波状消光、亚晶粒旋转重结晶现象和扭折带,铁白云石的机械双晶等显微变形现象。说明西南天山变质带中的变质岩在俯冲—抬升至地表的过程中,变质岩及脉体的主要变形机制为有流体参与的压溶作用和固态扩散物质迁移、晶质塑性变形和微破裂为主要变形机制,局部存在颗粒边界滑移。

Microstructural deformation mechanism of the vein with rutile in Southwestern Tianshan, Xinjiang

Southwestern Tianshan metamorphic belt in Xinjiang is one of the most important research areas related to subduction of oceanic crust metamorphic evolution. Microstructures of rock and minerals are the visually recording of deformation and metamorphism. Choosing a metamorphic rock which has a omphacite vein with rutile as sample to research microstructure. Utilizing microscopic examination to research the microstructure. In the vein, omphacite are fibrous, which have whisker crystal, intragranular microfracture and transgranular microfracture. Rutile have jagged grain boundary and intragranular microfracture. Quartz have undulatory extinction and directional elongation of single grain. In the host rock, garnet has porphyroblast trail. Omphacite has dynamic recrystallized aggregates. Glaucophane have intragranular microfracture and microlayering. Muscovite have undulatory extinction, subgrain rotation recrystallization and kink bands. Ankerite has mechanical twin. All of these deformation behaviours prove that, in the process of subduction-exhumation of the metamorphic belt, the main deformation mechanisms of vein and host rock include pressure solution which attributes to liquids, solid-state diffusive mass transfer, crystalline deformation and microcracks are main deformation mechanism. Grain boundary sliding exist in part of the rock.