青海省哇洪山断裂带中段构造变形特征及X光岩组分析  

CHARACTERISTICS OF DEFORMATION AND X-RAY PETROFABRICS IN THE MIDDLE WAHONGSHAN FAULT ZONE,QINGHAI PROVINCE

作　　者：张拴宏[1] 周显强[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081

出　　处：《大地构造与成矿学》2003年第1期29-36,共8页Geotectonica et Metallogenia

基　　金：国土资源地质大调查项目(DKD9902003)部分成果.

摘　　要：通过对哇洪山断裂带中段构造变形宏观及微观特征的研究,认为该断裂带经历了两种不同层次、不同性质的构造变形,早期以韧性变形为主,形成了沿断裂带广泛分布的NW-NNW向糜棱岩带;晚期以脆性变形为主,形成了广泛分布断层破碎带,并将早期的糜棱岩带错断。X光岩组分析结果表明,糜棱岩带构造岩内矿物排列定向性明显,其中石英变形以底面滑移或近底面滑移为主,兼有柱面滑移,为中低温-中温变形环境所形成;另外动态重结晶对变形岩石中石英优选方位的形成也可能发挥了重要作用。华里西晚期花岗闪长岩、印支期钾长花岗岩、花岗岩、二长花岗岩均没有明显的优选方位,因此韧性变形发生在该类岩石侵位之前。构造变形分析及同位素测年结果证实韧性剪切带形成于晚志留世,即加里东晚期。The Wahongshan fault zone in Qinghai Province is one of the most important faults in western China. In this paper, deformation and X ray petrofabrics have been studied in the middle segment of the fault. The results show that formation of the fault zone can be divided into two major stages: ductile shear deformation and brittle deformation. The early ductile shear leads to the formation of the NW NNW trending mylonite zones along the fault, which are intensely cut by the late formed brittle faults. X ray petrofabrics of rocks near the faults indicate that the minerals in the tectonites show a great orientation in the alignment. The quartz, which is a very important mineral in the tectonites, is deformed with basal face gliding or near basal face gliding, and sometimes with prismatic face sliding, which indicates that the rocks are deformed in an epithermal mesothermal or mesothermal environment, and the dynamic recrystallization also plays an important role on the formation of the quartz alignment. The results also show that plutons formed in Hercynian and Indosinian cycles have no great ductile deformation from the X ray petrofabrics, so these rocks are formed after the formation of the ductile shear zones. Structural deformation analysis and isotope geochronology of syntectonic muscovite indicate that the Wahongshan ductile shear zone is formed in late Silurian Period during late Caledonian epoch.

关 键 词：洪山断裂带 构造变形 X光岩组 青海 同位素测年 岩浆活动 

分 类 号：P542.3[天文地球—构造地质学]