黑沟断裂带及其对东秦岭北坡构造演化的控制

黑沟断裂带是东秦岭北部分隔秦岭地槽与华北地台的边界断裂。本文围绕黑沟断裂带,阐述了黑沟断裂带的地质特征,对比了黑沟断裂两侧的形成环境、变形特征及变质环境。由黑沟断裂南侧到北侧,存在以下几个变化极向性:形成环境由秦岭大洋环境到华北地台南缘改造大陆边缘环境,改造大陆边缘可进一步划分为洛南—栾川岛弧环境,熊耳山弧后盆地环境;变形由强烈的塑性变形到弱变形,变质由角闪岩相到低绿片岩相及低于低绿片岩相。在宽坪群内部存在一由南往北的递增变质带,由低绿片岩相→绿片岩相→低角闪岩相。宽坪群以及黑沟断裂带中存在高压相系。由此,作者从板块构造思想出发,认为黑沟断裂带是以板块结合带存在、发展并控制着东秦岭北坡构造环境的发展演化,其发展演化可划分为四个阶段:(1)中元古代俯冲阶段,(2)晚元古代推覆剪切阶段,(3)早古生代伸展阶段,(4)早古生代末挤压阶段。

THE HEIGOU FAULT ZONE AND ITS CONTROL OVER THE STRUCTURAL EVOLUTION IN THE NORTH SLOPE OF THE EASTERN QINLING

The Heigou fault in the northern part of the eastern Qinling is a boun- dary fracture between the Qinling geosyncline and the platform of the North China.The geological characteristics of the Heigou fault zone have been introduced briefly,and the environments,the deformed features and the metamorphisms occurring on both sides of the fault have also been discussed in this paper.Several changeful polar orientations appeared from the south to the north sides of the Heigou fault.The formational environ- ment was formed from the Qinling ocean to the reformed continental margin of the southern border of the North China platform.The reformed contin- ental margin can be divided into the Luonan-Luanchuan island arc and the Xiongershan back-arc basin environments.The deformation was changing from plastic intensity to weakness and the metamorphic facies ranged from amphibolite to low-grade greenschist.A zone of progressive metamorphism which was from the low-grade greenschist to greenschist and then to low- grade ampholite facies occurs in the Kuanping Group from south to north. There is a high-pressure facies system in the Kuanping Group and the Hei- gou fault.According to the theory of plate tectonics,the writer thought that the Heigou fault occurred and developed in a joint zone of plates, which controlled the development and evolution of the tectonic environment in the north slope of the eastern Qinling.The development and evolution can be divided into four stages.1)subduction in the middle Proterozoic era;2)napping and shearing in the late Proterozoic era;3)extension in the early Palaeozoic era;4)compression at the end of the early Palaeozoic era.