冀东太古宙结晶基底区构造单元划分

TECTONIC UNITS OF THE ARCHEAN CRYSTALLINE BASEMENT IN EASTERN HEBEI

本文从地质事件的角度出发,根据岩石成因类型,变质作用强度、期次,变形作用方式、构造样式,区域地球物理场特征及同位素地质年代学和矿化资料,将冀东太古宙结晶基底区划分为高压紫苏花岗片麻岩区、低压紫苏花岗片麻岩区、TTG杂岩区和岩浆构造混杂岩区四个构造单元,并提出高压紫苏花岗片麻岩区和低压紫苏花岗片麻岩区是冀东太古宙地壳同一时期不同深度层次或压力环境下的产物。岩浆构造混杂岩区是叠加于高压紫苏花岗片麻岩区背景之上长期活动的弧形线性巨型构造活动带。而TTG杂岩区是太古宙末期形成于地壳较浅部层次的花岗杂岩穹窿。

From the angle of geological events and on the basis of the genetic types of the rocks, metamorphic grades, deformation and tectonic styles, features of regional geophysical fields, isotopic geochronology and mineralization, the Archean crystalline basement in eastern Hebei may be divided into the following tectonic units. High-pressure charnochite-gneiss terrain The terrain consists mainly of the sodian charnockite-gneiss series and is tectonically manifested by a series of brachy or oval folds. It has undergone granulite-facies metamorphism twice. The types and origin of the gneissosity are complex;it is mainly represented by deformed planar structure. The supracrustal rocks occupy a small proportion. Low-pressure charnockite-gneiss terrain It is made up mainly of thepotassie charnockite-gneiss series, which forms a large oval structure in terms of space. It has been subjected to the early-stage high amphibolite-facies and latestage granulite-facies metamorphism. In this terrain planar structures formed by diapiric emplacement and tectonic deformation of the rock body have been both preserved. The supracrustal rocks represent a relatively large proportion. The terrain contains BIF type deposits of important econmic value. TTG complex terrain This terrain is composed of TTG granite complex, which forms an imcomplete dome. It has undergone amphibolite-facies metamorphism. The rocks in the center of the dome are massive, and gneissosity is well developed at its edges. Tectono-magmatic complex terrain The rock types are very complex, includig granite—gneiss, granulite, TTG complex, tectonite, stratified supracrustal rocks and retrogressive metamorphic rocks which mix together. In terms of space, they form a large linear arcuate body. This terrain has gone through metamorphism at least three times. The Mesozoic witnessed strong superimposition of magmatic activities. Gold mineralization is prevalent Study has indicates that the high-pressure and low, pressure charnockitegneiss terrains were formed contemporaneously at different depths or pressures in the Archean crust of eastern Hebei. The tectono-magmatic complex terrain is a long-active linear gigantic tectonic mobile zone superimposed on the high-pressure charnockite-gneiss terrain. The TTG complex terrain is a granite complex dome formed at the relatively shallow level of the crust at the end of the Archean.