嫩江地区中晚加里东期区域变质岩系构造背景

Tectonic setting of the middle and late Caledonian regional metamorphic rock in Nenjiang area

按板块构造划分,嫩江地区位于兴蒙造山带东段兴安地块与松嫩地块交会部位,区内多期次的构造叠加作用强烈,是研究兴蒙造山带构造演化的关键地区之一。从研究区中晚加里东期区域变质岩系的区域地质背景着手,结合现有的区域地层和构造资料,对区内中晚加里东期区域变质岩系岩石学及地球化学特征、变质变形特征进行分析,通过野外地质产状和岩石共生组合的分析、变质作用及变质相的划分、构造环境判别等方法对区内中晚加里东期所经历的构造背景问题进行研究,认为研究区经历了弧后拉张→岛弧火山喷发沉积→弧后边缘海盆地伸展→弧后边缘盆地沉积的大地构造背景。区内中晚加里东期区域变质岩系的研究,对于重建嫩江地区加里东期构造背景具有重要意义。

In terms of plate tectonics,the research area is located at the intersection of Xing＇an block and Songnen block in the eastern section of the Xing＇an-Mongolian orogenic belt. Impacted with many periods of strong tectonic superposition,this is one of the key areas to study the tectonic evolution of this orogenic belt. The study of the regional metamorphic rocks in the middle and late Caledonian period is of great significance for restructuring tectonic setting of the Caledonian period in the study area. Starting from the regional geological background of the middle and late Caledonian regional metamorphic rocks in the study area,and based on the present regional strata and tectonic data, this paper studies their petrological, geochemical characteristics and metamorphic deformational characteristics. Through the analysis of field geological occurrence,rock paragenetic association,metamorphism,metamorphic facies division and tectonic environment discrimination,this paper studies the tectonic setting of the middle and late Caledonian period in the study region. It is believed that this region underwent post-arc extension-island-arc volcanic eruption deposition-back-arc marginal sea basin extension-back-arc marginal basin deposition.