中国大陆中部中晚元古宙复合“三叉”裂谷系及演化初析

A PRELIMINARY ANALYSIS FOR THE RECURRENT THREE ARM RIFT SYSTEMS AND EVOLUTION OF THE CENTRAL PART OF THE CHINESE CONTINENT DURING THE MIDDLE LATE PROTEROZOIC

地处中国大陆中部的秦、祁造山带、华北地台南缘及扬子地台西北缘区，中、晚元古宙可能存在一个由两个三联点构成的复合“三叉”裂谷系。其中一个位于东秦岭以商南为三联点，其北东支为熊耳裂谷，西支和东南支分别为宽坪和红安裂谷。另一个位于西秦岭以天水为三联点，其北西支为中、祁连地轴南缘朱龙关群分布一线，西南支为扬子西北缘盐边—碧口群分布一线；二者曾发育成洋盆。东支仍为宽坪裂谷，其与东秦岭“三叉”系之西支为复合臂。构成的构造格局很象大西洋与其东侧几内亚海湾附近贝努埃—楚马“三叉”系构成之格局。

Abstract The area lying to the Qinling Qilian orogenic belts, the southern margins of the Huabei platform and the northwestern margins of the Yangtze platform in the central part of the Chinese central region has been thought by the author that there might exist a recurrent three arm rift systems with two triple junction during the middle late proterozoic.One lies in the Shangnan of the East Qinling,its northeastern breach is the Xinger rift.The southeastern breach is the Huongan rift,the western breach is the Kuanping rift.Another triple junction lies in the Qianshi of the West Qinling.Its northwestern breach is located along the southern margins of the central Qilian axis,the southwestern breach is located along the lines of the Eanpan Bikou and it is assumed that an open ocenic basin had existed along this two breach during middle late proterozoic.The eastern breach of this rift system is still the Kuanping rift and belongs to a recurrent breach with the western breach of the east Qinling three arm rift.This tectonic appearance seems much like the framework composed of the Atlantic Ocean now and the Balue Zuima three rift near the Guinan gulf. Key wards Qinling Qilian orogenic belts,Southern margins of Huabei platform,Northwestern margins of Yangtze platform,Recurrent three arm rift system