摩天岭褶皱带及邻区晚前寒武纪板块构造初析

A PRELIMINARY ANALYSIS FOR THE PLATE TECTONICS OF MOTIANLING FOLD AND ITS NEIGHBOURHOOD DURING THE LATE PRECAMBRIAN

摩天岭褶皱带位于扬子地台西北缘,主要由中、晚元古宇“碧口群”火山、沉积杂岩系组成。笔者认为:该套杂岩系在刘家坪—铜钱韧性剪切带以南,是一套构造混杂岩,属中晚元古宙“碧口”古洋盆消减、关闭过程中形成的产物;在该剪切带以北,碧口杂岩系则主要由一套弧前盆地杂砂岩系和一套钙碱性火山岩系组成,后者属喷发在以鱼洞子群为基底的南秦岭古陆南缘之上的岛弧火山岩系。晚元古宙末,由于介于南秦岭古陆与扬子古陆之间的碧口古洋盆关闭,最终形成了扬子古陆北缘晚元古宙碰撞型造山带。摩天岭褶皱带则属该碰撞造山带的超迭壳楔和碰撞混杂岩单元部分。

The Motianling folt belt is located in the northwestern margin of the Yantze plate. Its main body is composed of the middle - late Proterozoic 'Bikou Group' volcanic and sedimentary complex series. The author suggests that the complex series in the south of the Tongqian ductile shear belt should be a melange, which had been formed by the consuming and closing processes of the 'Bikou' ancient ocaanic basin during the middle- late Proterozoic . The 'Bikou' complex series in the north of Tongqian ductile shear belt is made of a graywacke series of the fore arc setting and a cale - alkali volcanic series. The latter belongs to an island arc volcanic series which had erupted on the southern margin of the south Qinling ancient continent with a basement being made of the Yudongzi Group. In the end of late Proterozoic the 'Bikou' ancieut oceanic basin between the Yantze old land and the south Qinling old land was closed to form a late Proterozoic collision oro-genic belt in the northwestern margin of the Yantze plate. The motianoling fold belt has been regarded as an overriding wedye and the collision melange part of the collision erogenic belts.