南秦岭三河口地区三河口群的解体和时代厘定

DISINTEGRATION OF THE “SANHEKOU GROUP”OF THE SANHEKOU AREA, SOUTHERN QINLING AND ITS AGE

在南秦岭西段文县北部三河口地区 ,广泛出露一套变质沉积岩系——三河口群 ,根据最新 1/5万区域地质调查成果 ,认为三河口群属一套总体有序、局部无序的构造混杂岩型非史密斯地层体 ,故而建议将三河口群解体 ,对前人以零星化石所代表的年代建立相对规整有序的地层系统予以重建。现据空间叠覆关系 ,将前人划分的桥头组、屯寨组和羊汤寨组三个地层单位重新厘定 ,认为该套变质沉积岩系由两个不同时代的岩片组成 ,分别相当于晚震旦世雪花太坪岩群和早泥盆世桥头岩组、羊汤寨岩组 ,两者是印支期构造混染带的重要组成部分。

The metamorphic “Sanhekou Group” is mainly distributed in the Sanhekou area of the western sector of South Qinling. The “Sanhekou Group” is regarded as a tectonic mélange non Smith stratified rock which is ordered in general but disordered in part according to the recent regional geologic surveying. So it is suggested that the Smith stratigraphic system of the “Sanhekou Group” which is based on the age of some fossils must be disintegrated. It must be redeterminated according to the regional superimposition relationships of the tectono stratigrahic unit of the Qiaotou, Tunzhai and Yangtangzhai Formations. The new stratigraphic system of the metamorphics is composed of two sheets complexes similar to the Xuehua taiping Group complex of Late Sinian age and the Qiaotou, Yangtangzhai Formation complexes of Early Devonian. Either of them is the main component of the tectonic mélange zone at Indosinian—Variscan stage.