从同位素年龄资料试述白乃庙群的解体及其构造学意义

术文主要讨论原白乃庙群地层岩石中所获得的几组同位素年龄资料的地层构造学意义,初步将争议很大的原白乃店群解体为白乃庙群（为中晚元古界,锆石年龄资料为1525～620Ma）和徐尼乌苏群（志留系,含蜂巢珊瑚、中巢三珊瑚等大量化石,Rb-Sr等时年龄数据为427.5±17Ma）。初步确定内蒙古中部白乃庙一带早古生代的占岛弧为一个人陆边缘弧,其火山链呈岛屿,走向近东西,弧后区是浅海。

THE DISINTEGRATION OF THE BOIN SUM GROUP AND ITS TECTONIC SIGNIFICANCE AS VIEWED FROM ISOTOPIC AGE DATA

This paper mainly deals with the stratigraphical and tectonic significance of several groups of isotopic ages obtained from the Boin Sum Group rocks. There have been a lot of disputes about the original Boin Sum Group. In this paper the group is divided into two parts: （1） the Boin Sum Group: middle-upper Proterozoic in age, with a zircon age of 1525 to 620 Ma; （2） The Xuniwusu Group: Silurian in age, containing coral fossils, with a Rb-Sr isochron age of 427.5±17.5 Ma. It has been determined preliminarily that the early Paleozoic paleo-island arc in the vicinity of Boiu Sum in the middle part of Inner Mongolia is a continental-magin island arc. Its volcanic chain occurs as islands striking nearly E-W, and its back-arc area is a shallow sea.