满洲里地区印支期花岗岩Rb-Sr等时线年代学证据

The Discovery of Indo_Sinian Granites in Manzhouli Area: Evidence from Rb-Sr Isochrons

满洲里－西旗地区为一重要的燕山期斑岩－次火山岩脉型浅成低温矿化区，较早期的花岗岩往往作为矿化围岩。关于本区是否存在印支期花岗岩，一直存在疑问。本文就区内四大矿区的早期花岗岩体（原推断为海西晚期或燕山早期）进行了系统的岩矿和Ｒｂ－Ｓｒ同位素年代学研究，得到两条线性关系甚好的等时线，年龄分别为２１１±２１Ｍａ和２２５．４±７．９Ｍａ，证明该区存在印支期花岗岩。原划分的海西晚期、燕山早期花岗岩相当一部分要解体划为印支期花岗岩。

Manzhouli area is an important metallogenic province of Yanshanian porphyry-subvolcanic vein-epothermal mineralization series. The granites of the earlier stage serve as the main country rocks for ore depostis. It has always been questioned whether Indo_sinian granite exists or not in this area. In the adjacent area within Mongolia and Russia and in the Da Hinggan Mountains to its east there are Indo_sinian granites, but in Manzhouli-Xiqi area, Triassic synthem has not been separated out, and no definite age evidence has been sugggested. Some systematic petrological-mineralogical and Rb-Sr isotopic geochronological studies were carried out on the early stage granites from four major ore districts,which were previously considered to be late Hercynian or early Yanshanian. Two Rb-Sr isochron ages (225±7.9 Ma and 211±21Ma)obtained in this study show fine linear correlation,suggesting the existence of Indosinian granites. A considerable portion of originally-defined late Hercynian and early Yanshanian granites should be reassigned to Indosinian.