甘肃北山地区后造山花岗质岩石的大地构造背景

TECTONIC SETTING OF OROGENIC GRANITES IN THE BEISHAN REGION,GANSU PROVINCE

Ｒｂ－Ｓｒ同位素研究结果表明，北山北部狼娃山南花岗闪长岩等时线年龄为２７８Ｍａ，北山南部野马街北斜长花岗岩和野马街南斜长花岗岩等时线年龄分别为３５１Ｍａ和３１１Ｍａ，结合北山地区已有的大量同位素年龄数据及大地构造背景，提出北山地区晚古生代热事件的存在及其重要构造意义。通过Ｓｒ、Ｎｄ和Ｐｂ同位素组成研究，认为哈萨克斯但板块延入本区，其基底主要由洋壳物质组成。

Rb-Sr isotopic studies of orogenic granites in the Beishan region,Gansu province,gave threeisochron ages:278 Ma(granodiorite south of Langwa Mountain in the northern part of theregion),351 Ma (plagiogranite north of Yemajie in the southern part of the region)and 311 Ma(plagiogranite south of Yemajie). On the basis of these data coupled with large amounts of iso-rope data available in the region and the tectonic setting,the author proposes the existence of theLate Paleozoic significance.Through a study of the Sr,Nd and Pb isotopic compositions, it issuggested that the Kazakhstan plate has extended into the region and that its basement is mainlycomposed of oceanic crust.