内蒙古乌兰浩特地区二长花岗岩年代学、岩石成因及其构造环境

Geochronology,petrogenesis and tectonic setting of monzogranite from Wulanhaote area,Inner Mongolia

内蒙古乌兰浩特地区太平山嘎查岩体主要岩石类型为黑云母二长花岗岩。所测得的LA-ICP-MS锆石U-Pb年龄分别为127.4 Ma和125.6 Ma,属于早白垩世。太平山嘎查岩体的地球化学特征表明岩体属于弱过铝质、高钾钙碱性系列的高分异I型花岗岩。样品(P9-48-1)的锆石Hf同位素组成显示黑云母二长花岗岩的ε_(Hf)(t)=+8.60±0.57,两阶段亏损地幔模式年龄为511~748 Ma,说明其岩浆源区主要为新元古代—显生宙期间从亏损地幔新增生地壳的部分熔融。太平山嘎查岩体应形成于伸展构造体制,该伸展构造体制的产生可能与古太平洋板块向欧亚大陆下的俯冲有关。

Taipingshangacha pluton in Wulanhaote area of Inner Mongolia is composed mainly of biotite monzogranite.The LA--ICP--MS zircon U--Pb dating shows that Taipingshangacha pluton was formed in Early Cretaceous with ages of 127.4 Ma and 125.6 Ma.Geochemical data show that the Taipingshangacha pluton is characterized by weakly peraluminous attribute,and falls on high-K calc-alkaline series,belonging to highly fractionated I-type granites.The zircon Hf isotope data of sample P9--48--1 indicate that the biotite monzogranite sεHf(t)=+8.60±0.57,and the model ages(T DM2)of two stages are from 511 Ma to 748 Ma,which implies that the biotite monzogranite might be derived from the partial melting of the crustal substance accreted from depleted mantle during Neoproterozoic--Early Phanerozoic.Combined with regional geological investigations,it is suggested that Taipingshangacha pluton was formed in extensional background,which may be related to the subduction of the Paleo--Pacific plate into Eurasia.