大兴安岭北部伊图里河地区二长花岗岩的成因及构造背景

Petrogenesis and Tectonic Setting of the Monzonite Granite in Yitulihe area,Northern Great Xing'an Range

本文对大兴安岭北段伊图里河地区黑云二长花岗岩进行了系统的地球化学及锆石U-Pb同位素年代学研究,旨在查明其成岩时代及岩石成因,并探讨其构造意义。研究结果表明,该黑云二长花岗岩的LA-ICP-MS锆石U-Pb年龄为123.3±0.8Ma,表明其形成时代为早白垩世晚期。岩石具有具有高硅、富钾、富铝的特征,A/CNK比值较大（0.96~0.99）,痕量元素具有轻稀土富集、重稀土亏损、富集Rb、K等大离子亲石元素和Th、Ce、Zr、Hf等高场强元素,贫Sr、P、Ti、Ba的特征。以上特征表明伊图里河地区花岗岩为具钾玄质系列岩石特征的铝质A型花岗岩,为中下地壳岩石部分熔融的产物,该期岩浆侵位活动可能发生在早白垩世晚期东部古太平洋板块向欧亚板块俯冲作用下的弧后伸展环境。

In this paper,the geochemistry and zircon U-Pb isotope chronology of the monzonite granites in Yitulihe area in the north of Greater Xing＇an Range is studied and their petrogenesis and tectonic signicicance are discussed.The results prove that the zircons from Yitulihe granites yielded a LA-ICP-MS U-Pb age of 123.3±0.8Ma,indicating intrusive time of the granites is the late early Cretaceous.The granites are rich in silicon,kalium and aluminum,A/CNK ratios ranging from 0.96 to 0.99.The trace elements are characterized by enrichment of LREEs relative to HREEs and enrichment of LILE such as Rb、K and HFSE such as Th、Ce、Zr、Hf,and poor Sr、P、Ti、Ba.These features suggest that the Yitulihe granites belong to aluminous A-type granite and have the characteristics of the shoshonitic rock,which representing the product of partial melting for the middle and lower crustal rocks and the period of magmatic emplacement events may occur in the late early cretaceous ancient eastern Pacific plate to Eurasian plate subduction of the back-arc extension environment.