大兴安岭南段乌兰毛都地区早白垩世花岗闪长岩的岩石成因及构造背景

Petrogenesis and tectonic setting of Early Cretaceous granodiorite in Wulanmaodu area of southern Great Xing an Range

通过探讨大兴安岭乌兰毛都地区花岗闪长岩的岩石学、年代学及全岩地球化学特征,以确定研究区花岗闪长岩的形成时代、岩石成因及其地球动力学机制。LA-ICP-MS锆石U-Pb定年结果表明研究区花岗闪长岩为早白垩世(132±2 Ma)岩浆作用的产物。全岩地球化学结果显示其具有高硅(SiO 2=66.68%~68.09%)、低铝(Al 2O 3=14.94%~15.35%)特征,富集轻稀土元素和大离子亲石元素(Rb、K),亏损重稀土元素和高场强元素(Nb、Ta、Ti),属于高钾钙碱性系列I型花岗岩。综合区域中生代花岗岩岩石学及地球化学特征,认为以乌兰毛都为代表的早白垩世I型花岗岩可能形成于活动大陆边缘环境,该期构造-岩浆作用与古太平洋板块俯冲作用密切相关。

Petrology,geochronology and whole rock geochemistry study have been conducted for the granodiorite in Wulanmaodu area of Great Xing an Range,in order to determine its formation age,petrogenesis and geodynamic mechanism.LA--ICP--MS zircon U--Pb data indicates that the granodiorite in Wulanmaodu area formed during the Early Cretaceous with the age of(132±2)Ma.The geochemical data shows that the granodiorite samples in the study area are characterized by high silicon(SiO 2=66.68%~68.09%)and low aluminum(Al 2O 3=14.94%~15.35%),and enriched in light rare earth elements(LREEs)and large-ion lithophile elements(LILEs;e.g.,Rb and K),and depleted in heavy rare earth elements(HREEs)and high field strength elements(HFESs;e.g.,Nb,Ta and Ti),suggesting that they are high-K calc-alkaline I-type granites.Based on the petrological and geochemical characteristics of the Mesozoic granites in the region,it is suggested that the Early Cretaceous I-type granites represented by the Wulanmaodu granodiorite may have formed in the active continental margin environment,and that the tectono-magmatism of this period is closely related to the subduction of the Paleo-Pacific plate.