内蒙古海拉尔北部八大关地区花岗岩的成岩时代、地球化学特征与成因
Age,Geochemistry and Petrogenesis of Granites from Badaguan Area in Northern Hailaer, Inner Mongolia

摘要： 内蒙古海拉尔北部八大关地区花岗岩以正长花岗岩和二长花岗岩为主，锆石UPb定年显示其形成于晚三叠世((212±17)~(2267±16) Ma)。岩石为弱过铝质(A/CNK=101~110)，分异指数(DI)介于925~958之间。岩石大离子亲石元素K和Rb以及LREE相对富集，高场强元素Nb、Ta、P、Ti 和Ba、Sr相对亏损，并显示中等铕负异常(δEu=051~071)。较低的10 000 Ga/Al值(平均191)以及较低的锆石饱和温度(平均683 ℃)等特征显示该花岗岩属于高分异Ⅰ型。锆石的εHf(t)值较高(450～1045)，Hf二阶段模式年龄为059～097 Ga，反映其源区物质为新元古代增生的基性地壳。综合区域其他地质研究成果，认为研究区晚三叠世花岗岩形成于蒙古—鄂霍茨克洋板块俯冲的活动大陆边缘环境。
Abstract: The granite of Badaguan is mainly composed of syenogranite and monzonitic granite. Zircon UPb isotopic dating yields age of (212±17)-(2267±16) Ma, indicating that they were formed in the Late Triassic. The granites are metaluminous with A/CNK ratios of 101-110 and differentiation index (DI) of 925-958. The granites are enriched in K, Rb and LREE, and depleted in Ba, Sr and HFSE, eg, Nb, Ta, P and Ti, with moderate Eu negative anomalies (δEu=051-071). The relatively low values of 10,000 Ga/Al (average at 191), low zircon saturation temperature (average at 683 ℃) and other geochemical features suggest that the syenogranite and monzonitic granites in the study area are high differentiation Itype granites. The zircons in the granites show high values of εHf(t) (450-1045) with twostage Hf model ages of 059-097 Ga, suggesting that they are derived from the newly formed crust which is separated from NeoProterozoic depleted mantle. Combined with the UPb ages and other geochemical features, we proposed that the granite of Late Triassic formed in an active continental margin setting of the MongolianOkhotsk oceanic plate