大兴安岭北段漠河富源沟林场早侏罗世花岗岩——年代学、地球化学特征及构造意义

EARLY JURASSIC GRANITES IN FUYUANGOU FOREST FARM OF MOHE COUNTY,NORTHERN DAXINGANLING MOUNTAINS:Chronology,Geochemistry and Tectonic Implications

通过对大兴安岭北段富源沟林场早侏罗世二长花岗岩进行岩相学、地球化学、LA-ICP-MS U-Pb定年研究,探讨其对该区构造演化的制约.该花岗岩主要由二长花岗岩组成,锆石测年结果显示,样品WJL030二长花岗岩结晶年龄为200±1 Ma,样品WJL032二长花岗岩结晶年龄为202±1 Ma,形成与早侏罗世.富源沟林场早侏罗世二长花岗岩为高钾钙碱性、偏铝质的I型花岗岩类,富集轻稀土和大离子亲石元素(Rb、K、Ba等),亏损重稀土和高场强元素(Nb、Ta和P).岩石为壳源成因,形成于俯冲环境,是玄武质下地壳部分熔融的产物.结合区域资料,花岗岩的侵位反映了研究区早侏罗世期间,漠河地区仍处于蒙古-鄂霍次克大洋板块俯冲于额尔古纳地块之下的构造环境.

Through the study of petrography,geochemistry and LA-ICP-MS U-Pb dating of the Early Jurassic granites in Fuyuangou Forest Farm,northern Daxinganling Mountains,the paper discusses their constraints on the regional tectonic evolution. Dominated by monzogranite,the granites are formed in Early Jurassic shown by the zircon dating results of samples. The geochemical analyses reveal that the monzogranite, belonging to high-K calc-alkaline,metaluminous I-type granitoid,is characterized by enrichment of LREEs and LILEs（Rb,K and Ba）,and depletion of HREEs and HFSEs（Nb,Ta and P）. The primary magma for the monzogranite is derived from partial melting of basaltic lower crust. Combined with the regional data,the emplacement of granites indicates that the Mohe region was still in the tectonic environment of subduction of Mongolia-Okhotsk oceanic plate beneath Erguna Massif during the Early Jurassic Epoch.