大兴安岭北部碧州地区满克头鄂博组流纹岩地球化学特征研究

Geochemistry Characteristics of Rhyolites in Manketou'ebo Formation from Bizhou Area, Northern Greater Xing'an Range

对大兴安岭北部碧州地区满克头鄂博组流纹岩进行了详细的地球化学特征研究。地球化学特征表明该期流纹岩属于高钾富碱钙碱性过铝质岩石,球粒陨石标准化稀土配分曲线呈轻稀土富集的右倾特征,原始地幔标准化图解显示大离子亲石元素Rb、K、Sr、Ba的富集及高场强元素Nb、Ta、P的强烈亏损,(La/Sm)N、(Sr/Ba)N变化幅度弱,综合反映其岩浆源区为过渡型地幔。流纹岩由过渡型地幔岩石减压熔融形成玄武质岩浆,上升到下地壳岩浆房中经结晶分异作用形成,同时也有一定程度的下地壳物质混染。根据区域对比并结合前人研究成果,认为满克头鄂博组流纹岩形成于火山弧挤压环境,可能与蒙古-鄂霍茨克洋的闭合密切相关。

The paper studied in detail the geochemistry characteristics of the rhyolites in Manketou＇ebo Formation from Bizhou area of northern Greater Xing＇an Range. Geochemical characteristics indicate that the rhyolites belong to high-K, rich alka- line, peraluminous and calc-alkaline series rocks, and the chondrite-normalized REE patterns demonstrate right-inclining on account of LREEenrichment.Meanwhile, the primitive mantle-normalized trace element spidergram shows the rhyolites enric- hing LILE （ Rb, K, Sr, Ba） and depleting HFSE （Nb, Ta, P） and with a narrow range of （La/Sm）N ,（Sr/Ba）N, which comprehensively reflect the source of this magma is close to transitional mantle. The rhyolites formed as follows ： the basaltic magma decompressing melted from the transitional mantle rocksrose to the magma chamber of the lower crust and went through fractional crystallization, but also a certain degree of melting of the lower crustmaterial mixed. According to the regional com- parison and the results of previous studies, it is believed that rhyolites in Manketou＇ebo Formation are formed in volcanic arc compressional environment and maybe closely related to the closure of Mongol-Okhotsk Ocean.