通过对大兴安岭中北段甘南地区黑甘地1井钻遇的二云二长花岗岩进行LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究,确定其形成时代、岩石成因,从而揭示区域构造背景.花岗岩的锆石呈半自形—自形,振荡生长环带明显.测年结果显示,二云二长花岗岩形成于161 Ma,为晚侏罗世早期岩浆事件的产物.地球化学分析结果显示,岩石具有高硅(SiO2 69.81%~74.3%)、富铝(Al2O3 13.5%~16.8%)、贫铁(Fe2O3 0.26%~0.6%)等特征,在化学成分上属于准铝质-弱过铝质系列.富集大离子亲石元素Rb、Ba、K和高场强元素Hf,贫Nb、Ta、Ti等高场强元素;相对富集轻稀土元素,亏损重稀土元素,为Ⅰ型花岗岩.岩浆起源于新增生加厚陆壳物质的部分熔融.研究结果表明晚侏罗世早期二云二长花岗岩的形成与蒙古-鄂霍次克缝合带闭合过程中的陆-陆碰撞环境有关,其形成时代限定了蒙古-鄂霍次克洋在大兴安岭中北段甘南地区的闭合时代为晚侏罗世早期.
The formation age and petrogenesis of the two-mica monzogranite drilled from HGD-1 well in Gannan area of central-northern Daxinganling Mountains are determined and the regional tectonic setting is revealed on the basis of LA-ICP-MS zircon U-Pb chronology and petrogeochemistry studies.The zircons in granite are subidiomorphic-idiomorphic,with obvious oscillatory growth zone.The dating results show that the two-mica monzogranite was formed at 161 Ma,which is the product of magmatic event in early Late Jurassic.Geochemical analysis results indicate that the granite is characterized by high Si(SiO2 69.81%-74.3%),rich Al(Al2O3 13.5%-16.8%),and poor Fe(Fe2O3 0.26%-0.6%),belonging to quasi aluminous-weak peraluminous series in terms of chemical composition,with enriched LILEs(Rb,Ba and K)and HFSE(Hf),and depleted HFSEs(Nb,Ta and Ti),and relatively enriched LREEs and depleted HREEs,which is of Ⅰ-type granite.The magma originates from the partial melting of newly thickened continental crust material.The study results reveal that the formation of the early Late Jurassic two-mica monzogranite is related to the continent-continent collision environment during the closure progress of Mongol-Okhotsk suture zone,and its formation age restricts the closing time of Mongol-Okhotsk Ocean to the early Late Jurassic in Gannan area of central-northern Daxinganling Mountains.