藏北多龙矿集区尕尔勤枕状玄武岩地球化学及SHRIMP测年

摘要

多龙是西藏班—怒成矿带中最大的斑岩Cu(Au)矿集区,其区域动力学演化历史一直是研究的热点.矿集区内尕尔勤地区侏罗系海相沉积地层中发现了枕状玄武岩块,对其成岩时代和岩石地球化学的研究,将有助于了解班公湖—怒江洋盆的演化历史.岩石地球化学分析显示,枕状玄武岩稀土元素总量较低(∑REE为38.01×10–6~63.56×10–6),轻重稀土分异不明显,标准化配分曲线属于平坦型,表现出E-MORB的特征.离子探针分析(SHRIMP)获得其锆石U-Pb年龄为(298±11)Ma,与区域晚石炭—早二叠地层中基性岩脉和玄武岩时代一致,可能是早二叠世班怒洋初始裂解时期大规模火山活动的产物.%Duolong is one of the largest porphyry Cu (Au) ore concentration areas, its dynamic history always being the hot topic for study. Pillow basalt was discovered in Jurassic marine sedimentary strata of Ga'erqin area. Geochronological and geochemical study is helpful to revealing the evolution history of Bangong Co-Nujiang Ocean. Geochemical data show that basalt has low REE (∑REE 38.01×10–6~63.56×10–6) and no significant differentiation between LREE and HREE. The chondrite-normalized REE patterns are flat, similar to features of E-MORB. SHRIMP dating shows that the age of pillow basalt is (298±11) Ma, coinciding with ages of mafic dykes and basalt in Late Carboniferous to Early Permian strata. All of these phenomena may be the products of large-scale volcanic activity for the opening of Bannu Ocean in early Permian strata.