【摘要】 西藏冈底斯岩浆弧叶巴组火山岩对于新特提斯洋俯冲时限的制约存在着重要的意义.通过对甲鲁朗地区叶巴组凝灰岩的LA-ICP-MS锆石U-Pb年龄和岩石地球化学组成的研究,锆石测年获得3件凝灰岩样品²⁰⁶Pb/²³⁸U年龄加权平均值分别为207.8±1.6 Ma、204.8±1.7 Ma和209.3±3.4 Ma,结合古生物化石证据,表明其形成于晚三叠世;凝灰岩样品富集轻稀土元素和大离子亲石元素（Rb、K、Th、U、Pb）,亏损重稀土元素和高场强元素（Nb、Ta、Ti、P）,同时亏损Sr元素,Eu负异常较明显.岩石地球化学特征表明叶巴组中酸性岩可能为壳幔混染成因.综合前人研究成果,认为叶巴组形成于新特提斯洋俯冲环境下的大陆边缘弧,新特提斯洋的俯冲从晚三叠世就已经开始.本研究为叶巴组的形成时代以及动力学背景提供了新的制约.更多还原

【Abstract】 The volcanic rocks of the Yeba Formation on the Gangdese magmatic arc,Tibet are of importance for limiting the initiation of the Neo-Tethyan oceanic slab subduction.This paper reports LA-ICP-MS zircon U-Pb ages and whole-rock geochemistry compositions of the tuffs from the Yeba Formation in Jialulang area.LA-ICP-MS U-Pb isotopic dating of the tuffs obtained²⁰⁶Pb/²³⁸U age weighted average values are 207.8±1.6 Ma,204.8±1.7 Ma and 209.3±3.4 Ma,based on this analysis above and the evidence of fossil organism as well,the tuffs of the Yeba Formation were formed in the Late Triassic.The tuffs exhibit LREE and LILE（Rb,K,Th,U,Pb）enrichment and HREE and HFSE（Nb,Ta,Ti,P）depletion,depletion of Sr as well,with negative Eu anomaly.Combining with geochemical characteristics,it has been suggested a mixing source from crust and depleted mantle for the intermediate-acid rocks from the Yeba Formation.Based on the previous studies,it is indicated that the volcanic rocks of the Yeba Formation were formed in the active continental margin arc setting with the subduction of the NeoTethyan oceanic slab,the initiation of the subduction occurred at Late Triassic.This study provides new constraints for the ages and dynamic settings of the Yeba Formation.更多还原