大兴安岭北段塔源二支线铅锌铜矿区岩浆岩岩石成因及其地质意义

Petrogenesis of magmatic rocks from Tayuanerzhixian Pb-Zn-Cu mining area in northern segment of Great Xing an Range and its geological significance

塔源二支线铅锌铜矿床地处额尔古纳地块东南缘,位于得尔布干成矿带东段。为确定塔源二支线铅锌铜矿区岩浆岩的岩石成因及其地质意义,对矿区岩浆岩开展了岩石学、地球化学以及同位素年代学研究。笔者在矿区识别出两期岩浆作用,早期发生于(296.1±2.3)Ma(早二叠世),侵入体为二长闪长岩;晚期发生在(136.5±2.1)Ma(早白垩世),侵入体为石英斑岩,晚期岩浆活动与成矿关系密切。研究表明:早二叠世二长闪长岩具有贫硅、富镁、富钙、低Al_(2)O_(3)和TiO_(2)的特征,原始岩浆可能起源于俯冲流体或熔体交代的亏损软流圈地幔的部分熔融,其形成与古亚洲洋的俯冲作用有关;早白垩世石英斑岩属于高钾钙碱性、弱过铝质系列岩石,具有富硅、富钾、富集大离子亲石元素Rb、K、Ba的特征,为A型花岗岩,可能来源于加厚/拆沉下地壳部分熔融,形成于蒙古-鄂霍茨克洋造山后伸展环境。

The Tayuanerzhixian Pb-Zn-Cu deposit is located in the southeast margin of the Erguna block,which belongs to the eastern segment of the Derbugan metallogenic belt.In order to determine the petrogenesis and its geological significance of magmatic rocks in the Tayuanerzhixian Pb-Zn-Cu deposit,petrological,geochemical and geochronological study has been conducted.Two periods of magmatism were identified in the mining area:represented by the early monzodiorite emplaced at(296.1±2.3)Ma(Early Permian),and the quartz porphyry formed at(136.5±2.1)Ma(Early Cretaceous),and the latter is closely related to mineralization.The results show that the Early Permian monzodiorite is characterized by poor Si,rich Mg,rich Ca and low Al_(2)O_(3) and TiO_(2),suggesting that the original magma may be derived from the partial melting of the depleted asthenosphere mantle metasomatized by subduction fluids or melts,which has a close relationship with the subduction of the Paleo-Asian Ocean.The Early Cretaceous quartz porphyry is rich in silicon,potassium and large ion lithophile elements Rb,K,Ba,belonging to the weakly peraluminous and high-K calc-alkaline series.The quartz porphyry is classified as A-type granite,probably derived from the partial melting of thickened/dismantled lower crust and formed in a post-orogenic extensional environment of the Mongolia-Okhotsk Ocean tectonic system.