西藏玉龙斑岩铜矿带南段日曲花岗闪长斑岩成因:锆石U-Pb年代学和地球化学约束

Petrogenesis of the Riqu Granodiorite Porphyry in Southern Yulong Porphyry Copper Belt: Constraints from Zircon U-Pb Geochronology and Whole-Rock Geochemistry

为探讨西藏玉龙斑岩铜矿带南段斑岩的成因及其动力学机制,对该铜矿带南段日曲岩体开展了岩石学、同位素年代学和地球化学研究。结果显示,两件花岗闪长斑岩锆石U-Pb年龄分别为(38.2±0.2)Ma、(38.8±0.2)Ma,为喜马拉雅早期;花岗闪长斑岩富集大离子亲石元素,亏损高场强元素,属弱过铝质高钾钙碱性花岗岩;斑岩具有C型埃达克岩的地球化学特征,为加厚下地壳部分熔融的产物,未经明显的地壳混染;源区残留相主要由角闪石、石榴子石、金红石组成,并经历了较弱的壳幔混合作用。研究表明,日曲岩体的形成与印度板块与欧亚板块碰撞诱发妥坝-芒康左行走滑断裂活动有关,下地壳部分熔融及少量幔源物质的混入使斑岩具有壳幔混合的特征。

In order to explore the genesis and geodynamic setting of porphyries in southern segment of the Yulong porphyry copper belt, petrology, isotope geochronology and geochemistry of the Riqu intrusion are performed in this study. Two granodiorite porphyries of the Riqu intrusion have zircon U-Pb ages of(38.2±0.2) Ma and(38.8±0.2) Ma, respectively, belonging to early Himalaya period. Granodiorite porphyry is weakly peraluminous high K calc-alkaline granite. It has enriched in large ion lithophile elements and depleted in high field strength elements. The porphyry has the geochemical characteristics of C-type Adakite, indicative of the product of partial melting of thickened lower crust, without significant crust assimilation. The residual phase of the source region is mainly composed of hornblende, garnet, and rutile. The parental magmas were formed by the partial melting of lower crust with minor addition of mantle components. Thus, the formation of the Riqu intrusion is related to the Tuoba-Mangkang left-lateral strike-slip fault activity triggered by Indian plate and Eurasian plate collision.