西藏加多捕勒铁铜矿床晚白垩世岩浆活动成因

Genesis of Late Cretaceous Magmatic Activity in the Jiaduobule Iron Copper Deposit,Tibet

加多捕勒铁铜矿床位于冈底斯Pb-Zn-Ag-Cu-Fe成矿带西段。矿区出露的复式岩体由黑云二长花岗岩(50.9±1.8Ma)和石英二长闪长岩组成。本文以石英二长闪长岩为研究对象,分析了岩体地球化学特征、SHRIMP锆石U-Pb年龄以及原位锆石Hf同位素与稀土元素。分析结果显示石英二长闪长岩具岛弧岩浆活动特征,锆石U-Pb年龄84.3±1.4Ma,为晚白垩世岩浆活动产物,锆石Hf同位素与稀土元素指示岩浆源区具壳幔混源特征,且以古老地壳物质的部分熔融为主。综合分析已有研究成果及本文数据,笔者认为矿区晚白垩世岩浆活动可能与低缓角度俯冲的新特提斯洋壳有关。

The Jiaduobule skarn iron copper deposit is located in the western part of the famous Gangdese Pb-Zn-Ag-Cu-Fe metallogenic belt. The biotite monzogranite,with age of 50. 9 ± 1. 8 Ma,and the quartz monzodiorite formed a duplex pluton in the Jiaduobule deposit. This paper focuses on the quartz monzodiorite to analyze its geochemistry,SHRIMP U-Pb dating,Hf isotope and REE of zircon. The results show that the quartz monzodiorite has the characteristic of arc magmatism. The SHRIMP U-Pb dating of zircons yields the age of 84. 3 ± 1. 4Ma,which represents the crystallization age of quartz monzodiorite,showing the rock formed in the late Cretaceous. The Lu-Hf isotope composition and the characteristics of REE demonstrate that the magma of quartz monzodiorite was mainly derived from the partial melting Mesoproterozoic crust,with a small number of mantle materials involved. By integration of existing research results and the data in this paper,we suggest that the late Cretaieous magmatic activity of the Jiaduobule iron copper deposit was probably related with the low-angle subduction of Neo-Tethys oceanic crust.