云南格咱岛弧带休瓦促Mo-W-Cu矿床两期岩浆作用的锆石U-Pb年龄、Hf同位素组成及构造意义

摘要

锆石LA-ICP-MS U-Pb定年结果显示,休瓦促Mo-W-Cu矿床含矿花岗闪长岩的形成年龄为202±3.5Ma,形成于甘孜—理塘洋壳向西俯冲时期;含矿二长花岗岩的形成年龄为83.3±1.7Ma,形成于燕山晚期造山后伸展环境.Hf同位素原位分析结果显示,花岗闪长岩中锆石的εHf(t)值为-2.87～4.12(平均为0.09),TMD1年龄541～828Ma,TDM2年龄为719～1109Ma,表明岩体形成的物质来源除壳源物质之外,也有幔源物质的混入;二长花岗岩中锆石的εHf(t)值为-7.96～-2.75(平均为-5.54),TMD1年龄为820～1019Ma,TDM2年龄为1102～1391Ma,εHf(t)＜0,表明岩石是由古老地壳物质的部分熔融形成的产物.休瓦促两期含矿岩体的锆石U-Pb定年与Hf同位素原位分析显示,区内存在晚三叠世和晚白垩世两期构造—岩浆—成矿作用.晚三叠世花岗闪长岩岩浆侵入及Cu多金属成矿作用与洋壳俯冲造山有关;而晚白垩世二长花岗岩岩浆侵入及Mo多金属成矿作用主要形成于陆—陆碰撞造山的构造背景.研究表明,从晚三叠世洋壳俯冲造山至晚白垩世造山后伸展作用过程中都存在构造—岩浆—成矿作用的发生,且在晚三叠世构造—岩浆活动的基础上叠加了晚白垩世的成岩成矿作用,这为区内复合叠加成矿作用的研究提供了例证.%The LA-ICP-MS zircon U-Pb dating results show that theore-bearing granodiorite from the Xiuwacu Mo-W-Cu deposit formed at 202 ± 3.5 Ma during which the Ganzi-Litang oceanic crust subducted westward;and monzonitic granite formed at 83.3 ± 1.7 Ma in a collisional orogenic environment in the Late Triassic.In-site Hf isotope analysis results show that the zircon in granodiorite has εHf (t) of from -2.87 tO 4.12 (0.09 on average),TDM1age of 541 ～ 828Ma,and TDM2age of 719 ～ 1109Ma.It shows that the intrusion was sourced from the crust with addition of mantle material.The zircons in monzonitic granite have εHf(t) values of-7.96～-2.75 (-5.54 on average),TDM1 age of 820～1019Ma and TDM2 age of 1102～1391Ma,indicating that monzonitic granite was the product of partial melting of ancient crust.Zircon U-Pb dating and in-situ Hf isotope analysis of two ore-bearing intusions in Xiuwacu show that there were two-period tectonic-magmatic-mineralization activities in the area in Late Triassic and Late Cretaceous respectively.The granodiorite magmatic intrusion and Cu polymetallic mineralization were related to oceanic subduction orogenesis in the Late Triassic,while the monzogranite magmatic intrusion and Mo polymetallic mineralization were mainly formed in the tectonic setting of continental-continental collisional orogeny in the Late Cretaceous.The study shows that the tectonic-magmatic-mineralization occurred from the subduction of oceanic crust in Late Triassic to the post-orogenic extension in Late Cretaceous,and the Late Triassic tectonic-magmatic activity was superimposed by the diagenesis and mineralization in Late Cretaceous.This provides a typical example for the study of compound superimposed diagenetic mineralization.