西藏驱龙矿区中新世侵入岩锆石微量和Hf-O同位素研究  

Zircon trace elemental and Hf-O isotopic compositions of the Miocene magmatic suite in the giant Qulong porphyry copper deposit, southern Tibet

作　　者：李秋耘[1,2] 杨志明[1,3] 王瑞 孙茂妤 曲焕春 LI Qiu-yun;YANG Zhi-ming;WANG Rui;SUN Mao-yu;QU Huan-chun(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Civil and Resource Engineering School,University of Science and Technology Beijing,Beijing 100083,China;Institute of Earth Sciences,China University of Geosciences.Beijing 100083,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]北京科技大学土木与资源工程学院,北京100083 [4]中国地质大学(北京)科学研究院,北京100083

出　　处：《岩石矿物学杂志》2021年第6期1023-1048,共26页Acta Petrologica et Mineralogica

基　　金：国家重点研发计划项目(2016YFC0600300);国家自然科学基金面上项目(41973037)。

摘　　要：碰撞环境下超大型矿床的形成通常经历了多期岩浆作用,但不同期次岩浆之间的成因关系以及成矿斑岩岩浆的形成机制尚未得到有效约束。位于青藏高原腹地的驱龙超大型斑岩铜矿床发育多套中新世岩浆岩,包括成矿前的花岗闪长岩(又称荣木错拉岩体)、成矿期二长花岗斑岩(简称P斑岩)和晚期二长花岗斑岩(简称X斑岩),以及成矿后的高镁闪长玢岩,且在花岗闪长岩中发现有闪长质包体。如此丰富的岩浆岩组合为系统研究碰撞环境下斑岩矿床成矿岩浆的形成机制提供了契机。本文系统分析了驱龙矿区各类岩浆岩中的锆石微量元素及Hf-O同位素组成,并估算了驱龙矿区中新世岩浆氧化还原状态,约束了岩浆起源及演化过程,特别是成矿斑岩的形成过程。研究结果显示荣木错拉岩体及闪长质包体中锆石具有高的Ce/Ce^(*)值(平均值分别为111、117)和相似的Hf-O同位素组成,其εHf(t)值主要变化于+7~+10及+7~+9之间,δ^(18)O值主要变化于+5.6‰~+7.1‰和+4.7‰~+7.0‰之间;而P斑岩中锆石具有类似的δ^(18)O值(+4.6‰~+6.4‰),但Ce/Ce;值(29~405,平均值149)及εHf(t)值(+5~+10)变化范围明显偏大;高镁闪长玢岩的锆石δ^(18)O值与P斑岩类似(+5.2‰~+6.3‰),但εHf(t)值(+3~+7)明显偏低,不过,其锆石Ce/Ce^(*)值(34~252,平均值159)也显示较大的变化范围。荣木错拉岩体及闪长岩包体正εHf(t)值、中等偏高的δ^(18)O值表明其起源于新生下地壳;高镁闪长玢岩较低的εHf(t)及δ^(18)O值显示其起源于Hf同位素组分已被强烈改造的地幔;而P斑岩变化、且整体介于荣木错拉岩体和高镁闪长玢岩之间的锆石Hf同位素组成表明其为荣木错拉岩体所代表的壳源岩浆与高镁闪长玢岩所代表的幔源岩浆混合的产物。驱龙中新世岩浆岩中高镁闪长玢岩中的锆石Ce/Ce^(*)值最高,表明高镁闪长玢岩所代表的岩浆氧逸度也最高,因此,P斑岩形成过�The formation of giant deposits in the collisional environment usually undergoes multiple stages of magmatism,but the genetic relationship between different stages of magmas and the formation mechanism of ore-forming porphyry magma has not been effectively restricted.The giant Qulong porphyry copper deposit,located in the hinterland of Qinghai-Tibet Plateau,has several stages of Miocene magmas,including pre-ore granodiorite (also known as RMCLpluton),ore-forming granite porphyry (P and X porphyry),and post-ore high-Mg diorite porphyry (HMD),and diorite enclaves are found in the granodiorite.Such abundant magmatic sequence provides a good opportunity for the systematic study of the formation mechanism of ore-forming magma of porphyry deposits in collisional environment.This paper systematically analyzed the zircon trace elemental and Hf-O isotopic compositions of various types of magmatic rocks in Qulong and estimates the redox state of Miocene magmas in the Qulong mining area,which constrain the origin and evolution of the magma,especially the formation process of ore-forming porphyry.The results show that the zircons in the RMCL pluton and the diorite enclaves before mineralization have high Ce/Ce^(*) ratios (average values of 111 and 117,respectively) and similar Hf-O isotopic compositions,with the value ofεHf(t) of+7~+10 and +7~+9 respectively,and the value of δ^(18)O of +5.6‰~+7.1‰ and +4.7‰~+7.0‰respectively.Whereas zircons from the ore-forming P porphyry have similarδ^(18)O values (+4.6‰~+6.4‰),but the Ce/Ce;ratios (29~405,with an average of 149) and the values ofεHf(t)(+5~+10) change variably.Zircons from the post-ore high-Mg diorite porphyry (HMD) have similar δ^(18)O values (+5.2‰~+6.3‰) with the P porphyry,but lowerεHf(t) values (+3~+7) and changeable Ce/Ce;ratios (34~252,with an average of 159).The positiveεHf(t) value and moderate-highδ;O value of the RMCL pluton and diorite enclaves indicate that they were originated from the juvenile lower crust.The lowεHf(t) and δ^(18)O va

关 键 词：斑岩铜矿 氧逸度 地幔熔体 锆石微量元素 HF-O同位素 

分 类 号：P588.12[天文地球—岩石学] P595[天文地球—地质学]