中拉萨地块强过铝质则弄群火山岩的成因机制及洋底沉积物参与弧岩浆作用的启示  

Petrogenesis of strongly peraluminous volcanic rocks of the Zenong Group in the Central Lhasa subterrane and implications for the involvement of ocean floor sediments in arc magmatism

作　　者：俞嘉嘉 唐菊兴[1] 陈伟[1] 刘畅[2] 贾立民 王艳凯 邸梦想 张书豪 YU JiaJia;TANG JuXing;CHEN Wei;LIU Chang;JIA LiMin;WANG YanKai;DI MengXiang;ZHANG ShuHao(State Key Laboratory of Deep Earth and Mineral Exploration,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resource,China University of Geosciences,Beijing 100083,China;Regional Geological Survey Institute of Hebei Province(Geotourism Research Center of Hebei Province),Langfang 065000,China)

机构地区：[1]中国地质科学院矿产资源研究所,深地探测与矿产勘查全国重点实验室,北京100037 [2]中国地质大学(北京)地球科学与资源学院,北京100083 [3]河北省区域地质调查院(河北地学旅游研究中心),廊坊065000

出　　处：《岩石学报》2025年第5期1759-1776,共18页Acta Petrologica Sinica

基　　金：中国地质调查项目(DD20230359);西藏自治区科技计划项目(XZ202401YD0006);中国地质科学院基本科研业务费(JKYQN202325、KK2407)联合资助详细信息。

摘　　要：鑫龙金矿是新发现的产于则弄群陆相火山岩的高硫化型浅成低温热液金矿床,则弄群火山岩成因、源区等的研究对于在中拉萨地块上寻找斑岩-浅成低温热液型矿床意义重大。本文对当惹雍措西地区则弄群火山岩进行了岩石地球化学、年代学及Sr-Nd-Pb-Hf同位素地球化学研究,旨在揭示其成因机制及其对成矿作用的影响。则弄群火山岩属于一套中酸性火山岩,出露安山岩、英安岩及流纹岩,更多以英安岩和流纹岩为主。锆石U-Pb年龄指示扎列拿组火山岩形成于126.3±1.4Ma,属于早白垩世。整体表现出钙碱性至高钾钙碱性系列特征(Na 2O+K 2O=3.04%~7.24%);安山岩显示准铝质至弱过铝质(A/CNK=0.96~1.06),英安岩和流纹岩显示强过铝质(A/CNK=1.14~1.30)。岩石具有中等轻稀土总量、轻稀土富集和Eu负异常特征(∑REE=94.4×10^(-6)~243.2×10^(-6),(La/Yb)_(N)=5.54~14.1,δEu=0.32~0.91),富集LILEs(如Rb、Th、Pb等)而亏损HFSEs(如Nb、Ta、Ti和P等),并且中性到酸性的Eu和HFSEs亏损程度逐渐增强,指示同源岩浆的分离结晶程度增强。火山岩具有富集的Sr-Nd-Pb同位素组成((87 Sr/86 Sr)i=0.71259~0.72043,ε_(Nd)(t)=-12.3~-7.89;(^(206)Pb/^(204)Pb)i=18.652~18.718,(207 Pb/^(204)Pb)i=15.728~15.770,(208 Pb/^(204)Pb)i=39.066~39.336),具有不同于地壳岩浆的Hf同位素组成(ε_(Hf)(t)=-8.55~-0.27)。则弄群扎列拿组火山岩为形成于洋陆俯冲背景下的弧岩浆,但不同于经典弧岩浆,它们普遍具有强过铝质、富Sr-Nd-Pb同位素特征。综合全岩地球化学、同位素特征,本文认为俯冲的洋底沉积物是造成这些地球化学特征的主要原因,指示洋底沉积物可能在弧岩浆作用中扮演了重要角色。同时,洋底沉积物可提供大量流体,促使地幔楔熔融,形成有利于运载Cu、Au成矿元素的富水、高氧逸度岩浆。The Xinlong gold deposit is a newly discovered epithermal gold deposit of high sulfidation in the continental volcanic rocks of Zenong Group.The study on the genesis and source area of the volcanic rocks in the Zenong Group is of great significance to the search for porphyry-epithermal type deposits in the Central Lhasa subterrane.In this manuscript,the whole-rock geochemistry,chronology and Sr-Nd-Pb-Hf isotope geochemistry of the volcanic rocks of the Zenong Group in the western Dangreyongcuo area have been studied in order to reveal their genetic mechanism and influence on mineralization.The volcanic rocks of the Zenong Group belong to a set of medium-acid volcanic rocks,with andesite,dacite and rhyolite,mainly dacite and rhyolite.Zircon U-Pb age indicates that the volcanic rocks of Zhaliena Formation were formed in 126.3±1.4Ma,belonging to the Early Cretaceous.The overall characteristics of calc-alkaline to high-K calc-alkaline series(Na 2O+K 2O=3.04%~7.24%);Andesite shows quasi-aluminous to weakly peraluminous(A/CNK=0.96~1.06),dacite and rhyolite show strong peraluminous(A/CNK=1.14~1.30).The rocks have the characteristics of medium light rare earth total content,light rare earth enrichment and negative Eu anomaly(∑REE=94.4×10^(-6)~243.2×10^(-6),(La/Yb)_(N)=5.54~14.1,δEu=0.32~0.91).The enrichment of LILEs(such as Rb,Th,Pb,etc.)and loss of HFSEs(such as Nb,Ta,Ti,P,etc.),and the depletion of neutral to acidic Eu and HFSEs gradually increased,indicating the fractional crystallization degree of homologous magmas.The volcanic rocks have rich Sr-Nd-Pb isotopic composition((87 Sr/86 Sr)i=0.71259~0.72043,ε_(Nd)(t)=-12.3~-7.89;(^(206)Pb/^(204)Pb)i=18.652~18.718,(207 Pb/^(204)Pb)i=15.728~15.770,(208 Pb/^(204)Pb)i=39.066~39.336).The Hf isotopic composition is different from that of crustal magma(ε_(Hf)(t)=-8.55~-0.27).The volcanic rocks of Zhaliena Formation in Zenong Group were formed in arc magmas under the background of oceanic subduction,but different from classical arc magmas,they are generally characterized

关 键 词：当惹雍措西地区 则弄群火山岩 Sr-Nd-Pb-Hf同位素 弧岩浆 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]