藏南晚白垩世弧岩浆分异作用:锆石U-Pb年代学、矿物学及地球化学证据  

Cretaceous arc magma differentiation in southern Tibet:Evidence from zircon U-Pb chronology,mineralogy and geochemistry

作　　者：管琪 张敏杰 曹军林[3] 史宏江[3] 李增胜 王对兴 GUAN Qi;ZHANG MinJie;CAO JunLin;SHI HongJiang;LI ZengSheng;WANG DuiXing(Hebei Key Laboratory of Strategic Critical Mineral Resources,Hebei GEO University,Shijiazhuang 050031,China;Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,College of Earth Sciences,Hebei GEO University,Shijiazhuang 050031,China;Shandong Province Nuclear Industry Geological Group 273,Yantai 264006,China;Shandong Institute of Geological Sciences,MNR Key Laboratory of Gold Mineralization Processes and Resource Utilization,Shandong Provincial Key Laboratory of Metallogenic Geological Process and Resource Utilization,Jinan 250013,China)

机构地区：[1]河北省战略性关键矿产资源重点实验室,河北地质大学,石家庄050031 [2]河北地质大学,河北省战略性关键矿产研究协同创新中心,地球科学学院,石家庄050031 [3]山东省核工业二七三地质大队,烟台264006 [4]山东省地质科学研究院,自然资源部金矿成矿过程与资源利用重点实验室,山东省金属矿产成矿地质过程与资源利用重点实验室,济南250013

出　　处：《岩石学报》2023年第5期1459-1483,共25页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(41602040);河北省自然科学基金项目(D2022403023)联合资助.

摘　　要：造山带岩浆作用记录了从大洋俯冲消减到陆陆碰撞的一系列地质过程,同时也蕴含了关于大陆地壳生成、生长的重要信息,其中,与俯冲相关的弧岩浆作用被认为是大陆地壳生长的主要机制。本文通过对西藏南部拉萨地体曲水县至贡嘎县一带出露的黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩开展同位素年代学、矿物学和岩石地球化学研究,探讨了该岩石组合的成因和弧岩浆的分异演化过程。锆石U-Pb定年结果表明,这些岩石的形成时代为91~88Ma。其中,黑云母二长花岗岩属中钾钙碱性偏铝质岩石系列(A/CNK=0.77~0.99),具高SiO 2(68.90%~69.18%)和Al_(2)O_(3)(15.21%~15.48%),低MgO(1.15%~1.16%)和Mg#值(~44),高Sr/Y比值(60~82),其地球化学特征与埃达克质岩石相似;镁铁质微粒包体的SiO 2含量为54.75%~54.96%,具有较高MgO含量(3.92%~5.40%)和Mg#值(52~61),并具弱的负Eu异常(δEu=0.79~0.82)。石英闪长岩为中钾钙碱性偏铝质岩石(A/CNK=0.84~0.88),其SiO 2含量为58.55%~63.32%,具有较高的Mg#值(44~48)和弱的负Eu异常(δEu=0.68~0.81)。另外,所有黑云母二长花岗岩、镁铁质微粒包体以及石英闪长岩样品的Sr-Nd同位素和锆石εHf(t)值相近((87 Sr/86 Sr)i=0.703594~0.703939,εNd(t)=+4.6~+4.8,εHf(t)=+10.9~+15.6)。矿物成分分析表明,黑云母二长花岗岩和镁铁质微粒包体中发育环带的斜长石An值由中心向边部逐渐下降,未发育反环带结构;石英闪长岩中的辉石为单斜辉石,所分析角闪石均为钙质角闪石,黑云母为镁质黑云母。综合上述特征,本文认为黑云母二长花岗岩、镁铁质微粒包体以及同生石英闪长岩分别代表了源自亏损地幔的母岩浆通过分离结晶作用所派生的不同阶段的产物:其中,石英闪长岩最先由基性岩浆发生以辉石、Ti-Fe氧化物和磷灰石为主的分离结晶作用形成,继而作为母岩浆进一步分异演化;镁铁质微粒包体是岩浆早期结晶的�Magmatism in orogenic belts reflects a series of geological processes from oceanic subduction to continental collision,and as a result,it contains important information about the formation and growth of the continental crust.Among different types of magmas,the subduction-related arc is considered to be the main mechanism of the continental crust growth.Here,we report geochronological and geochemical data of the tonalite and MME-host biotite monzogranite pairs in the Quxu-Gongar,southern Lhasa Terrane,to constrain the petrogenesis of this series of rocks and the evolution of arc magmas.Zircon U-Pb dating indicates that they were synchronously emplaced at 91~88Ma.The biotite monzogranites are medium-K calc-alkaline(A/CNK=0.77~0.99),with high SiO 2(68.90%~69.18%)and Al_(2)O_(3)(15.21%~15.48%),low MgO(1.15%~1.16%)and Mg#(~44),and high Sr/Y ratios(60~82),whose characteristics are similar to those of a typical adakite.The mafic microgranular enclaves(MMEs)have SiO 2=54.75%~54.96%,MgO=3.92%~5.40%and Mg#=52~61,with negative Eu anomalies(δEu=0.79~0.82).The quartz diorites are medium-K calc-alkaline rocks,exhibiting high Mg#(44~48)and weakly Eu depletions(δEu=0.68~0.81).All the biotite monzogranites,MMEs and quartz diorites have similar Sr-Nd isotopic compositions(initial 87 Sr/86 Sr=0.703594~0.703939,εNd(t)=+4.6~+4.8),with varying zirconεHf(t)values(+10.9~+15.6).The analysis of mineral composition shows that the An contents of the zoning plagioclase in the biotite monzogranites and MMEs gradually decreases from core to rim,and there is no reverse zoning structures.The pyroxene in quartz diorites is clinopyroxene,and the analyzed hornblende is calc hornblende,and the biotite is magnesium biotite.In summary,the biotite monzogranites,mafic enclaves and syngenetic quartz diorites represent they are formed from derivations of the fractional crystallization of mantle-derived magmas at different stages:the quartz diorites were formed at the first stage by the fractional crystallization of pyroxene,Ti-Fe oxide and apatite of

关 键 词：晚白垩世 弧岩浆分异 南部拉萨地体 西藏 

分 类 号：P588.12[天文地球—岩石学] P597.3[天文地球—地质学]