东昆仑造山带东段晚二叠世岩浆作用:来自尕之麻地区花岗岩的制约  

Late Permian Magmatism at the Eastern Segment of the Eastern Kunlun Orogenic Belt: Insights from Granites in the Gazhima Area

作　　者：王凤林 魏俊浩[1] 李小亮 张新铭 徐崇文 李艳军[1] WANG Fenglin;WEI Junhao;LI Xiaoliang;ZHANG Xinming;XU Chongwen;LI Yanjun(School of Earth Resources,China University of Geosciences,Wuhan 430074,Hubei,China;Qinghai Bureau of Environmental Geology Exploration,Xining 810008,Qinghai,China;Qinghai Bureau of Nonferrous Metals Geology and Mineral Exploration,Xining 810001,Qinghai,China)

机构地区：[1]中国地质大学(武汉)资源学院,湖北武汉430074 [2]青海省环境地质勘查局,青海西宁810008 [3]青海有色地质矿产勘查局,青海西宁810001

出　　处：《大地构造与成矿学》2022年第5期1028-1045,共18页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(42172084);青海省地勘基金项目([2020]-123)联合资助。

摘　　要：东昆仑造山带晚二叠世岩浆作用及构造背景研究薄弱。本文对东昆仑造山带东段尕之麻地区那更康切尔花岗闪长岩和新识别出的二长花岗岩开展了岩石地球化学及锆石Hf同位素分析,并对二长花岗岩进行了年代学研究。锆石U-Pb测年结果显示,二长花岗岩中11颗年轻锆石U-Pb谐和年龄为256±2 Ma,加权平均年龄为255±2 Ma,两者在误差范围内一致,表明其形成于晚二叠世;除此之外,还获得古元古代、早古生代等继承锆石和捕获锆石记录。岩石地球化学结果显示,二长花岗岩具高SiO_(2)(72.66%~73.74%)、Na_(2)O(4.94%~6.73%)含量,贫K_(2)O和Fe_(2)O_(3) T,属低钾‒中钾钙碱性岩石;富集大离子亲石元素和轻稀土元素,亏损高场强元素,具Eu正异常。花岗闪长岩SiO_(2)=63.31%~65.05%,K_(2)O=3.27%~3.66%,属高钾钙碱性准铝质岩石;富集Rb、K,亏损Nb、P和Ti,稀土元素配分型式呈明显右倾型,具有中等Eu负异常(0.53~0.58)。两者的104×Ga/Al值分别为1.51~1.84和2.27~2.35,Zr+Nb+Ce+Y值分别为13.4×10^(−6)~28.0×10^(−6)和333×10^(−6)~352×10^(−6)。结合岩相学特征,表明两类岩石均属于Ⅰ型花岗岩。二长花岗岩中晚二叠世锆石ε_(Hf)(t)=−5.6~12.8,二阶段模式年龄t_(DM2)=1461~436 Ma;花岗闪长岩锆石ε_(Hf)(t)=−5.6~−1.1,t_(DM2)=1456~1210 Ma。综合研究表明,壳幔混合作用形成的初始岩浆在上升过程中混染了早古生代和早二叠世地壳物质,并经历了岩浆分异结晶形成二长花岗岩和花岗闪长岩。二长花岗岩和花岗闪长岩地球化学特征差异也显示了岩浆混合作用的不均一性。结合构造背景,两者均形成于大陆边缘弧环境,与早二叠世晚期‒晚二叠世时期阿尼玛卿洋板片北向俯冲作用有关。The eastern Kunlun orogenic belt(EKLO)is an important accretionary orogen in Northwest China,however,studies on the origin and geodynamic setting of the Late Permian magmatism in the belt are rare.The recently discovered Gazhima monzogranite and the Nagengkangqieer granodiorite in the Gazhima area,the easternmost segment of the EKLO,yield an important research opportunity.This paper reports LA-ICP-MS zircon U-Pb dating results for the monzogranite,and geochemical and Hf isotopic compositions of the Gazhima and Nagengkangqieer granites.The LA-ICP-MS zircon U-Pb dating yielded similar intercept and weighted mean ^(206)Pb/^(238)U ages of 256±2 Ma to 255±2 Ma,indicating that it was emplaced in the Late Permian.The monzogranite exhibits high silic(SiO_(2)=72.66%–73.74%)and sodium(Na_(2)O=4.94%–6.73%),but low potassium and iron.It belongs to low-K tholeiitic to medium-K calc-alkaline rocks,and characterized by enrichment of LREE and LILEs(such as Rb,Ba,K,and Sr),and depletion of HFSEs(including Th,Nb,and Ti).In contrast,the Nagengkangqieer granodiorite has SiO_(2) of 63.31%to 65.05%,and belongs to high-K calc-alkaline and metaluminous rocks with K_(2)O of 3.27%to 3.66%and A/CNK of 0.91 to 0.95.It is enriched in Rb and K,but depleted in Nb,P,and Ti.The rock samples exhibit right-inclined REE patterns with significant negative Eu anomalies(Eu/Eu*=0.53–0.58).The monzogranite has low 10^(4)×Ga/Al ratios of 1.51–1.84 with Zr+Nb+Ce+Y values of(13.4–28.0)×10^(−6),whereas the granodiorite has relatively high 10^(4)×Ga/Al(2.27–2.35)and Zr+Nb+Ce+Y((333–352)×10^(−6))values.The geochemical and mineralogical features of the two types of granites show an affinity of Ⅰ-type granite.The monzogranite hasε_(Hf)(t)values of−5.6 to 12.8,with two-stage mode ages(t_(DM2))of 1461 Ma to 436 Ma,while the Nagengkangqieer granodiorite hasε_(Hf)(t)values of−5.6 to−1.1 and t_(DM2) of 1456 Ma to 1210 Ma.The geochemical and Hf isotopic characteristics,along with the occurrence of Paleoproterozoic to Early Permian in

关 键 词：Ⅰ型花岗岩 晚二叠世 岩浆混合 俯冲作用 大陆边缘弧 东昆仑 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]