冈底斯带中段中新世花岗斑岩成因研究:来自锆石U-Pb年代学、全岩地球化学及Sr-Nd-Hf-O同位素的制约  

Petrogenesis of the Miocene granitic porphyry in the middle Gangdese belt:Constraints from zircon U-Pb geochronology,whole-rock geochemistry and Sr-Nd-Hf-O isotopes

作　　者：崔婧嫄 孟元库 熊发挥[2] CUI JingYuan;MENG YuanKu;XIONG FaHui(College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266590,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]山东科技大学地球科学与工程学院,青岛266590 [2]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2024年第12期3734-3752,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(U2344202);山东省自然科学基金面上项目(ZR2023MD021);泰山人才工程项目(NO.tstp20240514)联合资助。

摘　　要：藏南冈底斯带广泛发育中新世埃达克质岩,这些埃达克质岩是研究冈底斯岩浆带后碰撞岩浆活动和地壳演化的理想载体。本文以冈底斯带中段出露在仁钦则地区的花岗斑岩为研究对象,对其进行了锆石U-Pb年代学、全岩地球化学、锆石原位Hf同位素、全岩Sr-Nd-O同位素和矿物电子探针的综合分析与系统研究,据此探讨了其岩石成因和源区性质,并结合氧逸度分析了其成矿潜力。锆石U-Pb定年结果显示,仁钦则花岗斑岩的成岩年龄为22.48±0.19Ma,属于中新世早期岩浆活动的产物。在地球化学组成上,仁钦则花岗斑岩属于高钾钙碱性系列,富集轻稀土和大离子亲石元素(Rb、Ba和Sr),亏损重稀土和高场强元素(Nb、Ta和Ti),并且显示弱的Eu异常(Eu/Eu^(*)=0.92~0.97);同时,具有高Sr、La和低Y、Yb含量,对应高Sr/Y(72.72~86.52)和(La/Yb)_(N)(23.07~28.58)比值,显示出埃达克岩的地球化学亲缘性。仁钦则花岗斑岩的锆石ε_(Hf)(t)值大部分为正值且具有较大的变化范围(-10.47~+5.14),全岩(^(87)Sr/^(86)Sr)_(i)值、ε_(Nd)(t)值和δ^(18)O值分别为0.705347~0.705511、-4.0~-3.3及6.21‰~9.69‰。综合分析后,我们认为仁钦则花岗斑岩的成因与冈底斯加厚的新生下地壳的部分熔融有关,并且有印度古老地壳物质的混入。此外,通过进一步全岩地球化学数据分析,认为岩浆源区可能残留有石榴子石和角闪石,缺乏斜长石和金红石。仁钦则花岗斑岩还显示出高的氧逸度值(lgf_(o2)=-11.29),推测该地区具有良好的斑岩铜矿成矿潜力。The Miocene adakitic rocks are widely exposed in the Gangdese belt and are the ideal objects for studying crustal evolution and post-collisional magmatic activities.Based on the zircon U-Pb geochronology,whole-rock geochemistry,zircon in situ Hf isotopes,whole-rock Sr-Nd-O isotopes,and mineral electronic micro-probe analyses,we conducted systematic studies on the identified granitic porphyry in Renqinze area in the middle Gangdese belt to discuss their petrogenesis and magma sources,and to analyses their metallogenic potential by in combination with the oxygen fugacity.Zircon U-Pb dating results show that the crystallization age of the Renqinze granite porphyry is ca.22.48±0.19Ma,belonging to the product of the Early Miocene magmatic activity.Geochemically,the granitic samples belong to the high-K calc-alkaline series,which are enriched in light rare earth and large ion lithophile elements(Rb,Ba,and Sr),and depleted in heavy rare earth elements and high field strength elements(Nb,Ta,and Ti)with an insignificant negative Eu anomaly(Eu/Eu^(*)=0.92~0.97).The Renqinze granite porphyry has high Sr and La,low Y and Yb concentrations,with high Sr/Y(72.72~86.52)and(La/Yb)N(23.07~28.58)ratios,suggesting an adakitic affinity.The zirconεHf(t)values of the Renqinze granite porphyry are mostly positive with wide variation ranges of-10.47~+5.14.The whole rock(^(87)Sr/^(86)Sr)i ratios,ε_(Nd)(t)andδ^(18)O values of the studied samples of the granite porphyry range of 0.705347~0.705511,-4.0~-3.3 and 6.21‰~9.69‰,respectively.Integrated with the comprehensive analyses,we conclude that the genesis of the Renqinze granite porphyry is mainly formed by the partial melting of the Gangdese juvenile lower crust,with minor ancient Indian crustal materials participated in as its source.In addition,through further analysis of the whole-rock geochemical data in this region,it is considered that garnet and hornblende may be the residues in the magma source,while plagioclase and rutile are absent.The Renqinze granite porphyry also has a

关 键 词：埃达克岩 中新世 冈底斯带中段 岩石成因 成矿潜力 

分 类 号：P588.13[天文地球—岩石学] P597.3[天文地球—地质学]