东天山白山钼矿区花岗岩的岩石成因:锆石U-Pb年代学、地球化学及Hf同位素约束  

Petrogenesis of granites in Baishan molybdenum deposit,eastern Tianshan,Xinjiang: Zircon U-Pb geochronology,geochemistry,and Hf isotope constraints

作　　者：王银宏[1] 张方方[1] 刘家军[1] 薛春纪[1] 王建平[1] 刘彬[1] 路魏魏 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]新疆地质矿产开发局第六地质大队,哈密839000

出　　处：《岩石学报》2015年第7期1962-1976,共15页Acta Petrologica Sinica

基　　金：中央高校基本科研业务费专项资金(2652015019;2652015032);中国地质调查局综合研究项目(1212011085471;1212011220923);高等学校博士学科点专项科研基金(20130022110001);高等学校学科创新引智计划(B07011);国家自然科学基金项目(40973035)联合资助

摘　　要：新疆东天山晚古生代中酸性岩浆活动广泛分布且已有较多研究成果。近年来在该区识别出印支期岩浆作用,然而研究者对其岩石成因、源区性质及相关动力学问题研究较少。白山钼矿区位于东天山康古尔-黄山韧性剪切带东段,是东天山多金属成矿带印支期斑岩型钼矿床,其矿体主要赋存于深部花岗斑岩体外接触带中。本文则对白山钼矿区深部花岗斑岩开展了岩石地球化学、锆石U-Pb年代学及Lu-Hf同位素组成研究。SIMS锆石U-Pb定年结果表明,白山花岗斑岩体大约侵位于226.8±3.2Ma。岩石地球化学结果表明,花岗斑岩具高Si O2含量(68.87%~72.82%)及全碱含量(6.85%~8.17%),铝饱和指数A/CNK为0.93~1.06,均小于1.1,为准铝质至过铝质I型花岗岩。岩石具有明显的轻重稀土分异和弱的Eu负异常,富集大离子亲石元素(K、Rb、Sr),相对亏损高场强元素(Nb、Ta、Ti、Th),具高Sr/Y和La/Yb比值的特点,显示与埃达克质岩石相似的地球化学特征。白山花岗斑岩锆石Lu-Hf同位素数据显示,其具较高的εHf(t)值(+8.0^+11.0)和较年轻的地壳模式年龄tCDM(556~758Ma)。结合岩石地球化学及同位素地球化学特征,本文认为白山花岗岩体可能来源于增厚下地壳物质的部分熔融,并可能混有幔源岩浆物质,形成于东天山碰撞造山作用之后的板内伸展阶段。The widespread Late Paleozoic intermediate-acid magmatic rocks in eastern Tianshan, Xinjiang have been studied in the past years. Recently, some Indosinian magmatism have been found, but the petrogenesis and sources of magmatic rocks and associated geodynamic settings were less constrained. The Baishan molybdenum deposit, located in the eastern section of the Kanggur-Huangshan ductile shear belt, is an Indosinian porphyry deposit in eastern Tianshan. This deposit mostly occurs in the exo-contact zone of the granite porphyry. This paper conducted major and trace elements geochemistry, zircon U-Pb dating and in-situ zircon Hf isotopic compositions for the granite porphyry rocks from the Baishan area. SIMS zircon U-Pb dating indicates that the granite porphyry rocks in the Baishan area were emplaced at 226. 8 ＋ 3.2Ma. Geochemically, the granite porphyry rocks are characterized by high SiO2 （68.87% ~ 72. 82% ） and total alkalis （6. 85% - 8.17% ）, with A/CNK values ranging from 0. 93 to 1.06 （ 〈 1.1 ）, suggesting that they are metaluminous to slightly peraluminous and are of I-type granite. The granite porphyry rocks are enriched in LREE and LILE （ K, Rb, and Sr） and depleted in HREE （ Nb, Ta, Ti, and Th）, with slightly negative Eu anomalies, and possess high Sr/Y and La/ Yb values, showing geochemical affinities similar to adakites. The Baishan granite porphyry rocks have homogeneous zircon Hf isotopic composition, with positive 8Hf （t） values （ ＋ 8.0 - ＋ 11.0 ） and young Hf isotopic crustal model ages （ 556 ~ 758Ma）. The geochemical and isotopic data in this paper, combined with the regional tectonic evolution, imply that the granite porphyry rocks in the Baishan area were formed in an intracontinental extensional stage, and their primary magmas were most likely derived from partial melting of the thickened lower crust, with the invasion of mantle components.

关 键 词：锆石U-PB定年 地球化学 HF同位素 花岗斑岩 白山钼矿床 东天山 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]