大兴安岭北段争光金矿英安斑岩地球化学特征、锆石U-Pb年龄及Hf同位素组成  

Geochemical Characteristics,Zircons U-Pb Ages and Hf Isotopic Composition of the Dacite Porphyry from Zhengguang Au Deposit in Northern Great Xing'an Range

作　　者：车合伟 周振华[2] 马星华[2] 欧阳荷根[2] 刘军[2] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地质学报》2015年第8期1417-1436,共20页Acta Geologica Sinica

基　　金：中国地质调查项目(No.12120113093600和No.1212011085260);中央公益性科研院所基本业务费项目(No.K1314);国家自然科学基金(No.41302061)联合资助的成果

摘　　要：争光金矿位于大兴安岭北段多宝山矿集区内,矿区内火成岩的成岩时代、岩石成因及成岩背景研究薄弱。因此,本文对矿区内英安斑岩进行了主微量元素、锆石U-Pb年龄和Hf同位素组成的系统研究,以期为探讨同时代火成岩的成因及矿床成矿背景提供帮助。锆石LA-ICP-MS U-Pb测年结果表明,争光金矿英安斑岩形成于早奥陶世(478~481Ma)。岩石地球化学特征显示,英安斑岩属准铝-过铝质高钾钙碱性系列,具有SiO_2≥56%(平均为63.91%)、高铝(Al_2O_3平均14.85%)、低镁(MgO平均2.70%)、低Y和Yb(Y=6.00×10^(-6)~7.74×10^(-6),Yb=0.70×10^(-6)~0.92×10^(-6))、高锶(平均368×10^(-6))、高Mg#(56.84~60.60)、轻重稀土分馏明显[(La/Yb)N=8.74~11.54]和Eu异常不明显的特点,类似于俯冲洋壳成因埃达克岩。锆石εHf(t)介于13.03~13.31之间,两阶段模式年龄(tDM2)为605~624Ma。综合岩石地球化学特征和锆石Hf同位素组成,我们认为争光英安斑岩由俯冲的新生洋壳发生部分熔融形成。本文研究结果也表明,早奥陶世,兴安地块和松嫩地块之间存在洋壳,并且该洋壳向兴安地块俯冲。Zhengguang Au deposit is located at the Duobaoshan ore-concentrated area, northern of Great Xing＇ an Range. In order to constrain petrogenesis of contemporaneous igneous rocks and corresponding metallogenic background, a systematic study on major and trace elemental, geochronology and Hf isotope geochemistry was performed for the dacite porphyry in the Zhengguang Au deposit. Zircon LA-ICP-MS U- Pb dating indicates that dacite porphyry formed in early Ordovician（478-481Ma）. Geochemical data show that the dacite porphyry belongs to metaluminous or peraluminous and high-K calc-alkaline series and is characterized by SiO2≥56% （on average, 63.91%）, high alumina contents （Al2O3, on average, 14.85%）, low magnesium contents （MgO, average 2.70%）, low Y and Yb contents （Y=6.00×10^-6-7.74×10^-6, Yb=0.70×10^-6-0.92×10^-6） , high strontium contents （an average of 368×10^-6）, high Mgu values, significant fractionation between light REE and heavy REEE[（La/Yb）N=8.74-11.54], and unobvious Eu anomalies. All of these geochemical features are similar to those of adakites generated by partial melting of a subducted oceanic crust. Furthermore, zircon εHf（t） range from 13.03 to 13.31 with Hf isotope Two-stage model ages（tDM2） from 605Ma to 624Ma. Both geochemical characteristics and Hf isotope compositions suggest that the dacite porphyry in the Zhengguang Au deposit was formed by partial melting of a juvenile subducted oceanic crust. The results of this study also demonstrate that there was a subduction of an oceanic plate, which is located between the Xing＇an block and Songnen block, beneath the Xing＇an block during the early Ordovician.

关 键 词：英安斑岩 锆石U-PB年龄 HF同位素 地球化学 争光金矿 

分 类 号：P618.51[天文地球—矿床学] P597.3[天文地球—地质学]