福建平和矾山地区花岗岩地球化学、年代学、Hf同位素特征及地质意义

Geochemistry,Zircon U-Pb Dating and Hf Isotope Composition of Granite in Fanshan Area,Pinghe County,Fujian Province,and Its Geological Significance

为了揭示矾山地区中生代花岗岩的成因、侵位时间及其与成矿的关系,在岩石地球化学研究基础上,进行锆石U-Pb-Hf同位素测试,并与紫金山矿田进行对比,为本区找矿预测提供依据.矾山地区花岗岩具有高钾、高碱、富硅、低钛等特征,富集轻稀土元素,具弱-中等负铕异常.富集大离子亲石元素（K、Rb、Th等）,亏损高场强元素（Nb、Ta、Ti等）,具有板块俯冲后伸展环境特征.对花岗岩岩体进行锆石U-Pb测年,获得了110Ma的年龄.花岗岩与花岗闪长岩Hf同位素特征相似,ε（Hf）（t）为-3.1-1.6,T（DM2）为1 066-1 366Ma,说明花岗岩主要来源于中元古代地壳物质的重融,同时显示出壳幔混合作用的特征.矾山地区与紫金山矿区构造、成岩、成矿特征相似,具有“紫金山式”铜金矿找矿潜力.

In order to study the chronological and geochemical characteristics of the Mesozoic granite and granodiorite from Fan-shan area and their relationship with the regional mineralization,the LA-MC-ICPMS zircons U-Pb dating method was employed to assess the ages and Hf isotope composition,preceded by their petrological and geochemical studies.In addition,the authors aim to provide more evidences that will facilitate the next phase of prospecting by making a comparison with Zijinshan copper-gold ore field.The metaluminous-peraluminous high-K calcalkaline granite series and granodiorite are characterized by high con-tents of K2 O,SiO 2 ,and low TiO 2 .These samples are enriched in light rare earth element (LREE)and large ionic lithophile elements (LILE,e.g.K,Rb,Sr,Cs),but depleted in high strength elements (HFSE,e.g.Nb,Ta,Zr,Ti),and have nega-tive Eu anomalies.The geochemical properties of granite and granodiorite are similar to those of the magmatic arc rocks,which suggest a backarc spreading setting.The zircon U-Pb dating of two representative samples yield an emplaced age of 1 10 Ma,in Early Cretaceous.Zircon grains from the granites have lower Hf-isotpe compositions withεHf (t )=-3.1-1.6 and younger Hf model ages (T DM2 )=1 066-1 366 Ma.In comparison with the metamorphic basement near the study area,we suggest that the granitic rocks are probably derived from a Mesoproterozoic crust,but the granodiorite may have originated from a Mesoprot-erozoic crust-mixed with a fraction of mantle materials.Based on the comparative study with Zijinishan Orefield,it is concluded that there are similar structural,lithogeneous and metallogenic features between the two areas,and there is huge prospecting potential to find “Zijinshan style”copper-gold polymetallic deposits in Fanshan area.