胶东地区郭家岭花岗闪长岩的地球化学特征及成因  

2003. Geochemistry and petrogenesis of Guojialing granodiorites from the northwestern Jiaodong Peninsula, eastern China.

作　　者：杨进辉[1] 朱美妃[2] 刘伟[1] 翟明国[1] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]台湾大学地质学系

出　　处：《岩石学报》2003年第4期692-700,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金(40132020);中国科学院知识创新工程项目(KZCX1-07-04)联合资助

摘　　要：本文系统地报道了郭家岭花岗闪长岩的主量元素、微量元素和Sr-Nd同位素组成,重点讨论了郭家岭花岗闪长岩的岩石成因、成岩物质来源及其地质意义。研究结果表明,郭家岭花岗闪长岩的SiO_2含量从62％至72％,Na_2O/K_2O=0.64-1.79,多数样品大于1.0;K_2O+Na_2O值为7.34-8.49％,铝指数A/CNK=0.82～1.1,属于准铝质或过铝质Ⅰ型花岗岩;高Sr含量(Sr>800μg/g)、低Y和Yb含量(Y<10 μg/g;Yb<1.0μg/g)、轻重稀土分馏强烈(La_N/Yb_N=17.4～47.8);这些地球化学特征类似于adakite、太古代TFG岩系、Na质花岗岩及HiSrBa花岗岩而不同于岛弧环境的英安岩。高的初始^(87)Sr/^(86)Sr比值(0.7094～0.7114),负的δ^(Nd)(t)值(-11.2～-17.5),表明花岗闪长岩与adakite、HiSrBa花岗岩的成因不同而类似于Na质花岗岩和TTG岩系,即郭家岭花岗闪长岩是由下部地壳镁铁质岩石脱水部分熔融作用形成的。Nd同位素与胶东地区基性脉岩的Nd同位素组成相近,表明二者有可能具有相似或相同的源区。但基性脉岩出露面积明显小于花岗岩,二者之间存在着 SiO_2成分间隔,并且基性脉岩的不相容元素明显高于花岗闪长岩,从而表明花岗闪长岩不是基性脉岩结晶分异的产物,这与由幔源岩浆直接分异形成的高Sr、Ba花岗岩(HiSrBa)的成因不同。因此,花岗闪长岩有可?Guojialing granodiorites, the main host rocks of gold ore deposits, were formed during late Yanshanian in the northwest of the Jiaodong Peninsula, eastern China. The data of occurrence, petrography, major and trace elements, and Sr and Nd isotopic components are reported, and the source and geological significance of the granodiorites are discussed in this paper. The granodiorites, with the characteristics of high SiO2 (62%similar to72%), Na2O/K2O=0.64similar to1.8 (most samples are more than 1.0), alkaline. concentrations ALK=7.34%similar to8.49%, and the aluminium index (A/CNK) 0.82similar to1.1, are enriched in Sr and Ba (Sr, Ba>500 mug/g) and depleted in Y (Y=2.85similar to9.16 mug/g), Yb (Yb=0.27similar to0.71 mug/g) and high field strength elements (HFSE) such as Nb, Ta, Zr and HE These geochemical features are similar to those of adakites, Archean TTG, Na-rich granites and high-Ba, Sr granites (HiSrBa) but different from those dacite of BADR in the are background. They have high (La/Yb)(N) and Sr/Y ratios and deltaSr(N) values (the deltaSr(N) of high Mg-# samples are more than 2), indicating the garnet and/or amphibole without plagioclase in the residue during magma genesis. delta(Nd) (130 Ma) values of Guojialing granodiorites are highly negative [delta(Nd)(130 Ma) = -11 to 17]. Compared with the Jiaodong metamorphic rocks and Linglong granites, they were not derived from the Precambrian basement. The geochemical features, similar to those of TTG and Na-rich granites and the mafic enclaves of Guojialing granodiorites containing acicular apatite indicate that the magma was derived from the lower mafic crust formed by previously ancient enriched mantle-derived magma underplating, but assimilated by an upper crustal component. They are different from adakites which were derived from partial melting of subducted oceanic slab with or without reaction with mantle peridotite and HiBaSr granites which were directly derived from crystal fractionation of mantle-derived magmas. Guojialing granodiorites were derived

关 键 词：胶东地区 郭家岭花岗闪长岩 地球化学 岩石成因 

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