金佛寺岩体地球化学特征及成因  

Geochemical Characteristics Petrogenesis of Jinfosi Pluton in Qilian Mountains

作　　者：胡能高[1] 苏建平[2] 张海峰[2] 冯备战[2] 

机构地区：[1]长安大学地球科学与国土资源学院,陕西西安710054 [2]甘肃地质调查院,甘肃兰州710050

出　　处：《地球科学与环境学报》2006年第1期5-12,共8页Journal of Earth Sciences and Environment

基　　金：国家重点基础研究发展规划国际重大合作项目(2001CB711001);中国地质调查局项目(DK0002019)

摘　　要：金佛寺岩体是一个晚志留世侵入于北祁连造山带中的花岗质岩体，主要由黑云母二长花岗岩，黑云母钾长花岗岩和黑云母石英二长岩组成。岩体中岩石w（SiO2）为67．09％～74．97％，叫（K2O）／w（Na2O）为1.18～1．83，w（MgO），w（TFeO），w（CaO）和w（Al2O3）随w（SiO2）增大而减小，而w（K2O）增大。ANCK为1．06～1．24，均属铝过饱和，σ为1.25～2．48，属钙碱性系列。EREE为（21．36～254．9）×10^6，与w（SiO2）呈负相关关系，多数稀土配分曲线相似；轻稀土分异明显大于重稀土。δ（Eu）为0．64～0．19，铕的亏损随w（SiO2）增大而增大。Ni，Cr，Co，Sc，V和Sr随w（SiO2）增大而变小，Rb增大，Th和Th／U比值呈正相关，Ta与Nb／Ta呈负相关。岩体的主量元素、稀土和微量元素的变异主要由深熔过程引起，而不是结晶分异作用引起的。主要源岩是富长英质的，而不是富泥质的，其矿物组合可能是普通角闪石＋黑云母＋斜长石＋钾长石＋石英，与北大河岩群很相似。The Jinfosi Pluton, a granitoid complex intruded in North Qilian Orogen Belt in late Silurian period, is mainly consisted of biotite monzogranite, biotite syenogranite and biotite quartz monzonite. The rocks of the pluton have 67.09%-74.97% w（SiO2 ）, 1.18-1.83 w（K2O）/w（Na2O）, and their w（TFeO）, w（MgO） ,w（CaO） and w（Al2O3） decrease and w（K2O） increases with increasing w（SiO2）. All rocks are peraluminous with ANKC of 1.06-1.24. The magmatic type belongs to calc-alkalic with σ=1. 25-2.48. The ∑REE varies from 21.36× 10^-6 to 254.90× 10 ^-6 and is negatively correlated to w（SiO2 ）. Most of REE patterns show similarities in fractionating behaviour： LREE has more obviously fractionation than HREE; δ（Eu） vary from 0.64 to 0.19 and negative Eu anomalies generally increase with increasing w（SiO2）; Ni, Cr, Co, Sc, V and Sr decrease and Rb increase with increasing w（SiO2）; Th is positively correlated to Th/U, but Ta is opposed to Nb/Ta. The variations in abundances of major, rare earth and trace elements in the pluton resulted mainly from the anatectic process and did not from the crystallization differentation. These data indicate that the source rocks of the pluton are mainly rich-felsic and poor-rgillaceous. The mineral assemblage of the source rocks is possible of hornblende ＋ biotite ＋ plagioclase ＋ K-- feldspar＋ quartz, which belongs to the Beidahe Group.

关 键 词：北祁连造山带 花岗岩 深熔作用 微量元素 金佛寺岩体 甘肃省 

分 类 号：P588.12[天文地球—岩石学] P594.1[天文地球—地质学]