四川盆地威远构造基底花岗岩地球化学特征及其构造环境  

Geochemical Characteristics and Tectonic Environment of Basal Granite in Weiyuan Structure,Sichuan Basin

作　　者：谷志东[1] 翟秀芬[1] 江兴福[2] 黄平辉[3] 钱洪英[2] 乔琳[2] 

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]西南油气田公司勘探事业部,四川成都610041 [3]西南油气田公司勘探处,四川成都610051

出　　处：《地球科学（中国地质大学学报）》2013年第S1期31-42,共12页Earth Science-Journal of China University of Geosciences

基　　金：国家科技重大专项"海相碳酸盐岩油气资源潜力与大油气田形成条件;分布规律研究"(No.2011ZX05004-001);中国石油股份公司科技项目"四川盆地开江古隆起解剖研究与风险勘探目标评价优选"(No.2013D-0704-04)

摘　　要：四川盆地威远构造钻入基底探井与航磁负异常揭示其基底为花岗岩类,通过对威117井基底花岗岩类的岩石学、地球化学特征分析,显示其为正长花岗岩,粒度由下而上逐渐变粗;主量元素具有高硅、高碱、高K2O/Na2O、富钾贫钠特征,属于高钾钙碱性、准铝质-弱过铝质系列;轻稀土元素富集、重稀土元素亏损,Eu强烈负异常,球粒陨石标准化配分曲线呈向右倾斜的海欧型;其富集高场强元素Th、U、Pb、Nd、Sm与大离子亲石元素Cs、Rb,亏损高场强元素Nb、Eu、Ti、Sc与大离子亲石元素Ba、Sr.威117井基底花岗岩类成因类型属于A2型花岗岩,可能是混有少量地幔岩浆的地壳部分熔融岩浆经高度分离结晶作用形成,推断该花岗岩类发育于晋宁运动后澄江期由伸展到裂谷的构造环境.The deep wells drilled into the basement in Weiyuan structure in Sichuan basin,and aeromagnetic negative anomalies confirm that the basement is composed of granitoids.The genetic types of granites,the sources of the magma and their original tectonic settings are discussed in light of detailed analysis of petrology and geochemistry of basal granites in W117well in this paper.Well core observation and thin section identification results show that syenogranite is the main rock type,with an upward-coarsening rhythm.The features of major elements include high Si content,high alkali value,high K2O/Na2O ratio,high K content but low Na content,suggesting that it belongs to high-K calc-alkaline and metaluminous-weakly peraluminous series.The LREE is rich,with HREE loss and intensely negative Eu abnormality,while the chondrite-normalized distribution shows right tilting seagull-like patterns.High field strength elements Th,U,Pb,Nd,Sm and large ion lithophile elements Cs,Rb are rich,while high field strength elements Nb,Eu,Ti,Sc and large ion lithophile elements Ba,Sr are depleted.The genetic type is A2granite,maybe formed by highly fractional crystallization of crust molten magma mixing with a small amount of mantle magma.This type of granite is deduced to have developed from extension to rifting tectonic environment during Chengjiang period after Jinning movement.

关 键 词：四川盆地 威远构造 基底花岗岩 地球化学 构造环境 

分 类 号：P588.121[天文地球—岩石学]