新疆阿尔金长沙沟一带奥陶纪辉长岩SHRIMP锆石U-Pb年龄及其地球化学特征  

SHRIMP Zircon U-Pb Age and Geochemical Characteristics of Ordovician Gabbro from Altun,Xinjiang Province

作　　者：徐旭明[1] 郭金城[1] 陈海燕[1] 段先乐[1] 张正平[1] 张志超[1] 

机构地区：[1]河北省区域地质矿产调查研究所,河北廊坊065000

出　　处：《西北地质》2014年第4期156-162,共7页Northwestern Geology

基　　金：中国地质调查局基础调查项目"新疆阿尔金地区1:5万(J45E012015;J45E012016;J45E012017;J45E013015;J45E013016;J45E013017六幅区调"(1212011085033)

摘　　要：通过对新疆阿尔金长沙沟一带详细的野外地质调查,笔者首次解体出了奥陶纪辉长岩。采用高精度SHRIMP锆石U-Pb测年法获得了其206Pb/238 U年龄加权平均值为（444.9±3.4）Ma（n=9,MSWD=1.83）,可能代表了南阿尔金洋盆封闭后的一次岩浆事件。对岩石地球化学研究,表明该区辉长岩分异指数DI=35.26～44.76,固结指数SI=20.24～31.43,反映岩浆结晶分异程度较低;里特曼指数σ=3.26～9.49,A/CNK=0.75～0.82,属准铝质钙碱碱性系列;稀土总量较高,∑REE=237.39×10-6～329.26×10-6,（La/Yb）N=6.14～8.55,轻、重稀土分馏较明显,REE配分曲线向右缓倾,Eu负异常不明显;Ba、Hf、Rb、Th、U含量明显偏高;Rb/Sr=0.04～0.47,明显低于陆壳平均值。结合区域地质背景及R1-R2图解指示：该套辉长岩应形成于板块碰撞前-碰撞后的抬升阶段,主要受阿尔金南深大断裂控制,为伸展构造环境下形成的幔源型侵入岩,可能为南阿尔金洋盆封闭后最近的一次伸展事件的产物。The Ordovician gabbro was firstly discovered in Changshangou, Xinjiang province. The authors got for the first time the zircon U-Pb age [444.9＋3.4 Ma （n=9, MSWD=1. 83）] of gabbro, whose occurence may represent a magmatic event after the closure of south Altun o- cean basin. Geochemical analysis show that the differentiation index （DI） is 35.26 to 44. 76 and the solidification index （SI） is 20. 24 to 31.43, which reflects a lower differentiation degree of magmatic crystallization; the values of Rittmann index （3.26-9.49） and A/CNK （0. 75-0.82） indicates that the gabbro is quasi-aluminous calc-alkaline to alkaline series; the content of REE is relatively high （ ∑ REE = 237.39 ×10^-6-329. 26 ×10^-6 ）, the fractionation of LREE and HREE is obvious （ （La/Yb）N =6.14-8.55）, the REE patterns show right oblique feature and unobvious negative Eu anomaly. Trace elements show enrichment of Ba, Hf, Rb, Th, U~ the value of Rb/ Sr is from 0.04 to 0.47, clearly lower than the average of continental crust. Combined with re- gional geological background and R1-R2 diagram, the authors hold that the gabbro is mantle-de- rived intrusive rock resulted from the plate uplift stage from pre-collision to post-collision, con- trolled by deep and major faults on the south of Altun. It is considered that the gabbro was formed in an extensional tectonic environment, probably he a result of lately extensional event after the closure of south Altun ocean basin.

关 键 词：SHRIMP锆石U-PB年龄 辉长岩 奥陶纪 地球化学 新疆 

分 类 号：P597[天文地球—地球化学]