新疆阿尔泰库卫岩体的SHRIMP锆石U-Pb年龄及其地球化学特征  

SHRIMP U-Pb zircon dating and geochemistry of Kuwei intrusion in the Altay Mountains, Xinjiang

作　　者：赵莉[1] 张招崇[1,2] 闫升好[3] 周刚 陈柏林[5] 柴凤梅[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室 [2]中国地质科学院地质研究所,北京100037 [3]中国地质科学院矿产资源研究所 [4]新疆地质矿产局第四地质大队 [5]中国地质科学院地质力学研究所

出　　处：《岩石矿物学杂志》2006年第3期194-202,共9页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(40572047);国家305项目(2001BA609A-07-02);教育部新世纪优秀人才支持计划(NCET-04-0728);科技部973资助项目(2001CB409807)

摘　　要：阿尔泰造山带的库卫地区分布有10余个镁铁-超镁铁质岩体，库卫岩体是其中面积最大的一个岩体。SHRIMP锆石U-Ph方法测年结果表明其形成时代为47±1Ma，暗示了该地区新生代曾发生过强烈的隆升过程。与阿尔泰山其他地区的镁铁-超镁铁质岩体相比，库卫岩体的地球化学特征具有特殊性，以低的TiO2、稀土元素、不相容元素含量及高的Al2O3含量为特征。较大的MgO含量变化范围（6．6％～20．1％）以及MgO与其他主要元素和Ni含量之间的相关性暗示着岩浆发生过橄榄石、斜方辉石和单斜辉石的分离结晶作用。低的稀土和不相容元素含量及平坦型的稀土元素配分模式和不相容元素比值（如La／Sm和Gd/Yb）暗示了其原始岩浆来自于亏损的软流圈地幔（石榴石二辉橄榄岩）的高度部分熔融。同时，高的La/Nb比值和在微量元素原始地幔标准化图解上显示出的明显正Pb异常暗示着岩浆在岩浆房中曾遭受过下地壳物质的同化混染作用，岩体中较低的Ni含量则可能是深部硫化物熔离作用的结果。More than ten mafic-ultramafic intrusions are distributed in Kuwei area of the Altay orogenic belt, and the Kuwei intrusion is the biggest one in this area. The SHRIMP U-Pb zircon dating yields an age of 47 ± 1 Ma, suggesting that strong uplift occurred in this area during Cenozoic. Compared with the mafic-ultramafic instrusions in other areas of the Altay Mountains, the Kuwei intrusion has some unique geochemical features in that it is characterized by low TiO2, REE and incompatible element contents, and high A1203 contents. The wide range of MgO contents （6.6 % -20.1% ） and the correlation between MgO contents, other major element contents and Ni contents imply that the fractional crystallization of olivine , orthopyroxene and clinopyroxenemight have occurred. Its low REE and incompatible element contents, flat chondrite-normalized REE patterns and incompatible element ratios （e. g. , La/Sm and Gd/Yb） indicate that the primary magma resulted from the high degree of melting of the depleted asthenospheric mantle （garnet peridotite）. In addition, its high La/Nb ratios and the markedly positive Pb anomalies in the primitive mantle normalized trace element patterns suggest that the magma must have been subjected to the contamination of low crust materials in the magma chamber. The relatively low Ni contents probably resulted from the immiscible sulfide melt at a relatively deep level.

关 键 词：镁铁-超镁铁质岩体 SHPIMP年龄 地球化学 岩石成因 库卫 阿尔泰 

分 类 号：P597.3[天文地球—地球化学] P591[天文地球—地质学]