新疆西准噶尔萨尔托海蛇绿混杂岩形成时代及构造环境分析  

The age and tectonic setting of Sartokay ophiolitic melange in western Junggar,Xinjiang

作　　者：何世平[1] 时超[1] 王超[1] 于浦生[1] 辜平阳[1] 查显锋[1] 

机构地区：[1]中国地质调查局西安地质调查中心,西安710054

出　　处：《地质科学》2013年第4期1033-1049,共17页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：中国地质调查局地质调查项目"新疆构造单元厘定及综合研究编图"(编号:1212011121094)资助

摘　　要：萨尔托海蛇绿混杂岩是西准噶尔地区达拉布特蛇绿混杂岩带的重要组成部分,其形成时代和构造环境颇具争议。通过LA-ICP-MS锆石微区原位U-Pb同位素测年,获得其中辉长辉绿岩的^(206)Pb/^(238)U加权平均年龄为388.8±1.1 Ma,确定该蛇绿混杂岩形成于中泥盆世。岩石地球化学分析表明,纯橄岩(蛇纹岩)属于低Si、低碱、高Mg的变质橄榄岩,REE呈∑REE偏低的平坦型分布模式,Cr、Ni和Co含量较高;变玄武岩属于高Ti、富Mg、富Fe、偏碱的拉斑系列,REE分布模式呈现ΣREE偏低、Eu异常不明显的平坦型曲线,微量元素分布模式为K、Cs、Th、Nb和P相对亏损的平坦型曲线,Zr/Nb比值低,总体表现出与E-MORB相似的特征。综合判断认为,萨尔托海蛇绿混杂岩形成于大陆裂谷向洋盆转化的构造环境,类似于"红海式"洋盆,为进一步深入认识新疆地区众多蛇绿混杂岩的形成构造环境提供了新思路。For Sartokay ophiolitic m61ange,as an important part of the Dalabute ophiolite in western Junggar of Xinjiang,it is widely controversial on its formation age and the tectonic setting. High resolution LA-ICP-MS in situ dating yields the zircon 206pb/238U weighted average age of 536.4±3.6 Ma from the gabbro-diabase in Sartokay ophiolitic m61ange,by which we believe that this ophiolitic m61ange formed in Middle Devonian. The geochemical characteristics prove that the Dunite（Serpentinite） belongs to the metamorphic peridotite with low Si, low alkali, and high Mg. The REE distribution pattern of the dunite is generally fiat with low ∑REE, high Cr, Ni and Co. The meta-basalt belongs to the subalkalictholeiite series rich in Ti, Mg and Fe, and the REE distribution pattern shows a fiat-type with lower ∑REE, and without obvious Eu anomaly. The trace element distribution of the meta-basalt is also fiat,with relatively depleted K, Cs, Th, Nb and P,lower Zr/Nb ratio. All these results indicate that Sartokay ophiolitic m61ange generally resembles the E-MORB type. Comprehensively, we consider that Sartokay ophiolitic m61ange formed in a tectonic setting where a continental rift was transforming into an ocean basin,which may be similar to the ＂ Red Sea type＂. This study provides a new clue to the further understanding of the tectonic settings of the ophiolites in Xinjiang.

关 键 词：LA—ICP-MS锆石U—Pb测年 地球化学特征 “红海式”洋盆 萨尔托海蛇绿混杂岩西准噶尔 

分 类 号：P588[天文地球—岩石学] P597[天文地球—地质学]