The discovery of Early Ordovician ophiolite mélange in Taerbahatai Mts.,Xinjiang,NW China
The discovery of Early Ordovician ophiolite mélange in Taerbahatai Mts.,Xinjiang,NW China
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作者：
Zhu Yong
本文报道了塔尔巴哈台山蛇绿混杂岩的发现。下石炭统黑山头群主要由泥岩、粉砂岩、凝灰岩、异源岩、火山角砾岩和熔岩组成，角砾岩包括蛇纹岩、辉长岩、玄武粗安岩、粗面岩和硅质岩。蛇绿岩m61岩群产于该火山岩地层底部，由蚀变辉长岩、蛇纹橄榄岩和硅质岩组成。橄榄岩经历了强烈的蛇纹石化作用，被蛇纹岩完全取代，但仍保留了橄榄石和斜方辉石的假象。火山作用明显晚于蛇绿混杂岩的侵位，蛇绿混杂岩底部的蚀变辉长岩中的单斜辉石颗粒较新鲜，呈出溶结构（而所有斜长石颗粒都被水钙铝榴石所取代，显示斜长石的假像）。所有出溶层状体都是棕色尖晶石。锆石SHRIMP法测得年龄为478.3±3.3Ma（MSWD= 1.09，n =14），代表塔尔巴哈台蛇绿混杂岩的侵位时代为早奥陶世。
We report a discovery of an ophiolite melange in Taerbahatai Mts.(Xinjiang,NW China),which underlies the Early Carboniferous Heishantou Group consisting mainly of mudstone,siltstone,tuff,alloclastic rocks,volcanic breccia and lava.The breccia includes serpentite,gabbro,basaltic trachyandesite,trachyte,and silicalite. The Ophiolite m61ange consisting of altered gabbro,serpentine peridotite,and silicalite occurs on the bottom of this volcanic stratum. Peridotite has undergone strong serpentinization and was completely replaced by serpentinite,but the pseudomorph of olivine and orthopyroxene still are preserved. Volcanism obviously postdated the emplacements of the Ophiolite melange,and the eruption was strong as large gabbro and other breccia are frequently observed.Clinopyroxene grains in the altered gabbro from the bottom of the Ophiolite melange are relatively fresh and show a kind of exsolution texture (whilst all plagioclase grains were replaced by hydrogrossular showing pseudomorph of plagioclase).All the exsolution lamellae are brown spinel.The spinel lamellae (or leafs) are parallel to each other.Zircon separated from this altered gabbro is dated to be 478.3±3.3Ma (MSWD=1.09,n=14) by SHRIMP method.This age represents the emplacement time of the Taerbahatai Ophiolite melange during the Early Ordovician epoch.