阿尔金山北缘冰沟蛇绿混杂岩中辉长岩锆石SHRIMPU-Pb定年及其地质意义

摘要

冰沟蛇绿混杂岩是阿尔金山红柳沟蛇绿混杂岩带的东段部分,岩石组合包括蛇纹岩、方辉橄榄岩、辉石岩和辉长岩等.蛇纹岩具高Mg,Mg/Fe值大于9,低Al、Ca、Na、K为特征,从稀土元素和微量元素特征来看,基性辉长岩和洋壳以及洋中脊玄武岩极为相似,而超基性岩与原始地幔较为接近.辉长岩获得锆石SHRIMP年龄为449.5±10.9Ma.蛇绿混杂岩的围岩为一套巨厚的碎屑岩、火山碎屑岩、火山岩,以及部分碳酸盐岩构成,其中含有具有洋中脊特征的枕状构造玄武岩,以及放射虫硅质岩,放射虫时代为奥陶纪中晚期,与辉长岩的SHRIMP年龄一致.这些证据进一步证实了红柳沟一带存在早古生代洋盆的地质事实.%Binggou ophiolite mange, the eastern part of Hongliugou ophiolite, Altyn Tagh, is composed of serpentinites, harzburgites.rjyroxeniteB and gabbros etc. Geochemistry analysis shows that the serpentinites are characterized by high Mg contents,with Mg/Fe ratio greater than 9, and low Al, Ca, Na, K contents. Determined by rare earth elements and trace elements compositions, the gabbro is very similar to MORB,and ultrabasic rocks are close to PRIM A. The SHRIMP U-Pb age of zircon from the gabbro is 449. 5 ?10. 9 Ma which is belongs to Middle to Late Ordovician. The country rocks of Binggou ophiolite melange are mainly composed of clastic rocks,pyroclastics, volcanic,and part of carbonates which combined to be a huge thick sequence. These rocks contain basalt which has characteristics of MORB and the pillow structure, and radiolarian cherts which formed in Middle to Late Ordovician that is consistent with the gabbro SHRIMP age. These evidences further convinced that die Early Paleozoic ocean basin has been existed in die Hongliugou area.