西准噶尔不同时代蛇绿岩及其构造演化

Tectonic Evolution of Different Dating Ophiolitesin the Western Junggar, Xinjiang

新疆西准噶尔有三个时代的蛇绿岩，它们都是古生代，但根据地层学和同位素定年可确定为中奥陶世、晚－中志留世和早－中泥盆世。这些蛇绿岩大多是肢解的蛇绿混杂，下部主要有方辉橄榄岩，夹有纯橄岩和二辉橄榄岩透镜体，中部是镁铁质一超镁铁质堆晶岩，其中有岩墙穿插，上都是基性熔岩夹有放射虫硅质岩。地质、岩石、矿物和地球化学特征表明，这三个不同时代蛇绿岩具有明显的相似性，它们都是在深的小洋盆地中形成的。西准噶尔地区自奥陶纪至泥盆纪，古小洋盆经历三次扩张一收缩同步运动，而不存在一个广阔的古大洋。小洋盆的形成和封闭共同造成了广大的古生代褶皱带。

Ophiolites in the west Junggar of Xinjiang are situated in between the Siberian and Sino-Koreancontinental plates geotectonically. All of the ophiolites are Paleozoic in age, and can be determined fromstratigraphy and isotopic dating as middle Ordovician, later-middle Silurian and early-middle Devonian. Most ofthe ophiolites were dismembered. occurring as ophiolitic melange. The lower part of these ophiolites mainlyconsists of harzburgite with some dunite and lherzolite lenses, the middle part consists of the cumulatic maficultramafic rocks with some minor ma fie dykes. and the upper part consists of basic lava interlayered withradiolarian chert and some pillows. The ophiolites of various age are of similarities in the petrochemistry andREE of the rocks. chemical composition of the olivine. pyroxene. plagioclase and spinel, and all formed probablyin the small deep sea basins. In the northern part of Xinjiang. pre-Ordovician formations are mainly platformtype (no flysch) of sediments including carbonate. elastic and glacial deposits. Since Ordovician deep sea basinsbegan to develops and the oceanic lithosphere (ophiolite) formed in the west Junggar. At the same time. theterrigenous deposit basin belonging to pre-Ordovician was closed by spreading of Ordovician small sea basin andby overthrust of the ophiolite nappes. The Silurian deep sea basins was developed to the north of the Ordovicianbasin and its spreading led to the closure of the Ordovician small ocean basin. The spreading of the Devonianbasin accompanied the closure of the Silurian basin.