摘要
西准噶尔位于西伯利亚,哈萨克斯坦和塔里木3个大陆板块的交汇处,其间存在着不同时代的洋壳残片,有晚寒武世—中奥陶世(523.2±7.2—489±53Ma)形成的夏坦河—唐巴勒蛇绿岩带,有志留纪和泥盆纪—早石炭世(395±1.2Ma)形成的玛依拉和达拉布特蛇绿岩带,有奥陶纪(444±27Ma)形成的洪古勒楞蛇绿岩带。按其岩石组合及地球化学特征可分为两种类型,即唐巴勒和洪古勒楞两类。前着代表弧后盆地拉张的产物,后者是在洋脊环境下形成的。从其分布大致可以反映出西准噶尔古生代洋盆不断向大陆俯冲的痕迹。
Four different ophiolite belts occur in West Junggar. They have been stronglytectonized and thus dismembered. The ages of crystallization of the cumulates the-rein are different. The Tangbale ophiolite is considered to be Late Cambrian (489±53 Ma) in age and represents an incompletely oceanic crust which formed in a back-arc basin. The Honguleleng ophiolite formed in the Ordovician (444±27 Ma) andrepresents typical oceanic crust in West Junggar. The age of the Mayila ophiolite isconsidered to be Silurian, which is determined by the age of radiolarians in thecherts associated with basalt. The Dalabute ophiolite formed in the Devonian--Early(395±1.2 Ma) Carboniferous, because most radiolarians in the cherts associated withpillow lavas are determined to be Early Carboniferous in age. It might form in acontractive small oceanic basin near an island arc. In fact, these ophiolite belts arefragments of oceanic crust of the ocean between the Siberian plate and the Kaza-khatan plate, which were emplaced onto the continental magin during differenttectonic stages. According to petrologic and geochemical data, West Junggar ophio-lites are classified into two types. (1) The first type is the incomplete ophiolite ofthe cumlate sequence made up of pyroxenite and gabbro. The upper volcanic seque-nce is complicated, with rich LIL elements which was formed in a back--arc basin,as exemplified by the Tangbale ophiolite. (2) The other type is the ophiolite of thecumulate sequence which was formed in typical magma chambers of mid--oceanridges. The cumulate sequence is composed of troctolite--gabbro. The geochemistry ofthe upper volcanic sequence indicates that it might form in an oceanic ridge enviro-nment and that the LIL elements are not enriched, as exemplified by the Hongulelengophiolite.
出处
《地质论评》
CAS
CSCD
北大核心
1992年第6期507-524,共18页
Geological Review
关键词
蛇绿岩
形成
时代
环境
ophiolite
back--arc basin
oceanic ridge
