内蒙古达茂旗哈尔陶勒盖地区蛇绿岩形成环境探讨

Tectonic environment of ophiolites in the Har Tolgoi area, Damao Qi, Inner Mongolia

内蒙古达茂旗哈尔陶勒盖地区蛇绿岩的堆晶岩为橄榄岩+辉石岩+辉长岩组合,即为PPG型;通过岩石化学、地球化学研究,首次从辉长岩中识别出有玻安岩存在,为本区蛇绿岩的形成环境从岩类学方面提供依据;玄武岩具洋脊玄武岩特征,但俯冲带组分(Th等)富集;在混杂带内分布有泥盆纪岛弧型中-中酸性火山岩,整合于硅泥质岩之上。基于上述几个方面的分析,提出本区蛇绿岩的形成环境应为SSZ型,既形成于初始俯冲,在俯冲带之上(弧前)形成新的洋壳,并逐渐向岛弧演化。

Cumulates in ophiohtes of the Har Tolgoi area, Damao Qi, Inner Mongoha, are represented by the peridotite＋pyroxenite＋gabbro association, i.e. the PPG type. Boninite is recognized for the first time from gabbro by petrochemical and geochemical studies, which provides petrological evidence for the tectonic environment of ophiolites inthe area. Basalt has the characteristics of MORB and is enriched in components （e.g. Th） of the subduction zone. In the mélange zone there occur Devonian island arc-type intermediate and intermediate-acid volcanic rocks, which conformably overlie siliceous pehte. Based on the above-mentioned analysis, the authors suggest that ophiohtes in the area formed in a SSZ-type environment, i.e. at the time of initial subduction. New oceanic crust formed above the subduction （fore-arc） zone and gradually evolved to an island arc