甘肃红石山蛇绿岩地球化学特征及构造环境

GEOCHEMISTRY FEATURES AND TECTONIC SETTING OF THE HONGSHISHAN OPHIOLITE IN GANSU PROVINCE

红石山蛇绿岩产出于塔里木板块北缘红石山深大断裂带中,主要由变质橄榄岩、辉长岩和玄武岩组成。玄武岩的主要地球化学特征与MORB相似,微量元素特征表明它属N-MORB。结合区域地质特征,认为红石山蛇绿岩早期为初始洋盆环境,晚期有洋脊扩张中心环境的玄武岩形成。早石炭世早期是洋盆发育的全盛期,早石炭世晚期洋壳发生消减,于二叠纪晚期构造侵位,伴有绿片岩相变质作用。

The Hongshishan ophiolitic migmatitic complex outcropped along the Hongshishan deep fracture, which was the northern marginal fault of the Tarim plate. The ophiolite was mainly composed of metamorphic peridotite, gabbro （ including the cumulated gabbro） and basahs. The discriminative diagrams indicated that the geochemical characteristics of the basalts were similar to the MORB. The REE patterns and spidergrams of trace elements showed that the meta-peridotite, gabbro and basahs had a genetic relation, and could be relevant to N-MORB. To synthesize the regional geology, the paper suggested that the Hongshishan ophiolite might record an initial oceanic basin in its early stage which resulted from an intracontinental rift between the Tarim and the Junggar （including the Turpan-Harmi area） plates, and in later stage （Early Carboniferous） a wide ocean with spreading ridge created. The isotopic datings of volcanic arc and calc-alkaline granitoids demonstrated that the oceanic crust subducted in late Early Carboniferous. The Tarim plate collided the Junggar plate in Middle Permian and the ophiolite emplaced in Late Permian, accompanied with a metamorphism of green schist facies.