青海拉脊山东段峡门蛇绿混杂岩带的物质确定及其构造意义

在拉脊山东段青海省民和县峡门镇以南地区新识别出一条蛇绿混杂岩带,其物质组成复杂,构造岩块主要由蛇绿岩岩块、外来岩块、火山岩岩块以及变沉积岩岩块组成. 基性火山熔岩和辉绿岩具轻稀土富集的"右倾"配分模式,大离子亲石元素Ba、Th、Sr相对富集,高场强元素P、Ti、Nb相对亏损,总体岩石地球化学特征与岛弧拉斑玄武岩类似. 岩石学、岩石地球化学、同位素年代学特征及区域资料综合研究认为,峡门蛇绿岩属与俯冲有关的SSZ型蛇绿岩,很可能是早古生代原特提斯洋俯冲消减的弧后小洋盆,属于弧后盆地扩张型蛇绿岩.

DETERMINATION OF THE XIAMEN OPHIOLITE MELANGE IN THE EASTERN SECTION OF LAJI MOUNTAIN,QINGHAI PROVINCE:Tectonic Implication

An ophiolite melange belt with complex material compositions is newly identified in Xiamen Town in the eastern section of Laji Mountain, Qinghai Province. The tectonic blocks are mainly composed of ophiolites, exotic blocks, volcanic rocks and meta-sedimentary rocks. The basic volcanic lava and diabase are characterized by right-dipping LREE enrichment patterns, enrichment of LILEs (Ba, Th and Sr), and depletion of HFSEs (P, Ti and Nb), with the general petrogeochemistry similar to that of island-arc tholeiite. The comprehensive study of petrology, petrogeochemistry, isotope chronology and regional geology show that the Xiamen ophiolite is of supra-subduction zone (SSZ) type, which is probably a back-arc small ocean basin formed by Early Paleozoic Proto-Tethyan Ocean subduction, belonging to back-arc basin spreading ophiolite.