关键词: 辉长岩, UPb测年, 东昆仑, 巴什康阔勒

Abstract: Major and trace element analysis were conducted in this study. The rocks have MgO contents between 578% and 123%, FeO contents between 516% and 104%, Al2O3 contents between 142% and 2156%, which is relatively high in all. The TiO2 contents of the samples range from 018% to 132% (average=077%), which is relatively high and similar to those of the island arc tholeiitic basalts (TiO2=084%). However, the rocks show relatively low contents of K2O (005%-053% with an average of 02%), consistent with those of the ocean ridge tholeiitic basalt (K2O=02%). The REE patterns are characterized by an enrichment of LREEs and a depletion of HREEs. The trace element spidergram shows enrichments for LILEs (except K), Ti and P, and depletions for Nb and Zr. It is suggested that the rocks formed in island Backarc basin. Zircon UPb dating was taken and two groups of age were obtained. The upper intercept age of (501±1) Ma (MSWD=025) indicates the crystallization age of the original rock during the Late Cambrian. The lower intercept age of (451±2) Ma (MSWD=0084) suggests the age of the metamorphism during the early stage of Late Ordovician. Combined with the result of major and trace element and zircon UPb dating, it is concluded that the subduction of oceanic crust began from the Late Cambrian and the subsequent collision happened no later than the Late Ordovician.

Key words: gabbro, UPb dating, Eastern Kunlun, Bashikangkuole