柴北缘锡铁山地区镁铁质岩石的时代及地球化学特征

摘要

This paper mainly focused on the mafic rocks in southwest Xitieshan area, which are composed of basalt, diabase and gabbro derived from the same primitive magma. Detailed geochemical studies show that the basalt in Xitieshan area have high concentrations of Fe, Ti, P and K, and are also characterized by OIB-type trace element patterns, displaying significant enrichment of LREE and LILE as well as HFSE. These data indicate that the mafic rocks were probably formed in an intraplate environment. Zircon U-Pb dating of the gabbro yielded a 206Pb/238U weighted average age of 520.8±7.0Ma. Combined with the chronology and geochemical data of the region, the authors infer that the North Qaidam was located in a tectonic background of archipelagic ocean where there existed a multi—island oceanic basin in Early Paleozoic period.%柴北缘锡铁山地区西南部出露一套镁铁质岩石,主要由玄武岩、辉绿岩及辉长岩组成,三者为同源岩浆演化的产物.地球化学分析表明,研究区玄武岩的TFe2O3(9.77％～11.49％)、TiO2(1.47％～2.17％)、P2O5(0.25％～0.40％)、K2O(0.28％～0.76％)含量较高,具有LREE富集的稀土元素配分型式,富集K、Rb、Ba、Th、Nb、Ta等不相容元素,呈现隆起型(驼峰式)分布型式,显示了典型的洋岛火山岩地球化学特征,为板内岩浆作用的产物.辉长岩中的锆石LA-ICP-MS U-Pb定年结果表明,本套镁铁质岩石的结晶年龄为520.8Ma±7.0Ma.结合区域年代学和地球化学资料,推测柴北缘地区在早古生代已发育成为一个成熟的多岛洋盆.