库鲁克塔格地区火山岩的岩浆过程与源区组成

Petrology, Geochemistry, Magmatic Process and Source Composition of Sinian-Cambrian Volcanic Rocks in Kuruktag Area

在新疆库鲁克塔格地区的震旦纪和寒武纪沉积岩地层中 ,分布有四层火山岩。它们分别产出于早震旦世的贝义西组、晚震旦世的扎摩克提组和水泉组以及早寒武世的西山布拉克组。其中 ,西山布拉克组和水泉组火山岩均属碱性玄武岩系列 ;扎摩克提组火山岩分属碱性玄武岩系列和拉斑玄武岩系列 ;贝义西组火山岩具有明显的双峰式组合特征 ,大部分属碱性火山岩。它们的多元素配分曲线均呈现出板内玄武岩的大隆起特征。斜长石的分离结晶作用导致少部分火山岩具有负铕异常。西山布拉克组和水泉组火山岩的SiO2 饱和度低于扎摩克提组拉斑玄武岩。相应地 ,前者的不相容元素丰度普遍高于后者。两者之间的差异主要是部分熔融程度的差异所致。稀土元素的强烈分馏以及重稀土元素显著贫化 ,意味着这些火山岩源自于大陆岩石圈地幔的石榴石二辉橄榄岩。Ba/Nb、La/Nb、Ba/La、Ba/Th和Rb/Nb比值证明 ,这些火山岩全部源自于富集型地幔源区 ,而且主要是EMI型地幔。

There exist four layers of volcanic rocks in Sinian and Cambrian strata of Kuruktag area, Xinjiang. They occur in Early Sinian Beiyixi Formation, Late Sinian Zhamoketi Formation and Shuiquan Formation as well as Early Cambrian Xishanbulake Formation respectively. Volcanic rocks of Xishanbulake Formation and Shuiquan Formation are of alkali basalt series, those of Zhamoketi Formation are of alkali basalt series and tholeiite series, and those of Beiyixi Formation are obviously characterized by bimodal assemblage and mostly belong to alkali volcanic rocks. Their multi_element distribution patterns show continental tumescence characteristics of intraplate basalt. Fractional crystallization of plagioclase led to the existence of negative Eu_anomalies in some volcanic rocks, while the cumulation of olivine resulted in the high MgO and low SiO 2 content of some volcanic rocks. The SiO 2 saturability of volcanic rocks of Xishanbulake Formation and Shuiquan Formation is lower than that of tholeiite of Zhamoketi Formation. Correspondingly, the abundances of incompatible elements in the first two formations is higher than those in the last formation, and the differences can be attributed to the different degrees of partial melting. The intense fractionation of REE and the obvious depletion of HREE suggest that these volcanic rocks were derived from garnet lherzolite of the mantle in the continental lithosphere. The Ba/Nb, La/Nb, Ba/La, Ba/Th and Rb/Nb ratios demonstrate that these volcanic rocks were exclusively derived from the enriched mantle, mainly the EMI type mantle.