中条山地区郭家沟基性-超基性岩体的岩石成因及地质意义

文章通过对中条山地区郭家沟基性-超基性岩体的岩石学、矿物学和岩石地球化学方面的分析研究,讨论了该岩体的形成时代、岩石成因、及其地质意义。郭家沟岩体侵入时代为元古代,可能与绛县群形成时代较为相近(2200Ma左右)。郭家沟岩体具有岩相分带现象,边缘相为辉长岩,向内渐变过渡为含长辉石岩、变余辉石岩(角闪石岩)等,在岩体的中心发育着磁铁透闪石岩;岩石中Mg O与其他主量元素线性相关,各类岩石地球化学特征较为相似,显示出岩石受分离结晶作用的影响,具有岩浆同源演化的趋势;岩石总体显示出低硅、低镁、高铁、高钛、高钙的特征,相对富集LREE和LILE,而亏损HREE和Nb、Ta、Zr、Y等高场强元素,轻重稀土分馏明显,具有较弱的Eu异常,V含量较高,具有阿拉斯加型侵入岩体和与火山弧相关的岩浆特征。从岩石组合及地球化学特征结合区域构造演化,认为岩体形成于大陆边缘弧的构造环境,从侧面也说明绛县群的形成环境应该是大陆边缘俯冲后的伸展环境,而非陆内裂谷。

Petrogenesis, geological significance of Guojiagou basic-ultrabasic intrusion in Zhongtiao mountains

According to the detailed study of petrology, mineralogy, geochemistry on the Guojiagou basic-ultrabasic intrusion in Zhongtiao Mountains, this work discussed the formation age, petrogenesis and geological significance of this intrusion. The age of this intrusion is the Proterozoic, which is similar with the Jiangxian group (about 2200Ma). The Guojiagou intrusion displays lithofacies zonation, with marginal facies of gabbro, gradual transition to inward with plagioclase-containing pyroxenite and palimpsest pyroxenolite (amphibolite), and central magnet tremolitite. The MgO content and other major elements in rocks have a linear correlation, and the geochemical characteristics of all kinds of rocks are similar, suggesting their influence by fractional crystallization, and a magmatic homologous evolution trend. These rocks generally show low silicon, low magnesium, high iron, high titanium, high calcium, LREE and LILE enrichment, loss of HREE, HFSE of Nb, Ta, Zr, Y, relatively obvious REE fractionation, weak Eu anomaly and high V content. They own characteristics of the Alaska intrusive rocks and volcano arc related magmatic features. Combined the rock assemblages and geochemical characteristics with the regional tectonic evolution, it is inferred that the pluton was formed in a continental marginal arc tectonic environment, and that the formation environment of the Jiangxian group should be a continental margin extensional environment after subduction, rather than an intracontinental rift.