山东蒙阴金伯利岩中蛇纹石化橄榄石的微组构特征及其地质意义

为探究山东蒙阴金伯利岩中蛇纹石化橄榄石的微组构特征、蚀变环境、元素迁移规律及其对金伯利岩表生演化的指示意义,对该区金伯利岩中部分蛇纹石化的橄榄石和完全蚀变的橄榄石进行了XRD、EPMA和LA-ICP-MS分析测试。结果表明,蛇纹石中少部分Mg被Fe、Al、Ca、Ni、Mn取代,其中Fe含量仅次于Mg;从蚀变橄榄石的中心到边缘,Li与Zn、Ba与Sc、Co与Y含量分别呈3组变化趋势;部分蚀变的橄榄石为负Eu异常、低氧逸度,推测其形成于封闭的还原环境;完全蚀变的橄榄石无Eu异常,氧逸度相对较高,推测其形成于更开放的偏氧化环境;未完全蚀变的橄榄石大部分微量元素含量都高于完全蚀变橄榄石;稀土元素在蛇纹石化过程中可能存在迁移活动。

Microfabric Characteristics of the Serpentinized Olivine from Kimberlite in the Mengyin Area,Shandong Province and Their Geological Significances

In order to explore the microfabric characteristics,alteration environment,element migration rules of the serpentinized olivine in the kimberlites in the Mengyin area,Shandong Province,and their indicative significances for the supergene evolution of the kimberlites,in this paper,the partly and totally serpentinized olivines in the kimberlite,as the research objects,have been analyzed by using XRD,EPMA,and LA-ICP-MS methods.The results show that Mg in serpentine was partly replaced by Fe,Al,Ca,Ni,and Mn.Fe contents are only less than Mg contents in serpentines.From the center to the edge of altered olivines,contents of Li and Zn,Ba and Sc,and Co and Y are changes respectively different.The partly altered olivines have negative Eu anomalies and low calculated oxygen fugacity values,implying that they were formed in a closed and reduced environment.The completely altered olivines have no Eu anomaly and relatively high calculated oxygen fugacity values,implying that they were formed in a relatively open and oxidized environment.The contents of most trace elements of the incompletely altered olivines are higher than those of the completely altered olivines.It is believed that the migration activity of rare earth elements could be happened in the serpentinization process of olivine.