蒙阴金伯利岩中磷灰石的矿物学特征及其成因意义  

Mineralogical Characteristics of Apatites in the Mengyin Kimberlite in Shandong Province and Their Genetic Significances

作　　者：雷雪英 杨志军 向正娇[1] LEI Xue-ying;YANG Zhi-jun;XIANG Zheng-jiao(School of Earth Sciences and Engineering Sun Yat-sen University, Guangzhou 510275 , China;Guangdong Provincial Key Lab of Geological Processes and Mineral Resource Survey, Guangzhou 510275 , China)

机构地区：[1]中山大学地球科学与工程学院,广州510275 [2]广东省地质过程与矿产资源探查重点实验室,广州510275

出　　处：《矿物岩石地球化学通报》2019年第2期409-417,共9页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金项目(41373025;41073021)

摘　　要：为探讨山东蒙阴金伯利岩的成因及其演化过程,对其中的磷灰石进行了矿物学及地球化学研究。SEM、EPMA和LA-ICP-MS测试结果表明,磷灰石可分为早期和基质同期两类;早期磷灰石常以较大(100～210μm)的半自形浑圆状出现在金伯利岩捕掳体内;具有特征CL图像和同心的、无序的明暗环带;Ca、P含量高,Sr、Si含量低,Ca、P分别与Sr、Si呈负相关关系;Th、U、Tb、Y含量高于原始地幔和基质同期磷灰石,LREE轻微亏损,HREE轻微富集;具明显负Eu异常,暗示其形成于还原环境。金伯利岩的富矿性与早期磷灰石有一定正相关性。基质同期磷灰石赋存在金伯利岩基质中,粒径变化较大(几微米到380μm),常呈放射状、填隙状等;无特征CL图像,Sr、Si含量高,Ca、P含量低;Ba、La、Sr含量远高于原始地幔和早期磷灰石,LREE明显富集,HREE强烈亏损;其微量元素配分模式指示金伯利岩初始岩浆的微量元素组成特征。In order to figure out the genesis of the Mengyin kimberlite and evolution processes of the kimberlite magma, the mineralogy and geochemistry of apatites in the Mengyin kimberlite, Shandong Province have been studied in this paper. The SEM, EPMA and LA-ICP-MS analytical results show that apatites can be classified into two groups of the early apatites and matrix contemporaneous apatites. The early apatites, generally with sizes varying from 100 μm to 210 μm, occurred as subhedral crystals in xenoliths of the kimberlite. Their characteristic CL images show concentric and chaotic bands of light and shade. They contain high Ca, P contents and low Sr, Si contents, with negative correlations between Ca and Sr, P and Si, respectively. Their Th, U, Tb and Y contents are higher than those of the primitive mantle and matrix contemporaneous apatites. Their REE patterns are characterized with slight depletion of LREE, slight enrichment of HREE, and obviously negative Eu anomalies. The matrix contemporaneous apatites generally occurred as radial and interstitial crystals in the matrix of kimberlite, with their grain sizes varying from a few microns to 380 μm. There is no characteristic for their CL images. They have relatively high Sr, Si contents and low Ca, P contents. Their Ba, La, and Sr contents are much higher than those of the primitive mantle and early apatites. Furthermore, their REE patterns are characterized with the obviously enriched LREE but strongly depleted HREE. The early apatites have negative Eu anomalies, implying that they were formed in a reduced environment. Meanwhile, there is a certain positive correlation between the ore-bearing potential of kimberlite and the occurrence of early apatites. The trace element distribution patterns of the matrix contemporaneous apatites indicate that they have similar characteristics of trace element compositions of the primitive kimberlite magma.

关 键 词：磷灰石 组成 结构 金伯利岩 岩浆演化 山东蒙阴地区 

分 类 号：P578.92[天文地球—矿物学]