胶东荣成榴辉岩中含铜磁黄铁矿出溶结构的磷灰石的发现及其意义  

Discovery of apatite with copper-bearing pyrrhotite exsolution in an eclogite from Rongcheng,eastern Shandong province.

作　　者：梁凤华[1] 曾令森[1] 陈晶[2] 陈方远[1] 

机构地区：[1]中国地质科学院地质研究所国土资源部大陆动力学重点实验室,北京100037 [2]北京大学物理学院电子显微镜实验室,北京100871

出　　处：《岩石学报》2006年第2期433-438,共6页Acta Petrologica Sinica

基　　金：科技部973重大基础研究项目(2003CB716504);中国地质科学院重点实验室专项资金(KL05-3)的资助

摘　　要：在苏鲁超高压变质带东北部胶东荣成地区的退变金红石榴辉岩中,我们发现了具含铜磁黄铁矿出溶结构的磷灰石。磷灰石在该榴辉岩中含量较高(≈5%),多为不规则形状,颗粒大小不一,粗大者可达1．2mm×0．6mm。样品中几乎所有的磷灰石均发育出溶结构,出溶棒可能分为相互垂直的两组,各自分别沿同一方向分布,出溶棒密度大,形状规则,宽度相似,长度最长可达0．1mm。在扫描电子显微镜下,利用X射线能谱仪测定出溶棒主要由Fe、Cu和S三种元素组成。由于很难准确确定三者的比例,暂将其定为含铜磁黄铁矿((Fe_(1-x)Cu_x)S)。报道的磷灰石含铜磁黄铁矿出溶结构,与江苏赣榆地区磷灰石的磁黄铁矿出溶结构,同产于苏鲁超高压变质带中,具有可对比性；磷灰石中Cu、Fe的溶解度可能是温压条件的函数；因此进一步精确研究磷灰石中这些出溶结构的成分和成因,将为深入探讨苏鲁超高压变质带不同地体变质条件、成因的差异及俯冲折返机制等问题提供重要线索。Apatites （≈5% ） with high density of copper-bearing pyrrhotite exsolution lamella were found as a mineral phase closely associated with garnets in a retrograde rutile eclogite in Rongcheng, northeastern Sulu ultrahigh pressure （UHP） metamorphic belt. These apatites in sample RC05-05 are subhedral to anhedral, and relatively large （ up to 1.2mm × 0.6mm big）. They have high density of exsolved rods or needles orientated possibly along two directions perpendicular to each other. All these rods or needles have regular shape and similar width （ 〈 1 μm） but variable length （5 - 100μm）. Energy-dispersive （EDS） analyses show that these rods mainly consist of Fe, Cu, and S. However, the ratio among these three elements could not be accurately measured due to their extremely small sizes. Therefore, we consider temporarily the exsolved rods as copper-bearing pyrrhotite with a formula （Fet-x Cux ）S. As compared to those apatites found in Ganyu, southwestern Sulu UHP belt by Zhu ＆ Massonne （2005）, the Rongcheng apatites have more complex chemistry and higher density of solid exsolution lamella by a factor of 5 - 10. Preliminary results also show that solubility of Fe, Cu, and S in the Rongcheng apatite is significantly higher than those in the Ganyu apatite, which may be due to （ 1 ） higher P and T peak metamorphic conditions; and/or （2） different partitioning of Fe, Cu, and S between garnet and apatite at UHP conditions. Solubility of Cu and Fe and their ratio in an apatite might be a function of temperature and pressure at which the apatite was formed. Therefore, Cu and Fe solubility in an apatite may furnish another important index to constrain the P and T conditions and geochemical environment of peak UHP metamorphism.

关 键 词：磷灰石 出溶结构 含铜磁黄铁矿 榴辉岩 苏鲁超高压变质带 胶东 

分 类 号：P588.348[天文地球—岩石学] P578.922[天文地球—地质学]