Discovery of pyrrhotite exsolution in apatite.

中国东部苏鲁地区(江苏赣榆)出露大理岩-榴辉岩块体,其菱镁矿大理岩中保存的白云石分解结构表明地壳物质俯冲深度达到-200公里。在与该大理岩共生的榴辉岩中,我们发现了磷灰石的磁黄铁矿出溶结构。磷灰石是该榴辉岩的主要副矿物,其自形程度较高,与石榴石共生。样品中几乎所有磷灰石均发育出溶结构,至少存在两组相互垂直的出溶棒,它们各自严格沿同一个方向分布。出溶棒形状规则,宽度相近(<1μm),但长度变化大(5-50μm)。利用高分辨能谱仪测定其能谱,结果表明,出溶棒主要由Fe和S两种元素组成,但不能准确地确定其Fe/S比值。我们把这种出溶棒初步确定为磁黄铁矿(Fe1-xS)。磷灰石由于含大量稀土元素和挥发...The dolomite decomposition texture preserved in magnesite-bearing marble coexisting with eclogites in a marble-eclogite block occurring in the Sulu UHP terrane (Ganyu, east China) has demonstrated that continental material can be transported to depths of 200 km and possibly recycled into the mantle. The eclogite coexisting with this UHP marble contains apatites showing exsolution texture. This apatite is an accessory mineral in the studied eclogite sample SQQ08 where it coexists with garnet, omphacite and rutile. Almost all apatite grains in sample SQQ08 show exsolved rods strictly orientated in at least two directions perpendicular to each other. All these rods have similar width (< 1 mu m) but variable length (5 similar to 50 mu m). The energy-dispersive ( EDS) analyses show that the rods mainly consist of S and Fe. However, the Fe/S ratio could not be accurately measured but we consider the rods as Fe1-xS ( pyrrhotite). Apatite contains abundant volatiles such as OH, F, Cl and, according to our observation, sulfur. Thus, the recycling of apatite in the deep mantle might be affected the cycle of water, sulfur and other volatiles in the Earth. The pyrrhotite exsolution in apatite from the Sulu eclogite reported in this paper might provide a new way to understand this fundamental problem.SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)002405-4102