Abstract—

Natural serpentine was experimentally recrystallized in the presence of chromite, corundum, and carbonatite as sources of Cr, Al, and Ca, respectively, at P = 5 GPa and T = 1300°C using a BARS multi-anvil high-pressure apparatus. The experimental products contained synthesized mineral assemblages corresponding to those of natural garnet peridotites. Electron probe microanalysis (EPMA) of the garnet indicates that its grains are clearly zoned, first of all, in Ca distribution. The garnet grains exhibit a zoned distribution of #Ca = 100Ca/(Ca + Mg) of two types: (i) a systematic prograde increase from the cores of the seemingly homogeneous grains to their rims and (ii) a drastic change in Ca# with the transition from the darker to paler domains of the grains. The compositional zoning apparently resulted from quantitative changes in the Ca, Al and Cr quantitative proportions in the crystallization area under the effect of the H₂O-rich (H₂O/CO₂ > 65) fluid. The quantitative ratio of these elements is a key factor at the crystallization of peridotitic garnets typical of different peridotite varieties.

中文翻译：

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富水流体控制的不同起始 Ca、Al 和 Cr 浓度下分带镁石榴石形成的实验模拟

摘要-

在铬铁矿、刚玉和碳酸岩分别作为 Cr、Al 和 Ca 来源的情况下，在P = 5 GPa 和T条件下，对天然蛇纹石进行了实验重结晶= 1300°C，使用 BARS 多砧高压装置。实验产品包含与天然石榴石橄榄岩对应的合成矿物组合。石榴石的电子探针微量分析 (EPMA) 表明，它的晶粒首先在 Ca 分布中有明显的分区。石榴石颗粒呈现出两种类型的#Ca = 100Ca/(Ca + Mg) 的带状分布：(i) 从看似均质的颗粒的核心到其边缘的系统性顺向增加和 (ii) Ca# 的急剧变化随着晶粒从较深区域到较浅区域的转变。组成分区显然是由于在CA，Al和Cr中的结晶区域定量比例为H的作用下量的变化₂ O丰富（H ₂ O / CO₂ > 65) 流体。这些元素的数量比例是不同橄榄岩品种典型橄榄岩石榴石结晶的关键因素。