Carbonatite compositions resulting from melting of magnesian calcite + olivine + clinopyroxene were experimentally determined in the system CaO–MgO–SiO2–CO2–H2O as a function of temperature and bulk H2O contents at 1.0 and 1.5 GPa. The melting reaction and melt compositions were found to be highly sensitive to H-loss or -gain during experiments. We hence designed a new hydrogen-trap technique, which provided sufficient control to obtain consistent results. The nominally dry solidus temperatures at 1.0 and 1.5 GPa are 1225–1250 °C and 1275–1300 °C, respectively. At 1.0 GPa, the solidus temperature decreases with H2O increasing to 3.5 wt% (1025–1050 °C), then remains approximately constant at higher H2O concentrations. Our nominally dry solidus temperatures are up to 140 °C higher than in previous studies that did not take measures to limit hydrogen infiltration and hence suffered from H2O formation in the capsule. The near-solidus anhydrous melts have 7–8 wt% SiO2 and molar Ca/(Ca + Mg) of 0.78–0.82 (XCa). Melting temperatures decrease by as much as 200 °C with increasing XH2O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{X}}_{{{\text{H}}_{{2}} {\text{O}}}}$$\end{document} in the coexisting COH-fluid. Concomitantly, near-solidus melt compositions change with increasing bulk H2O from siliceous Ca-rich carbonate melts to Mg-rich silico-carbonatites with up to 27.8 wt% SiO2 and 0.55 XCa. The continuous compositional array of Ca–Mg–Si carbonatites demonstrates the efficient suppression of liquid immiscibility in the alkali-free system. Diopside crystallization was found to be sensitive to temperature and bulk water contents, limiting metasomatic transformation of carbonated upper mantle to wehrlite at 1.0–1.5 GPa to < 1175 °C and < 7 wt% bulk H2O.

中文翻译：

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碳酸盐在含水上地幔中熔化

在 CaO-MgO-SiO2-CO2-H2O 系统中实验确定了由镁方解石 + 橄榄石 + 斜辉石熔化产生的碳酸岩组成，作为温度和体积 H2O 含量在 1.0 和 1.5 GPa 的函数。在实验过程中发现熔融反应和熔融成分对 H 损失或增加高度敏感。因此，我们设计了一种新的氢捕集技术，它提供了足够的控制以获得一致的结果。1.0 和 1.5 GPa 下的标称干固相线温度分别为 1225–1250 °C 和 1275–1300 °C。在 1.0 GPa 时，固相线温度随着 H2O 增加到 3.5 wt% (1025–1050 °C) 而降低，然后在较高的 H2O 浓度下保持大致恒定。我们名义上的干燥固相线温度比之前的研究高 140°C，这些研究没有采取措施限制氢渗透，因此在胶囊中形成了 H2O。近固相线无水熔体含有 7–8 wt% 的 SiO2，摩尔 Ca/(Ca + Mg) 为 0.78–0.82 (XCa)。随着 XH2O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs } \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{X}}_{{{\text{H}}_{{2}} {\text{ O}}}}$$\end{document} 在共存的 COH 流体中。同时，近固相线熔体组成随着大量 H2O 的增加而变化，从富含钙的硅质碳酸盐熔体到富含镁的硅碳酸盐熔体，含量高达 27。8 wt% SiO2 和 0.55 XCa。Ca-Mg-Si 碳酸岩​​的连续组成阵列证明了无碱体系中液体不混溶性的有效抑制。透辉石结晶被发现对温度和体积水含量敏感，在 1.0-1.5 GPa 至 < 1175 °C 和 < 7 wt% 体积 H2O 时，限制了碳酸盐化上地幔到 Wehrlite 的交代转化。