Antigorite is considered as the most important source of water in subduction zones, playing a key role during arc magma genesis. Although, these magmas seem more oxidized than mid-oceanic ridge basalts (MORB), the possible inherent link between the oxidation state of arc magmas and serpentinite-derived hydrous fluids is still not well established. Here, we have performed dehydration experiments of natural antigorite serpentinite containing 5 weight percent (wt%) magnetite at 3 GPa and in a temperature range from 600 to 900 °C using a multi-anvil apparatus. These experiments aim to reproduce the different stages of H2O release, forming chlorite, olivine and orthopyroxene and water. Our experimental set up permits to preserve the intrinsic high oxygen fugacity (fO2) of serpentinite during dehydration. The new olivine and orthopyroxene which formed in equilibrium with antigorite, chlorite and magnetite have high XMg numbers setting up the oxygen fugacity to high values, between 3.1 and 4.1 log units above QFM (Quartz–Fayalite–Magnetite buffer). Hematite is observed concomitantly with high XMg in olivine, of 0.94–0.97, generally at low temperatures, below 800 °C, in coexistence with chlorite. Once the magnetite is destabilized, upon chlorite breakdown which occurs above 800 °C, the oxygen fugacity decreases to 3.7 due to the decrease of the XMg of silicates. This study demonstrates the highly oxidizing nature of the fluids released from antigorite dehydration. Thus, at high pressure and high temperature conditions, fO2-sensitive elements such as carbon and sulfur are expected to be mobilized under their oxidized form, providing an oxidizing context for arc magmas genesis and assuming that they are not completely reduced by their percolation through meta-gabbro, meta-basalts and meta-sediments.

中文翻译：

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3 GPa 叶蛇纹石分解的内在性质：俯冲带蛇纹岩脱水氧化还原条件的实验限制

叶蛇纹石被认为是俯冲带最重要的水源，在弧形岩浆形成过程中起着关键作用。尽管这些岩浆似乎比大洋中脊玄武岩 (MORB) 氧化程度更高，但弧形岩浆的氧化态与蛇纹岩衍生的含水流体之间可能存在的内在联系仍未完全确定。在这里，我们使用多砧装置在 3 GPa 和 600 至 900 °C 的温度范围内对含有 5 重量百分比 (wt%) 磁铁矿的天然叶蛇纹石蛇纹岩进行了脱水实验。这些实验旨在重现 H2O 释放的不同阶段，形成亚氯酸盐、橄榄石、斜方辉石和水。我们的实验装置允许在脱水过程中保持蛇纹岩固有的高氧逸度 (fO2)。与叶蛇纹石、绿泥石和磁铁矿平衡形成的新橄榄石和斜方辉石具有高 XMg 值，将氧逸度设置为高值，高于 QFM（石英-铁橄榄石-磁铁矿缓冲液）3.1 到 4.1 log 单位之间。在橄榄石中观察到赤铁矿与高 XMg 值（0.94-0.97），通常在低于 800 °C 的低温下与绿泥石共存。一旦磁铁矿不稳定，在 800°C 以上发生绿泥石分解时，由于硅酸盐的 XMg 降低，氧逸度降低到 3.7。这项研究证明了叶蛇纹石脱水释放的流体具有高度氧化性。因此，在高压和高温条件下，碳和硫等 fO2 敏感元素有望在其氧化形式下移动，