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首页> 外文期刊>Contributions to Mineralogy and Petrology >Redox state of iron during high-pressure serpentinite dehydration
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Redox state of iron during high-pressure serpentinite dehydration

机译：高压蛇纹石脱水过程中铁的氧化还原态

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摘要

The Cerro del Almirez massif (Spain) represents a unique fragment of serpentinized oceanic lithosphere that has been first equilibrated in the antigorite stability field (Atg-serpentinites) and then dehydrated into chlorite-olivine-orthopyroxene (Chl-harzburgites) at eclogite facies conditions during subduction. The massif preserves a dehydration front between Atg-serpentinites and Chl-harzburgites. It constitutes a suitable place to study redox changes in serpentinites and the nature of the released fluids during their dehydration. Relative to abyssal serpentinites, Atg-serpentinites display a low Fe3+/Fe-Total(BR) (=0.55) and magnetite modal content (=2.8-4.3 wt%). Micro-X-ray absorption near-edge structure (mu-XANES) spectroscopy measurements of serpentines at the Fe-K edge show that antigorite has a lower Fe3+/Fe-Total ratio (=0.48) than oceanic lizardite/chrysotile assemblages. The onset of Atg-serpentinites dehydration is marked by the crystallization of a Fe3+-rich antigorite (Fe3+/Fe-Total =0.6-0.75) in equilibrium with secondary olivine and by a decrease in magnetite amount (=1.6-2.2 wt%). This suggests a preferential partitioning of Fe3+ into serpentine rather than into olivine. The Atg-breakdown is marked by a decrease in Fe3+/Fe-Total(BR) (=0.34-0.41), the crystallization of Fe2+-rich phases and the quasi-disappearance of magnetite (=0.6-1.4 wt.%). The observation of Fe3+-rich hematite and ilmenite intergrowths suggests that the O-2 released by the crystallization of Fe(2+)rich phases could promote hematite crystallization and a subsequent increase in fo(2) inside the portion of the sub-ducted mantle. Serpentinite dehydration could thus produce highly oxidized fluids in subduction zones and contribute to the oxidization of the sub-arc mantle wedge.
机译：Cerro del Almirez断层块（西​​班牙）代表了蛇纹石化的海洋岩石圈的独特片段，该碎片首先在反蛇纹岩稳定场（Atg-蛇纹石）中达到平衡，然后在榴辉岩相条件下脱水成绿泥石-橄榄石-原辉石（Chl-harzburgites）。俯冲。地块保留了Atg蛇纹石和Chl-harzburgites之间的脱水锋。它是研究蛇纹石中氧化还原变化和脱水过程中释放出的液体性质的合适场所。相对于深渊蛇纹岩，Atg蛇纹岩显示出较低的Fe3 + / Fe-Total（BR）（= 0.55）和磁铁矿模态含量（= 2.8-4.3 wt％）。在Fe-K边缘处的蛇纹石的微X射线吸收近边缘结构（mu-XANES）光谱测量结果表明，蛇纹石的Fe3 + / Fe-总比（= 0.48）比海洋蜥蜴石/温石棉组合低。 Atg-蛇纹石脱水的开始以与次橄榄石平衡的富含Fe3 +的反蛇纹石（Fe3 + / Fe-Total = 0.6-0.75）的结晶和磁铁矿含量的减少（= 1.6-2.2 wt％）为特征。这表明Fe3 +优先分配为蛇形而不是橄榄石。 Atg-击穿的特征在于Fe3 + / Fe-Total（BR）的降低（= 0.34-0.41），富Fe2 +相的结晶和磁铁矿的准消失（= 0.6-1.4 wt。％）。富含Fe3 +的赤铁矿和钛铁矿共生体的观察表明，富Fe（2+）相的结晶释放出的O-2可能促进赤铁矿结晶，并继而在次导管地幔部分内部增加fo（2） 。蛇纹岩的脱水因此可以在俯冲带中产生高度氧化的流体，并有助于弧下地幔楔的氧化。

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