Metamorphic olivine formed by the reaction of antigorite + brucite is widespread in serpentinites that crop out in glacier-polished outcrops at the Unterer Theodulglacier, Zermatt. Olivine overgrows a relic magnetite mesh texture formed during ocean floor serpentinization. Serpentinization is associated with rodingitisation of mafic dykes. Metamorphic olivine coexists with magnetite, shows high Mg# of 94–97 and low trace element contents. A notable exception is 4 µg/g Boron (> 10 times primitive mantle), introduced during seafloor alteration and retained in metamorphic olivine. Olivine incorporated 100–140 µg/g H2O in Si-vacancies, providing evidence for low SiO2-activity imposed by brucite during olivine growth. No signs for hydrogen loss or major and minor element diffusional equilibration are observed. The occurrence of olivine in patches within the serpentinite mimics the former heterogeneous distribution of brucite, whereas the network of olivine-bearing veins and shear zones document the pathways of the escaping fluid produced by the olivine forming reaction. Relic Cr-spinels have a high Cr# of 0.5 and the serpentinites display little or no clinopyroxene, indicating that they derive from hydrated harzburgitic mantle that underwent significant melt depletion. The enrichment of Mg and depletion of Si results in the formation of brucite during seafloor alteration, a pre-requisite for later subduction-related olivine formation and fluid liberation. The comparison of calculated bulk rock brucite contents in the Zermatt-Saas with average IODP serpentinites suggests a large variation in fluid release during olivine formation. Between 3.4 and 7.2 wt% H2O is released depending on the magnetite content in fully serpentinized harzburgites (average oceanic serpentinites). Thermodynamic modelling indicates that the fluid release in Zermatt occurred between 480 °C and 550 °C at 2–2.5 GPa with the Mg# of olivine varying from 68 to 95. However, the majority of the fluid released from this reaction was produced within a narrow temperature field of < 30 °C, at higher pressures 2.5 GPa and temperatures 550–600 °C than commonly thought. Fluids derived from the antigorite + brucite reaction might thus trigger eclogite facies equilibration in associated metabasalts, meta-gabbros, meta-rodingites and meta-sediments in the area. This focused fluid release has the potential to trigger intermediate depths earthquakes at 60–80 km in subducted oceanic lithosphere.

中文翻译：

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蛇纹石+水镁石对俯冲蛇纹岩中橄榄石反应的作用（瑞士策马特）

由蛇纹石+水镁石反应形成的变质橄榄石广泛分布在采尔马特Unterer Theodulglac​​ier的冰川抛光露头中的蛇纹岩中。橄榄石长满海底蛇纹石化过程中形成的遗迹磁铁矿网状结构。蛇纹石化与铁质堤坝的杆状皮炎有关。变质橄榄石与磁铁矿共存，Mg＃较高，为94-97，微量元素含量较低。一个显着的例外是4 µg / g的硼（> 10倍原始地幔），在海床改造期间引入并保留在变质橄榄石中。橄榄石在硅空位中掺入100–140 µg / g H2O，这为橄榄石在橄榄石生长期间施加的低SiO2活性提供了证据。没有观察到氢损失或主要和次要元素扩散平衡的迹象。蛇纹石内斑块中橄榄石的出现模仿了以前的水镁石异质分布，而含橄榄石的静脉和剪切带的网络记录了橄榄石形成反应所产生的逸出流体的路径。遗留的Cr-尖晶石的Cr＃高，为0.5，蛇纹岩几乎没有或几乎没有斜辉石，表明它们来自经过显着熔体耗竭的水合哈茨堡地幔。镁的富集和硅的耗竭导致在海底蚀变过程中形成水镁石，这是以后与俯冲有关的橄榄石形成和流体释放的先决条件。计算的采尔马特-萨斯州的块状水镁石含量与平均IODP蛇纹岩的比较表明，橄榄石形成过程中流体释放的变化很大。在3.4和7。释放2 wt％的H2O取决于完全蛇纹石化的Harzburgite（平均海洋蛇纹石）中磁铁矿的含量。热力学模型表明，采尔马特的流体释放在2–2.5 GPa下发生在480°C至550°C之间，橄榄石的Mg＃在68至95之间变化。但是，此反应释放的大部分流体是在<30°C的窄温度场，在2.5 GPa的更高压力和550–600°C的温度下，比通常认为的要高。因此，由蛇纹石+水镁石反应产生的流体可能会触发该地区相关的玄武岩，变长辉石，变质红柱石和变质沉积物中的榴辉岩相平衡。这种集中的流体释放有可能在俯冲的海洋岩石圈引发60-80 km的中等深度地震。