Abstract Subduction of crustal C governs the long-term global C cycling. The role of carbonates recycling in subduction zones and the related dissolution of C at various depths have been the subject of a large body of literature over the last decades. Much less is known about the contribution of carbonaceous material (CM) to the deep C cycling in subduction zones. This paper presents natural evidence for intense fluid-mediated leaching of CM in pelitic schists at high-pressure/low-temperature conditions relevant to the forearc region of subducting slabs. Manifestations of such process were identified along fluid pathways at various scales in the blueschist-facies subduction complexes of both Alpine Corsica and the Western Alps. Microstructural, whole-rock and Raman analyses across a selected metasomatic aureole were used to quantify the amount and mechanisms of C loss during fluid-rock interaction. In samples affected by intense fluid infiltration, >90% of the initial CM was removed from the rock. Microstructural and micro-Raman data indicate selective leaching of disordered CM relative to nearly crystalline graphite. The collected data allowed constraining the magnitude of fluid fluxes required to bleach the studied CM-bearing lithologies at different P-T-fO2 conditions, which corresponds to rather high time-integrated fluid fluxes in the order of ~106 m3/m2. In settings of large-scale fluid channelization, such as along regional-scale, lithological/tectonic boundaries or at the top of the subducted sedimentary pile, intense dissolution of subducted CM is expected. This process may thus exert a negative feedback on the sink of C phases into the deep mantle over the geological timescales and contribute to the release of isotopically light C from subducting slabs in forearc regions.

中文翻译：

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俯冲含碳物质的流体介导选择性溶解：对弧前深度碳循环和流体通量的影响

摘要 地壳碳的俯冲控制着全球碳的长期循环。在过去的几十年里，碳酸盐在俯冲带中循环的作用以及 C 在不同深度的相关溶解一直是大量文献的主题。关于含碳材料（CM）对俯冲带深部碳循环的贡献知之甚少。本文提供了在与俯冲板块前弧区域相关的高压/低温条件下，泥质片岩中 CM 发生强烈流体介导浸出的自然证据。在高山科西嘉岛和西阿尔卑斯山的蓝片岩相俯冲复合体中，沿着不同尺度的流体路径确定了这种过程的表现形式。微观结构，对选定交代光环的全岩和拉曼分析用于量化流体-岩石相互作用过程中 C 损失的数量和机制。在受强烈流体渗透影响的样品中，> 90% 的初始 CM 从岩石中去除。微观结构和微拉曼数据表明无序 CM 相对于近晶态石墨的选择性浸出。收集的数据允许限制在不同 PT-fO2 条件下漂白所研究的含 CM 岩性所需的流体通量的大小，这对应于大约 106 m3/m2 的相当高的时间积分流体通量。在大规模流体通道化的环境中，例如沿区域尺度、岩性/构造边界或俯冲沉积桩顶部，预计俯冲 CM 会发生强烈溶解。