Dehydration reactions in the subducting slab liberate fluids causing major changes in rock density, volume and permeability. Although it is well known that the fluids can migrate and interact with the surrounding rocks, fluid pathways remain challenging to track and the consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive fluid-rock interaction in a sequence of schists and mafic felses exposed in the Theodul Glacier Unit (TGU), Western Alps. This unit is embedded within metaophiolites of the Zermatt-Saas Zone and reached eclogite-facies conditions during Alpine convergence. Chemical mapping and in situ oxygen isotope analyses of garnet from the schists reveal a sharp chemical zoning between a xenomorphic core and a euhedral rim, associated to a drop of ~ 8‰ in δ¹⁸O. Thermodynamic and δ¹⁸O models show that the large amount of low δ¹⁸O H₂O required to change the reactive bulk δ¹⁸O composition cannot be produced by dehydration of the mafic fels from the TGU only, and requires a large contribution of the surrounding serpentinites. The calculated time-integrated fluid flux across the TGU rocks is 1.1 × 10⁵ cm³/cm², which is above the open-system behaviour threshold and argues for pervasive fluid flow at kilometre-scale under high-pressure conditions. The transient rock volume variations caused by lawsonite breakdown is identified as a possible trigger for the pervasive fluid influx. The calculated schist permeability at eclogite-facies conditions (~ 2 × 10^–20 m²) is comparable to the permeability determined experimentally for blueschist and serpentinites.

俯冲板块中的脱水反应释放出流体，导致岩石密度、体积和渗透率发生重大变化。尽管众所周知流体可以迁移并与周围的岩石相互作用，但流体路径仍然难以追踪，流体-岩石相互作用过程的后果往往被忽视。在这项研究中，我们调查了西阿尔卑斯山 Theodul Glacier Unit (TGU) 中暴露的一系列片岩和镁铁质长岩中普遍存在的流体-岩石相互作用。该单元嵌入采尔马特-萨斯带的变蛇绿岩中，并在高山辐合期间达到榴辉岩相条件。片岩中石榴石的化学绘图和原位氧同位素分析揭示了异形核和自形边缘之间存在明显的化学分带，这与 δ ¹⁸下降约 8‰有关O. 热力学和 δ ¹⁸ O 模型表明改变反应性本体 δ ¹⁸ O 组成所需的大量低 δ ¹⁸ O H ₂ O不能仅通过来自 TGU 的镁铁质长岩的脱水产生，并且需要大量的贡献周围的蛇纹石。计算出的穿过 TGU 岩石的时间积分流体通量为 1.1 × 10 ⁵ cm ³ /cm ²，高于开放系统行为阈值，并主张在高压条件下公里范围内普遍存在流体流动。由硬柱石分解引起的瞬时岩石体积变化被确定为普遍流体流入的可能触发因素。在榴辉岩相条件（~ 2 × 10 ^–20 m ²）下计算的片岩渗透率与蓝片岩和蛇纹岩通过实验确定的渗透率相当。