Abstract Focusing of fluid flow along Western Alps paleo-subduction interfaces (at the base of the Dent Blanche nappe, NW Italy), afforded by high strain rates, is testified by extensive chemical alteration accompanying previously documented shifts in O isotope compositions resulting from fluid-rock interactions at prograde to peak high-P, low-T conditions. Flushing of these structures by H2O-rich fluids led to the development of prominent metasomatic reaction zones within and among disparate rock types including the calc-schists of the Schistes Lustres complex and m- to km-scale slivers of metabasaltic/metagabbroic and meta-ultramafic rocks. Evidence for pressure solution, to produce a strong interface-parallel cleavage, presumably reflects at least local-scale redistribution of carbonate. Related to this redistribution, some samples exhibit evidence for albite dissolution and replacement by calcite ± dolomite ± paragonite. White mica, which exhibits high-Si cores related to prograde metamorphism is variably replaced by muscovite-rich rims interpreted as related to the influx of a CO2-bearing fluid at isobaric conditions based on thermodynamic modeling. Ratios of Ba, Rb, Cs, and N to K, all largely housed in micas (for N, as NH4+), indicate up to 60% loss of these elements within a few 10 s of meters of the interface contacts, presumably reflecting the preferential partitioning of these more fluid-mobile elements into the infiltrating fluids. Whole-rock δ15Nair shows some increase approaching the interface structures, from values of +3.8‰ to near +5.0‰, a trend consistent with Rayleigh-like loss during the partitioning of N into fluids from recrystallizing white-mica. Updip fluid flow along the studied structures resulted in the deposition of carbonate and SiO2, as reflected in the abundant, variably transposed, carbonate + quartz vein generations and more pervasive carbonation (within metasedimentary rocks) and silicification (within talc-rich ultramafic rocks). The O isotope shifts proximal to the structures appear to reflect the sourcing of the infiltrating fluids at greater depths in mafic/ultramafic parts of the down-going slab or structurally complex interface region. Although models of subduction-zone volatile cycling implicitly involve the flushing of fluids along or across subduction interfaces, the permeability of these regions, among disparate rocks types and evolving in response to the localization of deformation, likely dictates the magnitude of this transfer. Field-based studies of this type can yield insight regarding mechanisms of m- to km-scale fluid mobility but, given the fragmentary nature of the metamorphic rock record, do not permit quantitative assessment of the cycling of elements such as C at any individual modern (or ancient) margin.

中文翻译：

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在深古增生楔（西阿尔卑斯山）中沿瞬时俯冲界面的流体和质量传递

摘要 沿西阿尔卑斯古俯冲界面（位于意大利西北部 Dent Blanche 推覆底部）的流体流动集中，由高应变率提供，通过广泛的化学变化证明了这一点，伴随着先前记录的 O 同位素组成的变化，由流体-推进到峰值高 P、低 T 条件的岩石相互作用。富含 H2O 的流体冲刷这些结构导致在不同岩石类型内部和之间形成显着的交代反应带，包括 Lustres 片岩杂岩的钙质片岩和变玄武岩/变辉长岩和变质超镁铁质的 m 至 km 级薄片岩石。压力溶解的证据，产生强烈的界面平行解理，大概反映了至少局部尺度的碳酸盐重新分布。与这种重新分配有关，一些样品显示出钠长石溶解并被方解石±白云石±白云石取代的证据。白云母表现出与顺行变质作用相关的高硅核，被富含白云母的边缘不同程度地取代，这些边缘被解释为与基于热力学模型的等压条件下含 CO2 流体的流入有关。Ba、Rb、Cs 和 N 与 K 的比率，都主要位于云母中（对于 N，作为 NH4+），表明这些元素在距界面接触的 10 秒内损失高达 60%，大概反映了这些流体流动性更强的元素优先分配到渗透流体中。全岩 δ15Nair 在接近界面结构时有一些增加，从 +3.8‰ 到接近 +5.0‰，在 N 分配到来自重结晶白云母的流体中的过程中，这种趋势与 Rayleigh 样损失一致。沿研究结构的上倾流体流动导致碳酸盐和 SiO2 沉积，这反映在丰富的、可变转置的碳酸盐 + 石英脉生成和更普遍的碳化作用（在变沉积岩内）和硅化作用（在富含滑石的超基性岩内）。接近结构的 O 同位素移动似乎反映了在下行板片或结构复杂的界面区域的基性/超基性部分中更深的渗透流体的来源。尽管俯冲带挥发性循环模型隐含地涉及流体沿或穿过俯冲界面的冲刷，但这些区域的渗透率、在不同的岩石类型中并随着变形的局部化而演变，可能决定了这种转移的幅度。这种类型的基于实地的研究可以深入了解 m 到 km 级流体流动的机制，但是，鉴于变质岩记录的碎片性质，不允许对任何单个现代元素（例如 C）的循环进行定量评估。 （或古代）边缘。