Abstract Numerous studies exist on exhumed tectonic melanges along subduction channels whereas, in accretionary wedge interiors, deformation mechanisms and related fluid circulation in tectonic melanges are still underexplored. We combine structural and microstructural observations with geochemical (stable and clumped isotopes and isotope composition of noble gases in fluid inclusions of calcite veins) and U-Pb geochronological data to define deformation mechanisms and syn-tectonic fluid circulation within the Mt. Massico intra-wedge tectonic melange, located in the inner part of the central-southern Apennines accretionary wedge, Italy. This melange developed by shear deformation at the base of a clastic succession. Deformation was characterized by disruption of the primary bedding, mixing, and deformation of relicts of competent olistoliths and strata within a weak matrix of deformed clayey and marly interbeds. Recurrent cycles of mutually overprinting fracturing/veining and pressure-solution processes generated a block-in-matrix texture. The geochemical signatures of syntectonic calcite veins suggest calcite precipitation in a closed system from warm (108°-147 °C) paleofluids, with δ18O vlaues between +9‰ and 14‰, such as trapped pore waters after extensive 18O exchange with the local limestone host rock and/or derived by clay dehydration processes at T > 120 °C. The 3He/4He ratios in fluid inclusions are lower than 0.1 Ra, indicating that He was exclusively sourced from the crust. We conclude that: (1) intraformational rheological contrasts, inherited trapped fluids, and low-permeability barriers such as marly-shaly matrix, can promote the generation of intra-wedge tectonic melanges and the development of transient fluid overpressure; (2) clay-rich tectonic melanges, developed along intra-wedge decollement layers, may generate low-permeability barriers hindering the fluid redistribution within accretionary wedges.

中文翻译：

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圈闭流体在碳酸盐岩/页岩楔内构造混杂岩（Mt. Massico，南亚平宁山脉，意大利）的发育和变形过程中的作用

摘要 对沿俯冲通道挖出的构造混杂岩的大量研究存在，而在增生楔内部，构造混杂岩中的变形机制和相关流体循环仍未得到充分探索。我们将结构和微观结构观测与地球化学（方解石脉流体包裹体中惰性气体的稳定和聚集同位素和同位素组成）和 U-Pb 地质年代学数据相结合，以确定 Mt. 山内的变形机制和同构造流体循环。Massico 楔内构造混杂岩，位于意大利亚平宁山脉中南部增生楔的内部。这种混杂物是由碎屑层序底部的剪切变形形成的。变形的特点是主要层理的破坏、混合、变形粘土质和泥灰质夹层的弱基质中的合格石质和地层的残余物的变形。相互叠印的压裂/脉纹和压力溶液过程的循环循环产生了矩阵中的块纹理。同构造方解石脉的地球化学特征表明，方解石在封闭系统中从温暖的 (108°-147°C) 古流体中沉淀出来，δ18O 值在 +9‰ 到 14‰ 之间，例如与当地石灰岩进行广泛的 18O 交换后被困孔隙水母岩和/或通过粘土脱水过程在 T > 120 °C 下衍生。流体包裹体中的 3He/4He 比值低于 0.1 Ra，表明 He 完全来自地壳。我们得出的结论是：（1）地层内流变对比、继承的被困流体和低渗透屏障，如泥质-泥质基质，可以促进楔内构造混杂的生成和瞬时流体超压的发展；(2) 沿楔内滑脱层发育的富含粘土的构造混杂岩可能会产生低渗透屏障，阻碍增生楔内的流体再分布。