Aqueous fluids released during dehydration of a subducting slab have a large effect on the rheology of the subduction interface. While high‐pressure experiments and natural‐case studies link deformation with critical dehydration reactions during eclogitization, the exact interplay between these processes remains ambiguous. To investigate fluid–rock interaction and associated deformation at high‐pressure, we studied a suite of eclogites from the Tsäkkok Lens of the Scandinavian Caledonides that record prograde metamorphism within an Early Palaeozoic cold subduction zone. Our results show that in‐situ dehydration during the blueschist to eclogite facies transition produces fluid fluxes leading to rheological weakening and densification, consequently promoting ductile‐brittle deformation. Petrographic evidence, supported by thermodynamic modelling and thermobarometry, attest to a prograde passage from lawsonite‐blueschist to peak eclogite facies of ~2.5 GPa and ~620°C. Phengite‐bearing eclogites imply interaction with an externally‐derived fluid, whereas rare phengite‐free, kyanite‐eclogites only record internally‐derived fluid production. Models predict that prograde breakdown of chlorite, lawsonite and amphibole between 500 and 610°C lead to progressive dehydration and release of up to 4.6 wt.% of aqueous fluid. Microstructural data reveal elongated shapes of highly strained omphacite porphyroblasts, displaying minor yet gradual changes in misorientation towards the grain boundaries. Occasionally, these intragranular structures form subgrain cells that have similar sizes to those of neoblasts in the rock matrix. These observations point to the potential onset of dynamic recrystallization processes via dislocation creep. Moreover, the omphacite neoblasts and rutile show non‐random crystallographic preferred orientations (CPOs), which are characterized by the subparallel alignment of point‐like maxima in rutile [001] and [100] axes to those of [001] and (010) of omphacite neoblasts, respectively. Additionally, the [001] axes of these minerals are also subparallel to the weak stretching mineral lineation, and the (100) of rutile and the (010) of omphacite neoblasts are distributed in the plane of the foliation. This suggests that the development of their CPOs was coeval and structurally controlled. Garnet microfractures normal to the foliation are dilated and sealed predominantly by omphacite. The lack of obliquity between CPO and foliation plane, as well as the systematic orientation of garnet microfracture orientations, are consistent with coaxial deformation at peak‐pressure conditions. Unlike other studies, we show that neither an external fluid source nor channelized fluid flow is needed to facilitate a ductile‐brittle deformation of eclogite in a subduction setting.

中文翻译：

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榴辉岩脱水驱动的变形：流体排出与流变之间的相互作用

俯冲板块脱水过程中释放的含水流体对俯冲界面的流变性有很大影响。虽然高压实验和自然案例研究将变形与榴辉岩化过程中的关键脱水反应联系起来，但这些过程之间的确切相互作用仍然不明确。为了研究高压下流体-岩石相互作用和相关变形，我们研究了一组来自斯堪的纳维亚喀里多尼亚山脉 Tsäkkok 透镜体的榴辉岩，这些榴辉岩记录了早古生代冷俯冲带内的渐进变质作用。我们的研究结果表明，蓝片岩相到榴辉岩相转变过程中的原位脱水会产生流体通量，导致流变减弱和致密化，从而促进韧性脆性变形。岩相证据在热力学模型和温压测量的支持下，证明了从硬钠长岩-蓝片岩到约 2.5 GPa 和约 620°C 峰值榴辉岩相的过程。含多硅白云石的榴辉岩意味着与外部衍生流体的相互作用，而罕见的不含多白硅云石的蓝晶石榴辉岩仅记录了内部衍生的流体生产。模型预测，在 500 至 610°C 之间，绿泥石、硬钠石和角闪石会逐渐分解，导致逐渐脱水并释放出高达 4.6 wt.% 的水性液体。微观结构数据揭示了高度应变的绿辉石成斑细胞的细长形状，显示出朝向晶界的错误取向的微小但逐渐的变化。有时，这些颗粒内结构形成的亚颗粒细胞的大小与岩石基质中新生细胞的大小相似。这些观察表明动态再结晶过程可能通过位错蠕变开始。此外，绿辉石新生细胞和金红石显示出非随机晶体择优取向（CPO），其特征是金红石[001]和[100]轴中的点状最大值与[001]和（010）轴中的点状最大值呈近平行排列。分别为绿辉石新生细胞。此外，这些矿物的[001]轴也与弱拉伸矿物线状近平行，金红石的（100）轴和绿辉石新生细胞的（010）轴分布在叶理平面上。这表明他们的 CPO 的发展是同时代的并且在结构上受到控制。与叶理垂直的石榴石微裂缝主要由绿辉石扩张和密封。CPO 和叶理面之间没有倾斜，以及石榴石微裂纹方向的系统取向，与峰值压力条件下的同轴变形一致。与其他研究不同，我们表明，在俯冲环境中，不需要外部流体源或通道化流体流来促进榴辉岩的韧性-脆性变形。