Low‐angle subduction has been shown to have a profound impact on subduction processes. However, the mechanisms that initiate, drive, and sustain flat‐slab subduction are debated. Within all subduction zone systems, metamorphic dehydration reactions within the down‐going slab have been hypothesized to produce seismicity, and to produce water that fluxes melting of the asthenospheric wedge leading to arc magmatism. In this work, we examine the role hydration plays in influencing slab buoyancy and the geometry of the downgoing oceanic plate. When water is introduced to the oceanic lithosphere, it is incorporated into hydrous phases, which results in lowered rock densities. The net effect of this process is an increase in the buoyancy of the downgoing oceanic lithosphere. To better understand the role of water in low‐angle subduction settings, we model flat‐slab subduction in Alaska, where the thickened oceanic lithosphere of the Yakutat oceanic plateau is subducting beneath the continental lithosphere. In this work, we calculate the thermal conditions and stable mineral assemblages in the slab crust and mantle in order to assess the role that water plays in altering the density of the subducting slab. Our slab density results show that a moderate amount of hydration (1–1.5 wt% H₂O) in the subducting crust and upper lithospheric mantle reduces slab density by 0.5%–0.8% relative to an anhydrous slab, and is sufficient to maintain slab buoyancy to 300–400 km from the trench. These models show that water is a viable factor in influencing the subduction geometry in Alaska, and is likely important globally.

中文翻译：

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评估水在阿拉斯加平板俯冲中的作用

低角度俯冲作用已被证明对俯冲过程有深远的影响。但是，引发，驱动和维持平板俯冲的机制存在争议。在所有的俯冲带系统中，都假设在下沉的板块内发生变质脱水反应，从而产生地震作用，并产生使软流圈楔形物融化而导致电弧岩浆作用的水。在这项工作中，我们研究了水合作用在影响平板浮力和下沉洋洋板块的几何形状方面的作用。将水引入海洋岩石圈后，它便被掺入含水相中，从而导致岩石密度降低。此过程的最终结果是下降的海洋岩石圈的浮力增加。为了更好地了解水在低角度俯冲环境中的作用，我们以阿拉斯加的平板俯冲为模型，雅库塔特海洋高原的增厚海洋岩石圈在大陆岩石圈之下俯冲。在这项工作中，我们计算了板壳和地幔中的热条件和稳定的矿物组合，以评估水在改变俯冲板密度中所起的作用。我们的板坯密度结果表明适度的水合作用（1–1.5 wt％H俯冲的地壳和岩石圈上地幔中的₂ O）相对于无水平板降低了平板密度0.5％-0.8％，足以将平板的浮力维持在距海沟300-400 km处。这些模型表明，水是影响阿拉斯加俯冲几何形状的可行因素，并且在全球范围内可能很重要。