Assessing the Role of Water in Alaskan Flat‐Slab Subduction
Assessing the Role of Water in Alaskan Flat‐Slab Subduction
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DOI：
10.1029/2021gc009734
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发表时间：
2021-05
期刊：
影响因子：
3.7
通讯作者：
S. E. Petersen;T. D. Hoisch;R. Porter
中科院分区：
文献类型：
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作者：
S. E. Petersen;T. D. Hoisch;R. Porter
低角度俯冲已被证明对俯冲过程具有深远的影响。然而，引发、驱动和维持平板俯冲的机制仍存在争议。在所有俯冲带系统中，下降板片内的变质脱水反应被假设会产生地震活动，并产生水，使软流圈楔状物质熔化，从而导致弧岩浆作用。在这项工作中，我们研究了水合作用在影响板块浮力和下行海洋板块的几何形状方面所起的作用。当水被引入海洋岩石圈时，它会结合成含水相，从而导致岩石密度降低。这一过程的净效应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，我们模拟了阿拉斯加的平板俯冲，其中雅库塔特海洋高原的增厚海洋岩石圈正在俯冲到大陆岩石圈之下。在这项工作中，我们计算了板片地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片密度中所起的作用。我们的板片密度结果表明，俯冲地壳和上岩石圈地幔中的适量水化（1-1.5 wt% H2O）使板片密度相对于无水板片降低了0.5%-0.8%，并且足以维持距海沟300-400公里的板片浮力。这些模型表明，水是影响阿拉斯加俯冲几何形状的一个可行因素，并且可能在全球范围内都很重要。
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.