Effects of water transportation on subduction dynamics: Roles of viscosity and density reduction
Effects of water transportation on subduction dynamics: Roles of viscosity and density reduction
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DOI：
10.1016/j.epsl.2016.08.016
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发表时间：
2016-11-15
影响因子：
5.3
通讯作者：
Nakakuki, Tomoeki
中科院分区：
文献类型：
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作者：
Nakao, Atsushi;Iwamori, Hikaru;Nakakuki, Tomoeki
利用二维自洽岩石圈俯冲和全地幔对流模型，研究了水对板块迁移速率、板块几何形状、应力场和弧后扩张等俯冲动力学的影响。我们解决了与含水矿物相变相结合的水输送问题。通过含水岩石的本构和状态方程，地幔流动和水运移是相互作用的。我们的模型成功地再现了地幔楔中的水分布和沿板块的水分布，具有足够的分辨率，可与以前专注于地幔楔结构的模型相媲美。因此，水化作用导致的低密度降低了俯冲速率、弧后扩张和660 km深度处相界上的板块停滞，而水化作用导致的低粘度则增强了快速俯冲、海沟迁移和板块停滞。我们将这些结果归因于导致俯冲板块的含水浮力减少板块拉力和伴随的对上覆岩石圈的拉应力的机制。此外，含水弱化减弱了俯冲板块与楔状地幔和上覆岩石圈的力学耦合。因此，水能够在上覆岩石圈应力场和俯冲速率中产生两种相反的情况。因此，正如在汤加和马里亚纳等实际的俯冲带所观察到的那样，水有望成为产生广泛类型的俯冲构造和运动学的重要机制。这种观测到的俯冲模式的变化可能是由浮力的变化引起的，对应于楔形地幔和板块表面的含水量从相对干燥到百万分之几千的变化，而极端浮力的情况似乎在自然界中不会发生。因此，地幔中的水是更好地理解整个地幔尺度的板块动力学以及岛弧火山作用的关键。(C) 2016年作者。Elsevier B.V.出版
The effects of water on subduction dynamics, e.g., plate migration rate, slab geometry, stress field, and back-arc spreading, are investigated by using a 2-D self-consistent model for lithosphere subduction and whole mantle convection. We solve water transportation coupled with hydrous mineral phase changes. Mantle flows and water transportation are interactive through constitutive and state equations for hydrous rocks. Our model has successfully reproduced the water distribution in a mantle wedge and along the slab with sufficient resolution comparable to that of previous models that focus on the mantle wedge structure. As a result, low density owing to hydration reduces subduction rates, back-arc spreading, and slab stagnation on the phase boundary at 660-km depth, whereas low viscosity owing to hydration enhances rapid subduction, trench migration, and slab stagnation. We attribute these results to mechanisms that cause the hydrous buoyancy of subducting plates to reduce the slab pull force and the accompanying tensile stress on overlying lithosphere. In addition, hydrous weakening diminishes the mechanical coupling of the subducted slab with the wedge mantle and overriding lithosphere. Thus, water is capable of generating two opposite situations in the stress field of the overlying lithosphere and the subduction rate. Water is therefore expected to be an important mechanism for generating broad styles of the subduction structure and kinematics, as observed in actual subduction zones such as Tonga and Mariana. Such observed variation in the subduction mode can be caused by variation in buoyancy corresponding to the water content from relatively dry to several thousands of parts per million for the wedge mantle and slab surface, whereas the extremely buoyant case does not appear to occur in nature. Water in the mantle is thus key to better understand the whole-mantle-scale slab dynamics as well as island arc volcanic processes. (C) 2016 The Authors. Published by Elsevier B.V.