The mantle wedge's transient 3-D flow regime and thermal structure
The mantle wedge's transient 3-D flow regime and thermal structure
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地幔楔的瞬态 3-D 流态和热结构
DOI：
10.1002/2015gc006125
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Davies D
中科院分区：
文献类型：
--
作者：
Davies D
弧火山作用、挥发物循环、成矿作用和大陆地壳形成可能受到地幔楔流动状态和热结构的调节。通常假定楔形流遵循规则的角流模式。然而，结合水化流变学和热浮力的研究预测了内部小尺度对流（SSC）。在这里，我们系统地探讨地幔楔动力学的三维模拟。我们发现，如果楔形水化将粘度降低到 Pa s，尽管瞬态横向滚动（具有沟槽平行轴）在粘度为 啪。弧下和弧后的滚动不同。亚北极卷具有相似的海沟平行和海沟垂直尺寸，为100-150 km，并在1-5百万年的时间尺度上演变。另一方面，亚弧后不稳定性合并成细长的岩片，通常具有优先的海沟垂直排列，显示波长为150-400 km，在5-10百万年的时间尺度上变化。随着楔状体水化作用的增强、俯冲速度的加快和上部板块的增厚，弧后脊对弧下体系的调制作用也随之增强。我们发现，沟槽平行的楔速度和温度的平均值与二维模型中预测的一致。然而，岩石圈变薄通过SSC在三维中有所增强，从而扩大了含水熔融区域并移动了脱水边界。Subarc Richter-rollers产生随时间变化的沟槽平行温度变化， K，这超过了二维预测的瞬态50-100 K变化，可能有助于弧火山间距和一些弧下成像的可变地震速度结构。
Arc volcanism, volatile cycling, mineralization, and continental crust formation are likely regulated by the mantle wedge's flow regime and thermal structure. Wedge flow is often assumed to follow a regular corner‐flow pattern. However, studies that incorporate a hydrated rheology and thermal buoyancy predict internal small‐scale‐convection (SSC). Here, we systematically explore mantle‐wedge dynamics in 3‐D simulations. We find that longitudinal “Richter‐rolls” of SSC (with trench‐perpendicular axes) commonly occur if wedge hydration reduces viscosities to Pa s, although transient transverse rolls (with trench‐parallel axes) can dominate at viscosities of Pa s. Rolls below the arc and back arc differ. Subarc rolls have similar trench‐parallel and trench‐perpendicular dimensions of 100–150 km and evolve on a 1–5 Myr time‐scale. Subback‐arc instabilities, on the other hand, coalesce into elongated sheets, usually with a preferential trench‐perpendicular alignment, display a wavelength of 150–400 km and vary on a 5–10 Myr time scale. The modulating influence of subback‐arc ridges on the subarc system increases with stronger wedge hydration, higher subduction velocity, and thicker upper plates. We find that trench‐parallel averages of wedge velocities and temperature are consistent with those predicted in 2‐D models. However, lithospheric thinning through SSC is somewhat enhanced in 3‐D, thus expanding hydrous melting regions and shifting dehydration boundaries. Subarc Richter‐rolls generate time‐dependent trench‐parallel temperature variations of up to K, which exceed the transient 50–100 K variations predicted in 2‐D and may contribute to arc‐volcano spacing and the variable seismic velocity structures imaged beneath some arcs.