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首页> 外文期刊>Geochemistry, geophysics, geosystems >The mantle wedge's transient 3-D flow regime and thermal structure
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The mantle wedge's transient 3-D flow regime and thermal structure

机译：地幔楔的瞬态3-D流态和热力结构

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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 less than or similar to 1.10(19) Pa s, although transient transverse rolls (with trench-parallel axes) can dominate at viscosities of similar to 5.10(18)-1.10(19) 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 similar to 150 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.
机译：弧形火山作用，挥发循环，矿化作用和大陆壳的形成可能受地幔楔的流动状态和热力结构的调节。通常假定楔形流遵循规则的角流模式。但是，结合水化流变学和热浮力的研究预测内部小尺度对流（SSC）。在这里，我们系统地研究了3-D模拟中的地幔楔动力学。我们发现，如果楔形水合作用将黏度降低到小于或等于1.10（19）Pa s，粘度通常会发生SSC的纵向里氏辊（具有沟槽垂直轴），尽管瞬态横向辊（具有沟槽平行轴）在粘度类似于5.10（18）-1.10（19）Pa s。弧线下方和反弧线之间的滚动不同。地下弧状卷具有类似的平行于沟槽和垂直于沟槽的尺寸，为100-150 km，并且在1-5 Myr时间尺度上演化。另一方面，亚背弧不稳定会合并成细长的薄片，通常具有优先的沟槽垂直排列，显示出150-400 km的波长，并以5-10 Myr的时间尺度变化。随着楔形水化作用的增强，俯冲速度的增加以及上板的厚度增大，后背弧脊对亚弧系统的调节作用增加。我们发现楔形速度和温度的沟槽平行平均值与二维模型中预测的一致。但是，在3D模式下，通过SSC进行的岩石圈减薄在某种程度上得到了增强，从而扩大了含水熔融区域并改​​变了脱水边界。 Subarc Richter-rolls产生的随时间变化的与沟槽平行的温度变化高达150 K，超过了二维预测的瞬态50-100 K的变化，可能有助于弧火山间隔和成像的可变地震速度结构在某些弧线之下。

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