Convection in fluid layers at high Rayleigh number (Ra ∼10⁶) have a spoke pattern planform. Instabilities in the bottom thermal boundary layer develop into hot rising sheets of fluid, with a component of radial flow toward a central upwelling plume. The sheets form the “spokes” of the pattern, and the plumes the “hubs.” Such a pattern of flow is expected to occur beneath plate interiors on Earth, but it remains a challenge to use observations to place constraints on the convective planform of the mantle. Here we present predictions of key surface observables (gravity, topography, and rates of melt generation) from simple 3‐D numerical models of convection in a fluid layer. These models demonstrate that gravity and topography have only limited sensitivity to the spokes and mostly reflect the hubs (the rising and sinking plumes). By contrast, patterns of melt generation are more sensitive to short‐wavelength features in the flow. There is the potential to have melt generation along the spokes but at a rate which is relatively small compared with that at the hubs. Such melting of spokes can only occur when the lithosphere is sufficiently thin (  km) and mantle water contents are sufficiently high (  ppm). The distribution of volcanism across the Middle East, Arabia, and Africa north of the equator suggests that it results from such spoke pattern convection.

中文翻译：

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地幔对流的简单3D模型的重力，地形和融化速率

高瑞利数（Ra〜10 ^6）在流体层中的对流）有一个轮辐模式计划。底部热边界层中的不稳定性发展成热的上升流体片，其中一部分径向流流向中央上升流。床单形成图案的“辐条”，羽状物形成“轮毂”。预计这种流动模式会在地球板块内部下方发生，但是使用观测值对地幔的对流平面形施加约束仍然是一个挑战。在这里，我们根据流体层中对流的简单3D数值模型，提出了关键表面可观测值（重力，形貌和熔体生成速率）的预测。这些模型表明，重力和地形对辐条的敏感性有限，并且主要反映了轮毂（上升和下沉的羽状流）。相比之下，熔体生成的模式对流中的短波特征更敏感。有可能在轮辐上产生熔体，但与轮毂处相比，熔解的速率相对较小。仅在岩石圈足够薄时，才会发生辐条的这种熔化（  地幔中的水含量足够高（  ppm）。火山活动在赤道以北的中东，阿拉伯和非洲的分布表明，火山活动是由这种辐条模式对流引起的。