The understanding of the interactions between subduction-induced mantle flow and background mantle flow (being global or regional) remains incomplete despite its potential impact on subduction dynamics and associated deformation. Here we present the results of three-dimensional laboratory models of subduction zones at the scale of the upper mantle in which we systematically vary the plate's width and trench perpendicular background mantle flow. In particular, we test different mantle flow magnitudes and directions of flow, and evaluate their impact on the slab geometry in the vertical plane, trench shape evolution, and the superficial horizontal mantle deformation. While the chosen viscosity ratio between the convective mantle and the subducting plate in our models (∼100) is favorable to the deformation of the slab through mantle displacement, we show that the geometry of the slab in the vertical plane is only marginally affected by the imposed background flow. Instead, the background flow has a larger impact on the horizontal kinematics and deformation of the trench. It reduces along-trench variations of trench kinematics, which in turn decreases trench curvature, and it largely disturbs the pattern of mantle deformation at slab edges, inhibiting the development of toroidal cells. We also show that the thickness of the convective layer (here, the upper mantle) controls the toroidal component of the mantle flow and the length scale of trench curvature for large subduction zones.

中文翻译：

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3D俯冲带地幔流动与平板拉力之间的相互作用

尽管对俯冲动力学和相关变形有潜在影响，但对俯冲引起的地幔流和背景地幔流（全局或区域性）之间相互作用的理解仍然不完整。在这里，我们介绍了在上地幔尺度上的俯冲带三维实验室模型的结果，在该模型中我们系统地改变了板的宽度和垂直于背景地幔沟的沟槽。特别是，我们测试了不同的地幔流大小和流向，并评估了它们对板在垂直平面上的几何形状，沟槽形状演变以及表层水平地幔变形的影响。虽然在我们的模型中选择的对流地幔与俯冲板之间的粘度比（约100）有利于板因地幔位移而变形，我们显示出，平板在垂直平面上的几何形状仅受所施加的背景流的影响很小。相反，背景流对沟槽的水平运动和变形影响更大。它减少了沟槽运动的沿沟槽的变化，从而降低了沟槽的曲率，并且极大地干扰了板坯边缘的地幔变形模式，从而抑制了环形单元的发育。我们还表明，对流层（此处为上地幔）的厚度控制着地幔流的环形分量以及大俯冲带的沟槽曲率的长度尺度。背景流动对沟槽的水平运动和变形影响更大。它减少了沟槽运动的沿沟槽的变化，从而降低了沟槽的曲率，并且极大地干扰了板坯边缘的地幔变形模式，从而抑制了环形单元的发育。我们还表明，对流层（此处为上地幔）的厚度控制着地幔流的环形分量以及大俯冲带的沟槽曲率的长度尺度。背景流动对沟槽的水平运动和变形影响更大。它减少了沟槽运动的沿沟槽的变化，从而降低了沟槽的曲率，并且极大地干扰了板坯边缘的地幔变形模式，从而抑制了环形单元的发育。我们还表明，对流层（此处为上地幔）的厚度控制着地幔流的环形分量以及大俯冲带的沟槽曲率的长度尺度。