The Strength of the Lower Mantle

地球的内部行为是由对流控制的，因此地幔粘度的知识对我们的理解至关重要。大尺度上的地幔黏度是由冰期后的反弹和大地水准面反演得到的。这些研究表明，上下地幔之间的黏度存在显著差异，这被用来解释660公里不连续处俯冲板块的不同行为。这些板块表现出一系列的行为，从刚好在660公里的不连续面上方下沉到穿透不连续面，并在进入下地幔时变厚。因此，660公里黏度对比的大小和不渗透性显然会影响地幔对流的类型和冷却速率，但地球物理观测的分辨率不足以完全了解660公里不连续处周围物质的命运。在这里，我们建议测量过渡带和下地幔中存在的矿物和组合的流变性，从而为更充分地理解上下地幔之间的粘度对比提供所需的约束。

The internal behaviour of the Earth is controlled by convection hence knowledge of mantle viscosity is critical to our understanding. The viscosity of the mantle on large scales has been measured from post-glacial rebound and geoid inversions. These have shown that there is a significant contrast in viscosity between the upper and lower mantles which has been invoked to explain the varied behaviour of subducting slabs at the 660 km discontinuity. The slabs show a range of behaviour from ponding just above the 660 km discontinuity to penetrating the discontinuity and thickening as they enter the lower mantle. It is apparent therefore that the size and impermeability of the 660 km viscosity contrast affects the style of mantle convection and cooling rates but the resolution of the geophysical observations is not sufficient for a complete understanding of the fate of material around the 660 km discontinuity. Here we propose to measure the rheology of the minerals and assemblages present in the transition-zone and lower-mantle and so provide the constraints needed for a fuller understanding of the viscosity contrast between the upper and lower mantles.