On the interaction of two scales of convection in the mantle
On the interaction of two scales of convection in the mantle
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DOI：
10.1029/jb080i017p02529
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发表时间：
1975-06
影响因子：
--
通讯作者：
F. Richter;B. Parsons
中科院分区：
文献类型：
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作者：
F. Richter;B. Parsons
提出了上地幔在两个不同水平长度尺度上发生对流的系统。这与板块本身的存在、较老的海洋盆地中相对恒定的热通量背景以及从实验室和数值实验中获得的流体层对流知识是一致的。大规模的环流由板块本身和保持质量所必需的回流组成。小规模流动，类似于瑞利-贝纳德对流或其变体，一直是数值研究的主要目标，它提供了上地幔中必要的垂直热输送，为岩石圈底部提供了所需的热通量。取对流深度为650 km地震不连续，该深度表征了小尺度对流的水平长度尺度。通过一系列室内实验研究了小尺度对流与大尺度流动的相互作用。实验证明了对流在两个尺度上的合理性。此外，他们认为在快速移动的板块（绝对速度约为10cm y - 1）之下，小规模的对流将在地质短时间内以滚动的方式向大规模流动的方向排列。然而，在非常缓慢运动的板块之下，与板块运动不发生变化的时间相比，对流滚校所需的时间要长。这里的对流平台更有可能采取上升流和下升流的形式。因此，在移动边界下的对流层这一简单系统包含了解释各种表面特征的可能性。提出了双尺度思想的结果的观察检验，并批判性地讨论了该思想所依据的假设。
A system in which convection takes place in the upper mantle on two distinct horizontal length scales is proposed. This is consistent with the existence of the plates themselves, the relatively constant heat flux background in older ocean basins, and the knowledge of convection in fluid layers gained from laboratory and numerical experiments. The large-scale circulation consists of the plates themselves and the return flow necessary to conserve mass. The small-scale flow, analogous to Rayleigh-Benard convection or variants of this, which have been the main target of numerical study, provides the necessary vertical heat transport in the upper mantle that supplies the required heat flux at the base of the lithosphere. The depth of convection is taken to be down to the 650-km seismic discontinuity, and this depth characterizes the horizontal length scale of the small-scale convection. This system is studied by means of a set of laboratory experiments that explore the interaction of the small-scale convection with the large-scale flow. The experiments show the plausibility of convection on two scales. Furthermore, they suggest that beneath fast-moving plates (absolute velocities around 10 cm y−1) the small-scale convection will align itself as rolls in the direction of the large-scale flow in geologically short times. However, beneath very slow moving plates the times required for the alignment of convective rolls are long in comparison with times over which no changes in plate motions are to be expected. Here the convective planform is more likely to take the form of upwelling and downwelling spouts. Thus this simple system of a convecting layer beneath a moving boundary contains the possibility of explaining a wide variety of surface features. Observational tests of the consequences of the two-scale idea are suggested, and the assumptions on which this idea is based are critically discussed.