Title: Study of the Mantle Mixing Driven by Plate Motions
Abstract: Abstract Two new quantitative terms, the box replacement ratio and the pervasion ratio, are employed to investigate convective mantle mixing in this paper. The former is the ratio of the mantle boxes that have been replaced at least once by other mantle boxes to the total number of mantle boxes. The latter is the ratio of initial to final volumetric density of tracers which were initially confined in a small space. In this study we assume that mantle convection is steady, it is driven by plate motion or density anomalies in the mantle and the viscosities in the upper and lower mantle are different. In our numerical experiment the mantle is divided into 20736 boxes (5° × 5° × 300 km) and there are 2376 tracers placed on 5° × 5° grids at 100 km depth and at 100 km above CMB. The results show that the box replacement ratio of convective mantle mixing is over 80% for the whole mantle and is over 90% for upper mantle after 4 billion years. It means that most mantle boxes have been replaced. For two groups of 1681 tracers in a small space of 10° × 10° (at intervals of 0.25°) placed at the top and bottom of the mantle their pervasion ratios approach a constant and the initial tracers become widely distributed in the mantle after 3 billion years. These results indicate that the Earth's mantle, except for the lithosphere and “D” layer, has been mixed very well in the past 4 billion years. It is not likely that initial heterogeneity boxes greater than 5° × 5° × 300 km remain in the present mantle.
Publication Year: 2007
Publication Date: 2007-09-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 1
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