Abstract
In this study, we conduct numerical simulations of thermochemical mantle convection in a 2D spherical annulus with a highly viscous lid drifting along the top surface, in order to investigate the interrelation between the motion of the surface (super)continent and the behavior of chemical heterogeneities imposed in the lowermost mantle. Our calculations show that assembly and dispersal of supercontinents occur in a cyclic manner when a sufficient amount of chemically-distinct dense material resides in the base of the mantle against the convective mixing. The motion of surface continents is significantly driven by strong ascending plumes originating around the dense materials in the lowermost mantle. The hot dense materials horizontally move in response to the motion of continents at the top surface, which in turn horizontally move the ascending plumes leading to the breakup of newly-formed supercontinents. We also found that the motion of dense materials in the base of the mantle is driven toward the region beneath a newly-formed supercontinent largely by the horizontal flow induced by cold descending flows from the top surface occurring away from the (super)continent. Our findings imply that the dynamic behavior of cold descending plumes is the key to the understanding of the relationship between the supercontinent cycle on the Earth’s surface and the thermochemical structures in the lowermost mantle, through modulating not only the positions of chemically-dense materials, but also the occurrence of ascending plumes around them.
Highlights
It is often conjectured that the assembly and dispersal of supercontinents occurred several times during the Earth’s history (e.g., [1])
We carried out numerical experiments of thermochemical mantle convection, which incorporate the effect of the presence and drifting motion of the surface continent together with initially imposed chemically-dense materials, aiming at understanding the interrelation between the motion of the surfacecontinent and the behavior of chemically-dense heterogeneous materials in the lowermost mantle
We found that the presence of dense chemical heterogeneities in the lowermost mantle is of crucial importance for the occurrence of the supercontinent cycle
Summary
It is often conjectured that the assembly and dispersal of supercontinents occurred several times during the Earth’s history (e.g., [1]) This cyclic behavior, commonly termed “supercontinent cycle” or “Wilson cycle” [2], includes the formation of Pangea (about 330 Ma) and its breakup Among the events of breakup, some are caused by the impingement of ascending plumes beneath the supercontinent [7], even though some do not have any sign of ascending plumes [8]. This fact suggests the significance of the interrelations between the supercontinents and ascending plumes from the deep mantle in driving the supercontinent cycle. From several lines of seismological evidence, such as their sharp-sided structure, low Vs /Vp ratio and increased
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