An insulating plate drifting over a thermally convecting fluid: the thermal blanket effect on plume motion and the emergence of a unidirectionally moving mode

Abstract

Floating rather stably above the convective mantle, continents exert a thermal blanket effect on the mantle by locally accumulating heat and altering the flow structure, which in turn affect continent motion. This thermal-mechanic feedback has been captured by a simplified model―a thermally insulating plate floating freely over a bottom-heated convecting fluid. Previous studies have revealed that, as plate size increases, plate motion transitions from long-term stagnancy over cold downwelling to short-term stagnancy over hot upwelling, termed stagnant modes (SMs) I and II, respectively, and eventually to a unidirectionally moving mode (UMM) with no stagnancy. During SM I/II, the adjacent hot/cold plumes are observed to move toward/away from the plate. The present study quantifies these plume motions through analysis on a partially insulated loop model established for SM I and SM II, respectively. The model predictions are well verified by results of numerical simulation. Moreover, the dominant frequency of plate speed is shown to increase linearly with plate size, with an abrupt jump as the coupling mode transitions from SM I to SM II. This suggests that the enhanced thermal blanket effect with plate size enables an increasingly fast feedback between the slowdown of a plate and the strengthening of hot upwelling which boosts plate motion. When plate motion is boosted before it stops, the UMM emerges. The predicted critical plate size for the UMM is well validated by simulation results. Geological implications of the results for continent motion, continent–mantle coupling and particularly the migration of plume and subduction sites are discussed.

Flow reversal and multiple states in turbulent Rayleigh–Bénard convection with partially isothermal plates

“…These experimental results confirm that the insulating plate indeed poses a non-negligible effect on the dynamic coupling between the plate and underlying fluid, and that this effect varies with plate size. Numerical studies by Mao (2021Mao ( , 2022 have delved into details of the variations of plate motion with plate size and the underlying mechanism. In addition to the aforementioned set-up, investigations on turbulent convection based on non-uniform thermal boundary conditions have also been considered in recent years (Bakhuis et al 2018;Nandukumar et al 2019;Ostilla-Mónico & Amritkar 2020;Bassani et al 2022;Zhao et al 2022).…”

“…Numerical studies by Mao (2021Mao ( , 2022 have delved into details of the variations of plate motion with plate size and the underlying mechanism. In addition to the aforementioned set-up, investigations on turbulent convection based on non-uniform thermal boundary conditions have also been considered in recent years (Bakhuis et al 2018;Nandukumar et al 2019;Ostilla-Mónico & Amritkar 2020;Bassani et al 2022;Zhao et al 2022). For example, Zhao et al (2022) numerically investigated the 2-D RBC by applying sinusoidally distributed heating to the bottom plate and Ostilla-Mónico & Amritkar (2020) simulated the 3-D RBC with a top cold plate having a mixture of adiabatic and isothermal boundary conditions.…”