Convection Cells With Accumulating Crust: Models of Continent and Mantle Evolution.

Numerical calculations of two component cellular convection with a lighter component diffusing down from the top are a simple model of the convection of rocky planets with a crust. The crust either is mixed down, floats along the top as blobs (continents separated by ocean basins), or forms layers. The calculations are for very viscous fluid with density variations from temperature and the lighter component representing the crust. If variations are approximately the same size, the lighter component collects along the top into H‐shaped blobs/clusters that have a flat midsection with two lobes on each end. Elevations are calculated for a free upper surface and the shape resembles continent and ocean floor topography with level interiors and thickening (mountains) at the edges produced by sinking at the margins. Between each pair of clusters, thermal and concentration boundary layers resemble ocean basins with spreading centers. Convection is unsteady but introducing internal decay of the lighter concentration produces steady flow. Internal heating produces similar results along with periodic drifting and merging of blobs like some geological cycles. The fact that these features arise without phase changes or viscosity variation implies that blobs of continent‐like crust might be widely found on rocky planets. Plain Language Summary: A simple numerical model of fluid flow has circulation cells driven by buoyancy. The cells are propelled by convection cells like mantle convection. Along the top, a model of a crust with lower density accumulates into a row of shapes. These resemble continents separated by ocean basins. Each accumulation is shaped like a wide capital letter H with a middle plateau and thickening (like mountains) at both ends. Cold, dense surface fluid plunges down next to each end like ocean trenches and subduction zones. These accumulations extend above the fluid surface because of their low density. Midway between each pair of these accumulations, hot fluid rises from the bottom and spreads out. The surface is depressed like ocean basins although the center is slightly elevated like mid‐ocean ridges. Forming these features from flow of a single constant viscosity fluid has not been previously done so the dynamics are discussed. Key Points: Convection cells with lighter fluid diffusing down from the top produce shapes like continents and ocean basins for certain parametersAdding internal heating produces cycles of splitting, drifting, and merging like the Wilson cycleThe calculations are simple and include two diffusivities for temperature and composition. A MATLAB code is included [ABSTRACT FROM AUTHOR]