Birth and decline of magma oceans. Part 1: erosion and deposition of crystal layers in evolving magmatic reservoirs

TL;DR

This study combines laboratory experiments and theoretical modeling to understand crystal layer erosion and deposition in convective magmatic reservoirs, shedding light on magma ocean evolution and cumulate formation.

Contribution

It introduces an erosion law based on dimensionless numbers and explores crystal sedimentation dynamics relevant to planetary magma oceans.

Findings

Erosion rate depends on Rayleigh-Roberts and Shields numbers.

Particle deposition velocity scales with Stokes velocity.

Experimental results support the theoretical erosion framework.

Abstract

This paper is the first of a two companion papers presenting a theoretical and experimental study of the evolution of crystallizing magma oceans in planetesimals. We aim to understand the behavior of crystals formed in a convective magma and the implications of crystal segregation for the reservoir thermal and structural evolution. In particular, the goal is to constrain the possibility to form and preserve cumulates and/or flotation crusts by sedimentation/flotation of crystals. We first use lab-scale analog experiments to study the stability and the erosion of a floating lid composed of plastics beads over a convective viscous fluid volumetrically heated by microwave absorption. We propose an erosion law that depends only on two dimensionless numbers which govern these phenomena: (i) the Rayleigh-Roberts number, characterizing the strength of convection and (ii) the Shields number, that encompasses the physics of the flow-particle interaction. We further consider the formation of a cumulate at the base of the convective layer due to sedimentation of beads that are denser than the fluid. We find that particles deposition occurs at a velocity that scales with the Stokes velocity, a result consistent with previous experimental studies. The theoretical framework built on these experimental results is applied in a second paper on the evolution of magma oceans in planetesimals and the fate of particles in this convective environment.