Analyses of Mercury’s surface by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have identified a large portion of the surface to be comprised of Mg-rich basaltic and basaltic komatiitic compositional plains, likely of volcanic origin. However, the compositional differences of these ancient volcanic plains cannot be explained via fractional crystallization and require mantle heterogeneity with at least two distinct mantle lithothologies to produce the observed surface compositions.
Such heterogeneity is an expected consequence of Mercurian mantle crystallization from a magma ocean generated by the heat from planetary accretion and differentiation. Although magma ocean analyses cannot presently account for the recently observed high sulfur surface abundances and low oxygen fugacity, these models provide insight into potential mantle compositional stratification.
While prior studies of mantle convection on Mercury have examined a wide range of mantle thicknesses, viscosities, radiogenic contents, and temperatures, such models have yet to investigate the role of compositional stratification. By employing a three-dimensional (3-D) spherical finite-element convection model (CitcomS – modified to allow for mantle partial melting of appropriate rheologies, secular cooling of the core, and evolution of radiogenic heat production) that simulates mantle convection through the governing equations for conservation of mass, momentum, and energy, we examine mantle convection and melting for a compositionally stratified mantle. Melting of a post-magma ocean Mercurian mantle may generate the high temperatures required to produce the high-Mg volcanic plains observed on the Mercurian surface.
Acknowledgements: The MESSENGER project is supported by the NASA Discovery Program under contracts NAS5-97271 to the Johns Hopkins University Applied Physics Laboratory and NASW-00002 to the Carnegie Institution of Washington.