[M-GI30] Computational sciences on the universe, galaxies, stars, planets and their environments

[MGI30-P08] Mechanism of Magma Ascent from a Partially Molten Layer by a Coupled Magmatism-Mantle Convection System

*Kenyo U¹, Masanori Kameyama^2,3, Takehiro Miyagoshi³, Takatoshi Yanagisawa³, Masaki Ogawa¹ (1.The University of Tokyo, 2.Ehime University, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:Mantle Convection, Magmatism, Numerical Analysis, Partially Molten Plume, Melt-finger

Magma ascent from a partially molten layer at depth in the mantle of a rocky planet plays a crucial role in its volcanic history. This study investigates the formation of "melt-fingers", a finger-like magma ascent structure first identified in 2-D numerical models of the Moon (U et al., 2023, JGR Planets). Melt-fingers do not appear in the models of Mars, Venus, or the Earth, where partially molten plumes develop instead. To identify the agent that causes this difference between the Moon and the larger planets, we carried out a series of numerical experiments of a coupled magmatism-mantle convection system in the mantle where the viscosity is held constant. Our results reveal that the regimes of magma ascent can be delineated on the plane of two key parameters: the depth gradient of the solidus S_d and the scale of melt-buoyancy B_m, the latter being the ratio of the Rayleigh number to non-dimensional permeability of magma through matrix. Melt-fingers preferentially develop in smaller planetary bodies such as Mercury and the Moon, where both S_d and B_m are relatively low. In contrast, partially molten plumes develop in larger planetary bodies such as Mars and the Earth, where B_m is larger. These findings offer new insights into the style of volcanism on various planets.