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- Title
The Volcanic and Radial Expansion/Contraction History of the Moon Simulated by Numerical Models of Magmatism in the Convective Mantle.
- Authors
U, Ken'yo; Kameyama, Masanori; Ogawa, Masaki
- Abstract
To understand the evolution of the Moon, we numerically modeled mantle convection and magmatism in a two‐dimensional polar rectangular mantle. Magmatism occurs as an upward permeable flow of magma generated by decompression melting through the convecting matrix. The mantle is assumed to be initially enriched in heat‐producing elements (HPEs) and compositionally dense ilmenite‐bearing cumulates (IBC) at its base. Here, we newly show that magma generation and migration play a crucial role in the calculated volcanic and radial expansion/contraction history. Magma is generated in the deep mantle by internal heating for the first several hundred million years. A large volume of the generated magma ascends to the surface as partially molten plumes driven by melt buoyancy; the magma generation and ascent cause a volcanic activity and radial expansion of the Moon with the peak at 3.5–4 Gyr ago. Eventually, the Moon begins to radially contract when the mantle solidifies by cooling from the surface boundary. As the mantle is cooled, the activity of partially molten plumes declines but continues for billions of years after the peak because some basal materials enriched in the dense IBC components hold HPEs. The calculated volcanic and radial expansion/contraction history is consistent with the observed history of the Moon. Our simulations suggest that a substantial fraction of the mantle was solid, and there was a basal layer enriched in HPEs and the IBC components at the beginning of the history of the Moon. Plain Language Summary: We developed a numerical model of magmatism in the convecting mantle to understand the volcanic and radial expansion/contraction history of the Moon. In the early period of the calculated history, magma is generated in the deep mantle and ascends to the surface as partially molten plumes driven by melt buoyancy. The plumes cause volcanic activity, and the extension of partially molten regions by magma ascent causes radial expansion of the Moon. In its latter period, however, the Moon contracts with time because partially molten regions solidify as they are cooled from the surface boundary. The activity of partially molten plumes declines but continues for billions of years because some materials that host heat‐producing elements (HPEs) are enriched in compositionally dense components and remain in the deep mantle. The calculated history of radius change and volcanism is consistent with the observed lunar history. Our simulations suggest that a substantial fraction of the mantle was solid, and a dense layer enriched in HPEs developed at the base of the mantle at the beginning of the history of the Moon. Key Points: We numerically simulated magmatism in the convecting mantle of the Moon to understand its evolutionMagma is generated in the deep mantle and ascends to the surface as partially molten plumes driven by melt buoyancyExtension of partially molten regions by the plumes causes the observed expansion and active volcanism of the early Moon
- Subjects
MOON; MAGMATISM; VOLCANISM; VOLCANIC plumes; PLANETARY science; MAGMAS; BUOYANCY
- Publication
Journal of Geophysical Research. Planets, 2023, Vol 128, Issue 9, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2023JE007845