Distribution and Ti Content of Lunar Mare Basalts Produced by Internal Dynamics

The asymmetrical distribution of mare basalts is one of the most striking features of the surface of the Moon. Basalts cover about a third of the near-side surface while being present on only 1% of the far side surface. They were largely produced during one major episode of volcanic activity at 3.85-3.2 Ga, with smaller-volume eruptions lasting until 1 Ga.

The geological context of these volcanic activities involves the crystallization of the lunar magma ocean, which was produced in the aftermath of the Moon-forming event. Fractional crystallization of the magma ocean produced a radial gradient of compositions, including ilmenite-bearing cumulates (IBC) towards the end of the crystallization. IBC are dense. They are considered to sink down into lighter cumulates and drive mantle convection, leading to decompression melting and basaltic volcanism.

In this study, we aim to use numerical Stokes-flow simulations to study the participation of IBC in mantle flow and melt production, and investigate how this process influences the long-term thermo-chemical evolution of the Moon. This work takes into account newly available rheological parameters of lunar minerals obtained in deformation experiments. It also explores different initial conditions, testing whether or not localization of upwelling-induced volcanic activities requires asymmetrical distribution of crustal components and heat-producing elements at the onset of IBC overturn. Our models trace the production of melt, and make predictions of volcanic activities in terms of their timing, quantity, surface distribution, and Ti content. Preliminary results show that foundered IBC can participate in a strong upwelling on the near side, providing an early Ti-rich source for volcanism.