New Geophysical Constraints for Intrusive Magmatism at Large Martian Volcanoes: Implications for Crustal Thickness and Volatile Outgassing

Volcanic materials exert both downward and upward forces on a planet's lithosphere, depending on where they are emplaced. On Mars, numerous studies have used gravity and topography data to ascertain the contribution of each of these styles of emplacement to measured fields. We use a novel methodology that allows for the thickness of an intrusive body to vary to more thoroughly model how intrusive magma flexes the lithosphere and use this to estimate the relative proportion of intrusive to extrusive materials under major Martian volcanoes. We find proportions that imply larger volumes of intrusive material compared to erupted, which is more in line with non-geophysical methods. Our results additionally imply a significant volume of outgassed volatiles into the atmosphere relatively later in Martian history which has implications for the thickness and composition of the ancient Martian atmosphere.