The Gravitational Signature of Martian Volcanoes

Abstract

By modeling the elastic flexure of the Martian lithosphere under imposed loads, we provide a systematic study of the old and low‐relief volcanoes (>3.2 Ga, 0.5 to 7.4 km) and the younger and larger prominent constructs within the Tharsis and Elysium provinces (<3 Ga, 5.8 to 21.9 km). We fit the theoretical gravitational signal to observations in order to place constraints on 18 volcanic structures. Inverted parameters include the bulk density of the load, the elastic thickness required to support the volcanic edifice at the time it was emplaced (Te), the heat flow, the volume of extruded lava, and the ratio of volcanic products that form within (Vi) and above the preexisting surface (Ve). The bulk density of the volcanic structures is found to have a mean value of 3,206±190 kg/m3, which is representative of iron‐rich basalts as sampled by the Martian basaltic meteorites. Te beneath the small volcanoes is found to be small, less than 15 km, which implies that the lithosphere was weak and hot when these volcanoes formed. Conversely, most large volcanoes display higher values of Te, which is consistent with the bulk of their emplacement occurring later in geologic history, when the elastic lithosphere was colder and thicker. Our estimates for the volumes of volcanic edifices are about 10 times larger than those that neglect the flexure of the lithosphere. Constraints on the magnitude of subsurface loads imply that the ratio Vi/Ve is generally 3:5, which is smaller than for the Hawaiian volcanoes on Earth.

Constraints on Thermal History of Mars From Depth of Pore Closure Below InSight

“…(2004) find heat fluxes in excess of 35, 43, 48, and 50 mW m −2 for four Noachian terrains. Likewise, Broquet and Wieczorek (2019) generally obtain heat fluxes greater than 50 mW m −2 for ancient, eroded volcanoes. Although uncertain, all these estimates are very consistent with our constraint.…”

Earth-like Habitable Environments in the Subsurface of Mars

“…It is assumed that the volcanic bulges and northern lowlands are the possible source regions for the SNCs and the southern highlands are the source region for the regolith breccias (Cassata et al, 2018). In the estimation, an average solid crust matrix density range of 2000-3200 kg m -3 is used for the southern highlands' crust, consistent with its mineralogy (Ehlmann and Edwards, 2014), and 2600-3200 kg m -3 is used for the northern lowlands and volcanic bulges, consistent with their mineralogy and volcano-specific orbital gravimetry (Broquet and Wieczorek, 2019). It is assumed that the difference between the gravimetry density measurements and rock matrix density estimates is caused by pore space filled with ice or water.…”

The Composition of the South Polar Cap of Mars Derived From Orbital Data

“…The elastic deflection of the lithosphere () was computed using the loading model presented in Broquet and Wieczorek (2019) and Broquet et al. (2020) (the relevant equations are provided in Appendix ).…”

“…The elastic deflection of the lithosphere (W ) was computed using the loading model presented in Broquet and Wieczorek (2019) and Broquet et al (2020) (the relevant equations are provided in Appendix C). Importantly, lithospheric flexure will create long-wavelength relief at the base of the polar cap that is anti-correlated with the surface relief.…”