Evaluating the Thermal and Geochemical Evolution of Mars

Abstract:

While the current surface of Mars is analyzed from orbit and directly sampled by rovers, the specific internal processes that lead to the formation of the observed crust and how the crust and lithosphere evolved to its modern state are unknown. The constraints that arise from observed volcanic rocks indicate that Mars was hot enough for melt generation throughout its history. From orbital, surface, and meteorite analyses, the current crust is inferred to be ~50 km thick on average [1], basaltic in composition [2], and with known abundances of heat producing elements. We used geochemical and geodynamic approaches to model the evolution of the lithosphere and crust over time.

For the geochemical approach we calculated areotherms (conductive temperature profiles), combined with adiabats calculated from previous estimates of mantle potential temperatures of 1618 K today and 1723 K ~4 Ga [3], and compositionally based crustal and lithospheric mineral compositions, using Perple_X. We started by assuming an initially homogenous, undepleted crust [2] and mantle lithosphere [4]. We are developing a Mars-specific melt model using previous experimental data [5–7] to determine how the mantle has melted over time to produce the current observed crust, and from that production the modern mantle lithosphere.

For the geodynamic approach we calculated average mantle temperature profiles using CitcomS. Our models fix temperature at both the surface and at the CMB but are variable in internal heating rates. We considered core fractions of 0.45 and 0.4 of the total planet’s radius, consistent with geochemical constraints from above. From these, we determined the surface heat flux and mantle melt fractions through time. These values are compared to the geochemical results to evaluate the evolution and specific internal processes that lead to the generation of the martian mantle and lithosphere. This will result in a model of how the martian mantle and lithosphere may have evolved over the planet’s history into the present.

[1] Neumann et al. (2004) JGR

[2] Taylor and McLennan (2009) Planetary Crusts

[3] Filiberto (2017) CG

[4] Dreibus and Wänke (1985) Meteor.

[5] Matsukage et al. (2013) JMPS

[6] Collinet et al. (2015) EPSL

[7] Ding et al. (2020) JGR