The changing gravity field due to a superplume under the Tharsis Region

The Tharsis Region has been an interest of study for many years due to its large impact on the long wavelength gravity field and topography of Mars. The leading theory on the origin of the volcanic region is a combination of both isostatic flexure of a thickened crust and a small contribution due to a (possible) large superplume residing in the upper mantle. The isostatic balance, on which previous studies have relied, does not adequately explain the long-wavelength gravity field spectra. These long-wavelength signals contribute to large scale features in the mantle. We consider the presence of a dynamic mass anomaly below the Tharsis Region. This could help explain the geological surveys of the relative young lava flows. By looking at mantle dynamic models we can explore the effect of a superplume that is actively rising in the mantle and changing the geoid over time.

We ran a series of instantaneous axisymmetric finite element models of Mars with varying plume and subsurface structural variables constrained by InSight. We run the model for 50 years, thereby accounting for the total duration of satellite data acquisition. The deformation in the model allows us to calculate the change in dynamic topography and gravity anomaly.

Our preliminary results show dynamic topography rates of a few centimetres per year and gravity rates in the order of 0.1 μGal per year. These gravity rates should fall within the precision of the Mars Reconnaissance Orbiter gravity field estimates, but are masked by other geological surface mass changes. Our results show that with longer and dedicated gravity observations, we should be able to observe the large scale mantle dynamics of Mars.