Elastic Lithosphere Thickness Calculations from Numerical Thermal Evolution Models of Venus’ Interior with a Variable Thermal Conductivity

Abstract:

The elastic lithosphere thickness is a proxy for the surface heat flow and directly linked to the thermal state of the lithosphere. Elastic thickness estimates for Venus lie between 0 and 100 km, with 20 km or less representing a best fit for more than half of the planet [1]. These small values might be indicative of a high heat flow if such areas are isostatically uncompensated [2]. Such estimates can be used to constrain the thermal evolution of Venus’ interior.

In this study we run models using the mantle convection code Gaia [3] in a spherical annulus geometry to investigate the thermal evolution of Venus’ interior assuming a stagnant lid regime. We systematically test the effects of a pressure and temperature-dependent thermal conductivity and viscosity. All our simulations include an Arrhenius type rheology, latent heat consumption due to mantle melting, and heat pipe effects due to melt extraction. For the elastic thickness calculation we apply the same methodology as in [4].

Our models show that a strong depth-dependent thermal conductivity reduces the temperature variations in the interior leading to weaker mantle plumes and downwellings (Fig. 1a, b). Furthermore, the exact style of magmatism (i.e. extrusive or intrusive) directly affects the elastic lithosphere thickness. Our results show that due to an efficient magmatic heat transport, a thicker elastic thickness is obtained when considering pure extrusive magmatism compared to cases where a significant amount of melt remains trapped in the lithosphere (Fig. 1c). The differences between cases considering different magmatic styles decrease towards the present day, when the amount of melt production in the interior is smaller compared to the early evolution. In our models, we assumed a constant intrusive-to-extrusive ratio for the entire planet. We note, however, that the spatial variations of the elastic lithosphere thickness could be larger if specific regions show pronounced extrusive magmatic activity compared to regions where most melt remains trapped in the subsurface.

[1] Anderson & Smrekar, JGR 2006; [2] Smrekar et al., SSR 2018, [3] Hüttig et al, PEPI 2013; [4] Plesa et al., JGR 2016.