Estimating Venusian thermal conditions using multiring basin morphology

Abstract

Despite their critical roles in Venus’s geological evolution, neither heat flow through the Venusian lithosphere nor the corresponding tectonic regime in its geological past is well constrained. However, because impact basin formation is sensitive to thermal conditions at depth, studying large basin development can provide crucial insights into the past geological conditions of a planet. Here we model the formation of Mead Basin, the largest impact structure on Venus, and its two ring faults at approximately 190 km and 270 km diameter, to determine the thermal conditions in Venus’s crust and upper mantle at the time of impact. For present-day surface temperatures, we find that lithospheric thermal gradients no higher than 14 K km−1, corresponding to surface heat fluxes of 28 mW m−2, are required to reproduce the morphology of Mead Basin. These values are less than half of what is expected for an active lid planet, implying that Venus may have had a stagnant lid when Mead Basin formed, between 0.3 and 1 billion years ago. Modelling of Mead Basin, the largest impact feature on Venus, shows that it could only have got its shape, with the two ring faults at the correct position, if Venus were in a stagnant lid regime at the time of Mead Basin formation, between 0.3 and 1 billion years ago.