Mechanisms for cessation of magmatic resurfacing on Venus

Abstract

Proposed mechanisms of resurfacing on Venus about 0.3–1 Gyr ago usually involve either some form of tectonic resurfacing in which Venusian lithosphere is recycled mechanically or magmatic resurfacing where essentially immobile lithosphere is covered by lava. The focus of this study is mechanisms of magmatic resurfacing in the stagnant lid regime of mantle convection. Parameterized convection models suggest that cessation of magmatic resurfacing can occur in several ways. (1) The mantle temperature drops sufficiently such that mantle rising adiabatically does not cross the solidus. (2) The molten layer migrates below the solid/melt density inversion at 250–500 km so that no melt can escape. (3) Sublithospheric small‐scale convection stops and conductive thickening of the lid suppresses melting. In each case, inability of magma to penetrate thickened Venusian lithosphere may play a role. The timing of melt cessation and duration of late stage resurfacing depend on various factors such as mantle rheology, degree of mantle depletion, and depth of resurfacing. The models indicate that the waning stages of resurfacing which result in surface age variations can last ∼0.1–1 Gyr. A general trend of recent lithospheric thickening is also predicted. Some cases exhibit a rapid transition from relatively thin to thick lid as suggested by previous authors.