Felsic Tesserae on Venus Permitted by Lithospheric Deformation Models

Abstract

AbstractVenus tessera terrain contains the oldest rocks preserved on the surface of the planet. The composition of the tesserae is unknown, but recent observations of near‐infrared emissivity from orbit suggest that they are silica rich. This contrasts with previous interpretation that silica‐rich rheologies are too weak to produce tessera folds. We examine the range of compositions consistent with the observed folds in the tessera. We map folds in Tellus Regio tessera using the highest resolution Magellan radar images (∼100 m) and stereo topography (∼1 km). We use fold spacings as input into a buckling analysis that simulates power law rheology using contemporary dry‐mineral flow laws and modeled igneous rock compositions, consistent with a predicted dry lithosphere for Venus in the recent era. The folds have dominant wavelengths of 6–19 km with amplitudes of 500–1,000 m, consistent with low strains (1%–12%). We confirm that observed folds require heat flows of ≥40 K/km and strain rates faster than 10−16s−1, higher than today. These low strain folds are unlikely to have significantly modified the preexisting tessera surface, thus older impact craters must have been removed by an earlier geologic process. We demonstrate that the folds can form in dry crust with a SiO2 content ranging from 48% to 72%. Dry felsic rheologies could explain low emissivity signatures of tesserae that are attributed to a low Fe2+. If felsic, tessera materials may have formed in a prior era via partial melting of hydrous materials derived from recycling of surface waters into the Venus mantle.