Haasttse-baad Tessera Ring Complex: A Valhalla-Type Impact Structure on Venus?

Abstract

Venus preserves ∼1,000 impact craters, yet to date no impact basins larger than 300 km in diameter—common in the oldest terrains on Mercury, Mars and the Moon—are recognized on Venus. The tessera terrain is Venus' oldest recognized terrain. We describe a ∼1,500 km-diameter concentric ring-graben complex preserved on Haasttse-baad Tessera, Venus that we identify as the Haasttse-baad Tessera Ring Complex (HTRC). Based on geologic relations and numerical modeling, we propose that the HTRC may represent a Valhalla-type multiring impact basin formed late during the evolution of its host ribbon-tessera terrain (rtt). Formation of Valhalla-type impact basins could involve a unique three-layer target rheology with a thin elastic layer above a low viscosity layer above a deep strong layer. This multi-layer rheological sandwich is consistent with crustal rheology previously proposed for the formation of Venus' rtt. If the HTRC is a Valhalla-type impact basin, it would be Venus' oldest, and currently largest, impact structure, providing a rare window into Venus' ancient past and with implications for early crustal processes on Venus.