The magmatic evolution of three Venusian coronae
The volcanic and tectonic histories of Venusian coronae appear to be intricately linked. We explore that link through the construction of geological maps of three coronae using Magellan synthetic aperture radar (SAR) imagery and altimetry radar data. Each examined corona – Aramaiti, Bhumidevi and Zemire Coronae – is characterized by an annulus of concentric fractures, lava flows, tholi and clusters of small shields. Radial fractures occur at one corona (Bhumidevi Corona), whereas the other two coronae (Aramaiti and Zemire Coronae) occur within linear fracture belts. Based on observed timing relationships, we propose that the evolution of these three coronae is similar to large silicic caldera formation on Earth in that the formation of concentric fractures facilitated a mass evacuation of a magma reservoir residing underneath each corona resulting in subsequent corona collapse. Our model emphasizes the late-stage evolution of these coronae and predicts that all the erupted products could be basaltic. Such predictions are testable through continued geological mapping of coronae, as well as through in situ spectral analyses by Venusian landers.