Distribution of Small Shield Volcanoes at Venusian Coronae

One apparent manifestation of volcanism at Venusian coronae is small shield volcanoes, herein referred to as shields. Coronae are circular volcano-tectonic structures defined by concentric fractures or ridges, an interior topographic depression or bulge, and possible radial fractures. Shields are circular features that are cone, flat-topped, dome, or shield shaped, <<1 km in height, and typically <1-2 km in diameter. Here we investigate shield distribution at three coronae with the goal of unraveling the role they play in coronae volcanic evolution. Using Magellan SAR imagery of Aramaiti (26° S, 82° E), Bhumidevi (17° S, 343° E), and Zemire (32° N, 312° E) Coronae, we find that shields are located predominantly 1) along radial fractures and fracture belts and 2) inside the corona annulus. Shields are sparse on concentric fractures, which are associated with long lava flows and steep-sided domes and may be related to corona collapse. Based on terrestrial analogs, shields on radial fractures and fracture belts may represent small, indistinct batches of magma tapped from a mantle source that rise directly to the surface. The origin of shields inside the corona annulus remains ambiguous. The timing of shield formation is also ambiguous; however, they all appear to be undeformed. If the radial fractures and fracture belts formed from lithospheric impingement of a diapir, then shields outside of the corona annulus may have formed early in corona evolution. It is possible that shields inside the corona annulus reflect tapping of a magma chamber. Perhaps such tapping resulted in corona collapse and thus concentric fracture formation. The presence of shields on a topographic bulge in the interior of Aramaiti Corona raises an alternative possibility that the shields represent a period of magmatic resurgence. Future work should focus on constraining shield-timing relationships, especially with regards to coronae-related tectonic structures.