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Detailed Mapping in the Alpha Regio (V-32) Quadrangle, Venus, and Testing a New Model for Coronae Erin M. Bethell Department of Earth Sciences, Carleton University, Ottawa, Canada Detailed geological mapping of the Alpha Regio (V-32) quadrangle on Venus (0° to -25° N, 0° to 30° E) is being conducted as part of my PhD program, co-supervised by Drs. Ernst and Samson. Of particular interest to this project are the six densely clustered coronae contained in the Alpha Regio quadrangle, which include Kuan-Yin, Atargatis, Thouris, Cybele and Fatua coronae, as well as an unnamed coronalike structure (~60 km northwest of the annulus of Cybele corona). The quadrangle also contains structures attributed to Heng-o and Thermuthis coronae. Each corona in the quadrangle possesses a welldefined circumferential graben-fissure system. Fatua corona, in particular, also possesses a prominent radiating graben-fissure system that extends northwest and ~1500 km south into the Brynhild fossae in the Kaiwan Fluctus (V-44) quadrangle. The graben-fissure systems associated with coronae in the Alpha Regio quadrangle are being explored, through detailed structural mapping, as analogues to giant dyke swarms on Earth. In particular, giant circumferential dyke swarms are a newly discovered class of dyke swarm that are increasingly being recognized on Earth in association with large igneous provinces. They typically span 50°-180° in arc, are hundreds to thousands of kilometers in diameter, are interpreted to circumscribe mantle plume centers at the time of formation, and are sometimes associated with roughly coeval giant radiating dyke swarms. Modelling and multiple lines of evidence have demonstrated that radiating graben-fissure systems associated with coronae and volcanic centers on Venus can be underlain by laterally propagating, radiating dykes. We propose that circumferential graben-fissure systems associated with the annuli of Venusian coronae may also be underlain by dykes that are morphologically similar to giant terrestrial circumferential dyke swarms. The presence of circumferential dykes underlying the annuli of coronae would have significant implications for the underlying magmatic plumbing system.