Heng-o Corona, Venus: Dyke swarms record evolution of its underlying mantle plume

Coronae are enigmatic, quasi-circular/elliptical tectono-magmatic features, common across the surface of Venus ranging in size from 60 to 2600 km and with a mean diameter of 270 ± 190 km. This study undertook a detailed mapping (1:500,000 scale) of Heng-o Corona, the second largest on Venus. 24,600 graben-fissure lineaments were mapped, interpreted to be underlain by mafic dykes, and grouped into radiating, circumferential and linear swarms. A series of 5 nearly-concentric rings were identified from unflooded or partially flooded circumferential swarms. The largest of these has a diameter of 1970 km, which almost doubles Heng-o's known size (previously 1060 km based on its topographic annulus). This new diameter also narrows the gap between it and Artemis Corona, the largest on Venus, to only 630 km. Three major radiating graben swarms were identified, extending >700–1000 km from their sources within the central annulus. From cross-cutting relationships, we interpreted that the major radiating swarms formed first, upon initial plume arrival and flattening against the base of the lithosphere. The circumferential swarms followed, starting with the innermost ring, migrating with the leading edge of the plume head as it spread outward against the base of the lithosphere. The distinctive annular ridge/trough system (at about 500 km radius) is associated with the transition between plume head arrival and spreading. The centers of most of the radiating and circumferential swarms are aligned along a NNW-SSE trend that is interpreted to represent an underlying zone of lithospheric weakness. Additional graben-fissure systems in the study area are not associated with Heng-o Corona; some are linked with other magmatic centers nearly up to 1000 km outside the study area.