Giant circumferential graben-fissure systems: A key to the recognition of Venusian corona analogues on Earth

English Abstract:

Coronae are sub-circular tectono-magmatic structures on Venus, which typically have a raised annulus (up to c. 5 km in relief) and variable interior and exterior topography that allow division into a number of sub-types. The annulus is typically associated with a circumferential graben-fissure system and minor ridges. Graben-fissure systems are potentially linked to underlying dykes. Corona diameters are typically 200-300 km, but diameters up to >1000 km (and in the case of Artemis, 2600 km) are observed.

On Earth, several circumferential dyke swarms which are hundreds of kilometres in diameter have been recognized and are considered to be potential corona analogues (Ernst & Buchan, 1998, LPSC XXIX; Mäkitie et al., 2014, J. Afr. E. Sci.; Ernst et al., 2014, GSA Ann. Mtg.; Klausen et al., 2014, GSA Ann. Mtg.; Buchan & Ernst, this conf.). We summarize the characteristics of Venusian circumferential graben-fissure systems as a predictive guide to the recognition of terrestrial corona analogues: 1) sizes are typically hundreds of kilometres in diameter but can sometimes extend beyond a thousand kilometres ; 2) circumferential systems often only partially circumscribe their related corona; 3) circumferential systems are occasionally associated with radiating graben-fissure systems, and when they are, the foci of the radiating component can be offset from the center of the circumferential component; and 4) circumferential systems can occur as clusters. In addition, it should be noted that if circumferential dyke swarms on Earth are analogues to Venusian coronae then they should have had a primary raised annulus and other related topographic features that have since been eroded, but which may be recognized from the sedimentary record.