Volcanic history of the Derceto Corona, Astkhik Planum, Venus

Abstract:

Detailed mapping of a major-scale volcanic centre on Venus provides a complementary view to that of terrestrial large igneous provinces (LIPs): on Venus, the surface flood basalt relationships are preserved owing to the absence of erosion, but the plumbing system is only indirectly revealed. Herein we report on detailed mapping of the southern portion of the major Derceto Corona (DC) volcanic event located in southern Astkhik Planum (our map area: 1,920,000 km²) using full resolution (75 m/pixel) Magellan SAR images.

Thirty-seven distinct lava flow units together with those associated with grabens were mapped and grouped into eight main and multiple minor volcanic stages. On the east side of DC, the Eastern Stage flows extend for 750 km and are fed from NNW-NW-trending grabens (overlying dykes) and from more local (small shield) sources. The Kallistos-Ubastet Stage consists of the 1200 km long Kallistos Vallis and its flow field containing the overflow Ubastet Fluctus pulse, are all fed from an irregular chamber 30 x 10 km long on the south side of DC. Lavas of both the Eastern Stage and the Kallistos-Ubastet Stage flowed over a section of Vaidilute Rupes (escarpment) and spread out on its eastern side. A Western Stage flow field (>1000 km long) was sourced from the elliptical fracture system of DC; after flowing downslope it swings almost 180 degrees to follow a pre-existing rift, Hanghepiwi Chasma. On the north side of DC, a laterally propagating NE-trending graben set (overlying a dyke swarm) produces a 90 km long and 5 km wide “Great Dyke” that feeds a flow field.

Two flow stages (Western Stage-1 and the Great Dyke/NE-trending dyke swarms) are inferred to be fed from the elliptical-shaped down-sag caldera collapse of DC. The Eastern Stage flows are fed mostly from a region to the east of the corona, whereas the rest of the flows are fed via an older regional NW-trending graben system that was reused for magma transport from underlying chambers or laterally from the collapse of the central chamber. The total areal extent of the flows is 534,650 km² with an inferred volume of 26,730 km³ (assuming an average flow thickness of 50 m); this is consistent with LIP-scale area and also with LIP-scale volume if the expected underlying plumbing system was catalogued.