Graben-fissure systems in the Mead Quadrangle, Venus

English Abstract:

Detailed mapping of graben-fissure systems (the surface expressions of underlying dyke swarms) in a portion (10°-20° N, 30° -50° E) of the Mead Quadrangle is part of a systematic global effort to identify regional radiating systems (linked with known and cryptic magmatic centres), circumferential systems (linked with corona) and linear systems (linked with rifting).

A total of 32 different graben-fissure systems were mapped within the study area. Five are radiating systems, four of which (with maximum radii of 930, 210, 180 and 500 km) are associated with Pavlova, Didilia, Isong, and Ninmah corona, respectively. The fifth (with a maximum radius of 500 km) focusses on c. 37.1° E, 11.7° N, marked by a small edifice. An additional radiating system (1400 km in radius and spanning about 130 degrees of arc) has been identified based on converging trends from two spatially separate graben-fissure systems; its focal point (c. 39.5 ° E, 19.9°N) is not associated with any central volcanic/tectonic edifice and represents a newly-recognized cryptic magmatic center. Pavlova and Didilia coronae have graben-fissures along their annuli and these are interpreted as parts of circumferential systems. Additional systems are located on the corona annuli but these have trends that are oblique to the local trend of the annuli (neither normal nor parallel to it) and are therefore not part of radiating or circumferential systems genetically related to the coronae. Instead they are interpreted as part of older regional graben-fissure systems that are preserved in the uplifted corona annuli, but elsewhere are largely covered by lava flooding. An east-west linear system, in excess of 1800 km long and 900 km wide, is inferred to be the oldest in the study area, by the degree to which it is flooded by lavas.