Geological and structural mapping of ishtar terra margins on venus : implications for crustal plateau evolution

Abstract

The origins of crustal plateaus on Venus are poorly understood. Several formation models have been proposed, including four previously explored models: downwelling, upwelling, pulsating continents, and bolide impact models; as well as a waning heat-pipe model. Key predictions which vary across models include surface deformation, marginal deformation, and the tessera-plain onlapping relationships. Addressing this problem, we perform detailed mapping of five sites along the margin of Ishtar Terra, the highland region holding Venus’s highest peak, focusing on identifying surface units and sets of deformation lineaments. This work indicates that all tessera units and associated deformations are embayed by lava plains in four out of five studied areas. Plains-forming volcanism occurs after, or outlasts, all crustal plateau tectonism, which is consistent with three models: the pulsating continents, waning heat-pipe, and upwelling models. At the fifth site, tessera units appear to be embayed by plains, but it is also possible that this boundary is a linear fault system. Deformation relationships alone are unable to test models as they show a large variance in possible deformational histories given significant radar data uncertainties. A two times higher resolution radar imagery (i.e., 40 meters/pixel) and an order of magnitude better resolution topographic map (i.e., 450 meters/pixel) will be necessary to more rigorously test models via embayment relationships and deformation patterns. Our mapping also identifies some new features, including (1) embayment of tessera fractures alone on lava plains, as well as (2) 10-20 km long and 2-5 km wide eye-pattern ridges, composed of (3) V-shape lineaments.