Thrust faulting on Venus: Tectonic modeling of the Vedma Dorsa Ridge Belt

Abstract

Radar images from the Magellan mission reveal compressional ridge belts transecting several low-lying plains on Venus, including Atalanta, Vinmara, Lavinia, and Rusalka/Llorona/Vellamo Planitiae. Vedma Dorsa is an ∼1800 km long ridge belt with 0.5–1 km of relief in Llorona/Vellamo Planitiae. We analyze sections of the ridge belt that have an asymmetric topographic cross section, indicative of deep thrust faulting and shallow folding as the dominant formation mechanisms. We perform elastic dislocation and Monte Carlo tectonic modeling of thrust faulting at several locations along Vedma Dorsa to constrain the fault displacement (D), depth of faulting (z), and fault dip (θ). We find that the models are consistent with blind thrust faulting and folding as the dominant mechanism for producing Vedma, with preferred fault parameters of D ∼ 1–2 km, z ∼ 10–25 km, and θ ∼ 25–30°. The results support an upper fault tip >3 km below the surface (blind fault), and a change in dip at depth. Our preferred models and the additional fault complexities supported at each site suggest that this section of Vedma is an intermediate structure between lobate scraps and fold and thrust belts, incorporating morphometric aspects from both classifications. Observations of terrestrial fault depths and the best-fitting depth of faulting from our models lead to an estimated heat flux of 16–39 mW m−2 at the time of Vedma Dorsa's formation, consistent with formation over a cold, downwelling region of the mantle.