Timing of formation of Beta Regio and its geodynamical implications

Abstract

[1] Recent evidence suggests that the Beta Regio equatorial highland, generally considered to be a plume-related structure, was emplaced over a relatively short period of time in the recent Venus history (100-400 m.y.). We perform numerical simulations which use this evidence as a new constraint on geodynamic models and find that it is difficult to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity, topography, and rheology. One possible solution is that the effective viscosity contrast between the mantle and the lithosphere does not exceed about 10 4 . If our simple models do capture the basic dynamics of formation of Beta Regio, this value implies that the viscosity of the lithosphere is softer than olivine at subsolidus temperatures and that the Venusian lithosphere may not be much stronger than the terrestrial one.

Venus astra/novae: Estimates of the absolute time duration of their activity

“…Since early analysis of the Magellan data the Beta-Atla-Themis region of Venus is known as an area where volcanic features are concentrated (e.g., Head et al, 1992;Crumpler et al, 1997). From our analysis it follows that it is also an area where recent volcanic/tectonic activity was concentrated, a finding that agrees with the earlier analyses of this region involving the dark-parabola and clear-halo craters (Basilevsky, 1993;Strom, 1993;Head, 2002, 2007;Basilevsky et al, 2003;Vezolainen et al, 2003Vezolainen et al, , 2004. The last two of the described astra are in the boundary area between Bereghinya Planitia and Ishtar Terra.…”

Laufey Regio: A newly discovered topographic rise on Venus

“…Laufey displays nine and most are of a small to medium size (70–150 km) similar to those at western Eistla. Small‐scale rifting is present at each rise, but is typically associated with a single edifice, rather than the whole region, as seen at Atla [ Senske et al , 1992] and Beta [ Campbell et al , 1984; Moore and Schubert , 1995; Vezolainen et al , 2003]. Laufey's extensional deformation is concentrated in Nang‐byon Chasma that fractures the north flank of Var Mons.…”

Uplift of Beta Regio: Three‐dimensional models

“…Third, the models were steady‐state while the interaction between the plume and the lithosphere is a time‐dependent process. Vezolainen et al [2003] addressed these issues using an additional constraint: geomorphological estimates of the uplift time of Beta Regio. It turned out that it was difficult to obtain a fast uplift of Beta Regio suggested by the new constraints; it takes a long time to heat up a ∼400 km thick Venusian lithosphere.…”

“…It turned out that it was difficult to obtain a fast uplift of Beta Regio suggested by the new constraints; it takes a long time to heat up a ∼400 km thick Venusian lithosphere. As one of the possible solutions, Vezolainen et al [2003] proposed that the lithosphere has to be nearly as weak as on Earth. In this case the uplift is facilitated by the lithospheric flow.…”

“…In this case the uplift is facilitated by the lithospheric flow. Although Vezolainen et al 's [2003] model satisfies constraints on gravity and topography anomalies as well as the uplift rate, it is inconsistent with the laboratory constraints on the rheology of mantle minerals [ Karato and Wu , 1993] and with the high strength of the Venusian crust [ Mackwell et al , 1998]. In addition, a weak lithosphere seems to be inconsistent with the models of degassing history of Venus [ Franck and Bounama , 2003].…”