Postimpact modification by volcanic or tectonic processes as the rule, not the exception, for Venusian craters

Abstract

[1] We present three investigations that use the Venusian impact crater population to constrain the planet's resurfacing history. We evaluate stereo-derived topography for 91 Venusian craters that have a diameter (D) greater than 15 km. Craters with radar-bright floors have greater rim-floor depths and rim heights than craters with radar-dark floors. . For a 60 km crater, this represents differences of 290 m in rim-floor depth and 240 m in rim height. We interpret these results to indicate that dark-floored craters have experienced postimpact volcanic embayment and filling. We examine the population of craters with D > 20 km that have radar-dark halos surrounding their continuous ejecta (114 craters). We find that a portion of the halo has been removed for almost all dark-floored craters, consistent with our interpretation that dark-floored craters have been affected by postimpact volcanism. Finally, we assessed geologic histories of 12 large impact structures with stereo coverage. All but one of these structures has experienced postimpact volcanism or tectonic deformation, often in multiple episodes. In summary, widespread volcanic and tectonic activity occurred throughout the time period of emplacement of the crater population. Postulated resurfacing histories that consider the majority of craters to be at the top of the stratigraphic column are invalid, and the mean surface age of Venus is young (∼150 My).Citation: Herrick, R. R., and M. E. Rumpf (2011), Postimpact modification by volcanic or tectonic processes as the rule, not the exception, for Venusian craters,

Volcanically embayed craters on Venus: testing the catastrophic and equilibrium resurfacing models

“…The scarcity of obviously embayed impact craters on Venus, $ 6% of the total population (Schaber et al, , 1998, is a well-established observational fact. It strongly limits the possible variety of the modes of emplacement of the vast volcanic plains (e.g., regional plains) and leaves room only for a "delicate", Lichtenberg-type embayment, the results of which may be very difficult to see at Magellan resolution (e.g., Herrick and Rumpf, 2011).…”

The Physics of Changing Tectonic Regimes: Implications for the Temporal Evolution of Mantle Convection and the Thermal History of Venus

“…The total time scale of thermal equilibrium from cessation of the final yielding event is ~ 9 overturn times, or O (1) Gyr. This globally distributed volcanism may contribute to the partial volcanic flooding of crater floors that is observed at many large craters on Venus (Herrick & Rumpf, ). The globally distributed nature of this flooding is inconsistent with mantle plume volcanism, which is localized in a small number of regions such as Beta Regio (Kiefer & Hager, ), but it is well explained by the diffuse, globally distributed volcanism in the latter stages of the model described in this paper.…”

Venus: Interpreting the spatial distribution of volcanically modified craters

“…The floors of these craters have low radar backscatter relative to their ejecta blankets and rims—they thus resemble the volcanic plains. Neither impact melting nor eolian processes fully account for their morphological differences with the bright‐floored craters, which appear truly pristine [ Wichman , ; Herrick and Sharpton , ; Herrick and Rumpf , ]. In particular, dark‐floored craters have systematically shallower rim‐floor depths and rim heights than bright‐floored craters, implying partial filling of these craters and flooding of their surroundings.…”