The timing of giant radiating dike swarm emplacement on Venus: Implications for resurfacing of the planet and its subsequent evolution

Stratigraphic study of a distributed population of 118 giant radiating dike swarms on Venus reveals that within each dike-intruded region, emplacement of the swarms occurred prior to formation of most impact craters and rifts but subsequent to that of tessera, regional plains, and most wrinkle ridges. The density of impact craters superimposed on the swarm population (1.80+/-0.57 craters/10(6) km(2)), when compared with the average global density (2.011+/-0.14 craters/10(6) km2) and the densities reported for other geologic units, is consistent with the observed stratigraphy. On the basis of these data, we conclude that the population of giant radiating swarms formed during or slightly after the waning phases of an interval of widespread volcanic resurfacing. The stresses recorded by the dike swarm population, when combined with its age and compared with the predictions of several proposed resurfacing models, best support the hypothesis that the current surface formed as a result of the catastrophic foundering of a shallow depleted mantle layer. Formation of the dike swarms through shallow magma stalling is closely linked to and sensitively dependent upon the modern configurations of both long-wavelength gravity and topography. In addition, the surface stresses recorded by the dike swarm population are similarly correlated at a global level with these same long-wavelength characteristics. We interpret the old age of the dike swarm population to mean that there has been minimal alteration of either the long-wavelength topographic expression across most of the planet or the interior processes responsible for such changes since the cratering record was reset at least several hundred million years ago.