Age of rifting and associated volcanism in Atla Regio, Venus

Abstract

An estimation of the age of rifting and associated volcanism in Atla Regio is carried out based on photogeologic analyses of the stratigraphic relationships between rift‐associated features and impact craters which have associated radar‐dark paraboloids. The paraboloids are believed to be thin mantles of debris derived from the fallout of crater ejecta, and their “parent” craters are considered to be among the youngest 10% of Venus' crater population [Campbell et al., 1992]. In the area under study, there are three impact craters with associated dark paraboloids: 1) Von Schuurman, which is clearly superimposed on the Dali Chasma Rift; 2) Sitwell, which is superimposed on Ganis Chasma and may have been followed by subsequent rift‐associated fracturing; and 3) Luxemburg, which is superimposed on lavas from Ozza Mons and dissected by Dali Chasma fractures which, in turn, are covered by lavas from Maat Mons. This means that at least the last stages of tectonic and volcanic rift‐associated activity in Atla Regio are contemporaneous with the formation of impact craters which are young enough to preserve the associated dark paraboloids. If these craters represent the youngest 10% of the Venus crater population, and the average age of the venusian surface is about 500 m.y. [Schaber et al., 1992], this means that rifting and rift‐associated volcanism in Atla Regio were active as recently as during the last ∼50 m.y. In the current debate over models of Venus resurfacing the results of our study favor the equilibrium resurfacing model [Phillips et al., 1992].