Lithospheric Extension on Venus: how to form narrow rifts

Abstract

The Venusian rifts of Devana and Ganis Chasmata have been noted for their similar morphology to some rifts on Earth (i.e., the East African rift system). These are narrow rifts that are associated with localized deformation. This thesis aims to explore the link between lithospheric structure and rift style using a force analysis model, following previous work by Buck (1991), in order to determine under what conditions narrow rifts are predicted for Venus conditions. Results for two cases, one using a constant lithospheric thermal conductivity and another using a depth dependent thermal conductivity, are initially determined; Devana and Ganis Chasmata are predicted to be wide rifts rather than narrow rifts. Lithospheric weakening mechanisms (rheological weakening and diking) are implemented to determine their effect on localizing deformation and, thus, forming narrow rifts. Diking did not produce any effect on forming narrow rifts. Rheological weakening, likely due to a combination of melt and a transition to grain size sensitive creep, appears necessary to produce narrow rifts.