Mapping and modeling of radial fracture patterns on Venus

Abstract

Synthetic aperture radar images indicate numerous radial fracture systems on Venus. The formation of these systems has been attributed either to surface deformation related to subsurface dike emplacement or to fracturing caused by domical uplift above an ascending magma plume. We evaluate the dike emplacement hypothesis by investigating the relationship between the process of subsurface dike emplacement and the geometric attributes of radial fracture patterns, assuming the surface fracture patterns correspond to the patterns of dikes about a magma chamber below the volcanic summit. We select a radial fracture system for mapping and model its formation using a two‐dimensional analysis which idealizes the chamber as a pressurized hole in an elastic plate subject to a remote biaxial stress field. Radial fractures correspond to maximum principal stress trajectories, and the pattern of these trajectories is controlled primarily by four variables: the chamber radius, the magma pressure, the remote differential stress, and the remote principal stress direction. We find that stress trajectories also depend on the remote mean stress and that the location of isotropic points in the trajectory pattern can be used to interpret the mean stress state. These models are used to estimate the remote loading conditions under which dikes were emplaced. The mapped fracture pattern is consistent with dikes emplaced under remote differential stress conditions ranging from 2 to 8 MPa, calculated over a range of possible emplacement depths from 1 to 9 km. This is consistent with regional stress states on Earth.