Select problems in planetary structural Geology: Global-scale tectonics on Io, regional-scale kinematics on Venus, and local-scale field analyses on Earth with application to Mars

Abstract

Io's mountains are cataloged in order to investigate their formation. Of the 101 mountains imaged with sufficient coverage and resolution for further analysis, 4 are volcanoes, and 97 are tectonic massifs. Of the 97 tectonic mountains, ≥40 abut paterae (volcanic or volcano-tectonic depressions). This juxtaposition is unlikely to be coincidental as the probability of it occurring by chance is ∼1.08%. The observed mountain-patera association may be due to orogenic faults acting as conduits for magma ascent, thus fueling patera formation near mountains. As resurfacing buries a shell of material from Io's surface to the base of the lithosphere, its effective radius is reduced and it heats up. The volume change due to subsidence and thermal expansion is calculated as a function of lithospheric thickness. Conservation of volume dictates that this material is uplifted at Io's surface. By estimating the total volume of mountains, Io's average lithospheric thickness is constrained to ≥12 km. A kinematic analysis of Nefertiti Corona, Venus, reveals that the corona's interior moved east as a relatively coherent thrust sheet with most deformation occurring on the distal margin. Additionally, an en-echelon array indicates a history of semi-brittle deformation on the northern side of Nefertiti's tectonic annulus. Regional heating from the thermal diapir that formed Nefertiti probably reduced the crustal viscosity and enabled the semi-brittle deformation. The "Odessa Craters" in the Channeled Scabland of eastern Washington State are basaltic ring structures (BRSs) 50-500 m in diameter that are comprised of discontinuous, concentric outcrops of subvertically-jointed basalt and autointrusive basaltic dikes. It is postulated that they formed as follows: phreatovolcanic activity disrupted a relatively thin, active lava flow forming rootless cones; the lava flow inflated around the cones; tensile stresses caused concentric fracturing; dikes exploited the fractures and fed lava to the surface; and subsequent erosive floods excavated the structures. A second population of BRSs near Tokio Station, WA, are morphologically analogous to quasi-circular structures in Athabasca Valles, Mars (a region that is geologically similar to the Channeled Scabland). If the martian features formed as BRSs, then they indicate local water-lava interactions and at least two floods through Athabasca Valles.