FORMATION OF THE SATURNALIA FOSSAE GRABEN AND HALF-GRABEN, AND ADJACENT STRUCTURES, BY IMPACT-RELATED PROCESSES ON VESTA

Vesta is a unique, intermediate class of rocky body, between terrestrial planets and small asteroids, because of its size (average diameter of ~526 km) and differentiation into a crust, mantle and core (Russell et al., 2012). Impact cratering and impact-related processes are prevalent (e.g. Jaumann et al., 2012), because Vesta lacks a protective atmosphere. Previous work has shown that formation of the Rheasilvia impact basin induced the equatorial Divalia Fossae, whereas formation of the Veneneia impact basin induced the northern Saturnalia Fossae (Buczkowski et al., 2012; Bowling et al., 2013). We expand upon this work through photogeologic mapping of the Saturnalia Fossae and adjacent structures. Our work indicates that impact processes created and/ or modified all of the mapped structures (Scully et al., 2014). We find that the Saturnalia Fossae consist of five separate structures. Saturnalia Fossa A is the largest, with a maximum width of ~43 km and average depth of ~6.75 km. Fossa A is interpreted as a graben. Saturnalia Fossae B-E have maximum widths of ~15 km and average depths of ~2.5 km. Fossae B-E are interpreted as half graben formed by synthetic faults. We classify second-order, adjacent structures, with maximum widths of <1 km, as minor ridges, grooves and crater chains. Minor ridges have an average height of ~70 m and grooves and crater chains have an average depth of ~14.5 m. We propose that shear deformation, resulting from the Rheasilvia impact, formed the first subset of adjacent structures. In this case, we interpret minor ridges as the surface expression of thrust faults, and grooves and pit crater chains as the surface expression of extension fractures and/ or dilational normal faults. We further propose that ejection of secondary crater material formed a second subset of adjacent structures. Here, we interpret that bouncing and scouring of material ejected from impacts formed ejecta ray systems of grooves and crater chains. Finally, we interpret that impacted-induced seismic shaking formed the third subset of adjacent structures. In this case, seismic shaking induced flow of regolith, which subsequently accumulated under the control of the regional slope to form minor ridges. In this work we present findings on the expression of impact-related processes on this unique, intermediate solar system body.