Image: Journal of Structural Geology: "Structural relationships in and around the Rheasilvia basin on Vesta" Authors: Hiu Ching Jupiter Cheng and Dr. Christian Klimczak (Department of Geology, Structural Geology and Geomechanics Group, University of Georgia) Abstract The Rheasilvia basin is an impact structure occupying most of Vesta's southern hemisphere. Divalia Fossae, a set of circum-equatorial troughs, were previously proposed to be concentric around the basin, which is widely regarded as evidence that the Rheasilvia impact directly caused the formation of the troughs. Here, we produce a structural map of Rheasilvia that allows for geologic interpretations and quantitative analyses of structure orientations and densities. We mapped basin-bounding scarps, scarps within the basin, ridges, and undefined lineaments. Scarps abound near the basin rim, with ridges being densely located on the basin floor near the central mound, forming a spiral pattern. This pattern is well-preserved on the basin floor except in the area superposing the older Veneneia basin, indicating that pre-existing Veneneia structures substantially influenced those of Rheasilvia. This implies that the lithosphere must have remained highly shattered after the Veneneia impact until Rheasilvia was emplaced. The Divalia Fossae cross-cut the Rheasilvia basin, and reanalysis of the geometric relationship between both landforms reveals that the troughs are not concentric around the basin center. These results are inconsistent with the previous hypothesis of trough formation and require a reconsideration of Vesta's tectonic history. Highlights - Ridges, scarps, and lineaments of the Rheasilvia basin were mapped in detail. - Basin structures form a spiral pattern only in areas that do not superpose Veneneia. - Pre-existing Veneneia structures had a major influence on Rheasilvia structures. - Divalia Fossae crosscut the Rheasilvia basin-bounding scarps and floor. - Divalia Fossae lack a well-defined geographic relationship with the basin. Fig. 1. Overview map of the Rheasilvia and Veneneia basins displayed as hillshade generated from the Dawn Digital Terrain Model (DTM; Preusker et al., 2016) with the solar azimuth of 56°E and incidence angle of 45°, color-coded by elevation in south polar stereographic projection. Fig. 2. Hillshade maps of Rheasilvia Basin generated from the Dawn Digital Terrain Model (DTM) with four azimuths (the angular directions of the sun) and a fixed solar incidence angle of 45°. Fig. 3. Identification and classification of basin structures based on FC image, hillshades, and topographic profiles with examples of mapping. Fig. 4. Structural map of the Rheasilvia basin. Read More: Read the full articel at ELSEVIER - Journal of Structural Geology
