EXPLORING FORMATION MODELS FOR CERES THOLI AND MONTES

Dawn Framing Camera (FC) images of Ceres surface revealed tholi and mons, i.e., positive relief features with sub-circular to irregular basal shapes, tentatively interpreted as volcanic constructs [1]. Alternative formation mechanisms, e.g., uplifting by diapirism or shallow intrusions [e.g., 2], are not excluded and would imply different geological and thermal histories. We derived local digital elevation models from FC images and found that the tholis and mons have varying height to diameter ratios and flank slopes. The largest tholus on Ceres (6°N/310°E) has a ~100 km wide base, a steep-sided dome shape with flank slopes of 10°-20°. The relatively flat top has an altitude of ~5 km relative to surrounding and is dissected by a ~E-W trending pits chain. One of the highest mons on Ceres is located at 10°S/316°E. It is characterized by a cone-shaped profile with a ~30x20 km base, reaching a high of ~5 km relative to surrounding. Flank slopes approach a concave upward shape. Associated morphologies in the region include embayment contacts. Because of the varying morphometries of the reliefs, we explore several physical models of volcanic constructs, e.g., steep-sided dome and shield volcano. Physical models are based on radially spreading viscous gravity currents with a free upper surface [e.g., 3, 4]. Testing formation scenarios will exploit recently developed methods, such as time-variable viscosity and fixed-volume models [5], and constant flow rate models [6]. We aim to provide constraints on viable emplacement mechanisms for the different reliefs. C.A. Raymond, C.T. Russell, as well as the Dawn Instrument, Operations, and Science Teams are acknowledged.

[1] Platz et al. (2015), EPSC abstract 915, vol. 10; [2] Fagents, S.A. (2003), JGR, vol. 108, E12, 5139; [3] Huppert, H. (1982), J. Fluid Mech., vol. 121, pp. 43-58; [4] Lacey et al. (1981), EPSL, vol. 54, pp. 139-143; [5] Glaze et al. (2012), LPSC abstract 1074 ; [6] Glaze et al. (2015), LPSC abstract 1326.