Compositional gradients across mare-highland contacts: Importance and geological implication of lateral transport

Observations of mixing across mare-highland contacts using high-resolution Clementine data allow a new assessment of the relative importance of vertic al versus lateral mass transport on the Moon at least at mare-highland cont act. We analyze mare-highland contacts in the Grimaldi, Orientale, and Fecu nditatis basins and Tsiolkovsky crater through image-based nonlinear spectr al mixture modeling of Clementine ultraviolet-visible (UV-VIS) light spectr ometer multispectral data. The mare in these regions differ in ages, but th ey are characterized by having simple geological contacts. The symmetric di stribution of mare and highland soil constituents across their geological c ontact indicates that lateral transport is more efficient than deep vertica l transport during the formation of the observed mixing zones. Observations across the lunar limb with the Clementine UV-VIS filters show that there i s a stray light component of scattered light across high-contrast albedo bo undaries. However, the magnitude and spatial properties of scattered light do not significantly affect the nature of compositional boundaries determin ed here. Since repetitive meteorite bombardment governs lateral transport a cross the geological contacts and is a random process, a stochastic model i s developed to describe this lateral transport. Analysis of the power decay law for crater ejecta thickness indicates that the high-velocity ejecta tr avels long distances and follows a -3 power decay law. This results in an i nfinite variance, which requires an anomalous diffusion model since a class ical diffusion model would be invalid. Mathematical modeling supports this result where it is shown that classical diffusion produces a relatively poo r fit to profiles of material abundance, while the anomalous diffusion mode l fits the profiles adequately. These results indicate that high-velocity e jecta dominates the formation of the observed compositional gradients, whil e the ejecta near the crater rim is relatively less important. On the basis of these ejects distributions and the assumption of random impact craterin g, we derive a relationship that can be used as an index for relative age d ating of geological contracts as well as for investigating cratering rates.