ANCIENT VOLCANIC RESURFACING ON MERCURY?: ANALYSIS OF THE FORMATION OF THE INTERCRATER PLAINS

The intercrater plains are the oldest and most extensive geologic unit on Mercury, first identified in Mariner 10 data. Data collected by the MESSENGER mission provided more information about the intercrater plains, including their morphology, and mineral and chemical composition. These plains have been interpreted as volcanic in origin, but the high impact velocity at Mercury allows for the production of large quantities of impact melt, which may have contributed to more local resurfacing. Due to the variable morphology and color signature of the intercrater plains a combination of resurfacing from volcanic and impact processes is possible.

Here, we investigate the relative contribution of volcanic and impact processes in the formation of the intercrater plains through production of a 1:5M USGS map of the Derain quadrangle (H-10). The Derain quadrangle contains, on average, a more mature surface with few extensive smooth plains deposits or nearby large, recent impact basins; it represents an extensive area of “typical” intercrater plains. The smooth plains deposits are mapped at 1:2.5M and their distribution and color properties are analyzed to determine whether they could plausibly be related to any impact events. Redder spectral slopes in MDIS data are more consistent with volcanic plains, while bluer slopes are associated with basin impact melts. Thus far, the distribution of the smooth plains does not indicate that any of these materials were emplaced during large impact events. The presence of embayed and buried craters within smooth plains will be reported at the meeting to assess depths of smooth plains and provide evidence in support of a volcanic origin. Boundaries between smooth plains and intercrater plains are assessed to determine whether they are gradational and show a transition of smooth plains to intercrater plains through impact degradation or whether the boundaries are more abrupt and signal embayment of intercrater plains by smooth plains. These relationships provide a relative stratigraphy that will be used to further assess the origin of the mapped smooth plains materials. Variations in the intercrater plains morphologies are mapped and these subdivisions are informed by variations in areal crater density.