UNDERSTANDING EARLY VOLCANISM ON THE TERRESTRIAL PLANETS: COMPARISON OF LUNAR CRYPTOMARE DEPOSITS AND INTERCRATER PLAINS ON MERCURY

Volcanism is a process that can be identified on all of the terrestrial planets. The Moon and Mercury are better able to preserve their most ancient deposits because of their lack of plate tectonics and fluvial and aeolian erosional processes. Knowing the areal extent and spatial distribution of ancient volcanic deposits can aid in our understanding of the thermal history of a planetary body. However, before their spatial extent can be mapped, it is necessary to establish identification criteria in order to distinguish them from non-volcanic plains, such as the lunar light smooth plains deposits formed by impact processes. Studies of the lunar cryptomaria deposits and intercrater plains on Mercury can help to understand and distinguish among the different types of plains units. One important step to understanding the distribution of ancient volcanic deposits is quantifying how ancient terrains fill with volcanic material. Artificial flooding experiments using Lunar Orbiter Laser Altimeter (LOLA) topography data have been conducted on the Moon in heavily cratered terrain and a large basin to determine how they might fill with volcanic material. Map patterns and areal and volume measurements are compared with observed deposits on the Moon and Mercury. Additionally, the Schiller-Schickard region on the Moon represents a lunar analog of the types of stratigraphic relationships possibly present in the intercrater plains on Mercury, because it contains smooth ejecta deposits, maria, and cryptomare deposits. The intercrater plains are among the most heavily cratered terrain on Mercury and are thought to represent an areally substantial series of volcanic resurfacing events. However, some areas mapped as intercrater plains may not have been part of these events and may be impact deposits. Lunar cryptomare identified in the Schiller-Schickard region have likely been formed by Orientale basin ejecta and illustrate relations between volcanic smooth plains and impact-related plains material. Understanding the relationship between these two types of lunar plains materials will aid in understanding the formation of intercrater plains deposits on Mercury.