GEOLOGIC MAP OF THE CALORIS BASIN, MERCURY

The largest impact basin on Mercury, the 1,550km diameter Caloris basin, is a highly complex geologic landform. The basin is floored by a spectrally distinct, high-reflectance volcanic plains unit emplaced post-impact, that covers a low-reflectance impact melt unit at least 7.5-8.5km thick [1]. In addition, several spectrally distinct pyroclastic vents have been identified within the basin [2]. Surrounding the basin are various ejecta units, which include the Odin Formation, a knobby plains unit that is stratigraphically and morphologically consistent as being Caloris ejecta but has the lowest crater size-frequency of any of the units associated with Caloris emplacement [3]. While the knobs are thought to be Caloris ejecta blocks, the dark, smooth volcanic plains interfingering them have been interpreted to be younger than those flooring Caloris, implying a second plains emplacement event possibly involving lower albedo volcanic material. In addition, the Odin Formation shows two distinct sub-units. The bright sub-unit, which contains fewer and fresher craters, might represent a younger volcanic flow while the dark sub-unit, which has a higher concentration of knobs, might represent Caloris ejecta. Geologic maps are useful tools in compiling geologic data into a single, accessible data source. Previous work by Mariner 10 geologic mappers covered roughly 1/3 of the basin, leaving 2/3 of the basin unmapped. We created a high-resolution geologic map of the Caloris basin using recently acquired MESSENGER data, with the goal of synthesizing the results of these previous studies into a contextual framework for ease of access. If possible, we plan on integrating our detailed Caloris map into the Mercury global geologic map currently under construction.

References: [1] Ernst et al. (2015) Icarus, 250, 413-429. [2] Goudge (2014) J. Geophys. Res. Planets, 119, 635-658. [3] Denevi et al. (2013) JGR, 118, doi:10.1002/jgre.20075.