^1,2,3Erica R. Jawin, ¹Sebastien Besse,⁴Lisa R. Gaddis,⁵Jessica M. Sunshine,³James W. Head, ¹Sara Mazrouei
¹European Space Research and Technology Center, Noordwijk, Netherlands.
²Department of Astronomy, Mount Holyoke College, 50 College Street, South
Hadley, MA 01075, USA.
³Department of Earth, Environmental, and Planetary Sciences, Brown University,
Providence, Rhode Island, USA.
⁴USGS Astrogeology Science Center, Flagstaff, Arizona, USA.
⁵Department of Astronomy, University of Maryland, College Park, Maryland, USA

The localized lunar dark mantle deposits (DMDs) in Alphonsus, J. Herschel, and Oppenheimer craters were analyzed using VIS-NIR spectroscopy data from the Moon Mineralogy Mapper. Spectra of these localized DMDs were analyzed for compositional and mineralogical variations within the deposits and were compared with nearby mare basalt units. Spectra of the three localized DMDs exhibited mafic absorption features indicating iron-rich compositions, although the DMDs were spectrally distinct from nearby mare basalts. All of the DMDs contained spectral signatures of glassy materials, suggesting the presence of volcanic glass in varying concentrations across the individual deposits. In addition, the albedo and spectral signatures were variable within the Alphonsus and Oppenheimer crater DMDs, suggesting variable deposit thickness and/or variations in the amount of mixing with the local substrate. Two previously unidentified localized DMDs were discovered to the northeast of Oppenheimer crater. The identification of high concentrations of volcanic glass in multiple localized DMDs in different locations suggests that the distribution of volcanic glass across the lunar surface is much more widespread than has been previously documented. The presence of volcanic glass implies an explosive, vulcanian eruption style for localized DMDs, as this allows volcanic glass to rapidly quench, inhibiting crystallization, compared to the larger hawaiian-style eruptions typical of regional DMD emplacement where black beads indicate a higher degree of crystallization. Improved understanding of the local and global distribution of volcanic glass in lunar DMDs will further constrain lunar degassing and compositional evolution throughout lunar volcanic history.

Reference
Jawin ER, Besse S, LR Gaddis, Sunshine JM, Head JW, Mazrouei S (2015) Examining spectral variations in localized lunar dark mantle deposits. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004759]

Published by arrangement with John Wiley and Sons