The mineralogy of late stage lunar volcanism as observed by the Moon Mineralogy Mapper on Chandrayaan‐1

摘要

The last major phases of lunar volcanism produced spectrally unique high‐titanium basalts on the western nearside of the Moon. The Moon Mineralogy Mapper (M~3) on Chandrayaan‐1 has provided detailed measurements of these basalts at spatial and spectral resolutions necessary for mineralogical interpretation and mapping of distinct compositional units. The M~3 imaging spectrometer acquired data in 85 spectral bands from ～430 to 3000 nm at 140 to 280 m/pixel in its global mapping mode during the first half of 2009. Reflectance data of several key sites in the western maria were also acquired at higher spatial and spectral resolutions using M~3’s target mode, prior to the end of the Chandrayaan‐1 mission. These new observations confirm that both fresh craters and mare soils within the western high‐Ti basalts display strong 1 μm and weak 2 μm absorptions consistent with olivine‐rich basaltic compositions. The inferred abundance of olivine is observed to correlate with stratigraphic sequence across different mare regions and absolute ages. The apparent stratigraphic evolution and Fe‐rich compositions of these basalts as a whole suggest an origin from evolved residual melts rather than through the assimilation of more primitive olivine‐rich sources. Mare deposits with spectral properties similar to these late stage high‐Ti basalts appear to be very limited outside the Procellarum‐Imbrium region of the Moon and, where present, appear to occur as small areas of late stage regional volcanism. Detailed analyses of these new data and supporting measurements are in progress to provide further constraints on the mineralogy, olivine abundance, and compositions of these final products of lunar volcanism and the nature and evolution of their source regions.