The Nature of the Mars Pathfinder "Black Rock" Lithology: Comparisons with SNC Meteorites and OMEGA spectral images of Chryse Planitia

The initial interpretation of the Mars Pathfinder landing site was that it was covered with a single rock type, the "gray rock" spectral class that had variable levels and types of dust coatings. Re-analysis of the Imager for Mars Pathfinder (IMP) SuperPan indicated several occurrences in the near field of pebbles and cobbles of the distinctly different "black rock" spectral class.Where the gray rock spectra were characterized by a weak-to-Nonexistent long wavelength absorption, the black rock spectra had a strong absorption centered at, or longwards of 970 nm. In this paper, black rock spectra from the IMP SuperPan are compared with spectra of SNC meteorites and with OMEGA derived spectra from regions surrounding the MPF landing site in, and near Ares Vallis and in Chryse Planitia. A number of new occurrences of the black rock spectral class have recently been observed in supervised classifications of the SuperPan using a self organizing map artificial neural network approach. Spectra from these identifications, as well as previously recognized black rock occurrences were compared with SNC meteorite spectra. Comparisons were performed using spectral feature fits to the long wavelength absorption, overall spectral comparisons using a spectral angle metric, and comparisons on plots of spectral parameters such as 930 nm band depth and 754 to 1003 nm slope. Wheras there was not one single best match, several meteorites were found to have the most similar spectral character based on the metrics that were applied. These spectrally similar meteorites included olivine-phyric shergottites ALH 77005, EET 79001 lithology A, and Dar al Gani 735 (DaG 735). A paired specimen (DaG 476) of the latter meteorite has recently been noted as a good match to the thermal infrared spectrum of a region in Chryse with a unique spectral character. However, OMEGA derived spectra of this region appear more olivine-rich than DaG 735. More OMEGA derived spectral units from Chryse and Ares Vallis will be compared with the black rock spectra and compared in turn against SNC meteorite spectra in order to present likely candidates for the source region and mineralogic nature of the black rock spectral class.