A VERTICAL SECTION OF DECCAN BASALTS AS A SPECTROSCOPIC AND MINERAL ASSEMBLAGE ANALOG TO PHYLLOSILICATE STRATIGRAPHIES ON MARS

On Mars, Al-phyllosilicates, specifically kaolinite and montmorillonite, occur consistently above Fe/Mg-smectite clays. One hypothesis suggests that this stratigraphy formed from intense leaching. While current remote compositional analyses of the Martian surface focus on determining the presence or absence of single minerals, the mineral assemblages could reveal more about the environments in which the surfaces formed. We have studied mineral assemblages for a section of altered Deccan flood basalts as an analog for the Al over Fe/Mg phyllosilicate sections seen on Mars. The Deccan basalts have been found to be good petrologic analog to Mars from TES data and have been extensively altered. Visible and near-infrared spectra of the basalts at the base of the profile show weak hydration but are otherwise dominated by high-Ca pyroxene. Chemical and mineralogic analyses are consistent with basalt. The saprolite above the basalt preserves the texture of the original parent rock with corestones at the bottom and zeolites (chabazite, stilbite, and heulandite) in vesicles and fractures throughout. Spectroscopically, the saprolite contains smectite clays. Zeolites are visible in spectra of the bulk samples and large particle size separates but not in smaller separates. Laboratory analyses of saprolite samples show that more mobile cations have been leached from the parent basalt and that augite and pigeonite are present in one sample, although neither is visible in spectra. The saprolite is similar to Fe/Mg-smectite clays on Mars but is more Al-rich and has stronger absorptions in the spectra. Another layer of basalt above the saprolite preserves the saprolite as a bole horizon. This basalt is similar in all analyses to the basalt at the base. A laterite caps the profile and is the most leached section, containing almost exclusively residual Al, Fe, and Ti and lower Si. Spectroscopic and mineralogic analyses show a mixture of kaolinite and hematite, consistent with other laterites in the literature and characteristic of soils leached by well-drained, oxidizing solutions on Earth. Using these Deccan samples as an analog, we are analyzing visible and infrared data of Mars to look for associations of kaolinite and hematite. We will use mineral assemblages to better understand how these kaolinite layers on Mars formed.