MINERAL ASSEMBLAGES AND SPECTRAL SIGNATURES OF ALTERED LACUSTRINE PILLOW BASALTS: A NORTHEASTERN U.S. ANALOG FOR LAVA-WATER INTERACTIONS ON MARS

Past interactions between lavas and water on Mars are hypothesized to have occurred, but the criteria through which these interactions can be recognized from orbital remote sensing are not fully defined. Studies of terrestrial analogs can connect remote sensing signatures of aqueous alteration with the mineral assemblages and processes through which the assemblages formed. Early Jurassic Talcott Formation basalts in the Hartford Basin were emplaced within a lake, and the resulting pillow lavas were hydrothermally altered. We are investigating the mineral assemblages formed through lava-water interactions and their spectral signatures at an outcrop of these basalts and the underlying New Haven Formation sediments in Meriden, CT.

Ten samples were imaged in the laboratory at Headwall Photonics with hyperspectral imagers from 400-1000 and 950-2500 nm to understand finer-scale changes in mineralogy and spectral signatures with alteration. Outcrops of sediments and altered basalts were imaged in the field with Channel Systems hyperspectral imagers covering 420-720 and 650-1100 nm. Spectra of points on the outcrop and samples were measured with an ASD spectrometer. Laboratory analyses are ongoing to characterize mineralogy and chemistry.

Analyses of alteration rinds on basalts show changes in mineralogy and spectral signatures with increasing interaction with water. Spectra of the least altered portions of samples retain much of the original mafic signatures. Less altered samples at the base of the basalts often have Fe oxide and carbonate or clay coatings. Higher in the stratigraphy, samples appear more altered, generally with green rinds of Fe/Mg clays such as chlorite or smectite. Infrared spectra show changes from exterior to interior of the rinds such as weakening of the Fe/Mg-OH combination band that seem to correlate with the degree of interaction with water. Calcite is present throughout, and prehnite is identified higher in the section with the greener alteration. Imaging of the outcrop discriminates different units including unaltered, redder (less altered), and greener (more altered) zones as well as amygdules and veins filled with secondary minerals. Hyperspectral imaging could be used to recognize similar lava-water interactions on Mars based on the spectrally-detectable changes in mineralogy.