Characterization of Altered and Minimally Altered Basaltic Glasses Using Visible-thermal Infrared Spectroscopy, X-ray Diffraction, and Raman Spectroscopy

Introduction: The exploration of the Martian surface by the rovers Spirit, Opportunity, and Curiosity has indicated the widespread presence of clastic rocks of basaltic composition [1-3], many of which have altered to various extents. In this investigation, we have examined basaltic ash and tephra formed through hy-drovolcanism (the explosive interaction of magma with liquid water), glaciovolcanism (eruptions occurring below ice sheets), and impact processes (at the Lonar Crater in India [4-5]). We have utilized several analysis techniques available to the Mars Exploration Rovers and the Mars Science Laboratory rover. In particular, we have focused on VNIR reflectance and TIR emit-tance spectroscopy. We have performed standard thin section petrography and have utilized supporting X-ray diffraction (XRD) and Raman spectroscopy measurements. Alteration: Alteration of basaltic glass can occur under ambient temperatures over long time spans through the process of pedogenesis [6]. Alteration may occur more rapidly through hydrothermal alteration or nearly syndepositionally through deposition with steam in the case of hydro-or glaciovolcanism [7]. Basaltic glass can also alter through burial diagenesis [8], although examples of this alteration pathway were not examined in this study. The hydrated and oxidized alteration product of basaltic glass is palagonite. Palago-nite is recognized in all of these alteration pathways; however, the extent to which the glass is palagonitized in the latter alteration pathways led Schiffman et al. [6] to deem this form of alteration " palagonitic alteration ". Field Areas: We conducted field work at several hydrovolcanic eruption sites in Idaho, New Mexico, and Utah. Samples were collected by team members in past projects from glaciovolcanic sites in Washington state and Iceland. One of our team has also conducted extensive field work at Lonar Crater [e.g., 5]. Several sample of ambiently weathered basaltic ash collected by one of us from the summit of the Haleakala volcano were also examined. Analysis: Thin sections were made of a number of field samples for optical petrography. Powdered samples (ground to less than a 400 m mesh size) were sent to the RELAB facility at Brown University to have their 0.3 – 2.6 m bidirectional and 0.83 – 25 m bi-conical reflectance measured. MWIR emissivity of a number of samples was measured at Arizona State University, Stony Brook University, and the Southwest Research Institute. XRD analysis of samples was conducted at Auburn University and Raman spectroscopic analysis of several samples was conducted at the Ge-omicrobiology Laboratory at the University of Colora-do …