Characterization of Hydrothermal Alteration in Palagonitized Deposits Using Short-Wave Infrared Spectroscopy and X-Ray Diffraction Methods

Abstract

Abstract In this contribution, we evaluate the applicability of short-wave infrared spectroscopy to characterizing mineral assemblages in palagonitized glaciovolcanic edifices at Cracked Mountain, a basaltic volcano within the Garibaldi Volcanic Belt, and Kima Kho, a basaltic tuya within the Northern Cordilleran Volcanic Province. Second-order evaluation of the approach was established through comparison with data obtained by semi-empirical X-ray diffraction methods. Reflectance spectra show an increase in the depth of water and hydroxyl bands in samples with increasing amounts of hydrated minerals and decreasing amounts of amorphous materials (as determined through X-ray diffraction), indicating that the relative strengths of H2O- and OH-related absorption features may be used as a proxy for the degree of palagonite alteration (hydrated minerals crystallized from basaltic glass). In addition, the full width at half maximum of the OH- and H2O-related absorption bands decreased with the formation of zeolites, indicating that the full width at half maximum of OH- and H2O-related features may be used to estimate the degree of crystallinity across the progressive palagonitization process. Finally, short-wave infrared spectroscopy revealed a decrease in band depth of water-related absorption features with no change in the full width at half maximum along the devitrification or alteration process that converts analcime to chabazite to wairakite, indicating that spectroscopy may be used to identify the final dehydration and cementation stages of palagonitization. Results show that the short-wave infrared spectroscopy method is more robust in identifying poorly crystalline hydrated samples, while X-ray diffraction methods are better suited to understanding the crystalline components of palagonite. Short-wave infrared spectroscopy is a remote sensing technique that has proven to successfully characterize the state of H2O in hydrated clay-rich material and thus may serve as an invaluable tool in identifying stages of palagonitization not only on subglacial edifices on Earth but also on off-planet environs, including the Martian surface.