THE EFFECTS OF GLASS CRYSTALLINITY AND ERUPTION STYLE ON VISIBLE/NEAR-INFRARED AND THERMAL-INFRARED SPECTRA OF VOLCANIC TEPHRA

Sedimentary deposits containing iron-bearing glass have been identified on both the Moon and Mars using orbital spectroscopy, and some of these deposits are interpreted as resulting from explosive volcanism. However, the role of volatiles in these eruptions is unknown. On Earth, slower cooling during Strombolian or Plinian eruptions allows more mineral crystallization; while explosive volcanism related to near-surface ice or water can quickly quench lava, creating higher abundances of glass. Distinguishing different eruption styles on other planets from orbit can be difficult; therefore in this study we examine whether or not is it possible to determine eruption style using orbital spectroscopy of glassy volcanic tephras.

Wall et al. (2014) used X-ray diffraction of samples from 17 different eruptions with variable styles to determine tephra crystallinities. A change in crystallinity results from the rate of cooling of magmatic material. They found that crystallinity measurements can be used to distinguish different eruption styles on Earth. In this study, we acquired visible/near-infrared (VNIR) and thermal-infrared (TIR) spectra of all previously analyzed tephra samples from Wall et al. (2014), which are analogous to measurements taken by planetary orbital spectrometers such as the Moon Mineralogy Mapper and Diviner at the Moon and CRISM, OMEGA, and TES at Mars. Spectra were collected of the tephra samples as a whole rock, a sieved loose sample, and a compressed pellet. Preliminary VNIR results indicate that there are observable spectral trends related to groundmass crystallinity in the VNIR. Deconvolution of TIR spectra with igneous spectral libraries will allow us to determine the glass composition and content of all samples, which will also provide a secondary estimate of crystallinity. These results could help us identify locations of ice-magma interactions on Mars, and to better understand crystallinity variations in pyroclastic deposits on the Moon related to eruption column density. Further analysis of the relationship between eruption styles and mineralogy may lead to more detailed differentiation of planetary volcanic deposits.