Retrieving magma composition from TIR spectra: implications for terrestrial planets investigations

Alessandro Pisello,Gianluca Iezzi,Francesco P Vetere,Michele Lustrino,Matteo Bisolfati,Cristina Pauselli,Alessandro Maturilli,Daniele Morgavi,Diego Perugini

doi:10.1038/s41598-019-51543-9

Abstract

Emissivity and reflectance spectra have been investigated on two series of silicate glasses, having compositions belonging to alkaline and subalkaline series, covering the most common terrestrial igneous rocks. Glasses were synthesized starting from natural end-members outcropping at Vulcano Island (Aeolian Islands, Italy) and on Snake River Plain (USA). Results show that the shift of the spectra, by taking Christiansen feature (CF) as a reference point, is correlated with SiO2 content, the SCFM factor and/or the degree of polymerization state via the NBO/T and temperature. The more evolved is the composition, the more polymerized the structure, the shorter the wavelength at which CF is observable. CF shift is also dependent on temperature. The shape of the spectra discriminates alkaline character, and it is related to the evolution of Qn structural units. Vulcano alkaline series show larger amount of Q4 and Q3 species even for mafic samples compared to the subalkaline Snake River Plain series. Our results provide new and robust insights for the geochemical characterization of volcanic rocks by remote sensing, with the outlook to infer origin of magmas both on Earth as well as on terrestrial planets or rocky bodies, from emissivity and reflectance spectra.

Highlights

Emissivity and reflectance spectra have been investigated on two series of silicate glasses, having compositions belonging to alkaline and subalkaline series, covering the most common terrestrial igneous rocks
Spectral response of geologically relevant samples has been investigated in various ranges: visible (VIS), near infrared (NIR)[2,3,4], mid infrared and thermal infrared (TIR)[5,6], or for other vibrational spectroscopy techniques[7,8]
A first level characterization shows that shifting of the emissivity and reflectance spectra are readily parameterized by the silica content (SiO2 wt.%), the SCFM factor and the degree of polymerization NBO/T

Summary

Introduction

Emissivity and reflectance spectra have been investigated on two series of silicate glasses, having compositions belonging to alkaline and subalkaline series, covering the most common terrestrial igneous rocks. An important part of planetary studies is based on using spectroscopy to characterize analogue materials, in order to perform comparisons with spectroscopic data obtained with telescopic and/or in situ methods On this concern, spectral response of geologically relevant samples has been investigated in various ranges: visible (VIS), near infrared (NIR)[2,3,4], mid infrared (mid-IR) and thermal infrared (TIR)[5,6], or for other vibrational spectroscopy techniques[7,8]. No study exists focusing on glass as a proxy for magmatic bodies on planetary surfaces, especially for what concerns variation of spectral response of silicate glasses with evolving compositions (from mafic to silicic) or between different magmatic series (from subalkaline to alkaline). We focus on the TIR region, in particular for what concerns the wavelength range from 7 to 14 μm, with the aim to identify possible systematic variations that might be used to in depth interpretation of spectroscopic data

Methods

Results

Discussion

Conclusion