¹Danilo Di Genova, ¹Kai-Uwe Hess, ²Magdgdalena Oryaëlle Chevrel, ¹Donald B. Dingwell
¹Department Earth and Environmental Sciences, Ludwig-Maximilians-Universität, Theresienstrasse 41/III, 80333 München, Germany
²Departamento de Vulcanología, Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510, México D.F., Mexico

To develop Raman spectroscopy as a quantitative tool in both geosciences and planetary sciences the effect of iron oxidation state (Fe3+/Fetot) on the Raman spectra of basaltic and pantelleritic glasses has been investigated. We have used remelted pantellerite from Pantelleria Island and synthetic iron-rich basaltic glasses [from Chevrel et al. (2014)].
The Raman spectra of pantelleritic glasses reveal dramatic changes in the high wavelength region of the spectrum (800–1200 cm–1) as iron oxidation state changes. In particular the 970 cm–1 band intensity increases with increasing oxidation state of the glass (Fe3+/Fetot ratio from 0.24 to 0.83). In contrast, Raman spectra of the basaltic glasses do not show the same oxidation state sensitivity (Fe3+/Fetot ratio from 0.15 to 0.79). A shift, however, of the 950 cm–1 band to high wavenumber with decreasing iron oxidation state can be observed.
We present here two empirical parameterizations (for silica- and alkali-rich pantelleritic glasses and for iron-rich basaltic glasses) to enable estimation of the iron oxidation state of both anhydrous and hydrous silicate glasses (up to 2.4 wt% H2O). The validation of the models derived from these parameterizations have been obtained using the independent characterization of these melt samples plus a series of external samples via wet chemistry.
The “pantelleritic” model can be applied within SiO2, FeO, and alkali content ranges of ~69–75, ~7–9, and ~8–11 wt%, respectively. The “basaltic” model is valid within SiO2, FeO, and alkali content ranges of ~42–54, ~10–22, and ~3–6 wt%, respectively.
The results of this study contribute to the expansion of the compositionally dependent database previously presented by Di Genova et al. (2015) for Raman spectra of complex silicate glasses. The applications of these models range from microanalysis of silicate glasses (e.g., melt inclusions) to handheld in situ terrestrial field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars), volcanic, and submarine environments.

Reference
Di Genova D, Hess K-U, Chevrel MO, Dingwell DB (2016) Models for the estimation of Fe3+/Fetot ratio in terrestrial and extraterrestrial alkali- and iron-rich silicate glasses using Raman spectroscopy. American Mineralogist 101, 943–952
Link to Article [DOI: http://dx.doi.org/10.2138/am-2016-5534CCBYNCND]
Copyright: The Mineralogical Society of America

¹James J. Papike, ²Steven B. Simon, ¹Paul V. Burger,¹ Aaron S. Bell, ¹Charles K. Shearer, ³James M. Karner
¹Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.
²Department of Geophysical Sciences, The University of Chicago, Chicago, Illinois 60637, U.S.A.
³Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, Cleveland, Ohio 44106, U.S.A.

Pyroxene is arguably the most powerful, single-phase geochemical and petrologic recorder of Solar System processes, from nebular condensation through planetary evolution, over a wide range of temperatures, pressures, and fO2. It is an important mineral phase in the crusts and mantles of evolved planets, in undifferentiated and differentiated asteroids, and in refractory inclusions—the earliest Solar System materials. Here, we review the valence state partitioning behavior of Cr (Cr2+, Cr3+), Ti (Ti3+, Ti4+), and V (V2+, V3+, V4+, V5+) among crystallographic sites in pyroxene over a range of fO2 from approximately fayalite-magnetite-quartz (FMQ) to ~7 log units below iron-wüstite (IW-7), and decipher how pyroxene can be used as a recorder of conditions of planetary and nebular environments and planetary parentage. The most important crystallographic site in pyroxene with respect to its influence on mineral/melt partitioning is M2; its Ca content has a huge effect on partitioning behavior, because the large Ca cation expands the structure. As a result, distribution coefficients (Ds) for Cr and V increase with increasing Ca content from orthopyroxene to pigeonite to augite. In addition, it is noted that V3+ is favored over V4+ in olivine and pyroxene. In pyroxene in refractory inclusions, Ti3+ is favored over Ti4+ and incorporation of Ti is facilitated by the high availability of Al for coupled substitution. The most important results from analysis of pyroxene in martian meteorites (e.g., QUE 94201) are the oxygen fugacity estimates of IW+0.2 and IW+0.9 derived from partitioning and valence data for Cr and V, respectively, obtained from experiments using appropriate temperatures and melt compositions. In angrites, changes in V valence state may translate to changes in fO2, from IW-0.7 during early pyroxene crystallization, to IW+0.5 during later episodes of pyroxene crystallization. In addition to fO2, the partitioning behavior of Cr, V, and Ti between pyroxene and melt is also dependent upon availability of other cations, especially Al, for charge-balancing coupled substitutions.

Reference
Papike JJ, Simon SB, Burger PV, Bell AS, Shearer CK, Karner JM (2016) Chromium, vanadium, and titanium valence systematics in Solar System pyroxene as a recorder of oxygen fugacity, planetary provenance, and processes
American Mineralogist 101, 907-918.
Link to Article [doi:10.2138/am-2016-5507]
Copyright: The Mineralogical Society of America

¹Joshua L. Bandfield, ²Elena S. Amador
¹Space Science Institute
²Earth and Space Sciences, University of Washington, Seattle

Thermal Emission Imaging System (THEMIS) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral datasets were used to identify high bulk SiO2 and hydrated compositions throughout the Nilosyrtis Mensae region. Four isolated locations were identified across the region showing short wavelength silicate absorptions within the 8–12 μm spectral region, indicating surfaces dominated by high Si phases. Much more extensive exposures of hydrated compositions are present throughout the region, indicated by a spectral absorption near 1.9 μm in CRISM data. Although limited in spatial coverage, detailed spectral observations indicate that the hydrated materials contain Fe/Mg-smectites and hydrated silica along with minor exposures of Mg-carbonates and an unidentified hydrated phase. The high SiO2 and hydrated materials are present in layered sediments near the base of topographic scarps at the hemispheric dichotomy boundary, typically near or within low albedo sand deposits. The source of the high SiO2 and hydrated materials appears to be from groundwater discharge from Nili Fossae and Syrtis Major to the south, where there is evidence for extensive aqueous alteration of the subsurface. Although discontinuous, the exposures of high SiO2 and hydrated materials span a wide area and are present in a similar geomorphological context to previously identified deposits in western Hellas Basin. These regional deposits may reflect aqueous conditions and alteration within the adjacent crust of the martian highlands.

Reference
Bandfield JL, Amador ES (2016) Extensive aqueous deposits at the base of the dichotomy boundary in Nilosyrtis Mensae, Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.002]
Copyright Elsevier