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| Titel |
VNIR reflectance spectroscopy of glassy igneous material with variable
oxidation states |
| VerfasserIn |
Cristian Carli, Danilo Di Genova, Ted L. Roush, Werner Ertel-Ingrisch, Fabrizio Capaccioni, Donald B. Dingwell |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144301
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| Publikation (Nr.) |
 EGU/EGU2017-8111.pdf |
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| Zusammenfassung |
| Silicate glasses with igneous compositions may represent an abundant component of
planetary surface material via effusive volcanism or impact cratering processes. Several
planetary surfaces are mapped with hyper-spectrometers in the visible and near-infrared
(VNIR). In this spectral range, crystal field (C.F.) absorptions are useful to discriminate
iron-bearing silicate components. At the same time, in the VNIR reflectance spectroscopy
iron bearing glasses may exhibit a C.F. absorption at ∼1.1 μm. A weak C.F. absorption is
also present at ∼1.9 μm. These absorptions can be therefore diagnostic for glassy
component and can also affect the C.F. absorptions of mafic minerals when mixed in the
regolith.
So far, few studies investigated the spectral properties of systematic glasses compositions
and at different oxygen fucacity. For these reasons studying glassy materials, and their optical
constants, represents an important effort to document and to interpret, spectral features
of Solar System silicate crusts where glasses are present, but may be difficult to
map.
In previous work Carli et al. (2016) considered the composition of glassy igneous
materials produced in Earth-like atmospheric conditions (i.e. oxidized conditions). Here, we
expand on that effort by including glasses formed under more reducing condition. In this
study, glasses were produced at -9.3 log fO2 and 1400 ˚ C for a duration of 4 h at the
Department of Earth and Environmental Sciences at the University of Munich using a
gas-mixing furnace. The major element composition, sample homogeneity, and the
Fe3+/Fetot. ratio of run products were analytically determined. Moreover, Raman spectra of
the same samples were also acquired.
Afterwards, powders were produced with nine-grain size from 250-224 μm to 50-20 μm
and measured in bidirectional reflectance at Spectroscopy LABoratory (IAPS-INAF,
Rome). Reflectance spectra were acquired from 0.35 to 2.5 μm with a Field-Pro
Spectrometer mounted on a goniometer. Spectra were obtained with incident and
emission angles of 30˚ and 0˚ , respectively. Spectra showed both diagnostic
bands, reflectance diminished with increasing iron abundance. The comparison with
spectra collected from samples sythetized at “Earth-like” atmospheric conditions
showed:
1) Relatively higher reflectance in the visible; 2) less red slope in the IR; 3) deeper 1.1 μm
absorption band. Following Carli et al. (2016, Icarus), for all the spectra acquired at each
grain size, we apply the radiative transfer model to estimate the optical constant as a
wavelength’s function. Finally, we will report the retrieved optical constants for our samples
and we will compare them with those obtained from the same composition but at “Earth-like”
atmospheric conditions.
Reference: Carli et al. 2016, Icarus, doi:10.1016/j.icarus.2015.10.032. |
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