Investigating the Role of Compositionally-Diverse Glasses in Interpreting Martian Chemistry and Mineralogy as Viewed by TES

Details Investigating the Role of Compositionally-Diverse Glasses in Interpreting Martian Chemistry and Mineralogy as Viewed by TES Investigating the Role of Compositionally-Diverse Glasses in Interpreting Martian Chemistry and Mineralogy as Viewed by TES

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p23c0067m&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P23C-0067

Physics

Geophysics

5410 Composition (1060, 3672), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars

Scientific paper

Mineralogy and chemistry of the Martian surface are derived from Thermal Emission Spectrometer (TES) data by linear deconvolution using a spectral library containing the infrared spectra of a variety of phases [e.g. 1]. Obtaining successful results relies on utilization of a spectral library containing an accurate representation of the phases measured on the Martian surface. In order to explore the influence of a variety of glass compositions on the deconvolution of TES spectra, we synthesized five pristine glasses, obtained their thermal infrared spectra and conducted preliminary TES spectral deconvolutions using a spectral library containing the new glass spectra. The five new glasses have compositions relevant to Martian igneous processes. One basalt has a high-FeO, low-Al2O 3 composition linked to several Martian meteorites [refs in 3]. A second basalt is based on the Deccan Trap basalt that serves as a spectral analog to the TES Surface Type 1 (ST1) spectrum [2]. Similarly, one andesite is based on the Medicine Lake andesite that serves as a spectral analog to the TES Surface Type 2 (ST2) spectrum [2]. A second andesite represents the interstitial melt composition resulting from 90% crystallization of an anhydrous Martian meteorite basalt (described above) [3]. A dacitic glass represents the interstitial melt composition resulting from 80% crystallization of a hydrous Martian meteorite basalt [3]. Each glass was fused in either Pt or AgPd tubing vacuum sealed in SiO2 glass tubing for 72-96 hours. We collected thermal infrared spectra of the ≥500 μm fraction of the glasses at the Hawai'i Institute of Geophysics and Planetology with a ThermoElectron Nexus 470 FTIR interferometric spectrometer in thermal emission mode [4]. We obtained data from 200-4000 cm-1 at 2 cm-1 spectral sampling. Preliminary deconvolutions of ST1 and ST2 spectra indicate that the newly synthesized glasses may represent significant components in the Martian surface. ST1 and ST2 are modeled with high abundances of the andesitic interstitial melt endmember (17 vol% ST1 and 23 vol% ST2); ST2 is also modeled with 11 vol% of the analog TES basalt glass and 13 vol% of a high-silica and potassium glass [5]. Addition of the new glass spectral endmembers results in an overall increase in the total abundance of modeled glasses at the expense of plagioclase, pyroxenes and olivine. Modeling of distinct glass compositions does not necessarily indicate that each glass is present on the Martian surface. Different glass compositions and abundances may represent average glass chemistry much the way different plagioclase compositions are modeled to reflect average plagioclase composition in rocks. Average derived chemistries for glasses in ST1 (59 wt% SiO2 and 15.7 wt% FeO) and ST2 (64.2 wt% SiO2 and 10.5 wt%FeO) are influenced by inclusion of the new glass compositions in deconvolutions. Total derived bulk chemistries for ST1 and ST2, however, do not significantly change (e.g. ±1-2 wt% SiO2) with the addition of the new glass spectral endmembers. This likely reflects the partial substitution of chemically similar minerals with newly synthesized glasses. [1] M.S. Ramsey and P.R. Christensen (1998) JGR, 103, 577 596. [2] J.L. Bandfield et al. (2000) Science, 287, 1626 1630. [3] M.E. Minitti and M.J. Rutherford (2000) GCA, 64, 2535- 2547. [4] V.E. Hamilton and P.G. Lucey (2005) LPSC XXXVI, #1272. [5] M.B. Wyatt et al. (2001) JGR, 106, 14,711-14,732.

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