Integrated Spectroscopy of Mg-Fe-Ca Pyroxenes: A Foundation for Modern Remote Compositional Analysis of Planetary Surfaces

Full Metadata

Overview

Title
Integrated Spectroscopy of Mg-Fe-Ca Pyroxenes: A Foundation for Modern Remote Compositional Analysis of Planetary Surfaces
Contributors
Klima, Rachel L. (creator)
Pieters, Carle (director)
Mustard, John (reader)
Hess, Paul (reader)
Liang, Yan (reader)
Dyar, Melinda (reader)
Brown University. Geological Sciences (sponsor)
Doi
10.7301/Z0QN652C
Copyright Date
2008
Abstract
Detailed textural, mineralogical and chemical analyses of extraterrestrial materials have raised numerous questions about the igneous evolution and cooling histories of their parent bodies. Remote sensing using near-infrared imaging spectroscopy provides an opportunity to characterize the global mineralogy of a planetary body. Pyroxene compositions inferred from remotely detected spectra can be used to address petrologic questions about the magmatic evolution and cooling history of a planet. Deconvolution of spectral parameters and derivation of pyroxene mineralogy with the precision necessary to address geothermometric questions has until now remained elusive. We investigate a suite of synthetic pyroxenes with compositions spanning the full range of the Ca-Mg-Fe pyroxene quadrilateral to link the absorption band properties of pyroxenes directly to the mineral physics that control them: structure, bulk composition, and site occupancy. Pyroxene compositions were measured using an electron microprobe. Oxidation state and Fe2+ site occupancy were determined using room temperature and temperature series Mössbauer measurements. The Modified Gaussian Model (MGM) was used to deconvolve pyroxene spectra into component crystal field absorption bands.For Ca-free orthopyroxenes, we find that the 1 and 2 µm spin-allowed crystal field absorptions shift regularly with increasing iron content, defining a much tighter trend than observed previously. A spin-allowed crystal field absorption band at 1.2 µm is explicitly verified, even at low total iron contents, indicating the presence of Fe2+ in the M1 site. The addition of Ca to the lattice has a dramatic effect on pyroxene spectra until compositions reach roughly 30% wollastonite, at which point the pyroxene structure ceases to change significantly as more Ca is added. Transitions in pyroxene structure can be deduced from the positions of absorption bands. Because Fe2+-Mg2+ ordering in a pyroxene is in part a function of the thermal history of a pyroxene, the strength of the 1.2 µm M1 band holds great potential for assessing cooling history of pyroxene-dominated rocks from orbit. Using the relationships established by the synthetic pyroxene data set, we investigate a group of Howardite, Eucrite, and Diogenite meteorites and determine that M1 intensity ratios are consistent with the petrology and bulk composition of the meteorites.
Keywords
spectroscopy
Spectrum analysis
Pyroxene
Remote sensing
Notes
Thesis (Ph.D.) -- Brown University (2008)
Extent
xiv, 281 p.

Citation

Klima, Rachel L., "Integrated Spectroscopy of Mg-Fe-Ca Pyroxenes: A Foundation for Modern Remote Compositional Analysis of Planetary Surfaces" (2008). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0QN652C

Relations

Collection: