Integrated spectroscopy of magnesium-iron-calcium pyroxenes Rachel Louise Pillar Klima

ISBN: 9780549897859

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NOOKstudy eTextbook

295 pages


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Integrated spectroscopy of magnesium-iron-calcium pyroxenes  by  Rachel Louise Pillar Klima

Integrated spectroscopy of magnesium-iron-calcium pyroxenes by Rachel Louise Pillar Klima
| NOOKstudy eTextbook | PDF, EPUB, FB2, DjVu, audiobook, mp3, ZIP | 295 pages | ISBN: 9780549897859 | 6.33 Mb

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 spectroscopyMoreDetailed 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 Fe 2+ site occupancy were determined using room temperature and temperature series Mossbauer 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 mum 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 mum 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 mum 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.



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