Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science



Major Professor

Harry Y. McSween Jr.

Committee Members

Dan Britt, Larry Taylor


Subtle but progressive changes in the olivine and low-Ca pyroxene abundances and the olivine, low-Ca pyroxene,and diopside compositions are observed with increasing metamorphic grade in equilibrated (types 4-6)ordinary chondrites. These changes suggest that the meteorites experienced oxidation of metallic Fe during heating according to the reaction:

Fe + ½ O2 + (Mg,Fe)Si03 => (Mg, Fe)2Si04

metal    pyroxene    olivine

hypothesized by McSween and Labotka (1993), based on calculated normative mineralogy as well as incorporation of Fe2+ into ferromagnesian silicate phases. From this study, two observations support this hypothesis: (1) the modal olivine: low-Ca pyroxene ratio increases with petrologic type in L and LL chondrites and (2) Fe-enrichment in olivine and low-Ca pyroxene are observed from petrologic types 4-6 in the L chondrites. The behavior of the LL chondrites studied is inconsistent; however,a general Fe-enrichment in silicates is apparent.

Characteristic spectral absorption features in visible infrared spectra (VIS- NIR) are sensitive to the olivine/ low-Ca pyroxene abundance ratio and the Ca2+ and Fe2+ contents of pyroxenes. Therefore, metamorphic grade (petrologic type) in ordinary chondrites might be identified using characteristic spectra since each petrologic type has different olivine/ pyroxene abundances and pyroxene compositions. This work is applicable to the NEAR mission to 433 Eros and other ground-based spectroscopic studies of asteroids.

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