Date of Award
Master of Science
Harry Y. McSween Jr.
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.
Gastineau, Heather Kay, "A test for oxidation during metamorphism of L and LL chrondrites. " Master's Thesis, University of Tennessee, 2000.