Mathematics – Logic
Scientific paper
Dec 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975gecoa..39.1585d&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 39, Dec. 1975, p. 1585-1594. Research supported by the Max-Planck-Gesellschaft
Mathematics
Logic
4
Chondrites, Meteoritic Composition, Pyroxenes, Electron Probes, Error Analysis, Metamorphism (Geology), Microstructure, Mineralogy, Petrology, X Ray Diffraction
Scientific paper
The Shaw L-group chondrite differs from orthodox type 6 ordinary chondrites in ways which suggest that it experienced unusually high metamorphic temperatures and anatexis. Electron microprobe and single crystal X-ray diffraction data indicate that Shaw contains three pyroxenes: the augite and calcic orthopyroxene reported by other workers, and a second, Ca- and Al-poor orthopyroxene, interpreted as inverted protobronzite. Comparison of the Shaw assemblage with experimental data suggests that a two-phase (augite-protobronzite) assemblage developed at peak metamorphic temperatures of about 1250-1300 C, that partial reaction of augite and protobronzite produced calcic orthopyroxene and by-product spinel at temperatures approximately 150 C lower, and that protobronzite inverted to bronzite free of stacking disorder during subsequent slow cooling. Shaw differs sufficiently in texture and mineralogy from type 6 ordinary chondrites to justify its assignment to a separate petrologic type: L-7.
Brown Gerald E.
Dodd Robert T.
Grover John E.
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