Physics
Scientific paper
Nov 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985lpsc...16..116m&link_type=abstract
(Lunar and Planetary Institute, NASA, American Geophysical Union, et al., Lunar and Planetary Science Conference, 16th, Houston,
Physics
7
Cooling, Meteoritic Composition, Olivine, Pyroxenes, Ureilites, Evolution (Development), Inclusions, Iron Oxides, Manganese Oxides, Meteorites, Ureilites, Antarctic Meteorites, Cooling, History, Zoning, Chemistry, Olivine, Composition, Pyroxenes, Pca 82506, Yamato 790981, Alha77257, Samples, Meteorite, Electron Probe Methods, Calcium Oxide, Tem, Calculations, Fayalite, Manganese Oxide, Iron Oxide, Oxidation, Origin, Pigionites, Melting, Shock Effects, Heating, Diffusion, Reduction, Xrd, Allan Hills Meteorit
Scientific paper
To obtain some constraints on the cooling histories of ureilites, the chemical zoning of olivines and the compositional variations of pyroxenes in the PCAB2506, Y790981, and ALH77257 ureilites have been studied using an electron microprobe. Fayalite components and CaO contents in olivines show a gradual decrease toward the rims. The MnO/FeO variation of ureilite pyroxenes shows a subtle anticorrelation that is probably related to the redox reaction during their original crystallization. The chemical variation within a grain of Y79081 pigeonites may be attributed to partial melting due to shock heating. Cooling rates of 2-6 C/hr have been obtained from diffusional calculations based on the reverse zoning profile of Fa components at the grain boundary of ureilite olivines. It is assumed that iron diffusion controls the reduction reaction, although the reduction process may be more complex. Because iron diffusion is slower in pyroxene than in olivine, ureilite pigeonite would not show chemical zoning by reduction if their cooling rates were faster than about a 1 C/hr. This result is consistent with impact-produced excavation of the ureilite parent mass.
Miyamoto Manabu
Takeda Hidenori
Toyoda Haruki
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