Iron-magnesium Order-disorder In An Ortho-pyroxene Crystal From the Johnstown Meteorite
| Autor: | E. Brizi, Gian Mario Molin, Surendra K. Saxena |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 1991 |
| Předmět: |
Quenching
Magnesium Analytical chemistry Mineralogy chemistry.chemical_element ORTHO-PYROXENE SYSTEM RICH ORTHO-PYROXENE Pyroxene engineering.material Crystal Geophysics Augite Meteorite chemistry Space and Planetary Science Geochemistry and Petrology Earth and Planetary Sciences (miscellaneous) engineering Single crystal Chemical composition RICH Geology SYSTEM |
| Popis: | Equilibrium reversals of Fe 2+ Mg distribution between the M1 and M2 sites of an orthopyroxene from the Johnstown meteorite were achieved at several temperatures between 700 and 1000°C. One single crystal was used for the whole thermal treatment and for collecting all the X-ray data after quenching. The intracrystalline ion exchange for the bulk chemical composition: (Mg 1.453 Fe 0.441 Cr 0.024 Ca 0.054 Mn 0.015 Fe 0.005 Ti 0.003 Al 0.005 )(Si 1.960 Al 0.040 )O 6 is given by: ln K D = −3027(±39)/ T (K) + 0.872(±0.013)> where K D is the distribution coefficient for the reaction: Fe M2 2+ + Mg M1 = Mg M2 + Fe M1 2+ . A transmission electron microscopy (TEM) study of part of the crystal showed the presence of very thin augite lamellae and Guinier-Preston zones indicating a relatively rapid cooling of the host rock at temperatures close to 1000°C. The new temperature scale yields a relatively high quenching temperature of 379 (±8)°C for the pyroxene which appears consistent with a rapid cooling (estimated few degrees per hundred years) of a magmatic cumulate excavated by an impact on its parental body. |
| Databáze: | OpenAIRE |
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