6/4/2012 - Iron and Silicon fractionation in meteorites/R-chondrite chondrules


12:00 PM - 1:00 PM
3853 Slichter

Presented By:
Junko Isa - UCLA
Michelle Jordan - UCLA


Fe and Si are common elements in both planetary cores and the silicate portions of planetary bodies, making them useful tools for understanding differentiation of the chemically distinct reservoirs. Equilibrium Fe and Si isotope fractionation between metal and silicate phases in differentiated meteorites can be used as a proxy for understanding the isotope fractionation that accompanies core formation in a planetary body. I will review previous theoretical calculations and experimental work used to quantify equilibrium Fe and Si isotope fractionation. Additionally, I will discuss earlier measurements of fractionation in meteoritic samples as well as current work being done to definitively determine the equilibrium metal-silicate Fe isotope fractionation in a meteorite. ********************** Rumuruti (R) chondrites have the highest D17O bulk values (3 ‰) among meteorite groups and are one of the two most oxidized groups. R chondrites show textural similarities to ordinary chondrites (OC) but have 3´ higher matrix contents. In past papers it was suggested that R-chondrite chondrules were the same as OC chondrules and that the high bulk D17O values were associated with the large fraction of phyllosilicate-rich (hydrated) fine matrix. However, new data show that the O-isotopic compositions of relict olivine phenocrysts in chondrules from unequilibrated R chondrites are diverse: some have with very low D17O values (-4‰) but some others have D17O values reaching +3‰, similar to those in bulk R chondrites. Thus R chondrules are not identical to OC chondrules, but are sampling a different nebular reservoir.

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