HR: 10:50h
AN: V42A-03 INVITED     [Abstracts]
TI: Iron isotope fractionation in mantle minerals and the effects of partial melting and oxygen fugacity
AU: * Williams, H M
EM: williams@erdw.ethz.ch
AF: ETH-Zurich, Sonneggstr. 5, Zurich, CH8092 Switzerland
AU: McCammon, C
EM: catherine.mccammon@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitat Bayreuth, Bayreuth, D-95440 Germany
AU: Peslier, A H
EM: apeslier@mail.uh.edu
AF: Texas Center for Superconductivity, University of Houston, Houston, TX 77204 United States
AU: Halliday, A N
EM: halliday@erdw.ethz.ch
AF: ETH-Zurich, Sonneggstr. 5, Zurich, CH8092 Switzerland
AU: Levasseur, S
EM: levasseur@erdw.ethz.ch
AF: ETH-Zurich, Sonneggstr. 5, Zurich, CH8092 Switzerland
AU: Teutsch, N
EM: teutsch@erdw.ethz.ch
AF: ETH-Zurich, Sonneggstr. 5, Zurich, CH8092 Switzerland
AU: Burg, J
EM: jpb@erdw.ethz.ch
AF: ETH-Zurich, Sonneggstr. 5, Zurich, CH8092 Switzerland
AB: The oxygen fugacity of the mantle exerts a fundamental influence on mantle melting, volatile speciation and the development of the Earth's atmosphere. As changes in mantle oxidation state are generally reflected in the ferric iron contents of mantle minerals, the iron isotope signatures of mantle rocks should provide information about spatial and secular changes in mantle oxidation state. However, the exact nature of the processes governing iron isotope fractionation in igneous rocks remains poorly understood, limiting the use of iron isotopes as a proxy. We have investigated the relationships between Fe isotope fractionation, oxygen fugacity, melting and metasomatism with a combined MC-ICPMS Fe isotope and M\"{o}ssbauer spectroscopy study of spinels and silicate minerals from mantle xenoliths and massif samples originating from different tectonic settings. There exist large variations in the iron isotope compositions of olivines, pyroxenes and spinels. Clear correlations exist between the $\delta$$^{57/54}$Fe values of coexisting minerals, implying equilibrium isotope fractionation. Spinel $\delta$$^{57/54}$Fe values correlate negatively with relative oxygen fugacity, spinel Fe$^{3+}$/$\Sigma$Fe and Cr number; clinopyroxene $\delta$$^{57/54}$Fe values correlate negatively with clinopyroxene MgO content and Cr number. There do not appear to be strong relationships between the $\delta$$^{57/54}$Fe values of the minerals and chemical or isotopic indices of metasomatism. Taken together these observations imply that variations in the iron isotopic compositions of mantle rocks and minerals are largely a function of melting coupled with changes in mantle oxidation state.
DE: 3640 Igneous petrology
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting