HR: 0800h
AN: V21B-0607    [Abstracts]
TI: Orthopyroxene/Clinopyroxene Trace Element Partitioning Systematics in the Natural Sample
AU: * Wozab, S T
EM: stw0935@garnet.acns.fsu.edu
AF: NHMFL and Dept. Geological Sciences, FSU, 1800, E. Paul Dirac Dr., Tallahassee, FL 32306 United States
AU: Bizimis, M
EM: bizimis@magnet.fsu.edu
AF: NHMFL and Dept. Geological Sciences, FSU, 1800, E. Paul Dirac Dr., Tallahassee, FL 32306 United States
AB: It is well established that trace element partition coefficients (D) vary as a function of pressure, temperature (T) and composition, but experimental partitioning studies are expensive, time consuming and often produce a limited number of mineral partitioning data. However, fresh spinel peridotite xenoliths where opx and cpx are in major element equilibrium can provide abundant mineral/mineral partitioning data that allows exploring some aspects of partitioning systematics in the upper mantle. Here we present major and trace element data on pure mineral separates of spinel peridotites from the oceanic lithosphere (Oahu, Hawaii) and continental settings (Portillo Maar, New Mexico, N.E. Queensland, Australia). Our data, along with literature data, shows that D$^{opx/cpx}$ for the HREE, Y, Zr, Hf, Ti, Sc, V decrease with decreasing temperature (and, therefore, increasing Ca content in cpx), while Co, Mn, and Ni increase. Interestingly, where experimental data exists, the natural D$^{opx/cpx}$ are always lower and fall at the extension of the experimental data on an lnD$^{opx/cpx}$ vs. T plot, with good correlations between temperature and lnD$^{opx/cpx}$, e.g. T=355.2lnD$^{opx/cpx}$$_{Y}$+2016 with r$^{2}$ = 0.91, T=427.8lnD$^{opx/cpx}$$_{Er}$+2107 with r$^{2}$ = 0.9. These empirical thermometers may be used in the absence of major element data. Also, these systematic variations in the natural sample can be used to predict D$^{opx/cpx}$ for melting appropriate temperatures in the upper mantle where such Ds are not experimentally available, e.g. Co and Mn. The systematic difference between experimental and natural D$^{opx/cpx}$ also suggests that it is inappropriate to use experimental Ds to reconstruct peridotite bulk rock trace element contents, since this leads to overestimating these concentrations. This is especially true for abyssal peridotites where no reliable opx or bulk rock trace element data is available.
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting