HR: 0800h
AN: V31B-0606    [Abstracts]
TI: The Oxidation State of V in Olivine and Clinopyroxene as a Proxy for Oxygen Fugacity of Minettes
AU: * Davis, L L
EM: Linda.Davis@stockton.edu
AF: Washington and Lee University, Geology Department Science Building Addition Washington and Lee University, Lexington, VA 24450 United States
AU: Sutton, S
EM: sutton@cars.uchicago.edu
AF: The University of Chicago, 9700 South Cass Avenue Bldg. 434A , Argonne, IL 60439 United States
AU: Newville, M
EM: newville@cars.uchicago.edu
AF: The University of Chicago, 9700 South Cass Avenue Bldg. 434A , Argonne, IL 60439 United States
AU: Schreiber, H
EM: schreiberhd@vmi.edu
AF: Virginia Military Institute, Chemistry Department, Lexington, VA 24450 United States
AB: With some notable exceptions, the oxygen fugacity of minette sources is not well-studied, and the same is true for other mantle-derived ``lamprophyres''. The range in oxygen fugacity for lamproites is much better constrained and may be very helpful in guiding the work to be done on minettes and similar K-rich rocks. However, although source regions for minettes and lamproites are similar, they are distinct enough that the oxygen fugacities may vary greatly. It may also be that different sources for different minettes vary greatly in oxygen fugacity (fO₂). The lack of coexisting iron-titanium oxides, complex compositional variations in minerals present, and the presence of xenocrystic phases present difficulties in determining the oxygen fO₂of the minettes. Using XANES spectroscopy, we may be able to determine the redox state of the mantle source regions for a suite of Cenozoic, potassic mantle-derived rocks. As a first step towards constraining the redox state of the subcontinental lithospheric mantle in the western United States, olivine and clinopyroxene in minettes from Two Buttes, Colorado, were examined using Cr- and V XANES spectroscopy at the APS beamline 13-ID-GSECARS. The minette olivines yielded a range of values between V³⁺ and V⁴⁺. The Cr and V results suggest the olivines were produced at log fO₂~ -7.5. Since NNO (1300° C) ~-6.5, this is NNO-1. The cpx valences are generally consistent with V³⁺; however, measurements on clinopyroxene crystallized under known conditions are needed to better evaluate the data. The presence of V³⁺ in the olivines means the melts were not highly oxidizing.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 3615 Intra-plate processes (1033, 8415)
DE: 8439 Physics and chemistry of magma bodies
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005