HR: 11:35h
AN: V42A-06    [Abstracts]
TI: Similar oxygen fugacities in arc and MORB mantle source regions: evidence from V/Sc systematics
AU: Leeman, W P
EM: leeman@rice.edu
AF: Dept Earth Science, Rice University, Houston, TX 77005 United States
AU: * Lee, C A
EM: ctlee@rice.edu
AF: Dept Earth Science, Rice University, Houston, TX 77005 United States
AU: Canil, D
EM: dcanil@uvic.edu
AF: School of Ocean and Earth Sciences, University of Victoria, Victoria, BC V8W3P6 Canada
AU: Li, Z A
EM: zxli@rice.edu
AF: Dept Earth Science, Rice University, Houston, TX 77005 United States
AB: V/Sc systematics in peridotites and lavas are investigated to constrain the fO2 of the asthenospheric mantle. V/Sc ratios may see through certain processes that can modify barometric fO2 determinations in mantle rocks and/or magmas: early fractional crystallization, degassing, crustal assimilation, and mantle metasomatism. Melting models are combined here with a literature database on peridotites, arc lavas, and mid-ocean ridge basalts along with new, more precise data on peridotites. V/Sc ratios in primitive arc lavas from the Cascades magmatic arc are subtly correlated with fluid mobile elements (e.g., Ba and K), indicating that fluids may influence fO2 during melting. Despite evidence for fluid control in arcs, the average V/Sc-inferred fO2s of arc basalts, MORBs, and peridotites are remarkably similar (-1.25 to +0.5 log units from the FMQ buffer). This suggests that the upper part of the Earth's mantle may be strongly buffered in terms of fO2. Higher barometric fO2s of arc lavas and arc-related peridotite xenoliths may be respectively due to magmatic differentiation processes and to exposure to large time-integrated fluid fluxes incurred during the long term stability of lithospheric mantle.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting