Vanadium in peridotites, mantle redox and tectonic environments: Archean to present

New measurements of partition of vanadium (V) between spinel. garnet and a pigeonite-like high pressure (P) pyroxene and magnesian liquids on the mantle solidus as a function of oxygen fugacity (fO(2)) are presented. The spinel-liquid experiments show an effect of Cr/Al in spinel on partitioning, and further suggest that V exists as V3+, V4+ and V5- in melts at terrestrial fO(2). Vanadium is mildly incompatible in both 'pigeonitic' pyroxene and garnet between 4.5 and 6.5 GPa on the mantle solidus. Analysis of the fO(2)-sensitive partitioning for V between mantle minerals and melts are combined with compositional data from peridotite melting experiments to model the covariation of V and At in peridotite residues produced by non-modal, fractional melting under different fO(2) from 1.0 to 7.0 GPa. The partial melting models at 1.0 to 3.0 GPa tit the covariation of V and At in abyssal peridotites quite well at fO(2)s similar to those of mid-ocean ridge basalt. Many orogenic massifs and spinel lherzolite xenoliths represent mantle that formed at fO(2) higher than that produced at mid-ocean ridges in a range of tectonic environments. A large proportion of spinel-facies Archean cratonic lithosphere formed at fO(2)s significantly higher than those of abyssal peridotites possibly linking its formation to a convergent margin (arc) tectonic setting, The case for garnet-facies cratonic mantle is equivocal; it may have formed at significantly higher pressures (7.0 GPa), or within the spinel-facies at lower pressures but at significantly higher fO(2) than is observed for abyssal peridotites. The imbrication of both oceanic garnet-facies mantle with spinel-facies arc mantle may explain the datasets for some Archean cratons. Overall, the data for Archean mantle melts and residues make clear that models cannot look to reduced. mantle-derived volcanic gases containing H, and CO to engender early life synthesis, or to promote hydrogen escape and gradual oxygenation of the Archean earth system. (C) 2002 Elsevier Science B.V. All rights reserved.