The Mantle (peridotite) Record of Mantle Redox Through Time

The composition of Earth’s mantle, including the ratio of ferric to ferrous iron, has influenced melting, volatile extraction, the composition of Earth’s crust, the generation of ore bodies, and the composition of the atmosphere through time. Composition, pressure, and temperature determine oxygen fugacity (fO2), which is a convenient thermodynamic tool for modeling redox-dependent processes. Development of new fO2 proxies, combined with newfound understanding of the importance of mantle fO2 in Earth evolution, have driven new observations, experiments, and models and led to controversies concerning the fO2 of modern convecting mantle, whether fO2 has varied with time, and to what extent it influences crustal differentiation.

The fO2 of convecting upper mantle recorded by ridge peridotites varies by more than four orders of magnitude. Although much attention has been given to mechanisms that drive variations in mantle fO2 between tectonic settings and to comparisons of fO2 between modern rocks and ancient-mantle-derived rocks, comparatively little has been done to understand the origins of the high variability in fO2 recorded by peridotites from modern mid-ocean ridge settings. In this talk I’ll share what we have learned from mantle peridotites about ancient and modern mantle redox.