Fe3+ partitioning systematics between orthopyroxene and garnet in mantle peridotite xenoliths and implications for thermobarometry of oxidized and reduced mantle rocks - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Contributions to Mineralogy and Petrology Année : 2015

Fe3+ partitioning systematics between orthopyroxene and garnet in mantle peridotite xenoliths and implications for thermobarometry of oxidized and reduced mantle rocks

Résumé

We have investigated the partitioning of Fe3+ between orthopyroxene (Opx) and garnet (Grt) in well-equilibrated mantle xenoliths using Mössbauer spectroscopy. The samples cover a wide range of P–T conditions (2.1–6.6 GPa, 690–1,412 °C) and geothermal gradients, and are thus representative for Earth’s upper mantle in both on-craton and off-craton continental settings. Garnet has Fe3+/Fetot ratios of 0.03–0.13 and Fe2O3 contents of 0.24–1.00 wt%. Orthopyroxene has, on average, lower Fe3+/Fetot ratios (0.01–0.09) and Fe2O3 contents (0.05–0.63 wt%). In low-pressure, high-temperature samples, however, Opx is systematically richer in Fe2O3 than the coexisting Grt. The Fe3+ Opx/Grt partition coefficient (DOpx/GrtFe3+) shows no obvious relationship with temperature, but increases with decreasing pressure and with increasing NaOpx. The observed Opx/Grt Fe3+ systematics imply that the Opx–Grt Fe–Mg exchange thermometer is not robust against redox changes if total Fe is treated as Fe2+. An approximate evaluation of errors on T estimates due to redox effects predicts negligible deviations for strongly reduced conditions (<65 °C), but potentially large deviations (> to ≫100 °C) for strongly oxidized conditions, especially at very high pressure and when both P and T are calculated by iteration.

Domaines

Géochimie

Dates et versions

hal-01121606 , version 1 (02-03-2015)

Identifiants

Citer

Paolo Nimis, Alexey Goncharov, Dmitri Ionov, Catherine Mccammon. Fe3+ partitioning systematics between orthopyroxene and garnet in mantle peridotite xenoliths and implications for thermobarometry of oxidized and reduced mantle rocks. Contributions to Mineralogy and Petrology, 2015, 169 (1), pp.6. ⟨10.1007/s00410-014-1101-8⟩. ⟨hal-01121606⟩
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