Experimental tests of garnet peridotite oxygen barometry

Guðmundsson, Garðar; Wood, Bernard J.

doi:10.1007/bf00310717

Cited by 125 publications

(36 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In fact, as will be seen, mantle f O 2 is not constant with depth. Even if the Fe 3C / P Fe or bulk oxygen content of the mantle is constant, the f O 2 will be much lower in the deeper mantle as a result of crystal chemical effects (Ballhaus 1995;Gudmundsson & Wood 1995;Woodland & Koch 2003;Frost & McCammon 2008). The rise in the redox state of the mantle since core formation, therefore, is more accurately reflected in the Fe 3C / P Fe of the upper mantle (or better still the O/Fe ratio), which is in the range of 2-3 per cent in the present-day mantle (Canil & O'Neill 1996), but would have been much lower than this when in equilibrium with metallic Fe.…”

Section: The Evolution Of Mantle F Omentioning

confidence: 99%

“…Ballhaus 1995). Figure 3 shows oxygen fugacities calculated for garnet peridotite xenoliths from kimberlites by Woodland & Koch (2003) using the equilibrium (Gudmundsson & Wood 1995 The decrease in f O 2 with depth is mainly due to the positive volume change of equilibrium (3.1) (8.6 cm 3 mol K1 ), which favours the stability of the Fe 3 Fe 3C 2 Si 3 O 12 garnet component (skiagite) with increasing pressure. For a fixed garnet peridotite composition, pressure alone will drive f O 2 to lower levels.…”

Section: The Redox State Of the Present-day Mantlementioning

confidence: 99%

See 1 more Smart Citation

The redox state of the mantle during and just after core formation

Frost

Mann

Asahara

et al. 2008

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

Siderophile elements are depleted in the Earth's mantle, relative to chondritic meteorites, as a result of equilibration with core-forming Fe-rich metal. Measurements of metal-silicate partition coefficients show that mantle depletions of slightly siderophile elements (e.g. Cr, V ) must have occurred at more reducing conditions than those inferred from the current mantle FeO content. This implies that the oxidation state (i.e. FeO content) of the mantle increased with time as accretion proceeded. The oxygen fugacity of the present-day upper mantle is several orders of magnitude higher than the level imposed by equilibrium with core-forming Fe metal. This results from an increase in the Fe 2 O 3 content of the mantle that probably occurred in the first 1 Ga of the Earth's history. Here we explore fractionation mechanisms that could have caused mantle FeO and Fe 2 O 3 contents to increase while the oxidation state of accreting material remained constant (homogeneous accretion). Using measured metal-silicate partition coefficients for O and Si, we have modelled core-mantle equilibration in a magma ocean that became progressively deeper as accretion proceeded. The model indicates that the mantle would have become gradually oxidized as a result of Si entering the core. However, the increase in mantle FeO content and oxygen fugacity is limited by the fact that O also partitions into the core at high temperatures, which lowers the FeO content of the mantle. (Mg,Fe)(Al,Si)O 3 perovskite, the dominant lower mantle mineral, has a strong affinity for Fe 2 O 3 even in the presence of metallic Fe. As the upper mantle would have been poor in Fe 2 O 3 during core formation, FeO would have disproportionated to produce Fe 2 O 3 (in perovskite) and Fe metal. Loss of some disproportionated Fe metal to the core would have enriched the remaining mantle in Fe 2 O 3 and, if the entire mantle was then homogenized, the oxygen fugacity of the upper mantle would have been raised to its present-day level.

show abstract

Section: The Evolution Of Mantle F Omentioning

confidence: 99%

Section: The Redox State Of the Present-day Mantlementioning

confidence: 99%

The redox state of the mantle during and just after core formation

Frost

Mann

Asahara

et al. 2008

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

show abstract

“…Clearly, the abundance of Cpx cannot account for the systematic displacement of the off-craton Dariganga samples from the on-craton samples in terms of Opx/Grt Fe3+ distribution. II) Redox conditions versus oxygen fugacity …I profit to make a general comment that might go beyond the goal of this work… …Tens of works use to claim that oxygen fugacity decreases with pressure when compared with FMQ buffer, due to stabilisation of the skiagite component in garnet… …the habit to compare fO2 with FMQ buffer…is trivial…because FMQ buffer will never occur in peridotite rocks [and]…the commonly used equilibrium skiagite = fayalite + ferrosilite + O2 of Gudmundsson and Wood (1995), which involves only Fe-bearing phases, shows a slight negative slope with pressure while FMQ has a positive slope… R -As admitted by the reviewer, these interesting aspects go beyond the goal of the present work, as our aim is not to revisit redox estimates for mantle peridotites. We only use the available estimates to bracket the redox conditions expected to be relevant for lithospheric mantle sections, and the same method used to estimate the redox conditions (Stagno et al 2013) is used backward to calculate model Fe3+/Fetot ratios in Grt.…”

mentioning

confidence: 99%

“…R - Gudmundsson and Wood (1995) stated something different. The correct quotation is "Mössbauer data (Dyar et al 1989;Wood, unpublished) show that the Fe3+/SFe of orthopyroxenes of upper mantle composition is only about 0.05, an amount which can be neglected in the calculation of FeSiO3 activity."…”

mentioning

confidence: 99%

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

Nimis

Goncharov

Ionov

et al. 2015

Contrib Mineral Petrol

View full text Add to dashboard Cite

We have investigated the partitioning of Fe3+ between orthopyroxene (Opx) and garnet (Grt) in wellequilibrated 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%).\ud In low-pressure, high-temperature samples, however, Opx is systematically richer in Fe2O3 than the coexisting Grt. The Fe3+ Opx/Grt partition coefficient D Opx/Grt Fe3+ 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–\ud 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

show abstract

“…Records of mantle f O2 include mineral oxybarometers (e.g., Buddington and Lindsley 1964;O'Neill and Wall 1987;Gudmundsson and Wood 1995), Fe 3+ /ΣFe ratios of basaltic glasses (e.g., Christie et al 1986;Bézos and Humler 2005;Cottrell et al 2009), and abundances and ratios of redoxsensitive trace elements in basalts and peridotites (e.g., Shervais 1982;Canil 1999;Li and Lee 2004). Mineral oxybarometers that can be applied to peridotite samples provide direct estimates of f O2 in the upper mantle and play a key role in deciphering past and present mantle f O2 conditions.…”

Section: Introductionmentioning

confidence: 99%

Revisiting the electron microprobe method of spinel-olivine-orthopyroxene oxybarometry applied to spinel peridotitesk

Davis

Cottrell

Birner

et al. 2017

American Mineralogist

View full text Add to dashboard Cite

Natural peridotite samples containing olivine, orthopyroxene, and spinel can be used to assess the oxygen fugacity ( f O 2 ) of the upper mantle. The calculation requires accurate and precise quantification of spinel Fe 3+ /SFe ratios. Wood and Virgo (1989) /ΣFe ratios depends on the total concentration of Fe, and varies from ±0.012 to ±0.032 (1σ) in the samples analyzed; precision of uncorrected analyses is poorer by approximately a factor of two. We also present an examination of the uncertainties in the calculation contributed by the other variables used to derive f O2 . Because there is a logarithmic relationship between the activity of magnetite and logf O2 , the uncertainty in f O2 relative to the QFM buffer contributed by the electron microprobe analysis of spinel is asymmetrical and larger at low ferric Fe concentrations (+0.3/-0.4 log units, 1σ, at Fe 3+ /ΣFe = 0.10) than at higher ferric Fe concentrations (±0.1 log units, 1σ, at Fe 3+ /ΣFe = 0.40). Electron microprobe analysis of olivine and orthopyroxene together contribute another ±0.1 to ±0.2 log units of uncertainty (1σ). Uncertainty in the temperature and pressure of equilibration introduce additional errors on the order of tenths of log units to the calculation of relative f O2 . We also document and correct errors that appear in the literature when formulating f O2 that, combined, could yield errors in absolute f O2 of greater than 0.75 log units-even with perfectly accurate Fe 3+ /ΣFe ratios. Finally, we propose a strategy for calculating the activity of magnetite in spinel that preserves information gained during analysis about the ferric iron content of the spinel. This study demonstrates the superior accuracy and precision of corrected EPMA measurements of spinel Fe 3+ /ΣFe ratios compared to uncorrected measurements. It also provides an objective method for quantifying uncertainties in the calculation of f O2 from spinel peridotite mineral compositions.

show abstract

Experimental tests of garnet peridotite oxygen barometry

Cited by 125 publications

References 22 publications

The redox state of the mantle during and just after core formation

The redox state of the mantle during and just after core formation

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

Revisiting the electron microprobe method of spinel-olivine-orthopyroxene oxybarometry applied to spinel peridotitesk

Contact Info

Product

Resources

About