On the nonstoichiometry and point defects of olivine

Nakamura, Akio; Schmalzried, H.

doi:10.1007/bf01204323

Cited by 201 publications

(78 citation statements)

References 18 publications

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“…Calculations based on crystal field theory predicted many years ago that spin crossover could occur in Fe 2+ minerals at pressures within the lower mantle (Burns, 1993 and references therein). , which is supported by crystal chemical arguments (O'Neill et al, 1993a) and the results of thermogravimetric experiments (Nakamura and Schmalzried, 1983 (Dyar et al, 1989;Luth and Canil, 1993;Canil et al, 1994;Canil and O'Neill, 1996) (O'Neill et al, 1993a;Canil et al, 1994;McCammon, 2005a). At higher pressures in the upper mantle (above approximately 4 GPa) spinel is replaced by garnet, which also incorporates observable Fe 3+ (3 13% Fe 3+ /ΣFe) (Luth et al, 1990;Canil et al, 1994;Canil and O'Neill, 1996;Woodland and Koch, 2003;McCammon and Kopylova, 2004) (McCammon and Kopylova, 2004;McCammon, 2005a).…”

Section: Microscopic Properties: the Atomic Scalesupporting

confidence: 49%

Microscopic properties to macroscopic behaviour: The influence of iron electronic state

McCammon

2006

Journal of Mineralogical and Petrological Sciences

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Iron is the only major element in the Earth with multiple electronic configurations (oxidation and spin state). In the upper mantle and transition zone iron is predominantly Fe 2+ , but the small amount of Fe 3+ that is present significantly affects properties that are sensitive to defect chemistry, including electrical conductivity, diffusivity and hydrogen solubility. Fe 3+ also determines the oxygen fugacity, where the upper mantle is relatively oxidised due to the high Fe 3+ /ΣFe ratio in spinel, even though the overall Fe 3+ concentration in the upper mantle is low due to its concentration in modally minor phases. The transition zone contains a similar amount of Fe 3+ , but its distribution among all the major phases results in a significantly lower oxygen fugacity, near metal saturation. In the lower mantle the transition to (Mg,Fe)(Si,Al)O 3 perovskite involves the creation of significant Fe 3+(approximately 50% of available iron), even at reducing conditions, which is likely balanced in the bulk lower mantle by disproportionation of Fe 2+ to form Fe 3+ and metallic iron, and potentially in subducting slabs through reduction of oxidised species in the slab. The nature of Fe 3+ charge balance in (Mg,Fe)(Si,Al)O 3 perovskite largely determines the influence on physical and chemical properties, where electrical conductivity is enhanced, diffusivity is reduced, and elasticity and hydrogen solubility vary depending on the substitution mechanism. If Fe 2+ is more stable in the post perovskite phase relative to (Mg,Fe)(Si,Al)O 3 perovskite as suggested by experiments, both Fe 3+ /ΣFe and the nature of its influence on physical and chemical properties may be different in the post perovskite phase. The influence of spin crossover on mantle properties remains unclear. Recent models show that the growth of an (Mg,Fe)(Si,Al)O 3 perovskite rich lower mantle during core formation would progressively oxidise the mantle to present levels as a portion of the disproportionated iron rich metal phase became incorporated into the core, and the increase in oxygen fugacity during the later stages of Earth accretion would alter the partitioning behaviour of elements between mantle and core, resolving puzzles such as the siderophile element anomaly and the discrepancy between U-Pb and Hf-W systematics in the early Earth. Redox reactions involved in the movement of material across the lower mantle boundary could be related to the formation of deep diamonds, and potentially the rise of atmospheric oxygen through a mantle avalanche in the late Archean that disturbed the balance of volatile element cycles.

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Section: Microscopic Properties: the Atomic Scalesupporting

confidence: 49%

Microscopic properties to macroscopic behaviour: The influence of iron electronic state

McCammon

2006

Journal of Mineralogical and Petrological Sciences

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“…Results of thermogravimetric measurements on (Mg,Fe) olivines in progress in Schmalzried's laboratory challenge this assumption (Nakamura and Schmalzried, 1983a). In unbuffered samples (no excess FeO or Si0 2 ), the authors observe weight change proportional to PO/5 for Fe/Mg > 0.25.…”

Section: Point Defect Chemistrymentioning

confidence: 92%

High-Temperature Creep of Silicate Olivines

Kohlstedt

Ricoult

1984

Deformation of Ceramic Materials II

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“…For opx-buffered samples, the hydrogen concentration associated with Group I bands depends on oxygen fugacity to the ~ 1/6 power. For the charge neutrality condition 2[-V~e]=[Fe;~] a charge neutrality condition that has been proposed for olivine by several studies (e.g., Nakamura and Schmalzried 1983;Schock et al 1989) -the concentrations of both metal (Me) vacancies and doubly-charged oxygen interstitials have oxygen fugacity exponents of 1/6 (Stocker and Smyth 1978)2. Thus, they are two possible point defects that, when associated with hydrogen, are responsible for the Group I bands.…”

Section: (I) Constraints On Incorporation Mechanisms From Fo~ Exponentsmentioning

confidence: 98%

“…To determine the concentration of metal vacancies, [V~e], Nakamura and Schmalzried (1983) conducted a thermogravimetry study on reportedly unbuffered samples of (Mgl_ x Fex)2SiO 4 with x in the range 0.2-1.0. An extrapolation of their (18b) to x=0.1 yields ~250 and 1000 " 6 " VMe/10 Sl for oxygen fugacities of 10 -8 and 10-5 MPa, respectively.…”

Section: ~3) Comparison Of H Solubility With V~'e Concentrationmentioning

confidence: 99%