Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Benedix, Gretchen; Лауретта, Д. С.; McCoy, T. J.

doi:10.1016/j.gca.2005.03.048

Cited by 68 publications

(101 citation statements)

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“…2). Benedix et al (2005) used 2-pyroxene temperatures to calculate the fO 2 conditions recorded by Winona and silicates in IAB irons near the peak temperatures experienced by these meteorites. These temperatures and fugacities are also shown in Fig.…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…The experiments were designed to bracket these conditions using sealed silica tube experiments (closed squares) along the C-CO buffer and open-system gas mixing (open squares) experiments at ~IW-3. Kernouvé intrinsic oxygen calculated using the method of Benedix et al (2005) is also plotted for comparison. …”

Section: Experimental Techniquesmentioning

confidence: 99%

“…We observe substantial changes in olivine composition with increasing temperature; becoming more magnesian and reaching values that overlap those of primitive achondrites at the 1300 °C temperature step. We calculate that similar changes could have occurred during partial melting at temperatures that were more typically 1000-1100 °C (Benedix et al 1998(Benedix et al , 2000(Benedix et al , 2005, if we consider that slower diffusion rates (Misener 1974) are compensated by time scales on the order of tens of millions of years (Bogard et al 1967;Niemeyer 1979;Wadhwa and Russell 2000). We speculate that reduction of orthopyroxene could also occur given these temperatures and time, although only modest changes were observed in our experiments.…”

Section: Implications For Primitive Achondritesmentioning

confidence: 99%

“…In ordinary chondrites, chromite Cr/Cr + Al ranges from 1.0 in type 3 chondrites to 0.85 in type 6 chondrites like Kernouvé (Bunch et al 1967). Chromite compositions in winonaites and IAB irons have Cr/Cr + Al that ranges from 0.95 to 1.0, while Fe/ Fe + Mg ranges from 0.3 to 0.6 (Bunch et al 1970;Benedix et al 2005). In our experiments, chromite Cr/Cr + Al varies only marginally (Table 3), suggesting that trivalent cations are not redistributed during partial melting of a metamorphosed chondritic precursor.…”

Section: Implications For Primitive Achondritesmentioning

confidence: 99%

“…One application of these experiments address whether primitive achondrites could have formed from ordinary chondrite-like precursors by partial melting under reducing conditions. While changes observed in olivine and troilite compositions might support such an idea, differences in oxygen isotopic composition, Cr/Cr + Al in chromite, orthopyroxene compositions, and thermodynamic evidence against reduction during melting of primitive achondrites (Benedix et al 2005) firmly refute such an idea. …”

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confidence: 99%

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Partial melting of H6 ordinary chondrite Kernouvé: Constraints on the effects of reducing conditions on oxidized compositions

Ford

Benedix

McCoy

et al. 2008

Meteorit & Planetary Scien

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Abstract-Partial melting experiments at temperatures of 950-1300 °C were conducted on the H6 chondrite Kernouvé under reducing conditions using CO-CO 2 gas mixing and graphite-buffered sealed silica tubes to examine the effect of reducing conditions during melting of starting materials that are more oxidized relative to the oxygen fugacity conditions of the experiments. The experiments produced a range of mineralogical and compositional changes. Olivine exhibits significant reduction to compositions of Fa 2-5 at temperatures of 1300 °C. In contrast, orthopyroxene exhibits only slight reduction until the highest temperatures. Chromite is sometimes consumed by intruding sulfides, and displays increasingly magnesian compositions ranging as low as Fe/Fe + Mg of 0.1 at a constant Cr/Cr + Al ratio. The compositional changes with increasing temperature reflect a complex set of reactions, including oxidation-reduction. One application of these experiments address whether primitive achondrites could have formed from ordinary chondrite-like precursors by partial melting under reducing conditions. While changes observed in olivine and troilite compositions might support such an idea, differences in oxygen isotopic composition, Cr/Cr + Al in chromite, orthopyroxene compositions, and thermodynamic evidence against reduction during melting of primitive achondrites (Benedix et al. 2005) firmly refute such an idea.

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Section: Experimental Techniquesmentioning

confidence: 99%

Section: Experimental Techniquesmentioning

confidence: 99%

Section: Implications For Primitive Achondritesmentioning

confidence: 99%

Section: Implications For Primitive Achondritesmentioning

confidence: 99%

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confidence: 99%

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Partial melting of H6 ordinary chondrite Kernouvé: Constraints on the effects of reducing conditions on oxidized compositions

Ford

Benedix

McCoy

et al. 2008

Meteorit & Planetary Scien

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Deciphering Redox State for a Metal-Rich World

et al. 2022

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The Psyche mission’s Oxidation-Reduction Working Group is focused on understanding, determining, and applying the redox state of (16) Psyche to understand the origin of a metal-rich world. The oxidation-reduction state of an asteroid, along with its temperature, parent body size, and composition, is a key parameter in determining the history of an asteroid. Determining the redox state from spacecraft data is most easily done by examining potential metal-oxide buffer pairs. The occurrence of Ni, Fe, C, Cr, P and Si, in that order, in the metal or sulfide phase of an asteroidal body indicates increasingly reduced conditions. Key observations by the Imager and Gamma-Ray and Neutron Spectrometer (GRNS) of Psyche can bracket the redox state using metal-oxide buffers. The presence of Fe,Ni metal can be confirmed by the ratios of Fe/O or Fe/Si and the concentration of Ni variability in metal across the asteroid can be determined by GRNS. The FeO concentration of silicates is complementary to the Ni concentration of metal and can be constrained using filters on the Imager. The presence of FeO in silicates from ground-based observations is one of the few measurements we already have of redox state, although available data permit a wide range of silicate compositions and mineralogies. The presence of C, P or Si concentrated in the metallic, Fe-rich portion of the asteroid, as measured by GRNS, or Ca-sulfide, determined by imaging, would indicate increasingly reducing conditions. Linkage to known types of meteorites, whether metal-rich chondrites, stony-irons or irons, expands the mineralogical, chemical and isotopic data not available from remote observations alone. Redox also controls both silicate and metal mineralogy, influencing differentiation, solidification, and subsolidus cooling, including the relative abundance of sulfur in the core and possible magnetic signatures. The redox state of Psyche, if a fully-differentiated metallic core, might constrain the location and timing of both the formation of Psyche and any oxidation it might have experienced.

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Mercury

McCubbin,

Anzures

2025

Treatise on Geochemistry

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Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons

Cited by 68 publications

References 17 publications

Partial melting of H6 ordinary chondrite Kernouvé: Constraints on the effects of reducing conditions on oxidized compositions

Partial melting of H6 ordinary chondrite Kernouvé: Constraints on the effects of reducing conditions on oxidized compositions

Deciphering Redox State for a Metal-Rich World

Mercury

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