Massive chromite in the Brenham pallasite and the fractionation of Cr during the crystallization of asteroidal cores

Wasson, J. T.; Lange, David E.; Francis, Carl A.; Ulff-Møller, Finn

doi:10.1016/s0016-7037(98)00307-x

Cited by 59 publications

(63 citation statements)

References 18 publications

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“…This result is a strong argument in favor of the hypothesis that pallasites are igneous cumulates, as proposed by Wood (1978), Takahashi (1983), and Greenberg and Chapman (1984). However, we cannot definitely exclude that large, rounded grains of olivine in pallasites were formed from fragments by high-temperature annealing (Scott 1977b;Wasson et al 1999), because our experiments do not document the effect of sulfur on the rounding kinetics. A pallasite with a typical troilite content of 1 wt% would contain »5% of sulfide liquid at 1400°C, and sulfide liquid will coexist with olivine and solid metal down to »1000°C (the eutectic temperature in the Fe-Ni-S system; Urakawa, Kato, and Kumazawa 1987).…”

Section: Implications For the Thermal History Of Pallasitesmentioning

confidence: 47%

Morphological analysis of olivine grains annealed in an iron‐nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies

Saiki

Laporte

Vielzeuf

et al. 2003

Meteorit & Planetary Scien

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Morphological analysis of olivine grains annealed in an iron-nickel matrix:Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies Abstract-Two types of pallasites can be distinguished on the basis of the grain shape of olivine (rounded or angular). It has been suggested that these two types of textures resulted from different degrees of annealing at high temperature in the parent body. In order to characterize the kinetics of rounding of olivine grains in an Fe-Ni matrix, we carried out a series of annealing experiments using a mixture of olivine and Fe-Ni powder. We were able to reproduce, at a miniature scale, the range of textures in pallasites. The rate of rounding was rapid enough to be observed and measured at the scale of a few micrometers to 20 mm, even though the experiments were performed below the solidus of the Fe-Ni metal. For instance, grains »14 mm in diameter became nearly spherical within 7 days at 1400ºC. For the morphological analysis of olivine grains, we used two independent techniques: the "critical diameter method" and the "Gaussian diffusion-resample method," a new technique specially developed for our study. Both techniques indicate that the rounding time scale is proportional to the cube of the grain size and that morphological adjustments in our experiments occurred by volume diffusion in the olivine lattice, not by surface diffusion along the olivine-metal boundaries. We used our experimental data to estimate the time scales required for the development of olivine-metal textures in natural pallasites. We determined that small scale rounding of olivine grains in a solid metal matrix can be produced within relatively short time intervals: »100 years to produce rounded olivine grains 0

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Section: Implications For the Thermal History Of Pallasitesmentioning

confidence: 47%

Morphological analysis of olivine grains annealed in an iron‐nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies

Saiki

Laporte

Vielzeuf

et al. 2003

Meteorit & Planetary Scien

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“…As discussed by various authors (e.g., Wasson and Richardson, 2001), these negative trends are the opposite to those expected based on laboratory studies that yield D Cr values around 0.5 (e.g., Jones and Drake, 1983). To account for the negative trend Wasson et al (1999) suggested sampling biases resulting from the Cr-bearing phase (FeCr 2 O 4 or possibly CrN) being finely divided and commonly trapped in the metal of lowAu irons (and thus included in metallic samples) but coarse and avoidable when sampling the high-Au meteorites. Another possibility is that chromite was a liquidus phase, thus causing Cr to behave like a compatible siderophile (Ulff-Møller, 1998a) The sampling interpretation is supported by the presence of massive chromite in the Brenham main-group pallasite whereas the Cr content of the metal is low, ca.…”

Section: Element-au Trends In Group Iid; Comparison With Those In Gromentioning

confidence: 76%

Compositional trends among IID irons; their possible formation from the P-rich lower magma in a two-layer core

Wasson

Huber

2006

Geochimica et Cosmochimica Acta

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“…Chromites have been found in iron meteorites (Bunch et al, 1970;Bunch and Keil, 1971;Wasson et al, 1999;Fehr and Carion, 2004), stony iron meteorites (Wasson et al, 1999), and achondrites (Chikami et al, 1999). Some of them contain appreciable amounts of Zn (e.g., Bunch et al, 1970;Chikami et al, 1999).…”

Section: Meteoritesmentioning

confidence: 99%

“…The plots also show chromites low in Zn and Mn and associated with zincian chromites for altered/metamorphosed rocks. Data sources are as follows: Meyer and Boyd (1972), Stachel et al (2000), Taylor et al (2003), and Donnelly et al (2007) for diamond inclusions; Bunch et al (1970Bunch et al ( , 1972, Bunch and Keil (1971), Desnoyers et al (1985), Krot et al (1992), Ikeda et al (1997), Chikami et al (1999), Wasson et al (1999), and Fehr and Carion (2004) for meteorites; and Thayer et al (1964), Wylie et al (1987), Challis et al (1995), Weiser and Hirdes (1997), Gahlan and Arai (2007), and Johan and Ohnenstetter (2010) for low -temperature altered/metamorphosed peridotites and related rocks. Zincian chromite of possible deep recycling origin Relationships between Cr/(Cr + Al) atomic ratio and Mg#, and Cr -Al -Fe 3+ atomic ratios of zincian chromites and related spinels.…”

Section: Meteoritesmentioning

confidence: 99%

Zincian chromite inclusions in diamonds: Possibility of deep recycling origin

Arai

Ishimaru

2011

Journal of Mineralogical and Petrological Sciences

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It was reported by Meyer and Boyd (1972) that zincian chromite, having 2 wt% to 3 wt% ZnO and high (>0.9) Cr# (= Cr/(Cr + Al) atomic ratio), appears as inclusions in diamonds obtained from kimberlite. Zincian chromite is characterized by a low (<0.03) Mg# [= Mg/(Mg + ferrous Fe + Zn + Mn + Ni + Co) atomic ratio] and an appreciable amount of MnO (0.4 -0.5 wt%). The chemistry of zincian chromite is very different from commonly found chromite inclusions (magnesiochromite) in diamonds, which contain low amounts of ZnO (<0.1 wt%) and MnO (<0.1 wt%). Zincian and manganoan chromites are also commonly found in meteorites and in altered/ metamorphosed peridotites and related rocks. The chromites found in meteorites mostly have an intermediate Mg# (0.2 -0.5) and a high Cr# (mostly >0.8); moreover, the major -element chemistry of these chromites is similar to that of the magnesiochromite inclusions in diamonds. Spinels obtained from altered rocks show a chemical range that comprises the zincian chromite inclusions found in diamonds. The origin of these inclusions possibly lies in deep recycling. They were initially formed at the Earth's surface in altered/metamorphosed peridotites; they then sank deep down into the mantle and were entrained to the surface again by kimberlite magmatism.

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Massive chromite in the Brenham pallasite and the fractionation of Cr during the crystallization of asteroidal cores

Cited by 59 publications

References 18 publications

Morphological analysis of olivine grains annealed in an iron‐nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies

Morphological analysis of olivine grains annealed in an iron‐nickel matrix: Experimental constraints on the origin of pallasites and on the thermal history of their parent bodies

Compositional trends among IID irons; their possible formation from the P-rich lower magma in a two-layer core

Zincian chromite inclusions in diamonds: Possibility of deep recycling origin

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