Graves Nunataks 95209: A snapshot of metal segregation and core formation

McCoy, T. J.; Carlson, William D.; Nittler, L. R.; Stroud, Rhonda M.; Bogard, D. D.; Garrison, D. H.

doi:10.1016/j.gca.2005.09.019

Cited by 43 publications

(39 citation statements)

References 46 publications

(66 reference statements)

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“…This is to be expected, since the Ar-Ar age has been interpreted as the cooling age (McCoy et al 2006). It has been suggested that lodranites experienced a relatively slow cooling from the peak metamorphic temperature to the closure temperature of Ar, followed by a rapid cooling (McCoy et al 1997a).…”

Section: Thermal History In Acapulcoite-lodranite Parent Bodymentioning

confidence: 85%

“…Lodranites and the transitional acapulcoite GRA 95209 have previously been dated by 40 Ar-39 Ar chronology (McCoy et al 1997a(McCoy et al , 2006, and the 4.52 Ga 40 Ar-39 Ar age is significantly younger than the Hf-W isochron age. This is to be expected, since the Ar-Ar age has been interpreted as the cooling age (McCoy et al 2006).…”

Section: Thermal History In Acapulcoite-lodranite Parent Bodymentioning

confidence: 99%

“…In contrast, lodranites are characterized by their coarse-grained texture and non-chondritic compositions, e.g., rich in Ca-pyroxene and deficient in plagioclase, troilite, and highly incompatible elements (Takeda et al 1994;McCoy et al 1997a;Mittlefehldt et al 1998). It appears that some basaltic melt had been extracted during the formation of lodranites (McCoy et al 2006), while the rest of the acapulcoite-lodranite clan samples show no evidence of melt moving (Mittlefehldt et al 1998).…”

Section: Introductionmentioning

confidence: 99%

“…Although the acapulcoite-lodranite parent body did not experience a global melting event, some samples, e.g., Graves Nunataks (GRA) 95209 and Monument Draw, do preserve extensive metal-sulfide-phosphate veins that seem to reflect the initial stage of metal-silicate segregation in their parent body (McCoy et al 1996(McCoy et al , 2006. Numerous methods have been used to date the formation of acapulcoite-lodranite clan, however, most of the studies were focused on acapulcoites.…”

Section: Introductionmentioning

confidence: 99%

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¹⁸²Hf‐¹⁸²W chronometry and the early evolution history in the acapulcoite‐lodranite parent body

Lee

2008

Meteorit & Planetary Scien

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Abstract-An acapulcoite, Northwest Africa (NWA) 725, a transitional acapulcoite, Graves Nunataks (GRA) 95209, and a lodranite, NWA 2235, have been studied with the short-lived chronometer 182 Hf-182 W system in order to better constrain the early evolution history in the acapulcoite-lodranite parent body. Unlike the more evolved achondrites originating from differentiated asteroids-e.g., eucrites and angrites-bulk rock acapulcoites and lodranite are characterized by distinct 182 W deficits relative to the terrestrial W, as well as to the undifferentiated chondrites, ε w varies from −2.7 to −2.4. This suggests that live-182 Hf was present during the formation of acapulcoites and lodranites, and their parent body probably had never experienced a global melting event. Due to the large uncertainties associated with the isochron for each sample, the bulk isochron that regressed through the mineral separates from all 3 samples has provided the best estimate to date for the timing of metamorphism in the acapulcoite-lodranite parent body, 5 (+6/−5) Myr after the onset of the solar system. It is thus inconclusive whether acapulcoites and lodranites have shared the same petrogenetic origin, based on the Hf-W data of this study. Nevertheless, the formation of acapulcoite-lodranite clan appears to have post-dated the metal-silicate segregation in differentiated asteroids. This can be explained by a slower accretion rate for the acapulcoite-lodranite parent body, or that it had never accreted to a critical mass that could allow the metal-silicate segregation to occur naturally.

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Section: Thermal History In Acapulcoite-lodranite Parent Bodymentioning

confidence: 85%

Section: Thermal History In Acapulcoite-lodranite Parent Bodymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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¹⁸²Hf‐¹⁸²W chronometry and the early evolution history in the acapulcoite‐lodranite parent body

Lee

2008

Meteorit & Planetary Scien

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“…Among these meteorites, one is truly remarkable. Graves Nunatak (GRA) 95209 contains metal veins that sample the earliest melting of an asteroid as it began to heat up more than 4.5 billion years ago ( McCoy et al, 2006). These veins record a complex history of melting, melt migration, oxidation-reduction reactions, intrusion into cooler regions, cooling, and crystallization.…”

Section: Scientific Value Of Antarctic Meteoritesmentioning

confidence: 99%