The Shaw meteorite: History of a chondrite consisting of impact-melted and metamorphic lithologies

Taylor, G. J.; Keil, K.; Berkley, J. L.; Lange, David E.; Fodor, R. V.; Fruland, R. M.

doi:10.1016/0016-7037(79)90198-4

Cited by 68 publications

(56 citation statements)

References 32 publications

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“…This evidence includes 39 Ar ages of 4.52-4.38 Ga (Turner, Enright, and Cadogan 1978), Pb-Pb ages of whole rock and phosphate samples of 4.41-4.56 Ga, Pu fission track ages down to ~4.4 Ga (Pellas and Fieni 1988), and Ni metallographic cooling rates as low as a few °C/Myr (Scott and Rajan 1981). In contrast, Ar-Ar ages of shocked ordinary chondrites are generally <4.2 Ga, though a few ages (such as Shaw) that lie between 4.3 and 4.54 Ga may have been produced by early impacts (Bogard 1995;Bogard and Hirsch 1980;Taylor et al 1979;Turner 1969). In addition, Ni metallographic cooling rates of some strongly shocked chondrites are much faster (1°C/100 yr to 100°C/d), indicating post-shock cooling at relatively shallow depths of less than 1 km (Smith and Goldstein 1977).…”

Section: Introductionmentioning

confidence: 99%

³⁹Ar‐⁴⁰Ar chronology of R chondrites

Dixon

Bogard

Garrison

2003

Meteorit & Planetary Scien

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Because the meteorites with the oldest (Rumuruti, ~4.47 Ga) and the youngest (Acfer 217, ~4.30 Ga) ages are both breccias, these ages probably do not record slow cooling within an undisrupted asteroidal parent body. Instead, the process of breccia formation may have differentially reset the ages of the constituent material, or the differences in their age spectra may arise from mixtures of material that had different ages. Two end-member type situations may be envisioned to explain the age range observed in the R chondrites. The first is if the impact(s) that reset the ages of Acfer 217 and Rumuruti was very early. In this case, the ~170 Ma maximum age difference between these meteorites may have been produced by much deeper burial of Acfer 217 than Rumuruti within an impact-induced thick regolith layer, or within a rubble pile type parent body following parent body re-assembly. The second, preferred scenario is if the impact that reset the age of Acfer 217 was much later than that which reset Rumuruti, then Acfer 217 may have cooled more rapidly within a much thinner regolith layer. In either scenario, the oldest age obtained here, from Rumuruti, provides evidence for relatively early (~4.47 Ga) impact events and breccia formation on the R chondrite parent body.

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Section: Introductionmentioning

confidence: 99%

³⁹Ar‐⁴⁰Ar chronology of R chondrites

Dixon

Bogard

Garrison

2003

Meteorit & Planetary Scien

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“…Such a petrographic feature observed in lithology (II) is similar to the light-colored, vesicular region of the shock-melted meteorite Shaw (Taylor et al, 1979), the angular fragment in Ngawi (Fodor. and Keil, 1978), and the lithic fragment in Bovedy (Rubin et al, 1981).…”

Section: Petrography and Mineralogymentioning

confidence: 72%

“…On the basis of the REE patterns of glass and consti tuent minerals in the Bovedy and Semarkona clasts, as well as the presence of 16 Mg excesses due to in situ decay of the extinct radioisotope Tokyo 182, Japan 26A1 U112= 7 .2 x 105 y), it has been suggested that planetary differentiation must have begun at a very early stage of the solar system, i.e., prior to the end of accretion of unequilibrated ordinary chondrites and/or within a time scale com parable to the mean life of 26A1 (Hutcheon and Hutchison, 1989;. Others have proposed that these clasts were derived from melt sheets within large impact craters on their parent bodies (Taylor et al, 1979;Keil, 1982;Rubin, 1985;Grossman and Rubin, 1986). Grossman and Rubin (1986) described igneous clasts from the Manych (LL 3.4) and Ngawi (LL 3.6) chondrites that show a smooth decrease in element abundances with increasing volatility.…”

Section: Introductionmentioning

confidence: 99%

A noritic clast from the Hedjaz chondritic breccia: implications for melting events in the early solar system.

et al. 1992

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and Au were deter mined in a unique, noritic clast carrying a fractionated REE component from the Hedjaz (L) chondritic breccia by instrumental neutron activation analysis and isotope dilution mass spectrometry. The clast, previously described by Nakamura et al. (1990), consists of two lithologies, and is depleted in siderophile and moderately volatile lithophile elements when compared with its host meteorite. The REE abundance pattern of the clast is L-chondritic (1.4-1.6 x CI-chondrite) with a large (62%), positive Eu anomaly. Strontium is also enriched (3.2 x CI-chondrite) relative to trivalent REE.Chemical and petrologic data suggest that the elemental fractionations observed in the Hedjaz noritic clast could be accomplished in a single host-like parent body with several episodes of impact melting and heating. An impact melt enriched in feldspar components could have been generated in a neighboring region on a parent body, and then infiltrated into the precursor material of the clast. An enhancement of plagiophile elements would then be produced in the clast. Moderately volatile element and siderophile element fractionations could be related to gas /solid or gas /liquid processes and silicate/metal melt fractionations, respectively, which may have occurred during melting and formation of the clast.

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“…Petrographic precedents of equilibrated L chondrites which have experienced near complete shock melting or total shock melting are known and complete a consistent sequence while additionally accounting for the observations in this work. The L6 Chico (Norman and Mittlefehldt, 2002), the L chondrite melt rock PAT 91501 (Mittlefehldt and Lindstrom, 2001), L6 Shaw (Taylor et al, 1979) and the L6 Tenham melt breccia (Leroux et al, 2000) are examples of samples where, to different degrees, metal and silicate have been partitioned to an extent much greater than that observed in the samples included in this study because of their reaching higher whole rock temperatures.…”

Section: Box and Whisker Plots Of Mildly-shocked (N = 11) And Stronmentioning

confidence: 99%

Limit on the scale of impact-related metal/silicate segregation on L chondrite parent(s)

Friedrich

2006

Geochem. J.

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To assess the role of impact related reheating on compositional trends in the major elements of the L chondrite parent(s), I examined a suite of 37 L falls analyzed by Jarosewich (1990). After eliminating 8 samples prepared from quantities which differently sampled the chondrites considered, I found that suites of mildly-shocked (S3) and strongly-shocked (S4-S6) equilibrated L chondrite falls can be distinguished at statistically significant levels when compared based on their major element content. Graphical comparisons demonstrated that the differences arise because siderophiles are depleted with corresponding mass-balanced lithophile enrichment in strongly-shocked samples. Since the samples considered here were derived from volumes of between 1.5 cm 3 and 4.7 cm 3 , we can conclude that statistically significant post-metamorphic metal(sulfide)/silicate segregation occurred on a scale of at least this size.

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The Shaw meteorite: History of a chondrite consisting of impact-melted and metamorphic lithologies

Cited by 68 publications

References 32 publications

³⁹Ar‐⁴⁰Ar chronology of R chondrites

³⁹Ar‐⁴⁰Ar chronology of R chondrites

A noritic clast from the Hedjaz chondritic breccia: implications for melting events in the early solar system.

Limit on the scale of impact-related metal/silicate segregation on L chondrite parent(s)

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The Shaw meteorite: History of a chondrite consisting of impact-melted and metamorphic lithologies

Cited by 68 publications

References 32 publications

39Ar‐40Ar chronology of R chondrites

39Ar‐40Ar chronology of R chondrites

A noritic clast from the Hedjaz chondritic breccia: implications for melting events in the early solar system.

Limit on the scale of impact-related metal/silicate segregation on L chondrite parent(s)

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³⁹Ar‐⁴⁰Ar chronology of R chondrites

³⁹Ar‐⁴⁰Ar chronology of R chondrites