Laser probe sup 40 Ar- sup 39 Ar studies of the Peace River shocked L6 chondrite

Journal Article · Sat Oct 01 04:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90307-9· OSTI ID:5180533

McConville, P; Kelley, S; Turner, G ^[1]

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1. Sheffield Univ. (England)

Samples of matrix and melt glass from the shocked L6 chondrite Peace River have been subjected to {sup 40}Ar-{sup 39}Ar analysis using both stepped heating and localized outgassing by a laser probe. Stepped heating studies of three distinct samples of matrix gave indistinguishable and unusually well-defined low temperature ({sup 40}Ar/{sup 39}Ar) plateaux, corresponding to an age of 450 {plus minus} 30 Ma. In an attempt to investigate whether or not this plateau age is meaningful or is an artifact resulting from partial degassing, during the fragmentation of the parent body which commenced the exposure of Peace River to cosmic rays 40 Ma age, the authors have used a laser probe to analyze Ar from single 80 {mu}m diameter laser pits which release gas from a few micrograms of sample. On this scale no areas have ages younger than the plateau age, supporting the view that it is not an artifact. Measurements on the melt glass gave variable and meaningless ages, in some cases greater than the age of the solar system, due to retention of {sup 40}Ar and loss of K during melting followed by rapid quenching. This observation indicates the danger of attempts to date impact melt glass directly. The observation that argon has been retained by the glass and lost by the matrix can be understood in terms of a range of plausible annealing histories.

• OSTI ID: 5180533
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
AMORPHOUS STATE
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CHONDRITES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOCHEMISTRY
GEOLOGIC HISTORY
GLASS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LASER SPECTROSCOPY
LIGHT NUCLEI
METEORITES
NUCLEI
QUANTITATIVE CHEMICAL ANALYSIS
QUENCHING
RADIOISOTOPES
SPECTROSCOPY
STABLE ISOTOPES
STONE METEORITES
YEARS LIVING RADIOISOTOPES