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Book Chapter

40Ar/39Ar ages of impacts involving ordinary chondrite meteorites

By
Timothy D. Swindle
Timothy D. Swindle
1
Lunar and Planetary Laboratory and Departments of Planetary Science and Geosciences, University of Arizona, 1629 E. University Blvd., Tucson AZ 85721-0092 USA
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D. A. Kring
D. A. Kring
2
Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston TX 77058 USA
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J. R. Weirich
J. R. Weirich
3
School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe AZ 85187-1404 USA
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Published:
January 01, 2014

Abstract

Impact ages have now been determined for c. 100 ordinary chondrites, providing information about impacts in the asteroid belt throughout the history of the Solar System. Most notably, there is evidence for (a) impact events in the first 100 Ma of Solar System history, during the accretion of material; (b) an increase in impact ages produced between 3500 and 4100 Ma, presumably related to the suspected ‘lunar cataclysm’; (c) many L chondrites being degassed during the disruption of their parent body slightly less than 500 Ma ago; and (d) at least one younger event in the H chondrites. There are no 40Ar/39Ar ages that clearly match the cosmic ray exposure ages of any meteorites, which means that the collisions that liberated the fragments we now have as meteorites did not produce time–temperature histories capable of degassing radiogenic 40Ar. Since there is no way to know a priori whether an ordinary chondrite impact melt is the result of a recent or ancient event, much of the progress will continue to come from reconnaissance studies of shocked ordinary chondrites.

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Contents

Geological Society, London, Special Publications

Advances in 40Ar/39Ar Dating: From Archaeology to Planetary Sciences

F. Jourdan
F. Jourdan
Curtin University, Australia
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D. F. Mark
D. F. Mark
Scottish Universities Environmental Research Centre, UK
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C. Verati
C. Verati
University of Nice, France
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Geological Society of London
Volume
378
ISBN electronic:
9781862396623
Publication date:
January 01, 2014

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