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CitationSwindle, T. D., Isachsen, C. E., Weirich, J. R., & Kring, D. A. (2009). 40Ar‐39Ar ages of H‐chondrite impact melt breccias. Meteoritics & Planetary Science, 44(5), 747-762.
PublisherThe Meteoritical Society
JournalMeteoritics & Planetary Science
Abstract40Ar-39Ar analyses of a total of 26 samples from eight shock-darkened impact melt breccias of H-chondrite affinity (Gao-Guenie, LAP 02240, LAP 03922, LAP 031125, LAP 031173, LAP 031308, NWA 2058, and Ourique) are reported. These appear to record impacts ranging in time from 303 +/- 56 Ma (Gao-Guenie) to 4360 +/- 120 Ma (Ourique) ago. Three record impacts 300-400 Ma ago, while two others record impacts 3900-4000 Ma ago. Combining these with other impact ages from H chondrites in the literature, it appears that H chondrites record impacts in the first 100 Ma of solar system history, during the era of the lunar cataclysm and shortly thereafter (3500-4000 Ma ago), one or more impacts ~300 Ma ago, and perhaps an impact ~500 Ma ago (near the time of the L chondrite parent body disruption). Records of impacts on the H chondrite parent body are rare or absent between the era of planetary accretion and the lunar cataclysm (4400-4050 Ma), during the long stretch between heavy bombardment and recent breakup events (3500-1000 Ma), or at the time of final breakup into meteorite-sized bodies (<50 Ma).