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Accession Number N20130008965
Title Constraining the Flux of Impactors Postdating Heavy Bombardment Using U-Pb Ages of Impact Glasses.
Publication Date Mar 2013
Media Count 2p
Personal Author A. A. Nemchin M. L. Grange M. L. Norman R. A. Ziegler
Abstract Spherules of glass varying in size from a few micrometres to a few millimetres are common in the lunar regolith. While some of these glass beads are products of pyroclastic fire fountains others originate as impact melt ejected from the target that breaks into small droplets and solidifies as spherical particles while raining back to the lunar surface. These glasses preserve information about the chemical composition of the target and often contain sufficient amount of radioactive nuclides such as 40K to enable Ar-40-Ar-39 dating of individual beads. Studies measuring the age of glass beads have been used in attempts to establish variations in the flux of impactors hitting the Moon, particularly during the period that postdates the formation of major impact basins (1,2). These studies proposed a possibility of spike in the impact flux about 800 Ma (2) and over the last 400 Ma (1). More recently U-Th-Pb isotopic systems have been also utilized to determine the age of impact glasses from the Apollo 17 regolith (3). Our aim is to extend the application of the U-Pb system in impact glasses to spherules isolated from Apollo 14 soil 14163 in an attempt to further investigate the applicability of this isotopic system to the chronology of impact glass beads and gain additional information on the impact flux in the inner Solar system.
Keywords Apollo 17 flight
Chemical composition
Drop size
Impact melts
Radioactive isotopes

Source Agency National Aeronautics and Space Administration
NTIS Subject Category 54A - Astrogeology
84B - Extraterrestial Exploration
Corporate Author National Aeronautics and Space Administration, Houston, TX. Lyndon B. Johnson Space Center.
Document Type Conference proceedings
Title Note N/A
NTIS Issue Number 1319
Contract Number N/A

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