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Published January 28, 1972 | public
Journal Article

Gas-Retention and Cosmic-Ray Exposure Ages of Lunar Rock 15555

Abstract

The last lava flow in the Hadley Rille area of Mare Imbrium, as inferred from an argon-40-argon-39 experiment on a plagioclase separate from the lunar basalt 15555, occurred 3.31±0.03x10⁹ years ago. An argon-40-argon-39 experiment on a whole rock sample shows significant loss of radiogenic argon-40 and yields a well-defined, high-temperature plateau indicating a lower age of 3.22±0.03x10⁹ years. A cosmic-ray exposure age of 90±10x10⁶ years is determined from the ratio of spallogenic argon-38 to calcium.

Additional Information

© 1972 American Association for the Advancement of Science. Received 18 November 1971. We are indebted to J. Brown for the preparation of mineral separates and to T. Wen and D. A. Papanastassiou for the potassium analysis. Supported by NASA contract NAS-9-8074 and NSF grant GP-19887. Division of Geological and Planetary Sciences contribution number 2085.

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023