U-Th-Pb age of the Barwell chondrite - Anatomy of a 'discordant' meteoriteA Pb-Pb internal isochron for the Barwell L5-6 chondrite yields an age of 4.530 plus or minus 0.005 billion years, using the measured U-238/U-235 ratio of 135.24 plus or minus .17. If the terrestrial U isotope composition is used, an age of 4.559 billion years is obtained. The Pb isotopic composition is distinctly different from that of a terrestrial contaminant found in the fusion crust of the Barwell stone. When the U-Th-Pb data are plotted on the concordia diagram, the data define a line that intersects the concordia curve at approximately 4.53 and 0 billion years, and nearly all of the data plot above the concordia curve, regardless of the initial Pb correction. This discordancy and the Pb isotopic composition of the triolite are attributed to a recent reequilibration of Pb and not to terrestrial contamination.
Document ID
19800039438
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Unruh, D. M. (Geological Survey Denver, CO, United States)
Tatsumoto, M. (U.S. Geological Survey Denver, Colo., United States)
Hutchison, R. (British Museum /Natural History/ London, United Kingdom)