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Systematics in the Pb^(208)-Th^(232), Pb^(207)-U^(235), and Pb^(206)-U^(238) Systems

Steiger, Rudolf H. and Wasserburg, G. J. (1966) Systematics in the Pb^(208)-Th^(232), Pb^(207)-U^(235), and Pb^(206)-U^(238) Systems. Journal of Geophysical Research, 71 (24). pp. 6065-6090. ISSN 0148-0227. doi:10.1029/JZ071i024p06065.

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In a study of cogenetic zircons it was found that the measured Pb^(208)/Th^(232) and Pb^(207)/U^(235) ratios formed a linear array in the corresponding coupled Pb-U-Th evolution diagram, which has an upper intersection on the concordia curve at the same time point as that determined by the Pb^(206)/U^(238), Pb^(207)/U^(235) array. Although the U-Pb data lie in the accessible region for nonfractionating daughter loss, the Th-Pb results lie outside the corresponding region. The zircon concentrates analyzed were shown to be multiphase assemblages with variable U and Th contents and variable Th/U ratios, even within single crystals. The zircons contain local domains of high radioactivity which appear to be highly discordant. A relationship between discordance and the average concentration of U and Th in a sample is given. The degree of discordance increases with the concentration of U and Th and with the increasing Th/U ratio, causing preferential loss of Pb^(208) and the departure from the region accessible to a single phase without fractionation. The theoretical aspects of the (equation image) diagram from the viewpoint of single-phase and multiphase assemblages are discussed, and it is shown that the variability of the Th/U ratio is of fundamental importance in understanding the evolution of the Th-U-Pb system. The existence of these systematics in nature may provide an additional independent dating system and a further means of studying transport from natural systems.

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Wasserburg, G. J.0000-0002-7957-8029
Alternate Title:Systematics in the Pb208-Th232, Pb207-U235, and Pb206-U238 Systems
Additional Information:Copyright 1966 by the American Geophysical Union. (Received July 27, 1966; revised September 13, 1966.) We acknowledge discussions with C. Allègre, G. L. Davis, S. R. Hart, and L. T. Silver. Constructive casual and causal comments by G. R. Tilton were very valuable. We wish to thank Dean Bohnenblust for the use of an old Tauberian device. Most of the analyses reported here were made in the laboratories of the Carnegie Institution of Washington, and we thank L. T. Aldrich for the use of the mass spectrometers. The microprobe analyses were done by A. Chodos, and C. Chase performed many of the computations. This work was supported by contracts from the Office of Naval Research [Nonr-220(47)], the Atomic Energy Commission [AT(04-3)-427], and grants from the National Science Foundation [GP-5391, GP-2796]. California Institute of Technology Contribution 1421.
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Office of Naval Research (ONR)Nonr-220(47)
Atomic Energy CommissionAT(04-3)-427
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Caltech Division of Geological Sciences1421
Issue or Number:24
Record Number:CaltechAUTHORS:20141110-095505555
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Official Citation:Steiger, R. H., and G. J. Wasserburg (1966), Systematics in the Pb208-Th232, Pb207-U235, and Pb206-U238 Systems, J. Geophys. Res., 71(24), 6065–6090, doi:10.1029/JZ071i024p06065.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51493
Deposited By: George Porter
Deposited On:10 Nov 2014 18:10
Last Modified:10 Nov 2021 19:11

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