文章基本信息

标题：A relational database of global U–Pb ages
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作者：Stephen J. Puetz
期刊名称：Geoscience Frontiers
印刷版ISSN：1674-9871
出版年度：2018
卷号：9
期号：3
页码：877-891
DOI：10.1016/j.gsf.2017.12.004
语种：English
出版社：Elsevier
摘要：AbstractEnhanced understanding of how sampling techniques affect estimates of the global U–Pb age-distribution have, in turn, constrained U–Pb database design. Recent studies indicate that each continent has a unique age-distribution, as determined by zircon ages dated by the U–Pb isotope method. Likewise, broad regions within a continent also exhibit diverse age-distributions. To achieve a reliable estimate of the global distribution, the heterogenous composition of the continental crust requires sampling as many regions as feasibly possible. To attain this goal, and to provide a method for calculating age histograms, the records from a recent global U–Pb compilation are supplemented with 281,631 new records. These additions increase the database size to 700,598 records. In addition, the data are now restructured and made available as a relational database. After filtering the records by the six age-models included with the database, the results reveal two problems that might generally be unrecognized. First, an abrupt switch in the best-age at any given point (such as 1000 Ma) from206Pb/238U ages to207Pb/206Pb ages artificially depresses the age-distribution at the cutoff point. Second, rejecting analyses based on either absolute discordance or the magnitude of 2σprecision errors artificially depresses the age-distribution between 900 Ma and 2000 Ma. The results indicate that, when estimating the global U–Pb age-distribution, the methods for determining best-age and for rejecting records both require some attention. Possible solutions include using either an Accuracy Model or a Precision Model for estimating best-age, and then including all U–Pb records in the estimate, rather than rejecting any of them.Graphical abstractDisplay OmittedHighlights•700,598 record global U–Pb database, with GPS coordinates given for every sample.•Filtering form provides means for including only records that meet specified criteria.•Switch from206Pb/238U to207Pb/206Pb artificially depresses the 1000 Ma age-count.•When estimating the global age-distribution, rejecting records can be problematic.•Graphical outputs include U–Pb age histograms and cumulative age distributions.
关键词：KeywordsenU–Pb age-distributionHistogramGlobal databaseSamplingFilteringZircon