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标题：Statistical analyses of Global U-Pb Database 2017
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作者：Stephen J. Puetz ; Carlos E. Ganade ; Udo Zimmermann 等
期刊名称：Geoscience Frontiers
印刷版ISSN：1674-9871
出版年度：2018
卷号：9
期号：1
页码：121-145
DOI：10.1016/j.gsf.2017.06.001
语种：English
出版社：Elsevier
摘要：AbstractThe method of obtaining zircon samples affects estimation of the global U-Pb age distribution. Researchers typically collect zircons via convenience sampling and cluster sampling. When using these techniques, weight adjustments proportional to the areas of the sampled regions improve upon unweighted estimates. Here, grid-area and modern sediment methods are used to weight the samples from a new database of 418,967 U-Pb ages. Preliminary tests involve two age models. Model-1 uses the most precise U-Pb ages as the best ages. Model-2 uses the206Pb/238U age as the best age if it is less than a 1000 Ma cutoff, otherwise it uses the207Pb/206Pb age as the best age. A correlation analysis between the Model-1 and Model-2 ages indicates nearly identical distributions for both models. However, after applying acceptance criteria to include only the most precise analyses with minimal discordance, a histogram of the rejected samples shows excessive rejection of the Model-2 analyses around the 1000 Ma cutoff point. Because of the excessive rejection rate for Model-2, we select Model-1 as the preferred model. After eliminating all rejected samples, the remaining analyses use only Model-1 ages for five rock-type subsets of the database: igneous, meta-igneous, sedimentary, meta-sedimentary, and modern sediments. Next, time-series plots, cross-correlation analyses, and spectral analyses determine the degree of alignment among the time-series and their periodicity. For all rock types, the U-Pb age distributions are similar for ages older than 500 Ma, but align poorly for ages younger than 500 Ma. The similarities (>500 Ma) and differences (<500 Ma) highlight how reductionism from a detailed database enhances understanding of time-dependent sequences, such as erosion, detrital transport mechanisms, lithification, and metamorphism. Time-series analyses and spectral analyses of the age distributions predominantly indicate a synchronous period-tripling sequence of ∼91-Myr, ∼273-Myr, and ∼819-Myr among the various rock types.Graphical abstractDisplay OmittedHighlights•418,967 record global U-Pb database, with GPS coordinates given for every sample.•To estimate the U-Pb age-distribution, samples are weighted proportionally to areas.•Evidence that U-Pb accuracy and precision vary similarly, as a function of time.•Switch at 1000 Ma, from206Pb/238U to207Pb/206Pb ages, biases the age-distribution.•U-Pb age-distribution exhibits period-tripling cyclicity of 91, 273, and 819 myr.
关键词：KeywordsenTime seriesSpectral analysisPeriodicitySamplingReductionismZircon