metamorphism
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Legacy product - no abstract available
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Legacy product - no abstract available
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Legacy product - no abstract available
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Metamorphic map of Australia
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Legacy product - no abstract available
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Legacy product - no abstract available
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pt. 1. Igneous and metamorphic -- pt. 2. Sedimentary rocks -- pt. 3. Igneous and metamorphic
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No abstract available
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Legacy product - no abstract available
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The timing and duration of metamorphic events is commonly constrained by radiometric dating using the U-Pb or 40Ar-39Ar dating methods, or a combination of both. Each dating method can be applied to a different range of minerals, and a combination of the two methods can provide more complete timing constraints than either method on its own. Comparison of radiometric ages from different isotopic systems introduces the problem of systematic uncertainties arising from uncertainty in parameters such as decay constants and the age of method-specific reference materials. Over the past decade it has been increasingly recognized that the laboratory-based determinations of the 40K decay constants, on which the 40Ar-39Ar method is based, are relatively imprecise and that the values recommended by Steiger and Jager (1977) result in a systematic offset of 40Ar-39Ar ages relative to U-Pb-derived ages by up to ~1%. This problem has been addressed by several studies over the past decade, with the most recent study (Renne et al., 2010; 2011) providing refined estimates for the 40K decay constants, and very significant improvements in precision. Paleozoic and Paleoproterozoic examples will be presented which illustrate the improvements in the accuracy and precision of 40Ar-39Ar ages calculated using the revised decay constants, and discuss the implications for studies that use a combination of U-Pb and 40Ar-39Ar data to constrain the timing and duration of metamorphic, deformation, and mineralisation events. An Excel spreadsheet is available on request that allows recalculation of 40Ar-39Ar ages and uncertainties using the revised parameters of Renne et al. (2010; 2011), provided certain minimum information has been reported with the published ages.