| Reference Type | Journal (article/letter/editorial) |
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| Title | Geological age by instrumental analysis: the 29th Hallimond Lecture |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Compston, W. | Author |
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| Year | 1999 (June) | Volume | 63 |
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| Issue | 3 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_63/63-3-297.pdf+ |
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| DOI | doi:10.1180/002646199548475Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 1283 | Long-form Identifier | mindat:1:5:1283:0 |
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| GUID | 0 |
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| Full Reference | Compston, W. (1999) Geological age by instrumental analysis: the 29th Hallimond Lecture. Mineralogical Magazine, 63 (3) 297-311 doi:10.1180/002646199548475 |
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| Plain Text | Compston, W. (1999) Geological age by instrumental analysis: the 29th Hallimond Lecture. Mineralogical Magazine, 63 (3) 297-311 doi:10.1180/002646199548475 |
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| Abstract/Notes | AbstractThe need in geology for in situ U-Pb age determinations of minerals is illustrated by two examples: the internal age dispersion developed within the zircon SL13 shortly after original crystallization, and the occurrence within minerals of old cores and later overgrowths. SL13 contains rare μm-sized patches of unsupported radiogenic Pb and a mainly bimodal distribution of 206Pb/238U ages otherwise. Both observations are consistent with original crystallization at 580 Ma and Pb loss at 565 Ma. Age precision is controlled by the ions counted for radiogenic Pb, and varies with instrumental sensitivity, age and U contents of the target. Laser-ablation ICPMS has similar spatial resolution and sensitivity to SIMS but consumes more sample because of much greater hole-depth in practice. Like SIMS, the measured Pb+/U+ is biased and also changes with depth so comparison with a standard mineral is necessary. Analyses of reference zircons reported here indicate that the reproducibility of Pb/U ages by ICPMS is limited by residual bias, not ion counting errors. For multipurpose ICPMS at least, the Hg background at mass 204 prohibits the measurement of 204Pb for common Pb estimation. A third micro-analytical method, ‘CHIME’, and future developments in SIMS and ICPMS are discussed briefly. |
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