Quaternary geochronology using the U-Th-Pb method
- Univ. of California, Berkeley, CA (United States)
We describe a method of uranium-thorium-lead (U-Th-Pb) isotopic age dating for Quaternary rocks. The approach uses an instrumental mass discrimination correction for lead isotope ratios, which allows small enrichments of radiogenic {sup 206}Pb and {sup 208}Pb to be detected at the level of 0.001%. Igneous rocks hosting minerals with a range in {sup 238}U/{sup 204}Pb values of 100 can be dated with uncertainties of approximately {+-}15-20 kyr. A Quarternary rhyolite dated at 1.19 Ma by K-Ar yields a {sup 238}U-{sup 206}Pb age of 1.03{+-}0.10 Ma. A Holocene dacite (9.5 ka) has uniform {sup 206}Pb/{sup 207}Pb to within {+-}0.0015% in groundmass phases, but 1 mm plagioclase phenocrysts have lower {sup 206}Pb/{sup 207}Pb by 0.105{+-}0.002% indicating contamination of the magma after plagioclase crystallization. High precision {sup 206}Pb/{sup 207}Pb ratios may be a useful new tool for petrogenetic studies.
- OSTI ID:
- 102903
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 15 Vol. 59; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
Similar Records
Magmatism in the Carolina terrane: Isotopic evidence for a Grenville-age source for Late Proterozoic volcanics and a mantle source for Silurian Concord syenite
Using the U-Pb system of calcretes to date the time of sedimentation of clastic sedimentary rocks