Spatially-controlled carbonate U-Pb geochronology using LA-ICP-MS
Abstract
Several studies using conventional TIMS instrumentation have shown that U-Pb geochronology on sedimentary calcites can reliably return geologically useful information because of the high U/Pb of some carbonates. Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) has the potential of providing an alternative to laborious TIMS techniques. This work presents the first account of U-Pb LA-ICP-MS carbonate geochronology. In addition, this study has elucidated that concentrations of U, Pb can be sampled at ~100 μm spatial resolution in addition to returning useful age information. Carbonate from the Paleozoic Canning Basin (Australia), Cenozoic paleosoils from the Puna Plateau (Argentina), and Miocene shallow water carbonates from Columbia with known ages were analyzed at using a high Resolution single collector LA-ICP-MS (Element 2). Various U/Pb vs. Pb/Pb isochrons demonstrate that ages consistent with the geologic record were returned for all samples, with 1-sigma age errors as low as 5%. At least several samples with 238U/204Pb >20 and low common lead are required to successfully form isochrons. Most high 238U/204Pb samples exclude common lead as a major obstacle due to the analytical errors. Common lead can be estimated by using a Pb isochron and/or initial Pb 206Pb/204Pb from a 238U/204Pb vs. 206Pb/204Pb isochron. U concentrations range from 1 ppb-6 ppm. Isochrons constructed with high U samples do not have noticeably lower error than samples with low U. Modern loss of U and Pb are not observed within the analytical error; such an event may have affected all samples at some time previously. This technique shows that it is currently possible to at least constrain a series of samples and/or one high U/Pb sample to a geologic epoch and/or age using LA-ICP-MS. Additionally, preliminary Sr isotopic studies of the samples are consistent with the U-Pb geochronology.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.V51A2514J
- Keywords:
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- 1000 GEOCHEMISTRY;
- 1100 GEOCHRONOLOGY