U-series dating of carbonates using inductively coupled plasma-quadrupole mass spectrometry

We describe an analytical methodology to quantify U-238-U-234 and Th-230 using isotope-dilution systematics and inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) for geochronological purposes. This required characterization of the mass spectrometer detector performance over a large dynamic range, including a careful calibration between pulse and analogue ion-counting modes. Our methodology gives an analytical precision for U-234/U-238 and Th-230/U-238 4/parts per thousand and 7 parts per thousand (2 x standard error), respectively, and yields Th-230-ages with 4-5% uncertainty from 500 ng of U-238. We tested our methodology by analyzing carbonate samples (corals and speleothems) which were previously dated using MC-ICPMS; excellent agreement between both techniques was obtained. Our results indicate that ICP-QMS is suitable to obtain valuable meaningful geochronological data, but it is limited to dating samples older than 1 ka, and younger than 400 ka. Our methodology thus represents an attractive alternative to obtain geochonological data to select the most interesting samples prior to high-precision analysis. Moreover, such data would also valuable to build preliminary age-models, which can be further complemented with high-precision analyses. (C) 2011 Elsevier B.V. All rights reserved.