GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 259-7
Presentation Time: 9:00 AM-6:30 PM


HOLDER, Robert M., HACKER, Bradley R. and KYLANDER-CLARK, Andrew R.C., Department of Earth Science, University of California Santa Barbara, 1006 Webb Hall, University of California, Santa Barbara, CA 93106,

U-Pb calcite dating has long been overlooked due to the ubiquity of common Pb, low U concentrations, and lack of homogeneity within calcite crystals and carbonate rocks. These challenges can now be overcome using LA-ICP-MS. Carbonate samples can be screened for μ (238U/204Pb) within a few minutes to determine their potential as a geochronometer. The rapid collection of in-situ data means that heterogeneity is an asset, not a hindrance, as it can be used to populate well-defined discords in U-Pb concordia diagrams and provide precise intercept dates without the need for a common Pb correction. However, a comprehensive set of reference materials, demonstrated to be reproducible, is still needed before U-Pb calcite/carbonate dating becomes a common and robust geological tool.

 We report reproducible and accurate LA-ICP-MS dates from three carbonate samples of known isotope age (one calcite, 3.1 Ma; two limestones, 64 ± 4 and 254 ± 7 Ma) and we demonstrate reproducibility of four other large calcite crystals for use as secondary reference materials (10.6 ± 0.6 Ma; 12.9 ± 0.3 Ma; 40.0 ± 0.6 Ma; 42.0 ± 1.0 Ma).

Trace-element concentrations (e.g. Mg, Mn, Fe, Sr, Ba, REE) can be measured simultaneously using the same split-stream configuration commonly used in zircon and monazite dating.