NEW CA-TIMS AND LA-ICP-MS ANALYSES OF GJ-1, PLESOVICE, AND FC1 REFERENCE MATERIALS

Abstract:

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology relies on external reference standards to monitor and correct for different mass fractionation effects and instrument drift. Common zircon reference materials used within the community, including the KU Isotope Geochemistry Laboratory, are GJ-1 (²⁰⁷Pb/²⁰⁶Pb age: 608.53 +/- 0.37Ma; Jackson et al., 2004), Plesovice (337.13 +/- 0.37 Ma; Slama et al., 2008), and FC-1 (1099.0 +/-0.6 Ma; Paces and Miller, 1993). The age distribution of zircon reference material varies slightly from sample fraction to sample fraction, and the published results for GJ-1 are slightly discordant. As a result, using the published data for the distributed standard splits can lead to small systematic variations when comparing datasets from different labs, and more high precision data are needed to evaluate potential inhomogeneity of sample splits used in different laboratories.

Here we characterize these reference materials with cathodoluminescence, LA-ICP-MS traverses across grains, and high precision CA-TIMS to better constrain the ages and assess zoning of these standards, and present the data for comparison with other laboratories. Reducing systematic error by dating our own reference material lends confidence to our analyses and allows for inter-laboratory age reproducibility of unknowns. Additionally, the reduction in propagated uncertainties (especially in GJ-1, for which both the red and yellow variety will be analyzed) will be used to improve long-term reproducibility, comparisons between samples of similar age, detrital populations and composite pluton zircons.

Jackson, S.E., et al., 2004, Chemical Geology, v. 211, p. 47-69.

Paces, J.B. & Miller, J.D., 1993, Journal of Geophysical Research, v. 80, p. 13997-14013.

Slama, J., et al., 2008, Chemical Geology, v. 249. p. 1-35.