Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS.

A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16-32 µm. This was accomplished by introducing N2 into ICP to increase the sensitivity. The obtained U-Pb ages for zircon standards GJ-1, TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2σ) by simple external calibration against zircon standard 91500. Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages. The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy, but it may yield artificial high precisions for single analyses. Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses. Calibration against the NIST glasses using Si as an internal standard, a systematic deviation of 10%-30% was found for most trace elements including Zr. However, the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g., BCR-2G, BHVO-2G and BIR-1G), or calibration against NIST SRM 610 and using Zr as an internal standard. Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti). [ABSTRACT FROM AUTHOR]