ABSTRACT

The ablation protocols for 200 nm ultra violet-femtosecond laser ablation (200FsLA)—inductively coupled plasma mass spectrometry (ICPMS) have been examined using a quadrupole ICPMS and applied to zircon U–Pb age dating coupled to a multiple collector (MC)-ICPMS. As high spatial resolution is often required in small natural zircons, the following ablation protocols were examined: (1) a ~30 μm circular spot crater with 5 Hz repetition rate, and (2) a ~30 μm circular crater formed by rotation raster (a ~20 μm beam rotated along the circumference of a circle with a radius of 8 μm) at 10 Hz. A line raster with a ~30 μm crater at 5 Hz was also examined for comparison. The repetition rates were set in order to achieve the necessary signal intensity for zircon dating. During the spot and the rotation raster analyses there was almost no down-hole fractionation of ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁶Pb/²³⁸U, and additionally ²³²Th/²³⁸U. Therefore, precise zircon U–Pb chronology, that does not require a down-hole fractionation correction, is possible using optimized protocols for 200FsLA. However, absolute ²⁰⁶Pb/²³⁸U ratios deviated from the natural ratios in zircon by 1.4% for 200FsLA when using synthetic glass as a standard. This indicates that a standard with a matrix that matches the sample or close monitoring of the correction factor is still recommended.