Advancing (U-Th)/He Zircon Dating: Novel Approaches in Sample Preparation and Uncertainty Reduction

The laser microprobe (U-Th)/He dating method is a new and efficient technique that utilizes an interoperable and integrated suite of instruments, including the excimer laser system, quadrupole helium mass spectrometer, and quadrupole inductively coupled plasma mass spectrometer. To demonstrate the applicability of this new method, we applied both the conventional and laser microprobe techniques to the Sri Lanka zircon (LGC-1). We obtained twenty-two (U-Th)/He ages on nine shards using the laser microprobe method, showing an average (U-Th)/He age of 471.1 ± 16.6 Ma (1σ). This result is generally consistent with the mean conventional age (484.1 ± 9.6 Ma) for twenty-two zircon fragments. Both are nearly equal to the age value (~476 Ma) predicted by the He diffusion model and the thermal history model of Sri Lanka highland. The variations in the laser microprobe-derived ages are most likely caused by the uncertainties in volume measurements, which is also common in other studies. We used the Mahalanobis distance technique to reduce the volume measurement bias by identifying and eliminating abnormal data.