LA-ICPMS for In SituU–Th Dating of Holocene Stalagmites

Here, we present an in situU–Th dating approach of carbonate speleothems using laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) with a detection efficiency of 1–2%. By online addition of a 229Th–233U–236U isotope triple spike to the laser-generated aerosol, instrumental mass discrimination and U/Th elemental fractionation could be monitored and corrected. With this approach, the 234U/238U and 230Th/238U activity ratios of a flowstone sample in secular equilibrium could be accurately reproduced as unity with two-sigma uncertainties ±0.053 and ±0.050, respectively. The method was used for the determination of the formation ages of individual layers in natural stalagmites ranging between 210 and 1 thousand years ago (ka). The determined ages corresponded well with those obtained using conventional solution multi collector-ICPMS techniques after isotope separation. Particularly, Holocene stalagmites, as young as 1 ka, could be accurately dated with 2 standard error of ±76 years. This developed microdomain U–Th dating approach thus can be applicable for diverse research areas, such as paleoclimatology, oceanography, geomagnetism, and archeology.