230Th/238U dating of secondary carbonate micro-samples – Part 2: Combining portable laser ablation, H2DEH[MDP] based cloud-point extraction and Q-ICP-MS analysis for coral and speleothem dating

A new analytical approach has been developed for the collection and subsequent dating of carbonate micro-samples using the U/Th geochronometer. A portable laser ablation system adapted for in-situ collection of laser-induced particles was used to collect micro-samples of speleothems and coral samples. Sample recovery rates ranging from 36% for the most transparent samples to over 90% were measured from mg-sized ablations. After solubilization of the collected samples, uranium and thorium isotopes were quantitatively extracted and preconcentrated using a H 2 DEH[MDP]-based CPE system. Following microinjection analysis and integration of transient signals measured by Q-ICP-MS, U/Th ages were calculated using the IsoplotR geochronology toolbox. Although the results showed an inherently low precision due to reduced sample sizes, the calculated ages were in good agreement with their expected values for most samples, even from the detection of only a few 230 Th ions. The proposed methodology appears to be a promising prospective tool for minimally invasive cave studies that could complement existing approaches. • Minimally invasive sampling approach for the collection of milligram-sized speleothems and coral samples using a custom-built portable laser ablation system. • Particle collection efficiencies ranging from 30% to more than 90% were measured. • Cloud-Point Extraction used for the first time as sample preparation for 230 Th/ 238 U dating of carbonate samples. • Good agreement between calculated and expected ages obtained for most samples, even when only a few 230 Th ions are detected.