Recent advances in laser ablation ICP-MS techniques allow accurate U-Th-Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real-time mass bias correction via nebulisation of a solution containing enriched 233U and natural TI isotopes. The TI-U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured 205TI/233U ratios in the tracer solution allow direct measurement of 235U in monazite. Combined with high-sensitivity laser ablation ICP-MS measurements, direct measurement of 235U particularly improves the precision of U-Pb dating of young monazites. Correction for laser-induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count-rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP-MS technique more flexible for in situ U-Th-Pb analysis.
|Number of pages||12|
|State||Published - Dec 1 2001|
- Instrument mass bias
- Laser ablation ICP-MS
- Laser-induced elemental fractionation
- U-Th-Pb dating