Accurate U/Th determination on single crystals for (U/Th)/He thermochronology

Full text: The sensitivity of noble gas mass spectrometers facilitates 4He concentration measurements on single grains of apatite, zircon or titanite for (U/Th)/He thermochronology. Inter- and intracrystalline heterogeneity requires both [4He] and U/Th to be analyzed on the same individual mineral grain. In our laboratory, U/Th ratios are determined by isotope dilution QICPMS with blank, yield and choice of crystal being key procedural issues. We present a method for accurate/precise determinations of spike-enriched 235U/238U and 230Th/232Th on sub 10 pg quantities of U and Th from apatite resulting in (U/Th)/He ages with an uncertainty of 3 % (1 SD). (author)