The double dating technique employed here has the merit that zircons yielding Quaternary U–Pb ages can be immediately cross-checked by the U–Th method.
From 1987 until 2000, helium was measured by bulk degassing of multi-grain aliquots in a resistance furnace, and measuring the U-Th content on either the same or a different aliquot by XRF or TIMS (Zeitler et al., 1987; Lippolt et al., 1994; Wolf et al., 1996).We have determined the Th determination is 0.77% and 0.41%, respectively. Sample selection and grain size measurement Apatite grains are carefully handpicked in order to avoid U- and Th-rich mineral inclusions that may produce excess He (eg. Images of selected grains are captured by a CCD video camera mounted on the microscope and measured using image analysis techniques for the purposes of alpha ejection correction calculation. The effects of long alpha-stopping distances on (U-Th)/He ages. This age is consistent with some coral-based sea-level estimates, but it is difficult to reconcile with June Northern Hemisphere insolation as the trigger for the ice-age cycles.Simultaneous U–Pb and U–Th zircon dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on the ~ 0.1 Ma Toya Tephra, Hokkaido, Japan.