Thermoluminescence (TL) Dating of the Irosin Ignimbrite and Co-ignimbrite Ash Fall Deposits, South Luzon, Philippines

Abstract

 Four samples collected from the Irosin ignimbrite and co-ignimbrite ash fall deposit in southern Luzon, Philippines, were subjected to Thermoluminescence (TL) age-dating to further refine the timing of the ignimbrite eruption. IrTL-01 and -02 are the matrix part of the ignimbrite, IrTL-03 is a 10 cm-diameter lithic fragment from the ignimbrite, and IrTL-04 is co-ignimbrite ash-fall deposit collected at the summit crater of the Inascan cone, 80 km north of the eruption source. The ages obtained are 36 ± 8 ka for IrTL-01, 38 ± 10 ka for IrTL-02, 33 ± 8 ka for IrTL-03 and 45 ± 10 ka for IrTL-04. TL ages of IrTL-01 and -02 are in good agreement with a previously reported AMS ¹⁴C age of ca. 41 cal kBP. On the other hand, TL ages for IrTL-03 and -04 are not consistent with the ¹⁴C age. IrTL-03 (lithic fragment) exhibits a TL signal that is very clear and provides good data, however the fading TL signal may possibly account for the younger than expected TL age. The grain size and water content of IrTL-04 (ash-fall) may possibly account for an older than expected TL age. Further experiments are needed for more precise TL ages for IrTL-03 and -04.