Thermoluminescence Dating in Mt. Labo and North Davao, Philippines: Implications on Geothermal Models

Abstract

Thermoluminescence dating was used to obtain absolute ages for volcanic rocks in two geothermal exploration areas in the Philippines: Mt. Labo and North Davao. In Mt. Labo, eleven samples gave ages ranging from ~197-142 ka for the dacitic lava domes in the southwestern sector to ~27 ka for an andesitic pyroclastic flow at the Mt. Labo summit. These TL ages support the volcanic history of the area which was inferred earlier based on existing K-Ar and fission track dating. The youngest deposits (~27 ka) were likely derived from the same source being tapped by the present hot but partly acidic Mt. Labo geothermal system. The lava domes in the southwest (~197-142 ka) may be correlated with an older, neutral-pH but probably cooler system. In North Davao, twelve samples from Quaternary domes gave ages of ~0.21-238 ka. The youngest domes (<10 ka) are found in the western and southern sectors of Lake Leonard. Five of the six Paloc Pyroclastics gave Recent ages of < 1 ka while a Pleistocene age (~13 ka) was obtained for one sample. The TL ages for most of the pyroclastics are younger compared to the 14C dates (1,800-25,000 years BP) for this unit. These variations may be due to differences in TL accumulation process between younger and older rocks. The ages of the youngest domes and Paloc (<10 ka) likely represent the latest volcanism in the area. This activity probably provides the heat source for the Amacan-Ugos- Leonard geothermal system. The oldest dated rock (~933 ka) is hydrothermally altered and belongs to a fossil hydrothermal system in Masara.