Otake Hatchobaru Geothermal Field in Japan in Relation to the Thermoluminescence Index (TI)

Abstract

The thermoluminescence index (TI), a simpler application of the TL dating method, was applied for quartz in volcanic and altered rock from the Otake-Hatchobaru geothermal Field The heat-source rock for Otake and Hatchobaru has TI of 40 to 45 and 23 (equivalent to ka), respectively, Quartz from steaming grounds is smaller than 1 in Hatchobaru, and that in Otake ranges from 4 to 13 in TI. This may reflect on the reservoir temperature between Hatchobaru (<287o C) arid Otake (<238o C). Some quartz from non-steaming ground is larger than 100 in TI. Although there are two explanations for the large 1'1 values: one is the alteration age is old, and the other is the partial annealing of TL signals, the analysis of the paragenesis of alteration minerals suggests the former possibility. Thus, the TI can he used to estimate the age of volcanic eruption as well as hydrothermal alteration as the simplest technique.