Thermal History of the Akinomiya-Oyasu Geothermal Field, Northeast Japan

Abstract

The age of hydrothermal activity is rarely identified because the method for such alteration dating are limited. However, recent progress in the thermoluminescence dating method can easily get the time of alteration events. It is considered that the ages give us new ideas about geothermal activity that can be used for geothermal exploration. Fifty-six alteration ages are obtained by TL method for the Akinomiyageothermal area. The age range of alteration is 0.004 to The north part of study area is characterized by old alteration ages and not attractive for geothermal exploration. Many young alteration halos are developed in southern part. However, the youngest alteration age do not coincide with the highest temperature reservoir area. The reason for this disagreement is the effect of shallow fluid flow. The area has regionally developed Tertiary alteration zones and locally developed Quaternary ones. Underground temperature can be estimated by surface alteration age data. At depth, expected temperatures are and for surface alteration ages of respectively. This temperature is affected by the intrusion of a new heat source at around A depth of around 5km is expected for the top of the new heat source based on the age of intrusive rock and conductive heat transfer.