Evaluation of Cooling History of the Quaternary Takidani Pluton Using Thermoluminescence Technique

Abstract

The characteristics of thermoluminescence (TL) and Electron Spin Resonance (ESR) of quartz in the Takidani pluton were investigated to evaluate the cooling history of a Quaternary granitoid in an active volcanic chain. The Takidani pluton is composed mainly of granite and granodiorite, and shows a reverse zonal structure in terms of its whole-rock chemical composition. Paleodose values obtained using TL and the ESR-Ti center were similar. However, values for the ESR-Al center are lower. These results indicate that the thermal stability of the ESR-Al center is more unstable than that of the TL and ESR-Ti center. The TL age was strongly dependent on thermal processes that have effected the sample. The closure temperature is considered to be approximately 70?C, and the TL age indicates the elapsed time since cooling below the closure temperature. TL ages of three samples range from 91 to 152 ka. The cooling rate at an early stage in the history of the granitoid, including the solidification process, is considered to be approximately 600?C per million years. During the later stages accompanying uplift, the rate may have decreased to approximately 200?C per million years. TL and ESR techniques are a potentially useful new research tool for evaluating the cooling history of plutonic rocks, particularly the timing of exposure.