Gamma radiation-induced thermoluminescence, trace element and paramagnetic defect of quartz from the Sambagawa metamorphic belt, Central Shikoku, Japan

This study analyzes the Thermoluminescence (TL) emissions for five emission bands, trace element concentrations and defects in quartz grains extracted from metamorphic rocks and quartz veins in the Sambagawa metamorphic belt, central Shikoku. An emission of 500 nm with 195, 245, and 320–325 °C glow peaks are observed through the lowest to highest grade samples. A 450 nm emission band with intense 195 and 245 °C glow peaks and a 320–325 °C shoulder peak is found in the higher grade samples. A 570 nm emission band with a 170 °C glow peak is observed in the samples derived from the lower grade zones. These characteristics of TL emissions of quartz suggest that they can be an indicator for the identification of rock derived from different metamorphic grades. The higher metamorphic grade samples with 450 nm emission bands in particular show higher intensities of the E1′ center. This relation indicates that the activation of the E1′ center in higher metamorphic conditions possibly contributed to the 450 nm emission band. Also, the 500 nm emission band is generally observed in the samples with the signal intensities of the Aluminum hole center, suggesting that the center is the source of this emission band. We also observed that the lower metamorphic grade samples contain lower signal intensities of the Aluminum hole center, despite higher aluminum concentrations. This inconsistency indicates that the formation of interstitial aluminum ions cause local lattice distortion regions, where self-trapped excitons can be formed and presumably provide the 570 nm emissions.