ESR dates and thermal behaviour of Al and Ti centers in quartz for the tephra and welded tuff in Japan

Abstract A welded tuff in a geothermal area was dated by electron spin resonance (ESR) and thermoluminescence (TL). The ESR spectrum has a clear Ti center signal and weak Al center signal, which resembles the spectrum of the volcanic ash (Crystal Ash C1, Shinshu, Japan) annealed at 200°C for 20 hr. In this volcanic ash, the intensity of the Al center signal selectively decreased with the heat treatment. This result may suggest that this welded tuff sample was subjected to weak thermal annealing in the past, and only the Al center signal was reduced. From ESR, the equivalent dose (ED) was 49 Gy and the ESR date was 0.043 Ma for the Al center and the ED value was 300 Gy and the ESR date was 0.26 Ma for the Ti center. From TL, the ED value was 39 Gy and the TL date was 0.039 Ma, which are close to that of the Al center signal using ESR. A detailed thermal annealing experiment at 400, 800 and 1000°C for this sample, rose and smoky quartz was performed to investigate the variety of ESR signals of natural quartz and the influence of thermal annealing in the past.