Quartz is one of the minerals useful for electron spin resonance (ESR) dating. The E1′ center is one of well-known paramagnetic defects in crystalline quartz. This center has a unique feature; its intensity increases on heating. An electronic process to explain this increase was found to be controlled not only by the number of oxygen vacancies, which are the precursors, but also by the number of Al hole centers, which depend on the previous radiation dose and on the Al concentration.
The maximum intensity on heating is called the heat treated E1′ center, which has been posited to correspond to the number of oxygen vacancies in quartz and was found to be correlated with the ages of the host granites (Toyoda and Hattori, 2000). The experimental results on spin-spin relaxation times of the E1′ center indicate that external beta and gamma rays create oxygen vacancies in natural quartz rather than alpha or alpha recoil particles (Toyoda et al., 2005).
The correlation between the numbers of the oxygen vacancies in quartz and the ages of the host granite made it possible to distinguish the quartz of a sedimentary reservoir from another with different age of crystallization (Toyoda and Naruse, 2002). Quartz fractions extracted from leoss and atmospheric deposition in Japan and from sediments in Japan sea were analyzed by ESR. The temporal change of the contributions from two dust sources in China were discussed in the context of climate change.
The variation of electron spin resonance (ESR) signal intensities and thermoluminescence colour images (TLCIs) of quartz was investigated in the present study for various rocks and sediments in Japan, to discuss the possibilities of identifying the sediment provenance. The ESR signal intensity of the E1’ centre in the same grain size in granitic quartz varies from sample to sample, except for that in Quaternary samples of volcanic sediment, which is very low, close to the noise level. It was found that the diagram, ESR intensities of Al versus Ti-Li centre signal intensities, distinguish volcanic from the same grain size in granitic quartz as well as distinguish individual tephra from another. The TLCIs from volcanic quartz and some granitic quartz samples is almost red and that from the rest of granitic and metamudstone quartz is blue as results of TLCIs although the emission intensities are different. Our results suggest that examining the multiple-centre signal intensities of ESR and the TLCIs are effective to identify the source of quartz and to estimate the sediment provenance.
Yuya Yamamoto, Shin Toyoda, Kana Nagasima, Yasuhito Igarashi and Ryuji Tada
The Grain Size Influence on the E1' Centre Observed in Quartz of Atmospheric Deposition at Two Japanese Cities: A Preliminary Study
The grain size influence on the number of oxygen vacancies in quartz was investigated by ESR in atmospheric deposition collected at two Japanese cities, Fukuoka and Akita, in 1969 and 1971. The finer grain size fraction shows the highest value of concentration of oxygen vacancies, most closely resembling dust originating in the Taklamakan desert. Month to month and year to year variation of the dependence was also observed which could possibly be attributed to the variation of the mixture ratio of at least two dust sources in China, A conclusive statement can not be made at this stage.
In this study, measurements of electron spin resonance (ESR) signals from quartz grains from present-day river bed sediments of the Kizu River basin (western Japan) were used to estimate the mixing ratios of the possible source materials of these fluvial deposits. The dose-saturated ESR signal intensities obtained from the Al and Ti-Li centers in quartz grains were close to the range between the maximum and minimum intensities of their potential source rocks, meaning it was possible to estimate the mixing ratios of these sources. The results indicate that the dose-saturated Al and Ti-Li center ESR intensities can be used to quantitatively estimate the provenance of the sediments deposited by the Kizu River.
Taisei Fujiwara, Shin Toyoda, Ai Uchida, Hirotsugu Nishido and Jun-Ichiro Ishibashi
The alpha effectiveness value (k-value) for the ESR (Electron Spin Resonance) signal due to SO3- in barite was revised by comparing the dose responses of the signal intensities to gamma rays and to 4 MeV He+ ion doses in natural sea-floor hydrothermal barite samples actually used for dating. Of the values obtained for a synthetic, a natural old, and a natural young samples, the one for the natural young sample is tentatively adopted, which is 0.053 ± 0.006, although further works are still necessary to establish this value.
Shin Toyoda, Taisei Fujiwara, Ai Uchida and Jun-Ichiro Ishibashi
Electron spin resonance (ESR) dating of barite has been recently developed and is now practically applied to barite extracted from sea-floor hydrothermal deposits. The evolution of the accumulated dose to barite is simulated for an actual sample of barite in sea-floor hydrothermal sulfide deposit to find that the contribution of radioactive nuclei of 228Ra series can be important for the samples younger than 300 years old. Currently, any date over 50 years should be considered a maximum value when the 228Ra content is not obtained. The method to estimate the contribution from 228Ra series has to be developed in future for those in which 228Ra is not detected. The age limit of ESR dating of barite would be 5000 to 6000 years due to the decay of 226Ra, which is also found by simulation of the accumulated dose.
Tasuku Okumura, Shin Toyoda, Fumihiro Sato, Ai Uchida, Jun-Ichiro Ishibashi and Shun'ichi Nakai
ESR Dating of Marine Barite in Chimneys Deposited from Hydrothermal Vents
Electron Spin Resonance (ESR) dating of marine barite in chimneys deposited from hydrothermal vents was attempted to determine the time since hydrothermal activity occurred. In this study, we used Barite (BaSO4) precipitated in icroenvironments in the chimneys deposited from the hydrothermal vents at the Archaean site in South Mariana spreading centre (12°56.4'N, 143°37.9'E) and at Hakurei site in the Izena caldron (27°15'N, 127°04'E) for ESR measurements. ESR spectrum of marine barite is characterized by an electron-type centre with g values of 2.0034, 2.0022 and 1.9995 attributed to SO3-. The signal intensity increased with gamma ray dose. The dose rates of hydrothermal chimneys from the Archaean site and from the Hakurei site were calculated using a model that assumed a grain size and that incorporation of radionuclides after 226Ra in U series into the chimney, and assuming the efficiency of the defect formation by alpha particles to be the same as that for OSL. The ESR ages were estimated to be 470 years old for barite from the Archaean site and 5670 years old for one from the Hakurei site, although there is a considerable difference between the present ESR ages and the 210Pb/226Ra disequilibrium ages previously reported.
Hélène Tissoux, Shin Toyoda, Christophe Falguères, Pierre Voinchet, Masashi Takada, Jean-Jacques Bahain and Jackie Despriée
ESR Dating of Sedimentary Quartz from Two Pleistocene Deposits Using Al and Ti-Centers
One sample from a fluvial terrace of Loir river (France) deposited during isotopic stages 7-8 and two samples from isotopic stage 5 marine sediments of Echizen Coast (Japan) were dated by ESR of quartz grains. Both additive and regenerative techniques were used on Ti-Li and Ti-H centers of quartz. No change of sensitivity of the centers was observed during regeneration which significantly reduced the errors on the equivalent doses. Bleaching experiments indicated that the Ti-Li center is less sensitive to UV(ultra-violet)-A (365-412 nm) than to the full sun spectrum whereas UVA alone is sufficient to reset the bleachable component of the Al-center. This effect could be the origin of the strong overestimation of the ages determined using the Ti-Li center in this study. The comparison of the equivalent doses determined by the two Ti-centers indicated that bleaching before deposition of the fluvial sediment was apparently better than for the marine sample.
Yuya Yamamoto, Shin Toyoda, Kana Nagasima, Yasuhito Igarashi and Ryuji Tada
The temporal change in the number of oxygen vacancies in quartz was investigated by ob-serving the E1’ center in the atmospheric depositions collected at two cities in Japan in the recent past. The depositions collected at Fukuoka in March show the ESR intensities being correlated with the sum of the number of the days, in the month, on which Kosa was observed while no such correlation was found in the deposition those collected at Akita but a trend of decrease with time. The present results suggest that the number of oxygen vacancies in quartz might be useful to estimate quantitatively the contribution of the dust originated from China to the atmospheric deposition in Japan.