Taisei Fujiwara

ESR dating of barite in sulphide deposits formed by the sea-floor hydrothermal activities

Barite is a mineral newly found to be practically useful for electron spin resonance (ESR) dating of sulphide deposits formed by the sea-floor hydrothermal activities. The recent studies for the properties of the ESR dating signal in barite are summarised in the present paper as well as the formulas for corrections for accurate dose-rate estimation are developed including the dose-rate conversion factors, shape correction for gamma-ray dose and decay of (226)Ra. Although development of the techniques for ESR dating of barite has been completed, further comparative studies with other dating techniques such as U-Th and (226)Ra-(210)Pb dating are necessary for the technique to be widely used.

ESR Dating of Barite in Sea-Floor Hydrothermal Sulfide Deposits in the Okinawa Trough

ESR (electron spin resonance) ages were determined for barite crystals extracted from hydrothermal sulfide deposits taken at Daiyon-Yonaguni Knoll field, Hatoma Knoll field, Iheya North Knoll field, Hakurei Site of Izena Hole field, Yoron Hole field of the Okinawa Trough. The ages range from 4.1 to 16,000 years, being consistent with detection of 228Ra in younger samples and radioactive equilibrium/disequilibrium between radium and daughter nuclei. The variation of the ages within each sample is mostly within the statistical error range. The relative order of the ages is consistent with the result of 226Ra-210Pb method, but the determining absolute ages is still an issue. The order of ages of the 5 hydrothermal fields would be arranged, from young to old as follows; Yoron Hole field, Daiyon-Yonaguni Knoll field, Hatoma Knoll field, being nearly equal to Iheya North Knoll field.

The alpha effectiveness of the dating ESR signal in barite: Possible dependence with age

Abstract 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.

ESR dating of sea-floor hydrothermal barite: Contribution of 228Ra to the accumulated dose

Abstract 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.