Fission-track dating of Macusanite glasses with plateau and size correction methods

• Published in: Radiation measurements Vol. 36; no. 1; pp. 407 - 412
• Main Authors: Osorio A, A.M., Iunes, P.J., Bigazzi, G., Hadler N., J.C., Laurenzi, M.A., Norelli, P., Tello S., C.A., Guedes, S., Paulo, S.R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2003; Elsevier
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fission-track method; Geochronology; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Isotope geochemistry. Geochronology; Macusanite; Plateau correction; Size correction; Thorium thin films; Uranium thin films; Peru; Thorium thin films; Macusanite; Plateau correction; Fission-track method; Uranium thin films; Size correction; South America; pebbles; volcanic rocks; Ar/Ar; igneous rocks; heat treatment; neutrons; irradiation; fission-track dating; corrections; correlation; volcanic glass; thorium; fission; uranium; calibration; methodology
• ISSN: 1350-4487; 1879-0925
• DOI: 10.1016/S1350-4487(03)00161-6

Two Macusanite pebbles (MB1 and MB2) were dated with the fission-track method. Six irradiations were carried out in different nuclear reactors: Pavia (Italy), IPEN-CNEN (Brazil) and IPEN-Lima (Peru). Measurements of the thorium and uranium induced-fission per target nucleus using natural thorium thin films and natural U-doped glasses calibrated against natural uranium thin films, together with a λ F of 8.46×10 −17 a −1 were used to determine the ages. The apparent ages were corrected using the plateau and size correction methods. Track measurements were performed by different analysts, using different counting criteria. In addition, tracks were measured on samples which had been submitted to thermal treatment as well as on samples which had not been heated. Thermal treatments were carried out to erase the fossil tracks before neutron irradiation. No significant differences have been found in individual results, using the two Macusanite pebbles and the different nuclear reactors, age correction techniques, analysts, track-counting criteria, and thermal treatments before neutron irradiation. The great majority of the results (14/17) is compatible with the Ar–Ar ages of 5.12±0.11 and 5.10±0.11 Ma , Macusanite MB1 and MB2, respectively. However, the fission-track ages are systematically less (∼8%) than the Ar–Ar ages of the two Macusanite samples studied.