Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

Autor: Soares, Cleber José, 1984, Oliveira, Sandro Guedes de, 1973, Lixandrão Filho, Arnaldo Luis, 1983, Vellame, Igor Alencar, 1984, Hadler Neto, Julio Cesar, 1947
Přispěvatelé: UNIVERSIDADE ESTADUAL DE CAMPINAS
Rok vydání: 2013
Předmět:
Zdroj: Repositório da Produção Científica e Intelectual da Unicamp
Universidade Estadual de Campinas (UNICAMP)
instacron:UNICAMP
Popis: Agradecimentos: We thank Richard Ketcham and Jocelyn Barbarand for their constructive comments that helped improve the manuscript. This work is part of C.J. Soares's Ph.D. research and was financially supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP, Brazil) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, Brazil) Abstract: The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the rho(ed)/rho(is) ratios and independently determined [GQR](ed/is) values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L-0, is not measured in routine analyses. The L-0-value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L-0-values on the inference of sample thermal history is investigated and discussed. The measurement of the L-0-value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the rho(ed)/rho(is) ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the zeta-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado
Databáze: OpenAIRE
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