Fission track age

Kamata, H. and Watanabe, K. (1985) Comparison and examination of K-Ar age and fission track age of the volcanic rocks in central-north Kyushu, Japan. The age when the volcano-tectonic depression was initially formed. Assoc. Mineral Petrol Econ. Geologists, 80, 263-271 (in Japanese with English abst.). 

Miller, D. S. and G. A. Wagner (1981), Fission track ages applied to obsidian artifacts from South America, Nucl. Tracks 5, 147-155. 

Yegingil, Z. and T. Lunel (1990), Provenance studies of obsidian artifacts determined by using fission track ages and trace element analysis, Nucl. Tracks Rad. Meas. 17(3), 433. 

Brandon M. T. and Vance J. A. (1992) Fission-track ages of detrital zircon grains implications for the tectonic evolution of the Cenozoic Olympic subduction complex. Am. J. Sci. 292, 565-636. 

Garver J. 1. and Brandon M. T. (1994) Erosional exhumation of the British Columbia coast ranges as determined from fission-track ages of detrital zircon from the Tofino basin, Olympic Peninsula, Washington. Geol. Soc. Am. Bull. 106, 1398-1412. 

Garver J. 1., Brandon M. T., Roden-Tice M., and Kamp P. J. J. (1999) Erosional exhumation determined by fission-track ages of detrital apatite and zircon. In Exhumation Processes Normal Faulting, Ductile Flow, and Erosion, Special Publication 154 (eds. U. Ring, M. T. Brandon, G. S. Lister, and S. D. Willett). Geological Society of London, London, pp. 283-304. 

Table 2 Comparison of fission track ages and potassium-argon ages of volcanic material in deep-sea sediments.

Apatite fission track ages and thermal histories (Boettcher McBride, 1993) were obtained using the external detector method (Naeser, 1979). 

Figure 8. Vertical profile of apatite He and fission track ages in the N. White Mountains of California, after Stockli et al. (2000). He ages plot on a well-defined HePRZ consistent with 7 km of rapid exhumation at 12 Ma. A similar pattern is seen in the fission track data, but only the deepest samples directly date the exhumation event. Unlike the He ages, the fission track ages do not constrain the total amount of exhumation at 12 Ma. The position of the HePRZ is in excellent agreement with predictions based on laboratory diffusion measurements. Younger He ages at the base of the range document renewed cooling and exhumation.

The occurrence of extinct Pu tracks first became apparent when a large excess of fission tracks over that which would be expected from spontaneous fission alone was discovered (e g., Burnett et al. 1971). If calculated as a fission track age in the usual... 

Determination of a fission track age requires several further experimental steps to measure the uranium concentration. The uranium concentration is not measured directly, but a second set of fission tracks is created artificially in the sample by a thermal neutron irradiation. This irradiation induces fission in a tiny fraction of the atoms, which are present in a constant ratio to U in natural uranium. Knowing the total neutron fluence received during irradiation, the number of induced tracks provides a measure of the uranium concentration of the grain. Because the induced tracks are derived from a different isotope of uranium than the spontaneous tracks an important consideration in fission track dating is the assumption that the isotopic ratio of the two major isotopes of uranium, and is constant in nature. With the notable exception of the unique natural nuclear reactors of Oklo in Gabon (Bros et al. 1998), where this isotopic ratio is disturbed, this is a very safe assumption. Numerous measurements have shown that and are always present in their natural abundances of 0.73% and 99.27%, respectively. 

The fission track age, t, is then calculated from the ratio of spontaneous (ps) to induced (pi) track densities according to the standard fission track age equation (Fleischer and Price 1964, Naeser 1967) ... 

Measurement of a fission track age following Equation (3) requires the determination of three different track densities, ps, Pi and pd. The various different experimental strategies involved have been elaborated by Naeser (1979a), Gleadow (1981), Hurford and Green (1982) and Wagner and Van den Haute(1992) and are summarized in Figure 6. Of the five main alternatives, only the Population (PM) and... 

The application of fission track length studies to the interpretation of fission track ages depends on three properties of spontaneous fission tracks. 

When combined with the apparent fission track age, length distributions can be used to reconstruct the variation of temperature through time. 

Figure 11. Composite apatite fission track crustal profiles of mean fission track length ( ) and apparent apatite fission track age (O) plotted against depth for samples from several wells from the central Otway Basin in southeastern Austraha. These clearly illustrate the progressive decrease in mean track length and apparent apatite fission track age with depth, and the characteristic concave-up form of both profiles. After Gleadow and Buddy (1981b) and Green et al. (1989a).

Other examples of natural thermal annealing can be seen in the vicinity of shallow level igneous intrusions. Calk and Naeser (1972), for example, demonstrated a systematic reduction in the apparent apatite fission track age of an 80 Myr old granitic pluton with increasing proximity to the contact with a small (-100 m) basaltic intrusion emplaced -10 Myr ago. This pattern of age reduction within the granite was influenced by the thermal effect of the basalt intrusion and is consistent with the pattern of annealing observed in laboratory annealing experiments and deep drill holes. 

Figure 16. Plot of apatite fission track age against chlorine concentration for apatite grains in a suite of samples from the Stillwater Complex, Montana. Apatites from these rocks exhibit an unusually wide range of chlorine concentrations. A positive correlation is observed between fission track age and chlorine concentration up to about 4% Cl, reflecting an increasing resistance of the apatite grains to annealing.

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