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Fission-track annealing systematics in detrital apatite provide a promising means for evaluating the thermal histories of sedimentary basins. Significantly, the temperature range for fission-track annealing, 90° to 135°C (194 to 275°F), is similar to the temperature range for petroleum maturation. Compared to vitrinite reflectance measurements and other techniques currently used to monitor thermal histories of sediments, the fission-track annealing technique is superior, as it is not affected by chemical complexities or fluid composition. In addition, the kinetic laws for track annealing are relatively well characterized.
The usefulness of the technique is demonstrated by examination of natural annealing data from drill holes and by calculation of hypothetical fission-track age versus depth relations for particular thermal histories. These results are used to evaluate currently popular models for the evolution of sedimentary basins. Simple instantaneous stretching models for sedimentary basin evolution do not appear to predict thermal and subsidence histories consistent with fission-track data. Temperatures necessary to account for petroleum maturation and fission-track annealing require stretching rates that, in the published models, lead to subsidence of a factor of 2 to 3 times greater than that observed.
As the temperatures predicted by the simple tectonic stretching models are not consistent with the fission-track data, other factors that affect the temperature distribution in a sedimentary basin must be considered. These include basin hydrodynamics and the time-varying thermal properties of the basin sediments. It is concluded that the thermal history of petroleum source rocks within sedimentary basins is primarily controlled not by the processes and parameters that form the basis of the tectonic stretching models, but rather by processes operating within the basin. The relative thermal effects of these processes within basins can be effectively monitored using fission-track annealing systematics.
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