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An understanding of the thermal evolution of sedimentary basins is important in a variety of geologic disciplines for reasons related to economic importance of these features and because of implications for lithospheric tectonics and rheology. The importance of understanding the temperature history of sedimentary basins has led to development of a variety of methods of paleothermometry. The usefulness of these approaches is limited in many cases by the complexity of the thermally activated reaction(s) which in turn renders difficult the detailed theoretical understanding needed for precise temperature predictions. Recent work has demonstrated the potential of 40Ar/39Ar age spectrum analysis of detrital microclines in revealing this thermochronologic nformation. By irradiating feldspars with a known dose of fast neutrons, an isotopically distinct but chemically identical form of the daughter (39Ar) is produced from potassium, making the 40Ar/39Ar ratio of a geologic sample implicity proportional to age. If the sample has experienced a heating in the temperature range 100° to 200°C for geologic times, the transport kinetics of 40Ar in microcline are sufficiently rapid to cause partial outgassing of the sample. Given that the diffusion parameters for argon transport in microcline are known, a partially outgassed K-spar can yield information related to both the ages of crystallization and reheating as well as the temperature of the heating event. Detrital microcline separates analyze from deep drill cores obtained from the southern San Joaquin Valley (California), the North Sea, and the Albuquerque basin (Rio Grande rift) yield encouraging results and demonstrate the utility of this approach. In summary, 40Ar/39Ar analysis of detrital microcline crystals yields thermochronologic information in the temperature-time range of petroleum maturation and provides this technique with potential as both a useful exploration tool and as a means of probing the fundamental geodynamic processes of basin evolution.
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