Investigation for Dating the Petroleum Emplacement by Authigenic Illite UP>40Ar-39Ar Laser Stepwise Heating Technique

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摘要


    

Timing of petroleum emplacement is one of the important scientific problems in petroleum geology and isotope chronology. This study investigates the possibility of determining the age of petroleum emplacement by an authigenic illite UP>40Ar-39Ar laser stepwise heating technique. The sample is from the reservoir sandstone of the Tertiary Zhuhai Formation in the Pearl River Mouth Basin. The sandstone was gently disaggregated by repeated freezing-heating in order to reduce the detrital feldspar content. The released gases were first cleaned up through the specific apparatus, and then further purified by two Saes NP10R Zr/Al getters. An increasing ladder-shaped age spectrum is obtained for illite 06ZJ26I by 40Ar-39Ar laser stepwise heating. The weighted mean age (12. 1±2. 2) Ma(2σ) of the three initial lowest laser-power steps is interpreted as the minimum age of authigenic illite,  indicating the maximum age of petroleum emplacement. A plateau of (98. 0±0. 9) Ma is determined in high laser-power steps. The plateau age may represent the age of terrestrial detrital feldspar in the sandstone. Compared with the traditional K-Ar method, 40Ar-39Ar stepwise heating provides more precise age dates from illite samples.  
    

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