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【答案】应助回帖
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phu_grassman: 金币+3, really kind of you. 2013-04-06 20:34:46
luohouyong: 金币+300, 翻译EPI+1, ★★★★★最佳答案 2013-04-07 14:55:42
地质学内容专业，尤其是其中的名词，更是一头雾水，就这个情况了；仅供参考；
chemical inertness of inert gas make its abundance and isotope components remained uninfluenced during the geological process.
He3 is the original helium of the natural gas, while He4 is the decay product of radioisotopes of uranium and thorium. The formation difference between He3 and He4 can thus serve as the judging index natural gas’ origion.
Ar36 of the natural gas is originated from depositional stage’s atmosphere, and Ar40 is mainly come from decay of K40, which indicate the deposition effect of Ar.
Base on the theory of judging the natural gas’ origin by He isotopes, the content of Ar40 is related to the abundance of rock matrix and rock era, and because the abundance of matrix elements are in the same order of magnitude, Ar40 content is mail related to rock era.
Ar36, Ar38 and He3 is very low(n ×10-6) in rock. Ar40 and He3 that caused radioactive makes the isotope composition significantly changed.
The modern high accurate mass spectrometer technically supported the accurate determination of abundance of inert gas and isotope.
when the ratio of He3/He4 is greater than 1.4×10-6，it means there are some mantle source gas doped. Study of the eastern basin(Songliao basin) indicated that the existence of mantle sourced gas would greatly affect the Ar40/Ar36, thus, their ration can not be directly used to estimate of gas source rock’s age.
The mantle source gas He3/He4 value and Ar40/Ar36 are both increased. Judging by He isotope, mixing of mantle source gas can be eliminated, which makes the spontaneously produced and storaged natural gas’ era deposition effect more distinct. The earth crust originated He also has era depositional effect and the ratio of He3/He4 is negatively related to rock source element(element’s content). |
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