| 吉林陨石原始捕获的40Ar/36Ar比值及其地质意义 |
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| 引用本文： | 王松山.吉林陨石原始捕获的40Ar/36Ar比值及其地质意义[J].地质科学,1984,0(3):341-345. |
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| 作者姓名： | 王松山 |
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| 作者单位： | 中国科学院地质研究所 |
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| 摘 要： | 地球大气圈中40Ar/36Ar的现代比值被公认为295.5,在利用K-Ar法测定地球物质年龄时,它是校正大气氩混染量的重要参数。陨石中原始捕获(trapped)的(40Ar/36Ar)t比值是否和地球大气圈中氩同位素丰度相一致,这个问题不但在地质年龄测定中具有现实意义,而且对探索太阳系的形成和演化也有重要理论价值。近十几年,随着质谱分析技术的提高以及登月计划的实施,国外出现了一批有关月岩中氩同位素原始组分的资料,但至今对陨石中原始氩同位素丰度的报道很少。笔者采用40Ar/39Ar快中子活化技术和约克方程3,4],对吉林陨石雨2号标本进行了原始捕获的(40Ar/36Ar)t比值进行了测定,并探讨了它的地质意义。
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| 关 键 词： | , |
| 收稿时间： | 1983-06-09 |
| 修稿时间： | 1983-06-09; |
THE TRAPPED 40Ar/36Ar RATIO OF JILIN (Kirin) METEORITE AND ITS SIGNIFICANCE |
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| Wang Sungshan.THE TRAPPED 40Ar/36Ar RATIO OF JILIN (Kirin) METEORITE AND ITS SIGNIFICANCE[J].Chinese Journal of Geology,1984,0(3):341-345. |
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| Authors: | Wang Sungshan |
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| Institution: | Institute of Geology, Academia Sinica, Beijing |
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| Abstract: | The Jilin meteorite fell on March 8, 1976, in the district of Jilin, China, over an area of about 480 km2. The largest fragment (K-1), of mass about 1770 kg, was found at the westernmost point of the fall area, K-2 (400kg) was recovered a little to the east, and smaller fragments were found progressively eastward. The Jilin meteorite is an ordinary chondrite, classified into group H5.K-2 sample was measured by the 40Ar/39Ar method. The irradiation was performed in HIFAR reactor of Australia in a horizontal next-to-core facility which has a fast flux of about 3.6×l012n/cm2· sec.The irradiated K-2 sample was heated in the argon extraction line for 45-minute periods, and temperatures were measured by thermocouple and optical pyrometer. All the isotopic analyses of argon were made on a greatly modified AEI mass spectrometer opreating in the static mode. Peak hopping was employed and all data were taken digitally on-line with a HP-21 MX computer in which all the data reduction was done.Corrections for mass discrimination and line blank were applied in the normal way. The results of two cold and six hot blanks in the argon extraction line during the period when the Jilin meteorite were being measured gave the following values in units of cm3 STP: 40Ar=6.5×10-9, 39Ar=1.1×10-11, 37Ar=2.7×10-12 and 36Ar=2.2×10-11 All data have been corrected for blank and 37Ar decay, and also have been corrected neutroninduced interferences using (40Ar/39Ar)K=(2.7±0.2)×10-2, (36Ar/37Ar)Ca=(3.06±0.05)×10-4 and (39Ar/37Ar)Ca=(7.27±0.08)×10-4.When 40Ar/36Ar and 39Ar/36Ar released at all high temperatures (>1100℃) are plotted, an trapped 40Ar/36Ar ratio of K-2 sample, 0.94±1.9, is obtained, using the method of York (1969).From the plot of derived K/Ca ratio and the release of 40Ar and 37Ar versus temperature, it is concluded that the high-temperature release of argon is from Ca-rich phases with low K/Ca ratios, almost certainly the pyroxene (Wang et al., 1980). Therefore the trapped argon was probably released by pyroxene of K-2 Jilin meteorite. Note that most of trapped 40Ar/36Ar ratios of lunar soil and breccias are about 1, it is possible that the trapped argon of lunar and meteorites originate in solar wind. |
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