| 清原树基沟英云闪长岩40Ar/39Ar年龄谱 |
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| 引用本文： | 王松山,翟明国,胡世玲,桑海清,裘冀.清原树基沟英云闪长岩40Ar/39Ar年龄谱[J].地质科学,1986,0(1):97-100. |
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| 作者姓名： | 王松山 翟明国 胡世玲 桑海清 裘冀 |
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| 作者单位： | 中国科学院地质研究所 |
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| 摘 要： | 清原太古代花岗-绿岩地体位于华北断块北缘,辽宁地块铁岭-靖宇古隆起中部,分布面积约8,000平方公里,花岗岩与绿岩出露面积比为2.5:1。绿岩地层自下而上分为石棚子组、红透山组和南天门组。石棚子组与红透山组整合接触,南天门组不整合于红透山组之上。
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| 关 键 词： | , |
| 收稿时间： | 1985-01-10 |
| 修稿时间： | 1985-01-10; |
40Ar/39Ar AGE SPECTRUM FOR BIOTITE SEPARATED FROM QINGYUAN TONALITE, NE CHINA |
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| Wang Sungshan,Zai Mingguo,Hu Shiling,Sang Haiqing,Qiu Ji.40Ar/39Ar AGE SPECTRUM FOR BIOTITE SEPARATED FROM QINGYUAN TONALITE, NE CHINA[J].Chinese Journal of Geology,1986,0(1):97-100. |
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| Authors: | Wang Sungshan Zai Mingguo Hu Shiling Sang Haiqing Qiu Ji |
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| Institution: | Institute of Geology, Academia Sinica, Beijing |
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| Abstract: | The granite-greenstone terrain in the Qingyuan region, NE China consists of high grade meta-igneous and meta-sedimentary rocks as well as intrusive granitoides and migmatites. The greenstone belt is divided into three formations (from lower to upper) : the Shipengzi, Hongtoushan and Nantianmem Fms. Shujigou tonalite pluton intruded into the Hongtoushan Formation, and sample XL4/R8440 was collected from the marginal facies of this pluton. The measured biotite was separated from this tonalite.The biotite yielded a K-Ar age of 2535±30m.y.. Meanwhile, the same sample was measured by the 40Ar/39Ar technique. The irradiation wes parformed in 49-2 reactor, in a next-to- core H4 facility which has a fast neutron flux of abount 5.8×1012 n/cm2·sec. Intralaboratory standard 77-600 hornblende has a K-Ar age of 414.2±3.7 m.y., was used flux monitor. They were irradiated for 63.7 hours, equivalent to a fast neutron dose of about 1.3×1013n/cm2. The irradiated biotite was heated in argon extraction line for 20-minute periods at successively higher temperature from 430℃ to 1400℃, and the argon gas was measured isotopieally in a improved AEI MS-10 mass spectrometer, operated in the static mode. The 37Ar was corrected for radioactive decay. Argon isotopes produced by nuotron reaction on Ca and K targets during irradiation were corrected using the factors (40Ar/39Ar)k=7.15×10-3, (36Ar/37Ar)ca=2.64×10-4 and(39Ar/37Ar)ca=6.87×10-4.A 40Ar/39Ar incremental heating experiment performed on XL4/R8440 biotite yields a remarkble pattern. Apparent ages from step 2 to step 9, comprising over 95 percent of the release of 39Ar, are virtually concordant, and give a plateau age of 2578±6.5 m.y.. The simple age spectrum is regarded as a good evidence that this mineral has remained undisturbed since crystallization and cooling, and the age is interpreted as the time of tonalite intrusion. Because the Shujigou tonalite pluton intruded into the Hongtoushan Fm, and the boundary age between Archaean and Proterozoic was suggested at 2.5 b.y., it is hence inferred that the Hongtoushan and the Shipengzi Fms were deposited in Archaean. |
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