| 变质岩中白云母的钾-氩法适应性研究 |
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| STUDY OF ADAPTABILITY OF THE K-Ar METHOD FOR MUSCOVITE IN METAMORPHIC ROCKS |
| When muscovite in rocks undergoes a thermodynamic metamorphic process, its physical properties will change with the temperature increment. Below 700℃, its refractive index Nm is in the incremental stage, and the angle 2V, the luster and the elasticity do not change distinctly. Above 7001, the values of Nm and 2V decreas suddenly, and the physicaJ properties and optical features change greatly. It has been found that at the points of inflexion on the variation curves for Nm and 2V the escape of argon gas is strong.The curve of escape of argon gas for muscovite indicates that there are three critical temperature values, i. e. 300℃, 700℃ and 900℃. Accordingly three sections or phases for the argon escape could be divided, within the ranges of 300-700℃, 700-900℃ and above 1000℃-The amounts of gas-escaping are about 5%, 70% and 25% respectively.The K-Ar data given by muscovite which does not show abnormal physical properties, are quite reliable. The isotopic age value thus obtained may have an error of up to 5% due to the escape of argon caused by the increase of temperature. And this indicates that the mineral has never been subjected to a temperature over 700℃. |
| DIAO Nai-chang,ZHANG Hua-li,TANG Shu-lan,WANG Yan-ying.1986.STUDY OF ADAPTABILITY OF THE K-Ar METHOD FOR MUSCOVITE IN METAMORPHIC ROCKS[J].Acta Geoscientica Sinica,8(2):73-79. |
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