Sea water weathering effect on K-Ar age of submarine basalts |
| |
| Authors: | Minoru Ozima Kazuo Saito Masahiko Honda Sigeo Aramaki |
| |
| Institution: | Geophysical Institute, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan;Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan |
| |
| Abstract: | K-Ar dating and 40Ar-39Ar step heating experiments have been done for successive zones from the surface to the interior in two, altered dredged submarine basalts (16-2-6 and Aries V-23). The K contents show a systematic decrease (surface to the interior), whereas the K-Ar ages show a similar decrease in one sample (16-2-6) and almost no change in the other (Aries V-23).A simple diffusion model suggests that the K content decreases systematically from the surface to the interior, whereas the K-Ar age decreases or remains almost constant, depending on whether the times of solidification and of commencement of K-diffusion are close to each other or differ significantly. Comparison of the observed K content and K-Ar age variations within the rocks with the theoretical model then suggests that the solidification age of the sample Aries V-23 is much older than the commencement of the potassium-diffusion, the latter age perhaps being represented by the Eocene planktonic foraminifera on this sample. The 40Ar-39Ar isochron age obtained for the freshest specimen of Aries V-23 is 86.6 ± 3.7 m.y., supporting the above conclusion.The mathematical simulation indicates that an apparent concordance of the K-Ar age observed in some submarine basalts may be an artifact, only reflecting the significant gap between the solidification age and the time of the commencement of the K-diffusion in the rocks. Microprobe examination reveals that the potassium enrichment in the outer margin, is mainly due to K feldspar, which is an alteration product of plagioclase. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
