Sea water weathering effect on K-Ar age of submarine basalts

Details Sea water weathering effect on K-Ar age of submarine basalts Sea water weathering effect on K-Ar age of submarine basalts

Apr 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977gecoa..41..453o&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 41, Issue 4, pp.453-461

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Scientific paper

K-Ar dating and 40 Ar- 39 Ar 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 40 Ar- 39 Ar 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.

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