(Ar-40)/(Ar-36) in MORB glasses - Constraints on atmosphere and mantle evolution

Details (Ar-40)/(Ar-36) in MORB glasses - Constraints on atmosphere and mantle evolution (Ar-40)/(Ar-36) in MORB glasses - Constraints on atmosphere and mantle evolution

Mar 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985e%26psl..72..357s&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 72, no. 4, March 1985, p. 357-375.

Computer Science

33

Argon Isotopes, Earth Atmosphere, Earth Mantle, Geochemistry, Glass, Planetary Evolution, Chronology, Degassing, Oceans, Outgassing, Strontium Isotopes, Xenon 129

Scientific paper

Argon isotopic composition measurements of MORB glassy samples from the Pacific, Atlantic, and Indian Oceans are performed. There is a very large scatter in the (Ar-40)/(Ar-36) ratio, from 980 up to 24,400 for bulk-rock analyses, which is mainly due to atmospheric contamination. Using the stepwise heating technique, very high ratios are obtained, from 15,000 up to 25,250 which is the highest (Ar-40)/(Ar-36) ratio ever measured in MORB. A negative correlation between the highest (Ar-40)/(Ar-36) results from stepwise heating and (Sr-87)/(Sr-86) ratios is established, which is perfectly consistent with a two-layered mantle structure. From both Ar-40 and Xe-129 (Staudacher and Allegre, 1982) MORB systematics, a model is proposed for the kinetics of degassing: a very early and extensive burst, with a time constant of about 4 My, is followed by a slower process of present-day type, with a time constant of about 0.5 Gy. The mean age of the atmosphere is so determined to be around 4.4 Gy.

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