Mathematics – Logic
Scientific paper
Jan 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977gecoa..41...15f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 41, Issue 1, pp.15-32
Mathematics
Logic
62
Scientific paper
Conventional K-Ar ages of tholeiitic basalts of the Ferrar Group in the central Transantarctic Mountains indicate significant loss of radiogenic 40 Ar from this unit over much of its outcrop area. Argon loss varies inversely with amount of devitrified matrix in the basalts, which have not been thermally or tectonically disturbed since extrusion. 40 Ar/ 19 Ar age-spectra of these tholeiites are generally discordant and indicate significant inhomogeneity in the distribution of radiogenic 40 Ar with respect to 39 Ar, but are distinctly different from release patterns of thermally disturbed samples. Amounts of argon redistribution vary directly with amounts of devitrification and are reflected in progressive modification of the age spectra. A model of redistribution of radiogenic 40 Ar by devitrification of originally glassy matrix is suggested that is consistent with disturbance of the conventional K-Ar systematics as well as the 40 Ar/ 39 Ar age-spectra. Samples with substantial redistribution but minor loss of radiogenic argon yield age spectra whose apparent ages decrease from low-temperature to high-temperature steps, similar to those reported for some lunar basalts, breccias, and soils. Modification of all the age spectra is attributed to redistribution of radiogenic 40 Ar during progressive devitrification, although 39 Ar-recoil effects suggested by and (1974) may be a factor in some cases. Where devitrification involves most potassium sites within the basalt, 40 Ar/ 39 Ar age-plateaux may be formed that have no geologic significance.
Elliot David H.
Fleck Robert J.
Sutter John F.
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