Abstract

Potassium-argon and rubidium-strontium dating of 24 Proterozoic granites from the Northern Territory of Australia shows two main groups of ages averaging 1630 and 1440 million years. Both groups of granite were emplaced at the end of a period of folding. The regional structure connects the first period of folding with the lower, and the second with the upper, subdivision of what is regarded as Lower Proterozoic. The older group of granites (1630 million years) marks the top of the lower subdivision, and the younger group marks the top of the Lower Proterozoic. The base of the Proterozoic would naturally be much older than 1630 million years.

Major deviations from the average ages quoted are possibly due to recrystallization of mica or diffusion loss of argon resulting from local deformation or deeper burial of the rocks at the sample localities.

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