Significance of thorium, uranium and potassium in some Early Precambrian graywackes from Wyoming and Minnesota

J. J W Rogers*, K. C. Condie, S. Mahan

*Corresponding author for this work

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Thorium, uranium, and potassium concentrations have been measured by gamma-ray spectrometry in graywacke sequences from the Wind River Mountains of Wyoming and the Knife Lake area of Minnesota. Thorium concentrations are compatible with the clay, quartz, and lithic contents of the rocks, but the uranium contents are low, thus yielding Th/U ratios in the neighbourhood of 5 or above. Assuming that all post-depositional elemental abundance variations in the graywackes have been caused solely by radioactive decay since the rocks were formed (about 3 · 109 years ago), the initial Th/U ratios would have been in the range of 3-4. If the graywackes are random samples of the continental crust at their time of formation, them these data support the data of Fahrig and Eade (1968) to the effect that the continental crust 3 · 109 years ago had a Th/U ratio significantly higher than that of the whole earth.

Original languageEnglish
Pages (from-to)207-213
Number of pages7
JournalChemical Geology
Volume5
Issue number3
DOIs
Publication statusPublished - 1970
Externally publishedYes

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