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

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

Research output: Contribution to journalArticleResearchpeer-review

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.

LanguageEnglish
Pages207-213
Number of pages7
JournalChemical Geology
Volume5
Issue number3
DOIs
Publication statusPublished - 1970
Externally publishedYes

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Thorium
Uranium
thorium
continental crust
Precambrian
uranium
Potassium
potassium
Rocks
gamma ray spectrometry
radioactive decay
Quartz
graywacke
Gamma rays
rock
Spectrometry
Lakes
Rivers
Earth (planet)
quartz

Cite this

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title = "Significance of thorium, uranium and potassium in some Early Precambrian graywackes from Wyoming and Minnesota",
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.",
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Significance of thorium, uranium and potassium in some Early Precambrian graywackes from Wyoming and Minnesota. / Rogers, J. J W; Condie, K. C.; Mahan, S.

In: Chemical Geology, Vol. 5, No. 3, 1970, p. 207-213.

Research output: Contribution to journalArticleResearchpeer-review

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N2 - 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.

AB - 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.

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