THE RELATIONSHIP BETWEEN THE PETROLOGY AND THE THORIUM AND URANIUM CONTENTS OF SOME GRANITIC ROCKS
Th and U contents of granitic rocks are intimately related to modal compositions and general petrologic features. Correlations exist between Th content and common indices of general petrogenetic evolution, such as amount of dark minerals, percentage of anorthite in plagioclase, and ratio of K feldspar to plagioclase. Th content increases regularly toward the more acidic rocks, and the increase is most pronounced in the most highly alkaline samples. U content generally shows little, if any, relationship to modal composition or other petrologic features, and the increase in abundance of U toward the more acidic rocks is irregular. The greater petrogenetic control of Th than of U content may be explained on the basis of oxidation and repeated loss of U from magmas during the later stages of their differentiation. Such an explanation assumes that magraas are originally derived from a relatively homogeneous source; remobilization, however, of different types of sedimentary or other rocks might provide granitic magmas of widely different initial Th and U contents. The possibility that Th is added hydrothermally to granites is partly supported by unusually high abundance of Th in some red, porphyritic, allanite-bearing rocks, but the general petrologic control of Th abundances argues against major secondary addition of material. (auth)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-14-021787
- OSTI ID:
- 4175908
- Journal Information:
- Geochim. et Cosmochim. Acta, Journal Name: Geochim. et Cosmochim. Acta Vol. Vol: 17
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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