Origin of s-, a-and i-type granites: Petrogenetic evidence from whole rock th/u ratio variations
Regelous A, Scharfenberg L, de Wall H (2021)
Publication Type: Journal article
Publication year: 2021
Journal
Book Volume: 11
Article Number: 672
Journal Issue: 7
DOI: 10.3390/min11070672
Abstract
The origin and evolution of granites remain a matter of debate and several approaches have been made to distinguish between different granite types. Overall, granite classification schemes based on element concentrations and ratios, tectonic settings or the source rocks (I-, A-, S-type) are widely used, but so far, no systematic large-scale study on Th/U ratio variations in granites based on their source or tectonic setting has been carried out, even though these elements show very similar behavior during melting and subsequent processes. We therefore present a compiled study, demonstrating an easy approach to differentiate between S-, A-and I-type granites using Th and U concentrations and ratios measured with a portable gamma ray spectrometer. Th and U concentrations from 472 measurements in S-and I-type granites from the Variscan West-Bohemian Massif, Germany, and 78 measurements from Neoproterozoic A-type Malani granites, India, are evaluated. Our compendium shows significant differences in the average Th/U ratios of A-, I-and S-type granites and thus gives information about the source rock and can be used as an easy classification scheme. Considering all data from the studied A-, I-and S-type granites, Th/U ratios increase with rising Th concentrations. A-type granites have the highest Th/U ratios and high Th concentrations, followed by I-type granites. Th/U ratios in S-to I-type granites are lower than in A-type and I-type granites, but higher than in S-type granites. The variation of Th/U ratios in all three types of granite cannot be explained by fractional crystallization of monazite, zircon and other Th and U bearing minerals alone, but are mainly due to source heterogeneities and uranium mobilization processes.
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APA:
Regelous, A., Scharfenberg, L., & de Wall, H. (2021). Origin of s-, a-and i-type granites: Petrogenetic evidence from whole rock th/u ratio variations. Minerals, 11(7). https://doi.org/10.3390/min11070672
MLA:
Regelous, Anette, Lars Scharfenberg, and Helga de Wall. "Origin of s-, a-and i-type granites: Petrogenetic evidence from whole rock th/u ratio variations." Minerals 11.7 (2021).
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