Do S-type granites commonly sample infracrustal sources? : new results from an integrated O, U-Pb and Hf isotope study of zircon

Appleby, Sarah K.; Gillespie, Martin R.; Graham, Colin M.; Hinton, Richard W.; Oliver, Grahame J.H.; Kelly, Nigel M.. 2010 Do S-type granites commonly sample infracrustal sources? : new results from an integrated O, U-Pb and Hf isotope study of zircon. Contributions to Mineralogy and Petrology, 160 (1). 115-132.

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In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian (~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U–Pb and Hf isotope analyses in zircon in order to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430–400 Ma) I-type granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U–Pb data of inherited zircons, and high mean zircon δ18O values of 9.0 ± 2.7‰ (2SD) and 9.8 ± 2.0‰ for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains zircons with much lower δ18O values (6.8 ± 2.1‰), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains low-δ18O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like δ18O. Mixing trends in plots of δ18O vs. εHf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes 2010 > Geology and Landscape (Scotland)
ISSN: 0010-7999
NORA Subject Terms: Earth Sciences
Date made live: 22 Sep 2010 14:09 +0 (UTC)

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