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Rare earth evidence concerning the origin of granites of the Isle of Skye, northwest Scotland

1977; Elsevier BV; Volume: 36; Issue: 1 Linguagem: Inglês

10.1016/0012-821x(77)90192-3

1385-013X

R. S. Thorpe, Philip J. Potts, M.B. Sarre,

Geology and Paleoclimatology Research

Eleven samples of Skye granites, two samples of Torridonian sandstone and one sample of Lewisian gneiss have been analysed for ten rare earth elements (REE) by neutron activation analysis. The granites are representative of the main granite centres and compositional types. All granites have sub-parallel light-REE-enriched patterns with chondrite-normalised Ce(CeN) = 78–263,YbN = 16–60and CeN/YbN = 2.9–8.0. REE patterns for the Lewisian gneiss and Torridonian sandstone are similar to each other, withCeN = 32–61,YbN = 3–5and CeN/YbN = 8–18. These two rock types as well as the Glamaig granite have negligible Eu anomalies (Eu/Eu* > 0.9), and the other granites have Eu/Eu* in the range 0.83-0.34. The REE evidence suggests that Lewisian gneiss or Torridonian sandstone arenot suitable materials from which the granites could be derived by partial melting. The Western Red Hills granite intrusions show a systematic relation of REE content with Eu/Eu*. We suggest that the Glamaig granite is the most primitive, and was derived from a source with no Eu anomaly by fractional crystallization of a more basic magma. The later Western Red Hills granites might then have resulted from further fractional crystallization of magma with a composition like that of the Glamaig granite. The Coire Uaigneich and Eastern Red Hills granites may also be products of fractional crystallization, but from different magmas to those parental to the Western Red Hills granites. The basaltic parent magmas of the Skye granites may be "continental" tholeiites derived by interaction of basalt magma with Lewisian gneiss.