Age of the Corodale Gneisses, South Uist

Martin J. Whitehouse
Scottish Journal of Geology, 29, 1-7, 1 May 1993, https://doi.org/10.1144/sjg29010001

Synopsis

Whole-rock Sm-Nd and Pb-Pb ages of 2770 ± 140 Ma and 2900 ± 100 Ma respectively are presented from a suite of samples from the Corodale Gneiss unit of eastern South Uist, Outer Hebrides. The initial εNd value of c. + 2.4 and model μ1 value of 7.9 are typical of late-Archaean mantle source regions in the Lewisian and are similar to values obtained from other Lewisian mafic-ultramafic complexes. These data confirm that the igneous protoliths to the Corodale Gneisses belong to the earliest crust-forming episode in the Lewisian, and are not correlated with younger mafic intrusive rocks in South Harris. Although the Corodale Gneiss unit has undergone extensive tectonic disruption during formation of the Outer Isles Thrust, there has been little post-Archaean disturbance of large-ion lithophile elements: U and Th have remained immobile in most samples, and there has been limited redistribution of Rb within the Corodale Gneiss unit itself.

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