Is the Colonsay-west Islay block of SW Scotland an allochthonous terrane? Evidence from Dalradian tillite clasts

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Abstract
In the Scottish Caledonides context, the Colonsay-west Islay terrane has seemed anomalous and therefore likely to be allochthonous. New studies suggest, however, that its basement is not necessarily exotic but represents the missing early Proterozoic link between Greenland and Scandinavia. Recent interpretations of the Scottish mainland deformation history imply that the age of the Grampian events there resembles that of the late Proterozoic deformation previously identified in the Colonsay Group cover succession. Reconnaisance studies of Dalradian tillite provenance suggest that the Colonsay-west Islay basement was a source of Dalradian sediment and perhaps floored that basin. There is, therefore, less reason now to regard the Colonsay-west Islay terrane as allochthonous, and recent hypotheses of its tectonic emplacement being the cause of the Grampian orogeny should be viewed with caution.