Reply to Dewey and Ryan Comment on Searle, MP (2021) ‘Tectonic evolution of the Caledonian orogeny in Scotland: a review based on the timing of magmatism, metamorphism and deformation’

Abstract

AbstractI welcome the comment from Dewey and Ryan on my paper (Searle, 2021), and the chance to clarify some conflicting Caledonian tectonic models and new ideas. As outlined in the paper, my review was based on the geology of Scotland, not Ireland, Newfoundland or the rest of the Caledonian orogeny beyond, mainly because of length constraints, and the fact that my personal field experience lies mainly in Scotland. The Great Glen fault and the Moine Supergroup are not exposed at all in Ireland, so critical parts, and half of the Caledonian orogeny are missing in Ireland. I argue that the Caledonian geology of Scotland can be explained by a Laurentia – Midland valley arc-microcontinent collision, progressing from NW-directed ophiolite obduction in the Late Cambrian to crustal thickening and regional metamorphism during the Ordovician and Silurian, across the Dalradian and Moine metamorphic rocks. Caledonian structures do continue north into Greenland, as summarized by Leslie et al. (2008), but the geological evolution of the Scottish Caledonides does not require any collision with Baltica. The Dewey and Ryan comment raises major tectonic questions, which this reply addresses.