Field and petrological studies of the Highland Border Ophiolite demonstrate that it was obducted onto the Neoproterozoic–Ordovician rocks of the Dalradian block, and not emplaced against them by post-orogenic strike-slip movement. It was welded onto the upper, southward-younging limb of the already recumbent Tay Nappe (D1), and deformed by the Downbend Antiform (D4). However, its emplacement was not accompanied by significant internal deformation of the Dalradian block. As the ophiolite is correlated with those at Clew Bay, Tyrone and Shetland, this result will necessitate complete revision of the current model for basin closure on the southeastern margin of Laurentia.

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