Regional chemical and isotopic differences seen in Ordovician–Devonian igneous rocks of northern Britain are thought to be due to subduction-related and collision magmatism tapping a variety of mantle and crustal sources. Matching of spatial chemical variation across major fault zones restricts post-magmatic transcurrent movement north of the Southern Upland Fault (SUF) to a few tens of kilometres on each fault. A unique mantle isotopic signature present in the same area may restrict post-1.5 Ga movement to less than a few hundred kilometres. No such restrictions exist on displacement across the SUF, to the south of which all magmas show a Pb isotopic component derived from southern sources.

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