Upper Palaeozoic basins of the British Isles—Caledonide inheritance versus Hercynian plate margin processes

Hypotheses to explain the origin and location of Upper Palaeozoic sedimentary basins are presented. Group A basins were those Old Red Sandstone basins whose location and subsidence were controlled by Caledonide features, including active and remnant fore-arc basins (Midland Valley) and major transcurrent movements (Orcadian basin). Newer Granite plutonic magmas in the Southern Uplands subduction complex post-dated subduction and resulted from post-collision cratonization processes as yet little understood. Group B basins were those whose initial positions in space were controlled by palaeo-plate factors, in particular the location of granitoid plutons, but whose subsidence was controlled by active Hercynian (neoplate) processes. Some Group A basins were regenerated by this process (Midland Valley). A new hypothesis is presented to account for the origin of a Carboniferous rift-to-sag trend similar to that proven in modern continental margin basins such as the North Sea. The hypothesis is an adaptation of McKenzie's lithospheric stretching model, some of whose major features are well shown in the Carboniferous history of the north and central British Isles. Group B processes were controlled by Ligurian/Bretonic plate consumption in the S Brittany–Massif Central–Vosges areas. Group C basins in the Rheno-Hercynian zone also owe their location and origin to back-arc rifting and continental crustal ‘oceanization’ processes caused by Liguro-Bretonic subduction.