In Great Britain and Ireland, limited rifting north of the Variscan subduction front triggered Tournasian
to Viseanage volcanism of mainly alkaline basic composition (Leeder 1982; Maynard et al.
Apparently the provenance change does not coincide with the boundary between the Horton and Windsor groups, but instead with the emergence of new source rocks in the late Tournasian.
This exposure first occurred in the Late Tournasian but through-transport of Mira debris was almost completely blocked early in the Visean.
However, in the case of Isle Madame, it seems most likely that mid- to lower-crustal rocks were exposed within a Tournasian basin by continuing extension and transcurrent faulting.
the deeper Tournasian
levels, beneath both the Pokrovskoe 1 and
5 Ma that are scattered across the area; (d) Givetian to Early Tournasian plutons that are widespread throughout the region from the coast of Maine northward to the Quebec border.
The onset of Galway granite plutonism predated the Acadian in Britain and Ireland but correlates with the Emsian, the Late Emsian to Eifelian, and the Givetian to Early Tournasian plutonic groups in Maine.