The age of the paroxysmal Variscan orogeny in England

Summary Potassium–argon age-determinations on 10 basic igneous rocks from the English Midlands indicate two distinct episodes of magmatic intrusion. Geological evidence and Permo-Carboniferous isotopic age data from Britain confirm the well-known close relationship between magmatism and earth-movements. It is concluded that the paroxysmal phase of the Variscan orogeny in England occurred in the early Stephanian (Asturic phase), and that late-tectonic granitic magmatism in the active zone was penecontemporaneous with basaltic magmatism on the foreland around 295 m.y. A further period of basaltic magmatism close to 265 m.y. is equated with Saalic movements, and it is suggested that a primary mineralization event at 225 m.y. is of widespread occurrence and might be used to fix the Permo-Triassic boundary in Britain.