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Geological Society, London, Special Publications; 1964; v. 1; p. 159-175;
DOI: 10.1144/GSL.SP.1964.001.01.15
© 1964 Geological Society of London

Part 3: Original Data

The age of the paroxysmal Variscan orogeny in England

Frank Joseph Fitch, B.SC., F.G.S.

Department of Geology, Birkbeck College, Malet Street, London, W.C.1

John Alfred Miller, PH.D., F.G.S.

Department of Geodesy and Geophysics, Madingley Rise, Madingley Road, Cambridge

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.