Potassium‐argon measurements on the granites and some associated Rocks from Southwest England

Abstract

AbstractNew isotopic age determinations on all the granites of southwest England are presented and discussed in relation to the data of previous workers on the Dartmoor and Land's End granites, and with particular reference to the dating of the Hercynian orogeny in that region and to the more precise fixing of the Carboniferous‐Permian boundary. The possibility of a measurable non‐contemporaneity of the individual granites is shown, and their ages compared with those of Armorica and central Europe.The different granite phases within the composite plutons and the various associated late magmatic processes of pegmatitic injection, pegmatoid metasomatism, greisenisation, tourmalinisation and hydro‐thermal mineralisation, are shown to be pene‐contemporaneous.Some data on basic igneous rocks relative to the history of the Variscan fold‐belt in southwest England, and particularly to the Hercynian orogeny, are discussed.Age data on the Wolf Rock and Epsom Shoal phonolites are presented; their Mesozoic extrusion raises problems not yet resolvable.