The age and nature of the basement of southern Britain: evidence from Sr and Pb isotopes in granites

The isotopic study of granitic intrusions in southern Britain provides an indication of the age and geochemical nature of the South British basement, which is otherwise generally obscured from observation by sedimentary cover. This paper reports Pb isotopic compositions of feldspars in granites from SW England, Lundy, Mountsorrel and Shap, in addition to age and initial ⁸⁷Sr/⁸⁶Sr data on two of the granites. A review of published Rb–Sr age and isotope data for southern Britain and consideration of the new Pb data using the plumbotectonics model of Doe & Zartman (1979) indicate that the basement to southern Britain has an age of ∼800 Ma with an upper limit of 1200 Ma. The granites studied in this work have substantial components of crustally derived Sr and Pb.