U-Pb zircon ages for Late Precambrian igneous rocks in southern Britain

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Abstract
Seven new U-Pb zircon ages for volcanic and intrusive igneous rocks from southern Britain are as follows: 613 ± 4 Ma for the Coedana Granite, Anglesey, and 614 ± 2 Ma for the Padarn Tuff Formation of the Arfon Group, North Wales; 677 ± 2 Ma for a deformed granite of the Malvernian Complex and 566 ± 2 Ma for a rhyolitic tuff in the Warren House Formation, Malvern Hills; 603 ± 2 Ma for a granophyric diorite ('markfieldite') intrusive into the Caldecote Volcanic Formation at Nuneaton; 566 ± 2 Ma for the Uriconian volcanic group, Shropshire, and 560 ± 1 Ma for the Ercall Granophyre, which is intrusive into Uriconian volcanic rocks. Three of the four dated intrusive rocks contain a component of inherited zircon, but the dated volcanic rocks are composed of simple, single-stage zircon populations with no detectable amount of secondary Pb-loss. The ages clarify the timing of Precambrian magmatic events in southern Britain, and conform well with those in neighbouring Avalonian terranes. The new age of the Ercall Granophyre provides a reliable maximum age for the Early Cambrian (Atdabanian—late Tommotian) strata of England, and reconfirms a Precambrian age for the Padarn Tuff Formation and granophyric diorite ('markfieldite') which demonstrably underlie Early Cambrian strata.