Age and petrogenesis of the Lundy granite: Paleocene intraplate peraluminous magmatism in the Bristol Channel, UK

Abstract

The Lundy granite forms part of the Lundy Igneous Complex which is the southernmost substantive expression of the British Cenozoic Igneous Province (BCIP). Its Qz+Pl+Kfs+Bt±Grt±Tpz 16 mineralogy and peraluminous character contrast with other BCIP granites farther north but are similar to the granites of the adjacent Early Permian Cornubian Batholith. We present the results of mapping, petrographical and mineral chemical analysis, and the first U-Pb zircon ages for the granite (59.8 ± 19 0.4 -58.4 ± 0.4 Ma) and crosscutting basic dykes (57.2 ± 0.5 Ma) which confirm a Palaeocene age 20 for magmatism. Zircon inheritance is limited but two cores imply the presence of Lower Palaeozoic igneous rocks in the unexposed basement of SW England. The anomalous southerly location of the Lundy Igneous Complex is a consequence of mantle melting arising from the superposition of localised lithospheric extension, related to intraplate strike-slip tectonics, with the distal ancestral Icelandic plume. Granite generation primarily reflects crustal partial melting during the emplacement of mantle-derived melts. The change in geochemical character between the Lundy granite (peraluminous) and other BCIP granites (metaluminous / subalkaline) indicates a fundamental crustal source control between contrasting peri-Gondwanan and Laurentian basement provinces.

Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

“…3), do reflect lower plate basement but are undated (Goode & Merriman 1987). Rare inherited Mesoproterozoic and late Devonian zircons in the Early Permian Cornubian Batholith (Neace et al 2016), and Lower Paleozoic zircons in the Palaeocene Lundy Granite (Charles et al 2017), do not provide substantive constraint.…”