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 magmatism within both the British Cenozoic Igneous Province and the wider North Atlantic Igneous Province. Its Qz + Pl + Kfs + Bt ± Grt ± Tpz mineralogy and peraluminous character contrast with other British Cenozoic Igneous Province 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 ± 0.4 – 58.4 ± 0.4 Ma) and cross-cutting basic dykes (57.2 ± 0.5 Ma), which confirm a Paleocene age for magmatism. Zircon inheritance is limited but two cores imply the presence of Early 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 superimposition of localized 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 British Cenozoic Igneous Province granites (metaluminous or subalkaline) indicates a fundamental crustal source control between contrasting peri-Gondwanan and Laurentian basement provinces. Supplementary material: Sample locations, petrographic summaries, mineral chemistry data and secondary ionization mass spectrometry U–Pb analytical data are available at https://doi.org/10.6084/m9.figshare.c.3886783