A large explosive silicic eruption in the British Palaeogene Igneous Province

Abstract

Large-volume pyroclastic eruptions are not known from the basalt-dominated British Palaeogene Igneous Province (BPIP), although silicic magmatism is documented from intra-caldera successions in central volcanoes and from small-volume ash-layers in the associated lava fields. Exceptions are the Sgùrr of Eigg (58.7 Ma) and Òigh-sgeir pitchstones in the Inner Hebrides (>30 km apart), which have been conjectured to represent remnants of a single large silicic event. Currently available major element data from these outcrops differ, however, creating a need to test if the two pitchstones are really related. We employ a systematic array of methods ranging from mineralogy to isotope geochemistry and find that samples from the two outcrops display identical mineral textures and compositions, major- and trace elements, and Sr-Nd-Pb-O isotope ratios, supporting that the two outcrops represent a single, formerly extensive, pyroclastic deposit. Available isotope constraints suggest a vent in the Hebridean Terrane and available radiometric ages point to Skye, ~40 km to the North. A reconstructed eruption volume of ≥5km3 DRE is derived, suggesting a VEI 5 event or larger. We therefore argue, contrary to long-held perception, that large-volume silicic volcanism and its associated climatic effects were likely integral to the BPIP during the opening of the North Atlantic.

Petrogenesis of the Loch Bà ring-dyke and Centre 3 granites, Isle of Mull, Scotland

“…87 Sr/ 86 Sr was corrected for mass fractionation using 86 Sr/ 88 Sr = 0.1194. Repeat analysis of the NIST SRM-987 Sr standard gave 0.710257 ± 18 (2 sd, n = 14) for the duration of this study (see Meyer et al 2009;Troll et al 2019 for full analytical details). 143 Nd/ 144 Nd was corrected for mass fractionation using 146 Nd/ 144 Nd = 0.7219.…”

“…In fact, they have relatively low Ni, in line with the low MgO values, and they are thus typical for intermediate magmatic compositions from the region (cf. Emeleus and Bell 2005;Troll et al 2019).…”