Rifting and mafic magmatism in the Hebridean basins

• Published in: Journal of the Geological Society Vol. 172; no. 2; pp. 218 - 236
• Main Authors: Hole, M. J, Millett, J. M, Rogers, N. W, Jolley, D. W
• Format: Journal Article
• Language: English
• Published: London, UK Geological Society of London 01-03-2015; The Geological Society of London; Geological Society Publishing House
• Subjects: Argyllshire Scotland; basalts; Basins; Cenozoic; dike swarms; dikes; Europe; extension; Geophysics; Great Britain; Hebrides; Highland region Scotland; igneous and metamorphic rocks; igneous rocks; Inner Hebrides; intrusions; Inverness-shire Scotland; Isle of Skye; isotopes; large igneous provinces; mafic composition; magmatism; major elements; mantle; Melting; metals; Mull Island; Paleogene; Petrology; plate boundaries; Plate tectonics; rare earths; rifting; Scotland; solid Earth (tectonophysics); Strathclyde region Scotland; Temperature; Tertiary; thermal anomalies; trace elements; United Kingdom; upper mantle; volcanic rocks; Volcanoes; Western Europe; British Isles, Scotland, Highland, Skye; ANE, British Isles, Scotland, Highland, Inner Hebrides, Mull
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/jgs2014-100

Basalt dykes from the regional dyke swarm of the British Palaeogene Igneous Province (BPIP) were emplaced parallel to structural lineaments linking onshore and offshore volcanic edifices. Basalts that underwent minimal interaction with the crust have Mg# 60-75, εNd58 c. 8, 206Pb/204Pb c. 17.5, δ18O 5.9 ± 0.3 ppm, and 87Sr/86Sr <0.7040. Basalts with convex-upwards REE profiles ([La/Sm]N <1; [Sm/Yb]N >1) were generated by limited extents of melting (<10%) in the garnet-spinel transition of the upper mantle. Basalts with LREE-depleted ([La/Sm]N <1) or flat REE profiles require substantial (up to 20%) melting of spinel lherzolite. Modelling of major element compositions and olivine equilibration temperatures indicates that the mantle potential temperature was a maximum of 1530 °C beneath the BPIP at 58-60 Ma. Magmatism occurred at the periphery of a mantle thermal anomaly (proto-Iceland plume; TP ≤ 1560 °C) centred beneath western Greenland. The distribution of BPIP magmas was controlled by extensional tectonism driven by plate boundary forces resulting from plate reorganizations in the northern hemisphere starting at c. 62 Ma. The well-known mildly alkaline lava piles of Skye and Mull represent volcanoes on the flanks of the resulting rift system.