Incremental emplacement of the sheeted Glas Bheinn Porphyritic Dolerite, Ardnamurchan, NW Scotland

Abstract

Synopsis The c . 58 Ma Ardnamurchan Central Complex represents the deeply eroded roots of an ancient volcanic edifice that purportedly formed during three discrete phases of igneous activity. Although only a relatively small component of the first phase of magmatism (Centre 1), the Glas Bheinn Porphyritic Dolerite provides important insights into igneous emplacement mechanisms and age relationships on Ardnamurchan. New field observations combined with anisotropy of magnetic susceptibility analyses, which allow primary magma flow patterns to be reconstructed, suggest that the Glas Bheinn Porphyritic Dolerite consists of numerous inclined sheet intrusions that, overall, have a flower intrusive structure. Vertically ascending sheets that do not appear to be related to the Centre 1 focus are proposed to have been deflected into the inclined sheets and sills by the load of the overlying volcanic edifice. Cross-cutting relationships further suggest that some sheets of the Glas Bheinn Porphyritic Dolerite are later than several Outer Centre 2 cone sheets. These observations suggest that the Glas Bheinn Porphyritic Dolerite cannot be attributed to Centre 1. Supplementary material: AMS block sample locations and magnetic data are available at www.geolsoc.org.uk/SUP18562