Picritic magmas and the Rum ultramafic complex, Scotland

A. C. Skovgaard, J. McClurg, Linda Kirstein, M. Cheadle, C. H. Emeleus, W. J. Wadsworth, A. E. Fallick

Research output: Contribution to journalArticlepeer-review


Three small picritic dykes, intruded at a late stage in the evolution of the Rum basic-ultra-basic complex, Inner Hebrides, shed new light on the nature of the magmas responsible for the main complex. The magmas are of transitional (mildly alkalic) type, generated by relatively small-fraction (6-7%) melting of a depleted mantle source. Melting is tentatively deduced to have commenced at +/- 100 kin, straddling the garnet-spinel transition. Of the three samples, one (M9) is remarkable for the preservation of very primitive characteristics, with olivines of Fo(93) containing highly aluminous spinels; these appear unique within the British Tertiary Volcanic Province. Sr, Nd and Ph isotopes indicate only minor (less than or equal to4%) contamination with Precambrian crustal lithologies, reflecting the rapidity of ascent of the magma batches. The Rum picrites have Os-187/Os-188 ratios and trace element characteristics comparable to those of recent picrites from Iceland, suggesting minimal temporal change of the depleted parts of the Iceland plume over 60 Ma. Movements of the Long Loch Fault may have been instrumental in causing decompression melting of the spreading Iceland plume-head and facilitating ascent of the melts to near-surface levels.

Original languageEnglish
Pages (from-to)437-452
Number of pages16
JournalGeological Magazine
Issue number4
Publication statusPublished - Jul 2002


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