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Trace element and isotope constraints on crustal anatexis by upwelling mantle melts in the North Atlantic Igneous Province: an example from the Isle of Rum, NW Scotland

ROMAIN MEYER^*, GRAEME R. NICOLL, JAN HERTOGEN^*,, VALENTIN R. TROLL^,, ROBERT M. ELLAM^¶, and C. HENRY EMELEUS^#

^* Geo-Instituut, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Leuven-Heverlee, Belgium
Department of Geology, University of Dublin, Trinity College, Dublin 2, Ireland
^¶ Scottish Universities Environmental Research Centre, Rankine Ave., East Kilbride G75 0QF, UK
^# Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK

Author for correspondence: jan.hertogen{at}geo.kuleuven.be

Sr and Nd isotope ratios, together with lithophile trace elements, have been measured in a representative set of igneous rocks and Lewisian gneisses from the Isle of Rum in order to unravel the petrogenesis of the felsic rocks that erupted in the early stages of Palaeogene magmatism in the North Atlantic Igneous Province (NAIP). The Rum rhyodacites appear to be the products of large amounts of melting of Lewisian amphibolite gneiss. The Sr and Nd isotopic composition of the magmas can be explained without invoking an additional granulitic crustal component. Concentrations of the trace element Cs in the rhyodacites strongly suggests that the gneiss parent rock had experienced Cs and Rb loss prior to Palaeogene times, possibly during a Caledonian event. This depletion caused heterogeneity with respect to ⁸⁷Sr/⁸⁶Sr in the crustal source of silicic melts. Other igneous rock types on Rum (dacites, early gabbros) are mixtures of crustal melts and and primary mantle melts. Forward Rare Earth Element modelling shows that late stage picritic melts on Rum are close analogues for the parent melts of the Rum Layered Suite, and for the mantle melts that caused crustal anatexis of the Lewisian gneiss. These primary mantle melts have close affinities to Mid-Oceanic Ridge Basalts (MORB), whose trace element content varies from slightly depleted to slightly enriched. Crustal anatexis is a common process in the rift-to-drift evolution during continental break-up and the formation of Volcanic Rifted Margins systems. The ‘early felsic–later mafic’ volcanic rock associations from Rum are compared to similar associations recovered from the now-drowned seaward-dipping wedges on the shelf of SE Greenland and on the Vøring Plateau (Norwegian Sea). These three regions show geochemical differences that result from variations in the regional crustal composition and the depth at which crustal anatexis took place.

Key Words: North Atlantic Igneous Province • Isle of Rum • Vøring Margin • Volcanic Rifted Margins • crustal contamination • crustal anatexis • petrogenesis

This article has been cited by other articles:

				D. A. JERRAM, K. M. GOODENOUGH, and V. R. TROLL Introduction: from the British Tertiary into the future - modern perspectives on the British Palaeogene and North Atlantic Igneous provinces Geological Magazine, May 1, 2009; 146(3): 305 - 308. [Abstract] [Full Text] [PDF]

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