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

• Sr and Nd isotope ratios, together with lithophile trace elements, have been measured in arepresentative set of igneous rocks and Lewisian gneisses from the Isle of Rum in order to unravel thepetrogenesis of the felsic rocks that erupted in the early stages of Palaeogene magmatism in the NorthAtlantic Igneous Province (NAIP). The Rum rhyodacites appear to be the products of large amountsof melting of Lewisian amphibolite gneiss. The Sr and Nd isotopic composition of the magmas canbe explained without invoking an additional granulitic crustal component. Concentrations of the traceelement Cs in the rhyodacites strongly suggests that the gneiss parent rock had experienced Cs and Rbloss prior to Palaeogene times, possibly during a Caledonian event. This depletion caused heterogeneitywith respect to 87Sr/86Sr in the crustal source of silicic melts. Other igneous rock types on Rum (dacites,early gabbros) are mixtures of crustalmelts and and primarymantle melts. Forward Rare Earth Elementmodelling shows that late stage picritic melts on Rum are close analogues for the parent melts of theRum 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 traceelement content varies from slightly depleted to slightly enriched. Crustal anatexis is a common processin the rift-to-drift evolution during continental break-up and the formation of Volcanic Rifted Marginssystems. The ‘early felsic–later mafic’ volcanic rock associations from Rum are compared to similarassociations recovered from the now-drowned seaward-dipping wedges on the shelf of SE Greenlandand on the Vøring Plateau (Norwegian Sea). These three regions show geochemical differences thatresult from variations in the regional crustal composition and the depth at which crustal anatexis took place.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics

Geovetenskap med inriktning mot mineralogi, petrologi och tektonik

Publikations- och innehållstyp

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