Abstract
Ten samples of blueschist facies eclogites occurring as dykes in the ultramafic rocks of the Voltri Group were analysed for eigth rare earth elements (REE). Their patterns are clearly different from those of cognate eclogites enclosed in ultramafic rocks and similar to those of the volcanic rocks dredged from the Mid-Atlantic Ridge (MAR). This similarity confirms both the tholeiitic nature of the magma injected into the Pennidic oceanic basement and metamorphosed to eclogite, and the immobile character of REE during metamorphism up to 10 Kbar and 450°C. Depletion of LREE vs HREE and a positive Eu anomaly in the coarse-grained central portions of the former dykes suggest their derivation from a mush consisting of pyroxene and plagioclase plus trapped superferrian liquid. The high total REE content and the flat pattern of the fine-grained eclogites occurring at the borders of the dykes are consistent with their derivation from a rapidly crystallized superferrian liquid.
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