AGE AND NATURE OF PROTOLITHS IN THE CALEDONIAN BLUESCHIST-ECLOGITE COMPLEX OF WESTERN SPITSBERGEN - A COMBINED APPROACH USING U-PB, SM-ND AND REE WHOLE-ROCK SYSTEMS

High-pressure metamorphic rocks (almost-equal-to 20 kb) (eclogites, ec logitic metagabbros and glaucophane-schists) from western Spitsbergen were investigated for major and trace element (including REE) geochemi stry, as well as Nd isotopes and U-Pb zircon characteristics. The dist inct nature of protoliths of the various high-pressure rocks has been preserved to some extent. Eclogites and eclogitic metagabbros represen t Lower Proterozoic (2.1 Ga) alkali basalts and transitional MORB, res pectively. Glaucophane-schists probably represent Upper Proterozoic sp ilitized Fe-Ti gabbros or volcaniclastic mixtures, or both. The dating results indicate that the Caledonian high-pressure metamorphism occur red at ca. 475 Ma, whereas a Lower Proterozoic magmatic activity - der ived from a depleted mantle source - is also recognized. This event is the oldest magmatism detected so far in the Svalbard Caledonides. The age of the protolith of the glaucophane-schists is not strictly const rained; however, it formed between 1.0 Ga and 475 Ma.