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Proterozoic processes of magmatism and metasomatism in the Archaean rocks of the Pechenga palaeorift basement
Abstract. The results of new isotopic investigations of the Archaean rocks from the Kola Superdeep Borehole (SG-3) – gneisses by the U-Pb method on zircon and amphibolites by the Sm-Nd model method on the whole rock have been presented. Besides, some rocks of the Proterozoic Pechenga structure and its Archaean framing have been dated by the U-Pb method on zircon, baddeleyite and other accessory minerals. Tonalite gneisses from SG-3 unit II yielded the oldest age of 2814±17 Ma. Zircon from the rest gneiss units in the section yielded an age of 2.78-2.55 Ga. This age fixes metamorphic events of the Archaean. Model ages of protolith from amphibole rocks are divided into three groups: 2.50-2.25, 2.79-2.65 and 3.15-2.89 Ga. Amphibolites from the first group are comagmatic to basic-ultrabasic dykes of the northern framing and to volcanites from the lower formations of the Pechenga structure. Amphibolites from the second group correspond to the basic rocks of the Late Archaean greenstone belts that are very common in the NE Baltic shield. Amphibolites with the oldest protolith are likely to be relics of the Early Archaean greenstone belt on the enzymatic base. All the ages obtained on the rocks from SG-3 do not correlate with depth which is likely to reflect lamellar-block structure of the section. New geochronological data on the Pechenga structure are evidence of a few previously unknown magmatic impulses in its formation. The dating results for granitoids from the Archaean framing fix their Proterozoic age and metamorphic changes at the final stage of the Svecofennian orogeny.
Printed reference: Vetrin V.R. Proterozoic processes of magmatism and metasomatism in the Archaean rocks of the Pechenga palaeorift basement // Vestnik of MSTU. 2007. V. 10, No 1. P. -.
Electronic reference: Vetrin V.R. Proterozoic processes of magmatism and metasomatism in the Archaean rocks of the Pechenga palaeorift basement // Vestnik of MSTU. 2007. V. 10, No 1. P. -. URL: http://vestnik.mstu.edu.ru/v10_1_n26/articles/09_vetrin.pdf.
