THE BELOMORIAN ECLOGITE PROVINCE: SEQUENCE OF EVENTS AND AGE OF THE IGNEOUS AND METAMORPHIC ROCKS OF THE GRIDINO ASSOCIATION
K.A. Dokukinaa, T.B. Bayanovab, T.V. Kaulinab, A.V. Travinc, M.V. Mintsa, A.N. Konilova, and P.A. Serovb
aGeological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017, Russia
bGeological Institute of the Kola Science Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, 184209, Russia
cV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Eclogites, Archean, Paleoproterozoic, mafic dikes, U/Pb zircon dating, 40Ar/39Ar dating of micas and amphiboles, Sm/Nd dating, Belomorian province
Pages: 1023-1054
Abstract
Within the Belomorian eclogite province, near Gridino Village, rocks of different compositions (tonalite-trondhjemite-granodioritic gneisses, granites, mafic and ultramafic rocks) were metamorphosed. The metamorphism included subsidence with increasing pressure and temperature, an eclogite stage, decompression in the granulitic facies, and a retrograde stage in the amphibolitic facies. We attempted to characterize the succession and to date igneous and metamorphic events in the evolution of the Gridino eclogite association. For this purpose, we conducted the following studies: U/Pb isotope dating of zircon (conventional and SHRIMP II methods) from gneisses, a mafic dike, and a high-pressure granite leucosome; U/Pb dating of rutile from mafic dikes; 40Ar/39Ar dating of amphiboles and micas; and Sm-Nd studies of rocks and minerals. The Sm-Nd model ages of felsic (2.9-3.1 Ga) and mafic (3.0-3.4 Ga) rocks from the Gridino eclogite association and individual magmatic zircons with an age of ~3.0 Ga indicate the Mesoarchean age of metamorphic-rock protoliths. The most reliable result is the upper age bound of eclogitic metamorphism (2.71 Ga), which reflects the time of the posteclogitic decompression melting of eclogitized rocks under high-pressure retrograde granulitic metamorphism. The mafic dikes formed from 2.82 Ga to 2.72 Ga, most probably, at 2.82 Ga, in accordance with the age of crystallization of magmatic zircons from metagabbro. Amphibolitic-facies superimposed metamorphism and the "final" exhumation of metamorphic complexes at 2.0-1.9 Ga are associated with the later Svecofennian tectonometamorphic stage. Successive cooling of metamorphic associations to 300?C at 1.9-1.7 Ga is shown by U-Pb rutile dating and 40Ar/39Ar mica dating.
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