ISSN 1028334X, Doklady Earth Sciences, 2013, Vol. 448, Part 1, pp. 78–85. © Pleiades Publishing, Ltd., 2013. Original Russian Text © A.E. Mel’nik, S. G. Skublov, Yu.B. Marin, A.V. Berezin, E.S. Bogomolov, 2013, published in Doklady Akademii Nauk, 2013, Vol. 448, No. 2, pp. 197–205. 78 The origin of garnetites, which are quite abundant in highpressure metamorphic complexes, is still debatable. The idea about primary magmatic differen tiation of basites to Fe–Ti (garnetite protolith) and Mg (protolith of metabasite complimentary to garnetite) parts is the most popular [1 and others]. There are assumptions about the formation of garnetite as a result of metamorphic differentiation from active infiltration of fluid [2] and metasomatism with the for mation of a metasomatic column [3]. Extensive garnetization of eclogitic bodies as linear bands up to the appearance of garnetite containing up to 50% garnet and more was registered in Salma eclog ites within the northwestern part of the Belomorian mobile belt (BMB). The authors studied in detail the body of massive eclogites (Sample 46) with a size of up to 10 m in diameter in the key area of Salma eclogites, in the KuruVaara deposit mine. This body occurs in migmatizes tonolite–trondhjemite gneiss intruded by numerous veins of ceramic pegmatites [4]. Eclogites are strongly amphibolized at the contact with host gneiss with the formation of a garnet amphibolite rim (Sample 50) with a thickness of 1–2 m. The garnetite layer with a thickness of up to 60 cm (Sample 48) occurs between the amphibolite rim and the eclogite. Garnetite (Sample 48) contains garnet porphyro blasts with a size of ~1 mm (up to 50%), intergranular brownishgreen amphibole (20%), andesine (14%), rutile, and ore mineral (5%). In contrast to eclogitic garnet (Sample 46), garnet from garnetite contains numerous poikilitic inclusions of prevailing quartz (10% of the whole rock volume), abundant horn blende and rutile, and single grains of monoclinic pyroxene and biotite. Garnetite (Sample 48) and eclogite (Sample 46) located within the same body differ significantly in the chemical composition. Garnetite differs from eclogite by the high concentration of FeO* (18.0 and 12.1 wt %, respectively) and TiO 2 (1.38 and 0.43 wt %) and the low concentrations of MgO (6.1 and 12.1 wt %) and CaO (11.1 and 13.4 wt %). Garnetite is significantly enriched in V (by a factor of 6) and depleted in Ni, Cr, and Ba by one order of magnitude in comparison with eclogite. The concentrations of Y, Zr, Hf, Th, and REE in garnetite are almost two times higher. A difference in major and minor elements is regu larly observed in characteristic minerals of garnetite and eclogite as well. Garnet from garnetite differs from eclogitic garnet by the high concentrations of Fe, Ca, HREE, Y, and V and by low contents of Mg and Cr [4]; amphibole and monoclinic pyroxene, by the high Fe#, Ti, and V contents; and rutile, by the high con centrations of V, Zr, and Hf and the low contents of Cr and Nb. The contrasting chemical compositions of garnetite and eclogite do not result in qualitative change of the mineral association upon transforma tion of eclogite to garnetite, but have an impact on the compositions of rockforming, as well as accessory, minerals. The local U–Pb dating of zircon from garnetite performed on an ion microprobe SHRIMPII (Cen ter for Isotope Investigations, Russian Geological Research Institute) was accompanied by investigation of the distribution of rare and rareearth elements at the same points on an ion microprobe Cameca IMS4f (Yaroslavl’ branch of the PhysicoTechnological Insti tute) by the standard methodologies. The composition of zircons for plotting of the spectra of the REE distri bution was normalized to the composition of C1 chondrite [5]. The temperature of zircon crystalliza tion was calculated by the concentration of Ti in zir con [6]. Analysis of the Sm–Nd system of rocks and minerals was performed by the method of isotope dilu tion on a TRITON mass spectrometer (Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences). The method of sulfuric acid leaching including treatment of garnet crystals ground in an agate mortar by concentrated H 2 SO 4 at a tem perature of 180°C over 24 h was applied for selective New Data on the Age (U–Pb, Sm–Nd) of Garnetites from Salma Eclogites of the Belomorian Mobile Belt A. E. Mel’nik a , S. G. Skublov a , Corresponding Member of the RAS Yu. B. Marin b , A. V. Berezin a , and E. S. Bogomolov a Received May 5, 2012 DOI: 10.1134/S1028334X13010133 a Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Saint Petersburg b Saint Petersburg National Mining University, Saint Petersburg email: meliks1@yandex.ru GEOCHEMISTRY