Вестник МГТУ, 2021, Т. 24, № 1.

Хубер М. и др. Изотопные характеристики серы сульфидов Хибинского и Ловозерского массивов. The Lovozero intrusive complex has the form of a laccolith with a broad base. The drilling program combined with three-dimensional modeling of gravity data made it possible to decipher the internal structure of the massif down to the depth of 10 km. According to these data, the Lovozero massif consists of two zones principally different in density. In the Lovozero massif, agpaitic lujavrites (type locality) form a rhythmic layered complex similar to that in Ilimaussaq, Greenland. A south-western zone, composed of agpaitic syenite to a depth of at least 10 km, is the most probable locus of the magma conduit. In the central part of the massif, at the Seidjavr Lake, a local negative gravity anomaly was detected, which corresponds to a body of alkaline and analcime syenite. A north-eastern zone is suggested to be composed of ultrabasic alkaline rocks similar to that of the adjacent Kurga alkaline-ultramafic massif. The south-eastern, southern, and western contacts of the massif are almost vertical to a depth of 4 km within the nepheline syenite zone but become sloping more gently at depths below 8-10 km. The northern and north-western contacts dip at smaller angles, which vary from 50-60° at the surface to 30-40° at depths of 4-5 km but become nearly vertical from this level to depths of 9-10 km. The alkaline rocks forming the Lovozero massif are represented by plutonic, subvolcanic, and volcanic magma products (Arzamastsev et al., 2008). Alkaline rocks are a powerful data set for understanding connections between surface and mantle sulfur reservoirs over geological timescales. Alkaline magmas (silicate rocks and carbonatites) are associated with mantle plumes (Sasada et al., 1997; Marty et al., 1998; Ernst et al., 2010) and/or sub-continental lithospheric mantle (Goodenough et al., 2002; Downes et al., 2005) that has been metasomatised by fluids and melts derived from previously subducted slabs. Evolved alkaline rocks are also rich in sulfur-bearing minerals, which reflect the high solubility of sulfur in carbonatitic and alkaline silicate melts (Babiel et al., 2018). There have been a large number of sulfur isotope investigations of alkaline complexes, few have thoroughly investigated how crustal contamination, degassing and fluid evolution (i. e. changes in temperature-pH-fO2) altered the primary mantle signature. Understanding these processes is critical to unlocking the alkaline record of magma sources. Global data compilation reveals that 534S of alkaline magma sources fall between -5 and +5 %% VCDT. The igneous 534S time-series shows a temporal trend with Proterozoic alkaline magmas largely restricted to positive 534S values (0 - +5 % VCDT) and Phanerozoic suites showing greater 534S diversity from -5 to +4 % VCDT (Hutchison et al., 2019). Here, we present a study o f sulfur isotope signatures of the Khibina and Lovozero massifs and demonstrate that an enriched subduction-influenced source (534S of +1 to +6 % VCDT) can be reconstructed for the Kola alkaline province of the Fennoscandian Shield. Materials and methods The Khibina rock samples (01CH, 04CH and 10CH) were taken from massive nepheline syenite from Mt. Rasvumchorr outcrops. The Lovozero eudialyte-bearing nepheline syenites (01LV, 03LV, 04LV and 05 LV) were collected from the classical outcrops of lujavrite-foyaite-urtite rhythms, exposed at the foot of the western slope of Mt. Alluaiv (Fig. 2). These samples were described by petrography investigation in transmitted and reflected light with the polarized optical microscope Leica DM2500P (Fig. 3) and examined on the scanning electron microscope Hitachi SU6600 with the energy dispersion spectroscope (EDS) mode. The sulfide minerals have been chemically characterized by electron microprobe analysis. For the sulfur isotopes analysis the sulfide grains were hand-picked using a binocular magnifying glass, so the contamination o f the accompanying sulfide phases was not excluded. These studies were implemented at the Department of Geology and Soil Science at the Faculty of Earth Sciences and Spatial Management of the Maria Curie-Sklodowska University (UMCS, Lublin, Poland). The stable sulfur isotopes 534S study was carried out on the pentlandite ((Fe, Ni)9S8, samples 01CH, 10CH) and pyrite (FeS2, sample 04CH) from Khibina nepheline syenite and on the pentlandite ((Fe, Ni)9S8, sample 04LV), chalcopyrite (CuFeS2, sample 03LV) and pyrite (FeS2, samples 01LV, 05LV) from Lovozero eudialyte-bearing nepheline syenite. Sulfur isotope analysis was undertaken at the Mass Spectrometry Laboratory of the Institute of Physics of the Maria Curie-Sklodowska University (UMCS, Lublin, Poland) by triple collector isotope ratio mass spectrometer (IRMS), using SO2 as the analyzed gas. The sulfide mineral specimens were quantitatively converted to SO2 in a vacuum line by their oxidation with analytical grade CuO reagent at temperatures between 800 and 900 °C. Along with the analyzed specimens, an aliquot of 20 mg of the IAEA-S1 standard (Ag2S) was converted to SO2 and analyzed using the mass spectrometer. All results are reported here in standard delta notation as per mil deviations from the Vienna-defined Canyon Diablo Troilite (VCDT). The precision of 534S values was 0.05 %. 82