Comparative petrology and metamorphic evolution of the Limpopo (South Africa) and Lapland (Fennoscandia) high-grade terrains

Summary ?Detailed studies of rocks from the Limpopo (South Africa) and Lapland (Kola-Fennoscandia) high-grade terrains were carried out in order to reveal similar geological and thermodynamic conditions in their formation. Both complexes (1) are situated between Archean greenstone belts, (2) are younger than the belts, (3) are bounded by crustal-scale shear zones, (4) have a similar intrusive-like (harpolith) geometry, and (5) show similar reaction textures that reflect both breakdown and growth of garnet in each high-grade terrain. Local mineral equilibria within the textures indicate their successive formation with cooling of the granulite facies rocks. Some of the textures in the metapelites must have resulted from the following reverse reactions: Grt + Qtz ⇌Opx + Crd and/or Grt + Sil + Qtz ⇌ Crd. Based on these data, both the decompression cooling P-T path and the near-isobaric cooling P-T path were deduced for each HGT. However the near-isobaric cooling P-T path is not a characteristic of the central zones of both complexes studied. Similar structural framework of the high-grade terrains, similar morphologies (shapes of granulitic bodies), similar reaction textures developed in metapelites, and similar shapes of P-T paths suggest similarity in geodynamic history of both complexes.

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Zusammenfassung ?Vergleichende Petrologie und metamorphe Entwicklung der hochgradig metamorphen Terrains von Limpopo (Südafrika) und Lappland (Fennoscandia) Eingehende Untersuchungen an Gesteinen aus den hochgradig metamorphen Terrains von Limpopo (Südafrika) und Lappland (Kola-Fennoscania) sollen m?gliche ?hnlichkeiten in den geologischen und thermodynamischen Bildungsbedingungen aufzeigen. Beide Komplexe sind Lokale Mineralgleichgewichte innerhalb der Texturen weisen auf ihre schrittweise Bildung w?hrend der Abkühlung der granulitfaziellen Gesteine hin. Einige der Texturen in den Metapeliten gehen auf folgende reversible Reaktionen zurück: Grt + Qtz ⇌Opx + Crd und/oder Grt + Sil + Qtz ⇌ Crd. Diese Daten erm?glichten es, sowohl den P-T Pfad der Abkühlung bei Druckentlastung sowie den fast-isobaren P-T Pfad der Abkühlung für jedes HGT zu ermitteln. Der fast-isobare P-T Pfad der Abkühlung ist jedoch kein Charakteristikum der Zentralzonen beider Komplexe. Ein ?hnlicher struktureller Rahmen der hochgradigen Terrains, ?hnliche Morphologien (Ausbildung der Granulitk?rper), ?hnliche Reaktionstexturen in Metapeliten und ?hnliche P-T Pfade weisen auf ?hnlichkeiten der geodynamischen Entwicklungsgeschichte beider Komplexe hin.

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Received March 8, 1999; revised version accepted September 17, 1999     

P–T conditions of decompression of the Limpopo high-grade terrane: record from shear zones

The Southern Marginal Zone of the late Archean Limpopo Belt of southern Africa is an example of a high‐grade gneiss terrane in which both upper and lower crustal deformational processes can be studied. This marginal zone consists of large thrust sheets of complexly folded low‐strain gneisses, bound by an imbricate system of kilometre‐wide deep crustal shear zones characterized by the presence of high‐strain gneisses (‘primary straight gneisses’). These shear zones developed during the decompression stage of this high‐grade terrane. Low‐ and high‐strain gneisses both contain similar reaction textures that formed under different kinematic conditions during decompression. Evidence for the early M1/D1 metamorphic phase (> 2690 Ma) is rarely preserved in low‐strain gneisses as a uniform orientation of relict Al‐rich orthopyroxene in the matrix and quartz and plagioclase inclusions in the cores of early (M1) Mg‐rich garnet porphyroblasts. This rare fabric formed at > 820 °C and > 7.5 kbar. The retrograde M2/D2 metamorphic fabric (2630–2670 Ma) is well developed in high‐strain gneisses from deep crustal shear zones and is microscopically recognized by the presence of reaction textures that formed synkinematically during shear deformation: M2 sigmoid‐shaped reaction textures with oriented cordierite–orthopyroxene symplectites formed after the early M1 Mg‐rich garnet porphyroblasts, and syn‐decompression M2 pencil‐shaped garnet with oriented inclusions of sillimanite and quartz formed after cordierite under conditions of near‐isobaric cooling at 750–630 °C and 6–5 kbar. The symplectites and pencil‐shaped garnet are oriented parallel to the shear fabric and in the stretching direction. Low‐strain gneisses from thrust sheets show similar M2 decompression cooling and near‐isobaric cooling reaction textures that formed within the same P–T range, but under low‐strain conditions, as shown by their pseudo‐idioblastic shapes that reflect the contours of completely replaced M1 garnet and randomly oriented cordierite–orthopyroxene symplectites. The presence of similar reaction textures reflecting low‐strain conditions in gneisses from thrust sheets and high‐strain conditions in primary straight gneisses suggests that most of the strain during decompression was partitioned into the bounding shear zones. A younger M3/D3 mylonitic fabric (< 2637 Ma) in unhydrated mylonites is characterized by brittle deformation of garnet porphyroclasts and ductile deformation of the quartz–plagioclase–biotite matrix developed at < 600 °C, as the result of post‐decompression shearing under epidote–amphibolite facies conditions.     

Neoarchaean high-grade metamorphism in the Central Zone of the Limpopo Belt (South Africa): Combined petrological and geochronological evidence from the Bulai pluton

The Bulai pluton represents a calc-alkaline magmatic complex of variable deformed charnockites, enderbites and granites, and contains xenoliths of highly deformed metamorphic country rocks. Petrological investigations show that these xenoliths underwent a high-grade metamorphic overprint at peak P–T conditions of 830–860 °C/8–9 kbar followed by a pressure–temperature decrease to 750 °C/5–6 kbar. This P–T path is inferred from the application of P–T pseudosections to six rock samples of distinct bulk composition: three metapelitic garnet–biotite–sillimanite–cordierite–plagioclase–(K-feldspar)–quartz gneisses, two charnoenderbitic garnet–orthopyroxene–biotite–K-feldspar–plagioclase–quartz gneisses and an enderbitic orthopyroxene–biotite–plagioclase–quartz gneiss. The petrological data show that the metapelitic and charnoenderbitic gneisses underwent uplift, cooling and deformation before they were intruded by the Bulai Granite. This relationship is supported by geochronological results obtained by in situ LA-ICP-MS age dating. U–Pb analyses of monazite enclosed in garnet of a charnoenderbite gneiss provide evidence for a high-grade structural-metamorphic–magmatic event at 2644 ± 8 Ma. This age is significantly older than an U–Pb zircon crystallisation age of 2612 ± 7 Ma previously obtained from the surrounding, late-tectonic Bulai Granite. The new dataset indicates that parts of the Limpopo's Central Zone were affected by a Neoarchaean high-grade metamorphic overprint, which was caused by magmatic heat transfer into the lower crust in a ‘dynamic regional contact metamorphic milieu’, which perhaps took place in a magmatic arc setting.     

Holocene history of Lake Soldatskoje (Kola Peninsula, Russia) inferred from sedimentary diatom assemblages

A sediment core from Lake Soldatskoje, a small tundra lake located in the northern coastal area of the Kola Peninsula and surrounded by numerous archaeological dwelling sites, was analysed for diatom species. The core covers the entire Holocene, i.e. 10000 radiocarbon years. The diatom record has similarities with studies made earlier from tundra lakes of northern Russia and from Arctic lakes in general. The genus Fragilaria was dominant and many other small, benthic, nordic, cold-water diatom species typical of Arctic lakes were common, including Achnanthes minutissima Kützing, A. pusilla (Grunow) De Toni, Cyclotella tripartita Håkansson and Navicula absoluta Hustedt. Multivariable ordinations were used to characterize the changes in the diatom flora. Diatom-based pH and total phosphorus inferences indicate that the lake has become progressively more acidic and poorer in nutrients. Disturbances in the diatom stratigraphy of Lake Soldatskoje around 4000–5500 ¹⁴C yr BP may be related to human activity.     

Magnetic fabric evolution in ductile shear zones: examples in metagranites of the Aar Massif (Swiss Central Alps)

The Aar Massif forms part of the polycyclic basement of the External Crystalline Massifs in central Switzerland. Strong heterogeneous Alpine deformation produced a network of broad, anastomosing shear zones, with deformation strongly localized in mylonitic domains. This study investigates the combined effects of high‐strain deformation and synkinematic metamorphism on magnetic fabric evolution in Tertiary shear zones of the Aar granite and Grimsel granodiorite. In transects across several mesoscale shear zones with large strain gradients, magnetic fabric orientations are in excellent agreement with principal strain orientations determined from outcrop fabrics and strain markers. However, the magnitude and shape of the magnetic anisotropy do not change systematically with increasing finite strain, likely as a result of recrystallization and metamorphism. The overall pattern of steeply dipping fabrics is consistent with the main shortening stage of regional Alpine kinematics, while some mylonite structures reflect a local component of dextral shearing.     

Trace-element study and uranium-lead dating of perovskite from the Afrikanda plutonic complex, Kola Peninsula (Russia) using LA-ICP-MS

The U-Pb geochronology of perovskite is a powerful tool in constraining the emplacement age of silica-undersaturated rocks. The trace-element and U-Pb isotopic compositions of perovskite from clinopyroxenite and silicocarbonatite from the Afrikanda plutonic complex (Kola, Russia) were determined by laser-ablation inductively-coupled mass-spectrometry (LA-ICP-MS). In addition, the Sr isotopic composition of perovskite was measured by isotope-dilution mass-spectrometry to better constrain the relations between its host rocks. Perovskite from the two rock types shows a different degree of enrichment in Na, Mg, Mn, Pb, Fe, Al, V, rare-earth elements, Zr, Hf, Th, U and Ta. The perovskite ⁸⁷Sr/⁸⁶Sr values are within analytical uncertainty of one another and fall within the range of mantle values. The ²⁰⁶Pb/²³⁸U ages (corrected for common lead using ²⁰⁷Pb-method) of perovskite from silicocarbonatite statistically yield a single population with a weighted mean of 371?±?8 Ma (2σ; MSWD?=?0.071). This age is indistinguishable, within uncertainty, to the clinopyroxenite weighted mean ²⁰⁶Pb/²³⁸U age of 374?±?10 Ma (2σ; MSWD?=?0.18). Our data are in good agreement with the previous geochronological study of the Afrikanda complex. The observed variations in trace-element composition of perovskite from silicocarbonatite and clinopyroxenite indicate that these rocks are not related by crystal fractionation. The Sr isotopic ratios and the fact that the two rocks are coeval suggest that they were either produced from a single parental melt by liquid immiscibility, or from two separate magmas derived at different degrees of partial melting from an isotopically equilibrated, but modally complex mantle source.     

Eclogites from the Belomorian Mobile Belt (Kola Peninsula): geology and petrology

The paper focuses on the metamorphic geology of the oldest crustal eclogites discovered in the Late Archean tonalite-trondhjemite-granodiorite (TTG) complex of the Belomorian Mobile Belt on the Kola Peninsula. Eclogite bodies are, most likely, widespread. We studied one of the key objects, the Kuru-Vaara quarry, where several tens of retrogressed eclogite blocks randomly embedded in the TTG gneisses were stripped at the benches. Based on the field observations, two visually different types of eclogites have been recognized: “southern”, strongly retrogressed coarse-grained, and “northern”, well-preserved fine-grained. The southern eclogite blocks bear evidence of their partial melting with the formation of veins and melt percolation channels. The northern eclogite blocks show no evidence of melting. Despite the significant mineralogic difference, both types of eclogites can be assigned to amphibole eclogite facies. The applied jadeite solubility geobarometers yielded the minimum pressures of ～12 kbar for the northern eclogites and ～14–14.5 kbar for the southern ones. The used geothermometers yielded ～700°C and ～750°C, respectively. But the presence of quartz lamellae in Na-clinopyroxenes in both types of eclogites and their bulk compositions corresponding to high-Mg basalts suggest that the Kuru-Vaara eclogites might have reached the field of ultrahigh-pressure metamorphism. Analysis of the tentative P-T paths of metamorphic evolution for both types of eclogites showed that their burial–exhumation cycle might have taken as short as a few million years. The set of presented data suggests that the formation of the Kuru-Vaara eclogites was related to the subduction of the Archean oceanic crust, which should have differed in composition and structure from the modern oceanic crust.     

Depletion and enrichment processes in the lithospheric mantle beneath the Kola Peninsula (Russia): Evidence from spinel lherzolite and wehrlite xenoliths

A suite of spinel lherzolite and wehrlite xenoliths from a Devonian kimberlite dyke near Kandalaksha, Kola Peninsula, Russia, has been studied to determine the nature of the lithospheric mantle beneath the northern Baltic Shield. Olivine modal estimates and Fo content in the spinel lherzolite xenoliths reveal that the lithosphere beneath the Archaean–Proterozoic crust has some similarities to Phanerozoic lithospheric mantle elsewhere. Modal metasomatism is indicated by the presence of Ti-rich and Ti-poor phlogopite, pargasite, apatite and picroilmenite in the xenoliths. Wehrlite xenoliths are considered to represent localised high-pressure cumulates from mafic–ultramafic melts trapped within the mantle as veins or lenses. Equilibration temperatures range from 775 to 969 °C for the spinel lherzolite xenoliths and from 817 to 904 °C for the wehrlites.

Laser ablation ICP-MS data for incompatible trace elements in primary clinopyroxenes and metasomatic amphiboles from the spinel lherzolites show moderate levels of LREE enrichment. Replacement clinopyroxenes in the wehrlites are less enriched in LREE but richer in TiO₂. Fractional melt modelling for Y and Yb concentrations in clinopyroxenes from the spinel lherzolites indicates 7–8% partial melting of a primitive source. Such a volume of partial melt could be related to the 2.4–2.5 Ga intrusion of basaltic magmas (now metamorphosed to garnet granulites) in the lower crust of the northern Baltic Shield. The lithosphere beneath the Kola Peninsula has undergone several episodes of metasomatism. Both the spinel lherzolites and wehrlites were subjected to an incomplete carbonatitic metasomatic event, probably related to an early carbonatitic phase associated with the 360–380 Ma Devonian alkaline magmatism. This resulted in crystallisation of secondary clinopyroxene rims at the expense of primary orthopyroxenes, with development of secondary forsteritic olivine and apatite. Two separate metasomatic events resulted in the crystallisation of the Ti–Fe-rich amphibole, phlogopite and ilmenite in the wehrlites and the low Ti–Fe amphibole and phlogopite in the spinel lherzolites. Alternatively, a single metasomatic event with a chemically evolving melt may have produced the significant compositional differences seen in the amphibole and phlogopite between the spinel lherzolites and wehrlites. The calculated REE pattern of a melt in equilibrium with clinopyroxenes from a cpx-rich pocket is identical to that of the kimberlite host, indicating a close petrological relationship.     

Emplacement processes and cooling history of layered cyclic unit II-7 from the Lovozero alkaline massif (Kola Peninsula, Russia)

The Lovozero alkaline massif (Kola Peninsula, Russia) is composed of three major units. The central unit (80% of the volume) comprises numerous well developed layers composed, from bottom to roof, of an urtite–juvite–foyaite–lujavrite continuous lithological sequence (ijolite–foid-bearing alkali feldspar syenite in IUGS nomenclature). The mode of emplacement of the massif and the mechanism of formation of the layering are still under debate. Petrological, mineralogical (two stages of crystallisation) and structural evidence from the detailed analysis of one of these layers (unit II-7) is interpreted in terms of both mechanical (magmatic to sub-solidus, non-coaxial deformation) and thermal differentiation operating on a crystal-laden (alkali feldspar, high T nepheline, aegirine-augite) material of foyaitic composition. Textural and mineralogical data suggest that a sheet of foiditic magma intruded into solidified earlier units of the Lovozero layered sequence and acquired a sill-like structure on cooling.     

Stream water geochemistry from selected catchments on the Kola Peninsula (NW Russia) and in neighbouring areas of Finland and Norway: 2. Time-series

Stream water composition, measured weekly for 8–9 months in 1994 in three arctic catchments on and around the Kola Peninsula (Russia, Finland and Norway), is presented in the form of time-series. In all three catchments, snowmelt causes a major dilution of the stream water, as reflected by marked dips in electrical conductance. In the most polluted catchment (C2), the snowmelt flood (the major hydrological event at these latitudes) is reflected in the stream water by a pH dip and a pulse in technogenic heavy metals (Cu, Ni, etc.), Al and S. This results from melting of the snow laden with heavy metals and sulphate, and from leaching of the topsoil layer. In the most pristine catchment (C8), snowmelt causes no heavy metal pulse (remote location) but yields an increase in stream water Al (acidic lithology/overburden). In the intermediate catchment (C5), very subdued heavy metal and S increases are noticeable in the stream water, whilst its pH increases steadily until summer (basic lithology). Some elements (Cl, S) may be mobilised out of the snowpack before its complete thawing and reach the stream 1–2 weeks ahead of the heavy metals. The substrate (soil, overburden and bedrock) of a catchment controls to a large extent its ability to buffer acid inputs.     

Pro- and retrograde P–T evolution of granulites of the Beit Bridge Complex (Limpopo Belt, South Africa): constraints from quantitative phase diagrams and geotectonic implications

Interpretations based on quantitative phase diagrams in the system CaO–Na₂O–K₂O–TiO₂–MnO–FeO–MgO–Al₂O₃–SiO₂–H₂O indicate that mineral assemblages, zonations and microstructures observed in migmatitic rocks from the Beit Bridge Complex (Messina area, Limpopo Belt) formed along a clockwise P–T path. That path displays a prograde P–T increase from 600 °C/7.0 kbar to 780 °C/9–10 kbar (pressure peak) and 820 °C/8 kbar (thermal peak), followed by a P–T decrease to 600 °C/4 kbar. The data used to construct the P–T path were derived from three samples of migmatitic gneiss from a restricted area, each of which has a distinct bulk composition: (1) a K, Al‐rich garnet–biotite–cordierite–sillimanite–K‐feldspar–plagioclase–quartz–graphite gneiss (2) a K‐poor, Al‐rich garnet–biotite–staurolite–cordierite–kyanite–sillimanite–plagioclase–quartz–rutile gneiss, and (3) a K, Al‐poor, Fe‐rich garnet–orthopyroxene–biotite–chlorite–plagioclase–quartz–rutile–ilmenite gneiss. Preservation of continuous prograde garnet growth zonation demonstrates that the pro‐ and retrograde P–T evolution of the gneisses must have been rapid, occurring during a single orogenic cycle. These petrological findings in combination with existing geochronological and structural data show that granulite facies metamorphism of the Beit Bridge metasedimentary rocks resulted from an orogenic event during the Palaeoproterozoic (c. 2.0 Ga), caused by oblique collision between the Kaapvaal and Zimbabwe Cratons. Abbreviations follow Kretz (1983 ).     

Magmatic evolution of the differentiated ultramafic, alkaline and carbonatite intrusion of Vuoriyarvi (Kola Peninsula, Russia). A LA-ICP-MS study of apatite

The nature of the petrogenetic links between carbonatites and associated silicate rocks is still under discussion (i.e., [Gittins J., Harmer R.E., 2003. Myth and reality of the carbonatite–silicate rock “association”. Period di Mineral. 72, 19–26.]). In the Paleozoic Kola alkaline province (NW Russia), the carbonatites are spatially and temporally associated to ultramafic cumulates (clinopyroxenite, wehrlite and dunite) and alkaline silicate rocks of the ijolite–melteigite series [(Kogarko, 1987), (Kogarko et al., 1995), (Verhulst et al., 2000), (Dunworth and Bell, 2001) and (Woolley, 2003)]. In the small (≈ 20 km²) Vuoriyarvi massif, apatite is typically a liquidus phase during the magmatic evolution and so it can be used to test genetic relationships. Trace elements contents have been obtained for both whole rocks and apatite (by LA-ICP-MS). The apatites define a single continuous chemical evolution marked by an increase in REE and Na (belovite-type of substitution, i.e., 2Ca²⁺ = Na⁺ + REE³⁺). This evolution possibly reflects a fractional crystallisation process of a single batch of isotopically homogeneous, mantle-derived magma.The distribution of REE between apatite and their host carbonatite have been estimated from the apatite composition of a carbonatite vein, belonging to the Neskevara conical-ring-like vein system. This carbonatite vein is tentatively interpreted as a melt. So, the calculated distribution coefficients are close to partition coefficients. Rare earth elements are compatible in apatite (D > 1) with a higher compatibility for the middle REE (D_Sm : 6.1) than for the light (D_La : 4.1) and the heavy (D_Yb : 1) REE.     

Clinopyroxene megacrysts from Enmelen melanephelinitic volcanoes (Chukchi Peninsula,Russia): application to composition and evolution of mantle melts

Clinopyroxene megacrysts from young melanephelinitic lavas were divided into Cr-rich and Cr-poor suites. Sr, Nd, and Pb isotopic ratios of leached megacrysts and host lava are indistinguishable from each other and indicate a depleted source. Host lavas do not display chemical evidence for significant fractional crystallization, which is required to explain the compositional range of the megacrysts. This rules out a simple cognate genetic relationship between the two, and strictly defines megacrysts as xenocrysts. The well-defined correlations of trace elements with the Mg-numbers in the megacrysts are interpreted as the result of extensive fractional/equilibrium crystallization of magma over a large temperature range at near isobaric condition in the upper mantle. Trace element variations in megacrysts are consistent with fractional crystallization of clinopyroxene alone for the Cr-rich suite, and clinopyroxene + garnet for the Cr-poor suite from at least two bathes of related melts. Megacrysts parent magma might represent mantle melts, which were never erupted in their initial composition.     

Tracking Paleozoic evolution of the South Korean Peninsula from detrital zircon records: Implications for the tectonic history of East Asia

The southern part of the Korean Peninsula preserves important records of the Paleozoic evolutionary history of East Asia. Here we present SHRIMP U–Pb ages of detrital zircon grains from Paleozoic metasedimentary successions (Okcheon and Joseon Supergroups, Yeoncheon Group, Taean Formation, and Pyeongan Supergroup) that are incorporated into the major Phanerozoic mountain belts (Okcheon and Hongseong-Imjingang Belts) in South Korea, providing new insights for provenances and paleotectonic evolution of the South Korean Peninsula during Paleozoic time. The zircon ages from our samples display two distinct spectra patterns in their presence/absence of Neoproterozoic and/or Paleozoic populations. Our results, together with the available data from the Korean Peninsula, suggest that: (1) the Early to Middle Paleozoic successions in the Okcheon Belt were deposited in continental margin setting(s) formed by Neoproterozoic intracratonic rifting, (2) the Middle Paleozoic metasedimentary rocks in the Imjingang belt can be interpreted as molasse and flysch sediments along an active continental margin, (3) the Late Paleozoic to Early Triassic Taean Formation along the western Gyeonggi Massif represents a syn- to post-collision deltaic complex of a remnant oceanic basin, and (4) the Late Paleozoic to possibly Early Triassic Pyeongan Supergroup in the Okcheon Belt might represent a wedge-top and/or foreland basin. The spatial and temporal discrepancy between the South Korean Peninsula and the Central China Orogenic Belt during Paleozoic might reflect lateral variations in crustal evolution history along the East Asian continental margin during the Paleo-Tethyan Ocean closure.     

Volcanoplutonic association of the early-stage evolution of the Imandra-Varzuga rift zone,Kola Peninsula,Russia: Geological,petrogeochemical, and isotope-geochronological data

The western flank of the Paleoproterozoic Imandra-Varzuga rift zone consists of three volcanogenic-sedimentary series and layered mafic-ultramafic intrusions of different age (2.50–2.45 Ga). The earliest Monchegorsk and Monche Tundra layered massifs were formed about 2.50 Ga during the prerift stage of the evolution of the Imandra-Varzuga zone. The early rift stage (～2.45 Ga) produced layered intrusions of the Imandra complex and volcanic rocks of the Strelna Group, consisting of the Kuksha and Seidorechka formations. In terms of chemical composition, the volcanic rocks of the Seidorechka Formation belong to a single basalt-rhyolite series, mostly of normal alkalinity and both tholeiitic and calc-alkaline affinity. The rocks of the Imandra Complex are characterized by moderate LREE enrichment, relatively flat HREE patterns, and a positive Eu anomaly. Similar REE distribution patterns were observed in the volcanic rocks of the Seidorechka Formation, which show a gradual increase in REE content with increasing SiO₂. The upper part of the Seidorechka Formation in the southern Khibiny region is composed of metarhyodacites. They terminate the sequence of the Strelna Group and have a U-Pb zircon age of 2448 ± 8 Ma. This age presumably reflects the upper age boundary of the rocks of the Seidorechka Formation and the end of the early stage of the evolution of the Imandra-Varzuga zone. Xenogenic zircon from the same sample yielded a U-Pb zircon age of 2715 ± 42 Ma. A U-Pb age of 2202 ± 17 Ma was obtained for titanite and rutile and interpreted as the metamorphic age of the Seidorechka Formation. The metavolcanic rocks of the Seidorechka Formation have negative ?_Nd (T) varying from ?2.84 to ?2.32, and I_Sr values of 0.7041–0.7038, which are higher than those of the depleted mantle and suggest their derivation from an enriched mantle reservoir (EM1). The spatial association of the volcanic rocks of the Seidorechka Formation and the rocks of the Imandra Complex, similarity in the behavior of most major elements, similar REE distribution patterns, and close formation ages and isotope signatures give grounds to combine them in a single volcanoplutonic association.