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The Sumozero-Kenozero greenstone belt in the SE Baltic Shield is ∼400 km long and up to 50 km wide and includes two main units with a total thickness of ∼5 km. The lower unit consists of oceanic plateau-type submarine mafic-ultramafic lavas. The upper unit is made up of island arc-type volcanic BADR (basalt-andesite-dacite-rhyolite)-series rocks and adakite-series subvolcanic rhyolites. Both units are separated by major thrust zones from the 3.2 Ga TTG-gneisses of the Vodla Block microcontinent. Komatiites of the lower unit were derived from a liquid containing ∼30% MgO that erupted at a temperature of ∼1570°C. The komatiite liquid began melting at depths of 300–400 km in a mantle plume. The plume was 250°C hotter than the ambient mantle and had the thermal potential to produce oceanic crust with an average thickness of ∼35 km, which was at least in part unsubductable. The lower unit mafic-ultramafic lavas have high eNd(T) of +2.7 ± 0.3, relatively unradiogenic Pb isotope compositions (μ1 = 8.73 ± 0.20), are depleted in highly incompatible elements, and show Nb-maxima (Nb/Nb∗ = 1.2 ± 0.2, Nb/U = 43 ± 6). These parameters are similar to those found in a number of early Precambrian uncontaminated greenstones and in recent Pacific oceanic flood basalts (OFB). They are regarded as plume source characteristics. The BADR-series mafic-intermediate to felsic volcanic rocks and subvolcanic adakitic-series rhyolites from the upper unit have island arc geochemical signatures (enrichment in highly incompatible elements, large negative HFSE-anomalies, Nb/Nb∗ = 0.32 ± 0.10, Nb/U = 8.8 ± 2.5), but are characterized by high positive eNd(T) values of +2.4 ± 1.2, indistinguishable from the lower unit mafic-ultramafic sequences. They represent mantle wedge-derived and slab-derived melts, respectively, erupted in the inner and frontal parts of an intraoceanic island arc. U-Pb zircon age of 2875 ± 2 Ma for the upper unit BADR-series felsic volcanic rocks, and Pb-Pb and Sm-Nd ages of 2892 ± 130 and 2916 ± 117 Ma for the lower unit komatiites and basalts are in good agreement and correspond to the time of emplacement of both sequences. The Sumozero-Kenozero greenstone belt reveals the coexistence of fragments of unsubductable oceanic crust represented by the lower unit mafic-ultramafic volcanic sequences, and the products of subduction-related magmatism of the upper unit. This observation is reconciled within a single model implying that overthickened plume-generated oceanic crust was first intruded and overlain by mafic and intermediate-felsic melts coming from both subducting slab and overlying mantle wedge and, later on, accreted to and obducted onto the microcontinent of the Vodla Block.

Major- and trace-element concentrations and Nd-, Sr- and Pb-isotopic ratios are reported for the Dovyren layered mafic-ultramafic intrusion in the northern Baikal region, eastern Siberia. SmNd internal isochrons for an olivine gabbro from the layered series and a gabbronorite from a sill at the bottom of the Dovyren intrusion yield ages of 673 ± 22 and 707 ± 40 Ma, respectively. Initial isotopic ratios: 87 Sr 86 Sr (673) from 0.7101 to 0.7135, ϵNd(673 Ma) from −16.3 to −14.1 206 Pb 204 Pb from 16.80 to 17.14, 207 Pb 204 Pb from 15.477 to 15.501 and 208 Pb 204 Pb from 37.17 to 37.59, are similar to those of late Archean-early Proterozoic upper continental crust, but do not appear to be a result of wallrock assimilation in the magma chamber. These isotopic features, as well as high K, Rb and LREE and low Ti concentrations in the calculated composition of the Dovyren parental magma, may be explained by subduction of sediments derived from upper continental crust into depleted mantle and subsequent melting of the metasomatized peridotite.

Paleoproterozoic layered mafic-ultramafic intrusions are widespread in the eastern Baltic (Fennoscandian) Shield and mark the initial stages of continental rifting and outpouring of voluminous flood basalts. UPb zircon/baddeleyite ages have been determined for seven layered mafic intrusions and a subvolcanic felsic unit associated with two Paleoproterozoic volcanic-sedimentary belts: the Pechenga-Imandra-Varzuga belt in the Kola Peninsula, and the Sumi-Sariola belt in Karelia. The layered intrusions in the Sumi-Sariola belt show an age progression from 2449.0 ± 1.1 Ma for the Burakovka complex, located at the southeastern edge of the belt, to 2442.1 ± 1.4 Ma and 2441.3 ± 1.2 Ma for the Lukkulaisvaara and Tsipringa intrusions of the Olanga complex in northern Karelia (northeastern part of the belt). These age results indicate a total duration of mafic magmatism along the ca. 800 km belt in Karelia to be less than 10 m.y. The Pechenga-Imandra-Varzuga belt, Kola Peninsula, contains two distinct age groups of layered mafic intrusions and related rocks. The younger of these overlaps with the ages obtained for the Olanga intrusions and includes the 2441.0 ± 1.6 Ma Imandra lopolith and a spatially associated felsic subvolcanic unit dated at 2442.2 ± 1.7 Ma. The older group of mafic layered intrusions in the Kola Peninsula includes the 2501.5 ± 1.7 Ma Pana tundra intrusion, the 2504.4 ± 1.5 Ma Monche pluton and the 2505.1 ± 1.6 Ma General'skaya mountain intrusion. The temporal and spatial distribution of the 2.50-2.44 Ga rift-related igneous activity in the Baltic Shield is consistent both with the model of starting mantle plume, and with the model of passive rifting controlled by pre-existing lithospheric weaknesses.

The results of the partial wave analysis of the diffractive reaction π − A → π + π − π − A at the momentum 36 GeV/ c on the scintillator target are presented. A resonance at m = 1.8 GeV with J PC = 0 − + (π(1800)) is clearly seen in this reaction. The characteristics of π(1800) point to the possible exotic nature of this object.