Search

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070383 [ABSTRACT FROM AUTHOR]

This paper considers the results of detailed paleoseismic and geological investigations in a key site in the wall of the Imandra Lake depression (Kola Peninsula Region, Northeast of the Fennoscandian Shield). Study of different groups of paleoseismic deformations developed in the fault zone and the application of new methods and techniques made it possible to identify a large seismotectonic zone characterized by great earthquakes at the end of the Late Glacial and in the Holocene. The investigation data are indicative of the necessity to estimate the seismic potential in the Kola Atomic plant area in a different way. [ABSTRACT FROM AUTHOR]

For the first time Pb isotope composition was established in Lovozero rocks and raremetal ores, which is important for identifying their sources. The world's largest layered intrusion of agpaitic nepheline syenite-the Lovozero alkaline massif-is located near the center of the Kola Peninsula in Russia. This superlarge complex plutonic body hosts the economically important loparite and eudiallyte deposits [1]. These deposits contain immense resources of REE, Nb, Ta, Zr, and constitute a world class mineral district. The Lovozero massif belongs to the Kola ultramafic alkaline and carbonatitic province (KACP) of Devonian age. Previous bulk rock studies have shown that the initial Sr and Nd isotope ratios of Lovozero rocks plot in the depleted mantle quadrant of Sr-Nd diagrams [2]. More recently, Hf isotope data obtained by Kogarko et al. (3) confirm that the Lovozero and Khibina massifs with ɛ between 6 and 8 are derived predominantly from a depleted mantle source. It was shown that Sr, Nd, and Hf abundances are significantly elevated in the Kola alkaline rocks, and thus their isotopic compositions are relatively insensitive to minor contamination by the overlying crustal rocks. By contrast, Pb in the KACP rocks is a much more sensitive indicator of a crustal component. In this paper we investigate the lead isotopic signature of all resentative types of Lovozero rocks (Table 1) in order to further characterize their mantle sources. The Lovozero massif consists of four intrusive phases. Rocks of phase I (mostly nepheline syenites) comprise about 5% of the total volume, phase II (urtites, foyaite, lujavrites) forms the main portion of the massif comprising 77% in volume, and phase III (eudialyte lujavrites) contributes about 18%. Country rocks are represented by Devonian effusive rocks and Archean gneisses. [ABSTRACT FROM AUTHOR]

New data are presented on the characteristics of the upper mantle transition zone of the Kola Peninsula (the northeastern part of the Fennoscandian Shield) at a depth of about 410–660 km. The studies were carried out on the basis of a new broadband seismic network. Converted waves from the boundaries of 410 and 660 km were identified for all stations. The arrival times of these phases are recorded and analyzed. It has been established that the lithosphere of the studied region has some higher seismic velocities relative to the IASP91 global model. For the first time, a phase has been identified for this region, which may indicate the presence of a layer of lower velocities in the upper mantle at a depth of about 350 km. [ABSTRACT FROM AUTHOR]

The Neoarchean subalkaline magmatism of the Keivy structure is manifested by the emplacement of the latite–monzonite–granite (LMG) volcano-plutonic association. The measured 143Nd/144Nd ratio in rocks is 0.511061–0.511365; the values of model ages fall within the interval of 3.14–3.21 Ga with εNd(2670) varying from 2.2 to –1.3. The initial 176Hf/177Hf ratios in zircon are within the range of 0.280950–0.281069, and composition data points make up a field in the region of the evolutionary trend of the chondritic uniform reservoir. As based on isotope and geochemical data, the protoliths of all rocks are assumed to be basic. In terms of the εHf(T) value, the data points of the zircon composition fall within the domain of the crust with 176Lu/177Hf = 0.015 and an age of 3.0–3.3 Ga. This suggests that the parental melts were probably formed predominantly from material that spent a long time in the crust. The parental melts of the LMG association presumably formed as a result of the melting of metasomatically altered basic rocks during the intrusion into the lower crust of basaltic plutons, which were parental for the rocks of the dyke suite and gabbrolabradorite intrusions in the upper crust. [ABSTRACT FROM AUTHOR]

Detailed studies have shown that a change in the eudialyte occurrence forms (and the moment of its crystallization) is a new geochemical criterion for rare metal ore content in alkalic magmas (eudialyte ores). A new principle of the presence of ores in alkalic magmas has been formulated: a prerequisite for the formation of an ore deposit is early saturation of alkalic magmas with an ore mineral. If the ore component concentration is significantly lower than the cotectic (saturation), then melt saturation and crystallization of an ore mineral will take place at later stages of rock formation in a small volume of the interstitial melt, when the phenomena of convective‒gravity differentiation and segregation of mineral phases in the form of ore deposits are hampered. This leads to dispersion of the ore components in the form of xenomorphic grains of accessory minerals. Rocks of the differentiated complex (lower zone of the Lovozero deposit) and rocks of the Khibiny massif contain xenomorphic eudialyte and are not promising for eudialyte ores. Eudialyte deposits are associated with the upper zone of the Lovozero intrusion where euhedral early eudialyte occurs. The initial magma is saturated with eudialyte after crystallization of about 80% of the intrusion. The proposed criterion is applicable to the largest alkalic massifs in the world. The Ilimaussaq massif (Greenland), the rocks of which contain early crystallized, euhedral eudialyte, hosts a superlarge eudialyte ore deposit. Unlike the Khibiny massif and the Pilanesberg alkalic complex, the rocks of which contain late xenomorphic eudialyte, this massif has no deposits of this type. [ABSTRACT FROM AUTHOR]

The isotopes of helium were studied in the contact zones with the country rocks of the intrusions of different size (the alkaline-ultrabasic Ozernaya Varaka massif and the Lovozero massif of nepheline syenites). In case of medium-sized Ozernaya Varaka intrusion, helium extracted by powdering from igneous rocks of the intrusion and from the country fenites showed the same isotope composition exceeding the average crustal value by more than an order of magnitude. This is caused by the relatively rapid crystallization of the intruded small volume of the melt accompanied by the separation of igneous fluids and their permeation into the enclosing rocks. The distribution of helium isotopes at the contact of the larger Lovozero massif with gneisses is characterized by low-nearly crustal-He/He ratios in igneous rocks (nepheline syenites of the endocontact and by increased values (to 110 × 10) in fenites of the exocontact. It is suggested that the increased He/He ratios registered in fenites correspond to the beginning of the intrusion process and that the low values in nepheline syenites are related to the completion of crystallization of the rocks of a differentiated complex. [ABSTRACT FROM AUTHOR]

The article presents a study on uranium-lead dating of protolith and paleoproterozoic tectonic and metamorphic transformations of the Archean Keivy terrain located in Kola Peninsula in Russia. It states that the Keivy terrain is composed of tonalite-trondhjemite association (TTG), Lebyazhinskaya Series and metavolcanic rocks, schists, and alkaline granites. It states that the age was estimated with the use of Sensitive High Resolution Ion Micropobe (SHRIMP) II, a secondary ion mass-spectrometer of high resolution, on zircons. It says that based of the uranium-lead dating, the age of the Keivy terrain is in the range of 1762-1721 million years (Ma).

Experiment on electromagnetic sounding of the Kola Peninsula using unique mobile measuring complex of the low-frequency sounding was conducted, allowing to investigate a geoelectric section with a depth of several kilometers on distances up to 100 km from the stationary transmitting aerial. Excess on the order of amplitudes of the vertical component above the horizontal at all frequencies of sounding was registered in a number of points of measurements. This feature managed to be explained quantitatively by circulation of current on regional faults with the closure of current through the sea-before unknown galvanic coastal effect. Interpretation of the results of modeling and neural network solving of inverse problem essentially specifies the fault tectonics of the central part of the Kola Peninsula. Anomaly remote from the observation profile was found out-local pinch of a crustal conductive layer consisting of graphitized rocks and associated with the zone of overthrust. [ABSTRACT FROM AUTHOR]

The article reports on the study which contains new geochemical and isotopics data for volcanogenic complexes of the Arvarench Unit of the Imandra-Varzug structure (IVS) in Kola Peninsula, Russia. It mentions the use of traditional lithological and stratigraphic methods on the basis of signs when studying problems of stratigraphy and correlation of volcagenic-sedimentary sections of the Paleoproterozoic intracratonic riftogen IVS. It provides four conclusions based on the results obtained such as that the formation of primary melts for komatiite, some basalt, and andesite of the Arvarench Unit was controlled by melting of the Archean enriched mantle component.