Crystalline Massif Research Articles

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2020

On the Russian territory of the East European Platform, seismic observations were carried out by 47 stationary seismic stations. In 2020, 36 seismic events of tectonic and technogenic-tectonic nature were registered. As before, weak natural and man-made seismicity was recorded on the territory of the Voronezh crystalline massif and the Baltic Shield: in Karelia, border areas with Finland, near the Kandalaksha Bay, within the Khibiny, Kovdor massifs and in the Vite-Guba area of Imandra lake on the Kola Peninsula. A feature of seismicity in 2020 is the occurrence of earthquakes in the paleorift structures of the northeast of the East European Platform: in the Kirov Kazhim and Central Russian aulacogens. The total volume of seismic energy released in 2020 is Е=7.16·109 J, which is 2 times lower than in 2019, but 2 times more than the energy released in 2018.

Shaping the crustal structure of the SW-Alpine Foreland: Insights from 3D Geological modeling

Reactivation processes play a significative role in the localization of deformation but still remain hard to establish at the lithospheric scale. In this work, we built a 3D structural model, which enables to bridge the gap between the main tectonic structures observed at the surface and the geometry of the major interfaces (the Mohorovičić-discontinuity (hereafter Moho) and top of the basement) inferred from geophysical data acquired in the external Western Alps and their foreland. The geometry of these tectonic structures is interpreted in relation to their geodynamic evolution. The main results of this study highlight: (1) a strong contribution of thick-skinned Pyrenean-Provence and Alpine tectonics, (2) a lithospheric rooting of Variscan shear zones and related faults, and (3) the regional-scale influence of these inherited structures on the post-Paleozoic strain localization in the study area. Our 3D model shows that the pattern of Variscan shear zones that were developed at the end of the Paleozoic involved the whole crust, as emphasized by the Moho offsets. These shear zones were reactivated and localized Meso-Cenozoic deformation. The Variscan deformation pattern controlled the geometry of extensional basins, the propagation of Pyrenean-Provence deformation, and finally the Alpine deformation at crustal scale. Our 3D model shows minor crustal thickening (ca. 40 km) located below the Pelvoux External Crystalline Massif, which probably resulted from both Pyrenean and Alpine tectonic phases. In contrast, the southern part of the Alpine front shows a thinned crust (ca. 18 km) resulting from extensional Meso-Cenozoic phases between the Cévennes margin and the Durance basin.

Protracted magmatism and crust–mantle interaction during continental collision: insights from the Variscan granitoids of the external western Alps

Variscan granitoids and associated mafic rocks exposed in the External Crystalline Massifs (ECM) of the Western Alps document the Variscan stages from the early Carboniferous collision to the early Permian post-collisional setting. Our study focuses on the Central part of the ECM, synthesizing newly acquired and existing geochronological, whole-rock geochemical and isotopic data. We identified two distinctive magmatic series: (i) high-K calc-alkaline granitoids, which range from magnesian (MgG) to ferro-magnesian (FeMgG) rocks; (ii) ultra-high-K metaluminous (UHKM) rocks (“durbachites”). These series were emplaced roughly simultaneously between ca. 350 and 300 Ma, with two main episodes during the Visean (ca. 348–335 Ma) and the late Carboniferous (305–299 Ma), with a more limited activity in between. A younger Permian event at ca. 280–275 Ma has also been identified in one granitoid pluton. Contemporaneous emplacement of these two series reflects concomitant crustal anatexis and melting of LILE–LREE-rich metasomatized lithospheric mantle. Trace elements and Nd–Sr isotopes reveal significant hybridization between these two magmatic end members, by magma mixing, or assimilation of crystallized mafic ultrapotassic enclaves in the high-K calc-alkaline granitoids. Granitoid composition evolves over time, especially SiO2, Mg#, Sr/Y, La/Yb and Nb/Ta, possibly explained by increasing differentiation of magmas over time, changes in the crust versus mantle sources mass-balance, and decrease in melting pressure due to the orogenic collapse. The εNdi values of both high-K calc-alkaline granitoids and durbachites decreases from [− 3.8; − 2.9] to [− 6.4; − 5.2] between 345 and 320 Ma, possibly indicating an increasing influence of subducted/relaminated crustal material contaminating the lithospheric mantle source. εNdi values then rise to [− 3.7; − 0.5] during the late Carboniferous, possibly due to progressive exhaustion of the enriched mantle source, or advection of the asthenosphere during the post-collisional stage.Graphic abstractPossible geodynamic scenario along the central-eastern segment of the Variscan Belt, which may account for the temporal evolution of Variscan magmatism in the External Western Alps.

Structural Evolution, Exhumation Rates, and Rheology of the European Crust During Alpine Collision: Constraints From the Rotondo Granite—Gotthard Nappe

AbstractThe rheology of crystalline units controls the large‐scale deformation geometry and dynamics of collisional orogens. Defining a time‐constrained rheological evolution of such units may help unravel the details of collisional dynamics. Here, we integrate field analysis, pseudosection calculations and in situ garnet U–Pb and mica Rb–Sr geochronology to define the structural and rheological evolution of the Rotondo granite (Gotthard nappe, Central Alps). We identify a sequence of four (D1–D4) deformation stages. Pre‐collisional D1 brittle faults developed before Alpine peak metamorphism, which occurred at 34–20 Ma (U–Pb garnet ages) at 590 ± 25°C and 0.9 ± 0.1 GPa. The reactivation of D1 structures controlled the rheological evolution, from D2 reverse mylonitic shearing at amphibolite facies (520 ± 40°C and 0.8 ± 0.1 GPa) at 18–20 Ma (white mica Rb–Sr ages), to strike‐slip, brittle‐ductile shearing at greenschist‐facies D3 (395 ± 25°C and 0.4 ± 0.1 GPa) at 14–15 Ma (white mica and biotite Rb–Sr ages), and then to D4 strike‐slip faulting at shallow conditions. Although highly misoriented for the Alpine collisional stress orientation, D1 brittle structures controlled the localization of D2 ductile mylonites accommodating fast (∼3 mm/yr) exhumation rates due to their weak shear strength (<10 MPa). This structural and rheological evolution is common across External Crystalline Massifs (e.g., Aar, Mont Blanc), suggesting that the European upper crust was extremely weak during Alpine collision, its strength controlled by weak ductile shear zones localized on pre‐collisional deformation structures, that in turn controlled localized exhumation at the scale of the orogen.

On the occurrence of a Variscan eclogite in the Argentera-Mercantour Massif, Western Alps: Implications for the evolution of the southern Variscan belt

The newfound Bois de Sélasse eclogite in the eastern Argentera-Mercantour Massif (External Crystalline Massifs, Western Alps) is crucial for better constraining the tectonic evolution of the southern part of the European Variscan belt. The whole-rock composition of this eclogite aligns with that of a basaltic protolith with a normal mid-oceanic-ridge affinity, and U-Pb dating on igneous zircon cores reveals an emplacement age of 524 ± 5 Ma. The emplacement may have occurred either in the oceanic lithosphere to the north of the active Gondwana margin or within a back-arc basin during the subduction beneath Gondwana. Exceptionally preserved prehnite−pumpellyite to eclogite facies minerals provide evidence of prograde metamorphism along a standard oceanic subduction geotherm (≤10 °C/km). Peak eclogite facies conditions are constrained at 610−660 °C and 1.9−2.3 GPa by thermodynamic modeling combined with Ti-in-zircon and Zr-in-rutile thermometry. A minimum age for eclogite facies metamorphism is established at 339 ± 6 Ma by U-Pb dating on metamorphic zircon rims. The protolith of the Bois de Sélasse eclogite is indeed older than the Variscan oceans, but it was similarly affected by Variscan subduction. We discuss the implications of this new finding in the context of the European Variscan belt.

Late-orogenic extension ceases with waning plate convergence: The case of the Simplon normal fault (Swiss Alps)

The Simplon normal fault in the Western Alps caused tens of kilometers of orogen-parallel extension during convergence of the European and Adriatic plates, but the slip rate of the fault and the time when normal faulting ended are still debated. Here, we constrain the slip history of the Simplon fault with low-T thermochronology and thermo-kinematic modeling. Closely spaced samples from an elevation profile in the center of the fault yield zircon (U–Th)/He ages (ZHe) that are nearly invariant over an altitude of 1.4 km and cluster around ∼6 Ma. In contrast, apatite (U–Th)/He ages (AHe) increase with altitude from 3.4 ± 0.3 to 4.6 ± 0.7 Ma, while the AFT ages range from 4.4 ± 0.7 to 5.8 ± 1.5 Ma. In addition, recently published 40Ar/39Ar ages constrain that our samples moved through the brittle-ductile transition (i.e., ∼300 °C) at 8–10 Ma. Our thermo-kinematic inverse modeling shows that these age data can be explained by a single phase of normal faulting, which lasted from 19.8 ± 1.8 to 5.3 ± 0.3 Ma and caused 45 ± 10 km of extension. The slip rate of the 30°-dipping model fault is 3.5 ± 0.3 km/Myr and equivalent to an exhumation rate of ∼1.8 km/Myr. Our modeling reveals that the altitude-dependent difference between ZHe and AHe ages reflects the thermal relaxation after faulting stopped at ∼5.3 Ma. Since then, exhumation by erosion continued at a rate of ∼0.5 km/Myr. Remarkably, the end of slip on the Simplon fault coincides with the cessation of reverse faulting at 6 ± 2 Ma in the external crystalline massifs of the Alps (Aar, Mont Blanc, Aiguilles Rouges) and with a decrease in strain rate by one order of magnitude at 5-4 Ma in the Swiss molasse basin and the Jura mountains. This temporal coincidence suggests that normal faulting in the internal part of the Alps ceased when plate convergence waned and the under-thrusting of European continental lithosphere beneath the Adriatic plate came to an end.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2018–2019

Seismic observations by 48 stationary seismic stations, including twelve temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2018–2019 is a unique Kandalaksha earthquake of November 5, 2019 with ML=3.8 in the Belomorsky region. Its focal mechanism was represented by a normal fault. For the first time, a noticeable earthquake with МL=3.4 was recorded on September 5, 2019 at the Pashninskoye and Beregovoye fields in the Timan-Pechora oil and gas province. It was felt in Neftepechorsk working settlement with an intensity of up to 4 MSK-64. As before, weak natural seismicity was recorded on the Baltic Shield: in Karelia, in areas bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula, on the Voronezh crystalline massif territory, especially in the zone of its junction with the DnieperDonetsk trough.

A Three-Dimensional Density Model of the Upper Crust at the Junction of the Losevo and Vorontsovka Terranes (Voronezh Crystalline Massif)

A Three-Dimensional Density Model of the Upper Crust at the Junction of the Losevo and Vorontsovka Terranes (Voronezh Crystalline Massif)

Three-dimensional magnetotelluric imaging of the Edough massif and its overlying formations (Northeast Algeria)

The Edough massif (NE Algeria) is the easternmost coastal crystalline massif of the Maghrebide belt, whose current structural position remains poorly known. Magnetotelluric (MT) data from 15 stations were collected along three profiles across the Edough massif and its neighboring formations in the period range of 0.001–1000 s to assess the deep electrical resistivity structure. A phase tensor dimensionality analysis indicates that the measured data are dominated by 3-D effect of underlying geological structure, thus revealing a complex subsurface structure. A 3-D inversion model was obtained using the full impedance tensor and the vertical magnetic field transfer function including bathymetry and topography. Our preferred 3-D geo-electrical model shows heterogeneous electrical structures and are related to the known geological features of the region. We mainly observe a clear resistivity contrast characterizing the upper/middle crust. The Edough massif appears generally as a homogenous resistive structure. The shallow conductive structures are associated with the Mio-Plio-Quaternary deposits and Flysch units. Most of conductive bodies are likely related to the iron/magnetic anomaly. These may likely correspond to the suture zone. Under the Neogene basin, the high resistivities with a north dipping strong angle may correspond to the African basement.

Ambient‐Noise Wave‐Equation Tomography of the Alps and Ligurian‐Provence Basin

AbstractTaking benefit of the AlpArray temporary network and permanent networks in W‐Europe, we construct a 3‐D onshore‐offshore velocity model of the crust and upper mantle using ambient‐noise wave‐equation tomography. We use a frequency‐dependent phase traveltime misfit function in an iterative procedure to refine a recent 3‐D Vs model computed from a Bayesian two‐step ambient noise tomography. Observed waveforms consist of vertical‐component noise correlations from 600 broadband stations in the Alps and surroundings, including ocean‐bottom seismometers in the Ligurian sea. We perform 3‐D inversion in the 5–85 s period range. In the long‐period band (20–85 s), an elastic approximation is considered, while in the 5–20 s band, we account for the effect of water layer in the Ligurian sea by applying a fluid‐solid coupling for acoustic‐elastic waveform simulations. The resulting Vs model enhances the shape and contrast of velocity structures, accounting for 3‐D and finite‐frequency effects. It emphasizes the deep sediments of the Ligurian‐Provence basin and focuses on the low‐velocity anomalies of the crust in the W‐Alps. We obtain a high‐resolution Moho depth map covering the Alps and Ligurian sea. In the W‐Alps, this map confirms the deepening of the European crust following the subduction beneath Adria and the existence of major structures such as the Moho jump beneath the external crystalline massifs and shallow depths associated with the Ivrea Body. It provides further constraints on the deep structure beneath the Ligurian‐Provence basin, regarding the lateral and along‐strike crustal‐thickness variations from the oceanic domain to the conjugate margins.

Miocene cave sediments record topographic, erosional and drainage development in the Western European Alps

The dynamic Neogene evolution of the Western European Alps included exhumation of the external crystalline massifs, thrust propagation to the foreland, drainage network reorganization, and major climatic variations. To constrain possible interactions between those factors, accurate geomorphological and sedimentological archives are required. However, intra-orogenic areas are subject to erosion, and extensive glacial cover during the Quaternary erased most of the geomorphic markers in the Alps. For these reasons, the genesis of the main features of the modern landscape, such as the major valleys and the drainage network, remains poorly understood. This study highlights how recently discovered karstic archives from the perched paleo-karst of the Obiou peak (Dévoluy massif, SE France) record the tectonic and drainage-network evolution of this part of the Alps during the Neogene. The Obiou caves are located at 2250-2380 m elevation, ∼1600 m above the modern Drac valley; they contain fluvial deposits including sand-clay units and rounded crystalline cobbles derived from the adjacent Ecrins-Pelvoux massif. As the Dévoluy and Ecrins-Pelvoux massifs are currently separated by the axial Drac valley (a major tributary of the Isère River), these cave sediments must have been deposited by a radial drainage system before incision of the modern Drac. We report new multi-method results from these sediments, including cosmogenic-nuclide burial dating (21Ne, 10Be, 26Al in quartz), provenance analysis (clast petrography and heavy-mineral analysis), and detrital thermochronology (apatite fission-track and (U-Th)/He) combined with a paleo-environmental reconstruction from palynology. 21Ne/10Be dating of cobbles and sand constrains the burial age to 11.5 ± 1.5 Ma, providing a maximum age for the modern axial drainage system and a minimum long-term incision rate of ∼140 m/Myr for the Drac valley. Comparison of the combined data to both modern rivers and nearby Oligocene foreland-basin deposits provides evidence for two successive drainage reorganizations. Early Miocene exhumation and development of high topography in the Ecrins-Pelvoux massif, linked to localized thrusting on a crustal-scale ramp, led to initial deflection of the antecedent radial drainage network, beheading its headwaters by establishment of the axial upper Durance valley. Subsequent propagation of thrusting into the subalpine Dévoluy massif and associated uplift during the mid to late Miocene led to establishment of the modern drainage system.

MORPHOSTRUCTURAL EVOLUTION AND GEOMORPHOLOGICAL MAPPING IN CRYSTALLINE MASSIF IN NORTHEASTERN BRAZIL

This work addresses the morphostructural evolution of the Crystalline Massif in northeastern Brazil. Highlights as a test area the northwest of the State of Ceará, evaluating the Massif of Meruoca, as a result of the intrusion of post-tectonic granitoid from the orogenic collapse of Brazilians in the Middle Domain area Coreaú/Província Borborema. In addition, the reactivations of the Café-Ipueiras Fault and the Transbrazilian Lineament promoted morphotectonic events during the Cretaceous and Cenozoic, conditioning the elevation or exhumation of the relief. The operational procedures were divided into four stages: 1) Literature review; 2) Interpretation of SRTM images; 3) Elaboration of thematic mapping; 4) Fieldwork. The geomorphological mapping of the Meruoca Massif provided the identification of morphosculptural units classified in the 3rd taxon according to the Ross methodology (1991), denouncing the work of differential erosion on the morphing structure in the preparation of relief compartments that are individualised in the larger set of the geomorphological landscape.

Moissanite in Rocks of the Bobruisk Ledge of the Belarusian Crystalline Massif of the East European Craton

A large range of minerals, native, intermetallic, amorphous compounds containing K, Na, Fe, Mn, Ca, Ba, Sr, Cu, Pb, Co, Ni, Sn, Zn, Al, Ce, Nd, La, Pr, Sm, Y, Yb, Nb, Hf, W, Mo, Zr, Cr, V, Ag, Ti, Si, has been found in the Bobruisk buried ledge of the Belarusian crystalline massif in the western part of the East European craton. As, P, Bi, O, H, F, Cl, S, Se, C, B, N F. Among them there is moissanite. It forms xenomorphic and subidiomorphic separations up to 1.5 mm in size and is represented by a hexagonal polytype modification 6H. Inclusions inherent in meteorites were found in one of its grains – sinoite (Si2N2O), xifengite (Si5Fe3) and awaruite (Ni3Fe). Moissanite, the native, intermetallic, amorphous compounds associated with it, are developed in the form of scattered, poor, multi-grained inclusions in the rocks of three structural-material complexes of the centuries. This indicates the superimposed nature of mineralization. The whole set of crystalline and amorphous secretions observed with moissanite is proposed to be designated as Bobruiskites. Mineral formation, with a high degree of probability, is due to the impact interaction of the meteoroid with rocks of the East European craton.

Late Alpine multistage exhumation of the northwestern Rhodope Metamorphic Complex (northern Rila Mountains, Bulgaria)

AbstractThe Rhodope crystalline massif is an Alpine metamorphic complex exposed across several mountain ranges in southern Bulgaria and northern Greece which has experienced a complex history including continental collision, partial subduction and syn-metamorphic nappe stacking followed by syn- to post-contractional extension. We present new 40Ar/39Ar and fission-track data from samples taken from both sides of the North Rhodopean Detachment that were combined with detailed structural studies to investigate the tectonothermal evolution of the northern Rila Mountains. A migmatite from the hanging wall of the North Rhodopean Detachment yields a 40Ar/39Ar muscovite age of 100.79 ± 0.55 Ma, a zircon fission-track age of 38.6 ± 1.9 Ma, and an apatite fission-track age of 21.4 ± 1.5 Ma. A biotite schist from the footwall of the detachment yields 40Ar/39Ar biotite age of 34.90 ± 0.15 Ma, and zircon and apatite fission-track ages of 35.6 ± 5.6 and 13.3 ± 1.1 Ma, respectively. Our new data give evidence of a multistage exhumation of the study area. Late Early Cretaceous (~ 101 ± 0.6 Ma) cooling of the Variscan high-grade metamorphic basement through 440–400 °C was caused by either erosion of the emplacing thrust sheet, or post-contractional denudation. Fast exhumation along the North Rhodopean Extensional System drove a pulse of increased tectonic denudation and cooling during the Eocene (39–35 Ma). Exhumation of the rocks in the northern part of the Rila Mountains below 110 ± 10 °C during the middle–late Miocene was associated with displacement along a system of normal faults.

Anomalous position of Paleozoic faults of Western Donbas

Statement of the general problem. The oil and gas-bearing province of Eastern Ukraine is located in the Dnipro-Donetsk Basin (DDB). It covers the Paleozoic structural floor and is buried under younger sediments. The Paleozoic structural floor of the territory is represented as a long rift graben. The maximum thickness of the sedimentary cover in the graben is 15–17 km. According to geophysical data, the thickness of the earth's crust is 31–32 km under the axial part of the DDB and increases towards the sides. But according to the maximum thickness and facies characteristics of the Paleozoic deposits, the thickness of the Earth's crust below them could not exceed 20 km. The modern thickness is 1.5 times higher. Therefore, such a geological-geophysical model of the structure of the DDB is contradictory. Analysis of recent research and publications. The removal of the contradiction is possible due to the detection of a series of Hercynian thrusts with total amplitude of thrusts of the order of 50 km. Such thrusts began to be established on the northern and southern flanks of the DDB. Hercynian thrusts have a southwestern vergence. In the north, the Voronezh crystalline massif is pushed onto the DDB along the Noviy thrust with an amplitude of 9–10 km. In the south, the South Donbas melange zone is established, which pushes the folded Donbas onto the Ukrainian shield. On its continuation to the northwest is the southern side of the DDB - the so-called Southern monocline. The well-studied Pavlograd-Petropavlovsk coal mining district of Western Donbass with operating coal mines is located within its borders. An unsolved part of the overall problem. Numerous faults with relatively small amplitudes are established within the Paleozoic Southern Monocline. Together, they form a system of horsts and grabens with a north-western extension. But the bottom parts of the grabens are 1–3 km higher than the tops of the horsts. Such a geological situation is anomalous. This indicates the post-fault dislocation of the horst-graben system as a whole. The purpose of the article is identification of the causes of the anomalous structural position of the graben-horst system in the modern geological structure of the Southern Monocline and in the general model of the geological structure of Eastern Ukraine. Research materials and methods. Were involved more than 390 geological sections, constructed based on the data of more than 10,000 wells. Of them, 265 wells revealed the folds that are being analyzed. In addition, were used data of catagenetic transformations of the sedimentary section. Presentation of the main research material. The South Donbas mélange zone falls to the northeast and continues under the Southern Monocline. It is located in the upper block of this regional thrust structure and is in an allochthonous setting. According to geological data, the true amplitude of the thrust of Western Donbas on the Ukrainian shield is 15–20 km, and the vertical component of this amplitude exceeds 3 km. Such spatial parameters explain the abnormality of the structural position of the horsts and grabens of Western Donbass - their southwestern flanks were significantly raised relative to the northeastern flanks during thrusting. Scientific novelty. Therefore, in the modern geological structure, the Dnipro-Donetsk "basin" is not a rift, but a post-rift Hercynian folded region. It is formed by high-amplitude thrusts on the northern and southern flanks. The Hercynian fold region is buried under Mesozoic and Cenozoic sediments and is further complicated by Laramian and Attic fold-thrust dislocations of lesser intensity. Conclusions. The thrust model brings the geophysical parameters into the correspondence with the geological data and is confirmed by the actual material.

On Some Accessory Minerals in Upper Paleozoic Granites of the Khrami Crystalline Massif

The Khrami crystalline massif is exposed within the Black Sea – Central Transcaucasian terrane (Georgia). The massif is built up of Preсambrian gneiss-migmatite complex, the packet of Middle Paleozoic (?) metasandstones and protrusions of mantle serpentinites; Paleozoic gabbroids; Middle-Upper Paleozoic granitoids and rocks of volcanogenic-sedimentary complexes and Upper Paleozoic quartz-porphyry - granite-porphyry formations. A number of scientists have studied the granitoids of the Khrami crystalline massif, but detailed investigations on some minerals using modern analytical facilities have not been conducted yet. The Late Variscan granitoids of the Khrami massif are represented by biotite-hornblende-allanite-, biotite-microcline- and biotite-garnet-bearing granites and aliaskites. We have studied in detail the accessory minerals - garnet and allanite in the Late Variscan granites of the massif. Their microprobe analysis has been performed. According to the microprobe analysis of the studied garnets, the centre of the crystal is homogeneous, while the peripheral part is zonal. The amount of FeO decreases slightly from the centre to the periphery, while the amount of CaO and MgO significantly decreases; a well-expressed increase in MnO content is recorded. The variation in almandine content is insignificant. The amount of pyrope and grossular drops sharply from the centre to the periphery while the number of spessartine increases. The amount of Al2O3 in all varieties of granitoids is similar. In our opinion, the garnet formation occurred in two stages: during the crystallization process of granitic magma and its subsequent post-magmatic stage. The core of the garnet was formed in the magmatic stage, but its periphery - was in the cooling stage of granitic magma. According to the results of the microprobe study of allanite, the same - two stages of their formation have been conducted: during the crystallization process of granitic magma and in its next post-magmatic stage. The genesis of allanite in the biotite-hornblende-allanite-bearing granites of the massif is due to the concentration of REE in the granitic magma and the introduction of calcium by hydrothermal solutions. These allanites belong to the cerium variety with high content of Ce2O3, La2O3 and Nd2O3.

Geotraverse «Granite—Odesa—Kryvyi Rih—Pereschepine

The article examines the results of research carried out by the methods of reflected waves and common depth point (MRW-CDP) on the «Granit» geotraverse, which crosses the whole of Ukraine from the southwest to the northeast and passes through the territories of Odesa, Mykolaiv, Dnipropetrovsk, and Kharkiv regions, west of Belgorod region of Russia. In structural and tectonic terms, the geotraverse crosses large geological structures: the marginal part of the Scythian Plate (SP), the Ukrainian Shield (USH), the Dnieper-Donetsk Basin (DDB) and the southern slope of the Voronezh Crystalline Massif (VCM). The analysis of the features of the registered wave field and the completed structural constructions of the consolidated crust and upper mantle in the section of the «Granite» geotraverse shows a complex heterogeneous structure with certain spatially correlated regularities, against the background of which there are numerous inhomogeneities characteristic of both individual blocks and their individual intervals. The cross-sections of all the studied geostructures are characterized by a high level of saturation with non-extended, unevenly distributed reflective elements, which occupy positions from subhorizontal to steeply sloping in space. With all the diversity of the mutual location of both individual boundaries and their groups, a fairly strict correlation is established, which primarily provides information about the nature of stratification, deformations, and the stress state of the structures of the consolidated crust and upper mantle. In the modern structure of the crust, a significant role belongs to faults and tectonic plates, the vast majority of which are manifested as inclined zonal bodies with different orientations. Systems of faults and plates form a complex hierarchical interdependence. The «crust-mantle» transition zone is a complex, laterally variable area, with a thickness of 3 to 7 km, caused by systems of subhorizontal stratification, expressed by the concentration of reflective elements. The largest homogeneous and contrasting region of the transition is manifested in the structures of ancient consolidation, with a thickness of the crust of about 40 km. As a result of the research, more detailed information on the structure of individual tectonic elements was obtained, and some general principles of the structure of the transition zone from the ancient continental platform to the active folded belt were clarified.

Про кузинську світу Мармароського покриву Українських Карпат

In 1957, L. G. Tkachuk and D. V. Gurzhiy have singled out the Upper Paleozoic Kuzian suite in the north-western part of the Marmarosh crystalline massif at the Rachiv area. It consists of phyllites, limestones, quartzites and dolomites. The suite is widely distributed in the Dilovets subcover of the Marmarosh nappe at the Rakhiv and Chyvchynian areas. There are two alternative points of view upon the age of the Kuzian suite. Some geologists attribute it to Paleozoic time (Upper Devonian-Lower Carboniferous), the others attribute its lower part to the Upper Paleozoic, and the upper one: to Triassic. One can notice the existence of the different estimation of the lithological composition and different estimation of the lithological composition and the volume of the Kuzian suite.Thus, in 1970 A. K. Boiko has devided it into Muntselulska (Lower) phyllite-quartzite one of Paleozoic age and Upper (Triassic) phyllite-carbonate one for which he saved the name Kuzian suite. The important is that a stratigraphic interruption was fixed between the above-mentioned units. The phyllite-carbonate Kuzian suite is dated on the basis of transgressive occurrence of the middle Triassic dolomites on it, discovery of the post-Paleozoic mosses in its lower part at the Soimul Mountain, and in the upper one: the complex of spores and pollen of Mesozoic age. Geologists, that do not recognize the idea of belonging of the part of suite to Mesozoic, indicate the next contradiction. If we accept the Mesozoic age of the Kuzian suite, so we must affirm that carbonate series of Middle Triassic-Jurassic were deposited on the massif at the same time, and 5–8 km southerly, the regional metamorphism of the Kuzian suite occurred within that zone (by the way, according to some facts at an interval of 148–178 and 175–181 mln years, and according to another information: at an interval of 196–221 mln years. This remark is not correct because the age of the Kuzian suite is Lower Triassic (251.9–247.2 mln years), but metamorphism occurred much later. In those sections where the Kuzian suite lies on the Muntselulska one, basal conglomerates consisting of pebbles and quartzitic fragments of underling suite are present in its bottom. Rocks of the Muntselulska and Kuzian suite are similar by their metamorphism intensity. For the Mesozoic Kuzian suite the manifestations of the main magmatism are characteristic, unlike the Upper Paleozoic acids. The facts testify to that the Mesozoic Kusian suite is existing, but there is a certain indefinity as to its finer dividing, stratigraphic volume and correlation with deposits of Middle Triassic. To avoid confusion, it is expedient to alter the name of the Mesozoic Kuzian suite and to name it, for example, Neo-Kuzian.

Large thrusting and late faulting shape the Aiguilles Rouges crystalline massif (Western Alps), structural implications

Although the Helvetic nappes of the Western Alps have been widely studied, their style, amount, and timing of deformation during the Alpine orogeny remain a subject of controversy. The discussion partly arises from various interpretations of the external crystalline massifs geometry and of the cover/basement relationships. Here, we apply structural analysis based on new field data, microtectonics, and 3D geological modeling on the Aiguilles Rouges and Mont-Blanc massifs, to better quantify their tectonic evolution and their relationship with the nappe stacking. Our results show large thrusting of the Helvetic Mesozoic sedimentary cover above the Aiguilles Rouges basement towards the WNW. The basal contact of the Helvetic nappes, which we call the Helvetic Basal thrust (HBT), often corresponds to a décollement level localized above the Triassic unconformity, but that locally also affects the basement. We suggest that most of the subalpine ranges are klippes above the HBT, and estimate the shortening of the thrust from previously published cross-sections to be between 13 and 32 km. According to published ages, we argue that the HBT was active in the Oligo-Miocene, between ∼30 and ∼14 Ma. After ∼14 Ma and until ∼6 Ma, the HBT is offset by late steep out-of-sequence faults, including back-thrusts and the Mont-Blanc shear zone that was previously a ramp of the HBT. The transition of the major thrust system from the HBT rooting above (east) of the Mont-Blanc to the Alpine sole thrust rooting below (west) of the Aiguilles Rouges occurred between 18 and 14 Ma.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2016–2017

Seismic observations by 46 stationary seismic stations, including seven temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, and by two arrays were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2016–2017 is a manifestation of swarms of weak earthquakes in the northwest in the Leningrad region and the adjacent territory of Finland, as well as earthquakes on the Ukrainian Shield with Мs(est.)=3.8 in Krivoy Rog, where mass explosions are carried out in mines, but earthquakes of moderate magnitude МL=2.6–3.9 also occur (2007, 2013). Weak earthquakes in the peripheral parts (in the southwest, west and northwest) and in zones associated with paleorift structures: in the northeast – with the Kirov-Kazhim and Central Russian aulacogenes continue to be recorded. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula and in the territory of the Voronezh crystalline massif.