East European Plate Research Articles

Meta-Ultramafic Rocks of the Maksyutov Complex, Southern Urals: High-Pressure Si-Al Metasomatism and Carbonatization at the Crust-Mantle Interface in the Subduction Zone

The eclogite-blueschists Maksyutov Complex is characterized by a complex fold-and-thrust structure that was developed during the Late Devonian collision between Baltica (East European Plate) and the Magnitogorsk Arc, that was formed during the Early Devonian intraoceanic subduction. Eclogites are the most studied rocks of the complex; their formation and exhumation are usually associated with the collisional stage of orogen development. At the same time, the origin of meta-ultramafic rocks, which together with eclogites form sheeted and lenses within metasedimentary rocks (shales and quartzites), still remains unknown. This paper presents the results of the first detailed petrological study of meta-ultramafic rocks, represented by antigorite-chlorite and magnesite-antigorite metaharzburgites, chlorite-antigorite metaorthopyroxenite. Mineral compositions and textural relationships between minerals in metaharzburgites indicate at least two stages of rock transformations. Minerals of the early mineral paragenesis (first stage) – olivine, accessory chromite and low-fluorine Ti-clinohumite – have a metamorphic genesis; ultrahigh-pressure (UHP) conditions of their formation are discussed. At the second stage, there was a partial replacement of olivine by orthopyroxene-bearing parageneses with Cr-Al antigorite and/or high-chromium chlorite. Based on the phase equilibria modeling using the Perple_X software package, it was found that the formation of antigorite-orthopyroxene paragenesis was associated with Si-Al metasomatism at: T ~ 630°С, P ~ 2 GPa, logaSiO₂~ –0.6, logaAl₂O₃~ – 2.5. It is important to note that the mineral paragenesis are highly sensitive to aSiO₂: a slight decrease in lgaSiO2 relative to the above value would lead to the growth of olivine with antigorite, and an increase would lead to the growth of orthopyroxene. The latter may explain the formation of meta-orthopyroxenites, which are widely distributed among the meta-ultramafic rocks of the Maksyutov Complex. Similar calculations performed for the range of XCO₂= 0.01–0.05 in H₂O-CO₂fluid showed replacing silicate minerals by magnesite under the established thermodynamic conditions. Carbonation and Si-Al metasomatism are specific features of high-pressure transformations of meta-ultramafic rocks, which have not been established in the associated eclogites, quartzites, and shales. Such selectivity of fluid influence on different rock types is interpreted as a result their different tectono-metamorphic evolution: meta-ultramafic rocks are fragments of the suprasubduction mantle, which were tectonically combined with the rocks of the subducting plate (eclogites and metasedimentary rocks).

Features of earthquake epicenters and mineral deposits spatial relationship in the Urals

Introduction. Recent Ural mountain belt is an N-S Paleozoic orogen rejuvenated in the NeogeneQuaternary period. It separates the East European plate located to the west of it and the West Siberian plate located to the east of it. The Uralian orogeny presumably occurred at the Paleozoic time as a result 36 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 4. 2021 ISSN 0536-1028 of these plates interaction, which affected the geologic structure of the region. In the modern era, low tectonic activity in the bowels of the Urals continues supported by rare tangible earthquakes with a magnitude from 2.0–3.0 to 5.0–5.5, 3.0 – 3.5 on the average, and the intensity in the epicenter from 3.0–4.0 to 5.0–6.0 on MSK-64 scale. Research aim is to analyze the spatial relationship of sensible earthquakes epicenters and mineral deposits in the Urals. Research methodology included estimating the position of Ural earthquakes epicenters and mineral deposits relative to the geologic and tectonic structures of Paleozoic time, recent epoch, and the modern era. Research results. Most earthquake epicenters in the Urals are concentrated within the western part of the Uralian Orogeny to the west of the Main Uralian Fault (MUF), while most mineral deposits, especially ore deposits, are concentrated within the eastern part of the Uralian orogeny to the east of MUF. In the axial zone of MUF, earthquake epicenters are close and sometimes coincide. Consequently, the processes of ore deposits and earthquake foci formation are of a similar nature

Valentinite and Colloform Sphalerite in Epithermal Deposits from Baia Mare Area, Eastern Carpathians

Valentinite forms through the alteration of stibnite in sulphide deposits. Colloform sphalerite is a widespread mineral in low-temperature deposits, particularly those of the Mississippi-Valley type. We identified valentinite and colloform sphalerite in hydrothermal deposits occurring in the Baia Mare area. The Baia Mare metallogenic district of Neogene age occurs in the northwestern part of the Neogene volcanic chain within the Eastern Carpathians. The Neogene volcanism from Baia Mare area is related to the subduction processes of the East European plate under two microplates, Alcapa and Tisza-Dacia/Tisia, in the post-collisional compressive phase. We have identified valentinite in the Dealul Crucii and Baia Sprie deposits, associated with other epithermal minerals, in the absence of the stibnite. Valentinite is deposited in the final phase of the epithermal process after calcite and manganese-bearing calcite. Micro-Raman and microprobe determinations indicate the presence of valentinite. The formula of valentinite is close to stoichiometric Me2O3 and contains small amounts of tin as an antimony substituent. Colloform sphalerite was identified in the Baia Sprie ore deposit associated with minerals formed in the final epithermal phase. It was deposited on idiomorphic crystals of stibnite, which it corrodes. Its structure and an alternate banding, exhibited on the nano-/microscale, were identified by optical microscopy, SEM (scanning electron microscopy), and BSE (backscattered electron microscopy) imaging. These structures are typical for colloform sphalerite and suggest a genesis due to episodic precipitation. The spherical nano/micro-particles (nodules) are characteristic of the colloform sphalerite from Baia Sprie. Raman analysis indicates the presence of a colloform sphalerite with low iron content. The typical diffraction lines for sphalerite were identified in X-ray diffraction: 3.118 Å (111), 1.907 Å (220), 1.627 Å (311). Microprobe analysis certifies the presence of sphalerite with the stoichiometric formula close to ZnS. Iron content is low (0%–0.0613%), but Sb (0.7726%–2.6813%), Pb (0.56%–1.1718%), Bi (0%–0.1227%) are also present. The negative correlation between Zn and Sb suggests the simultaneous deposition from the same epithermal fluids. Valentinite and colloform sphalerite were formed at low temperatures (100–150 °C) at the end of the epithermal process.

Some features of the structure of the mantle of the Eastern Mediterranean and their geodynamic interpretation

We consider specific velocity anomalies and the corresponding mantle structures of the East Mediterranean-Black Sea-Caspian region. The anomalies are located on latitudinal and longitudinal seismic tomography sections obtained by constructing 3D P-velocity model of Eurasia applying the Taylor approximation method. The depth of the study is of 50—2900 km. The accuracy of determination of the velocity VP is about ± 0.015 km/s. Velocity sections are shown in residual values ΔVP. Physical and mineralogical mantle model of Pushcharovsky was used for the cross sections specification.In the 25—30° E cross sections between latitudes of the 34—48°N high-velocity slabs sinking from the northern edge of the African plate and the southern parts of the East-European plate towards each other are seen. Slabs are connected at a depth of about 600 km in the upper mantle transition zone in the area of 42—43° N. Below the slabs junction high-velocity mantle zone thickens and extends to a depth of 1000—1200 km that occurs as a result of slabs relatively high-velocity material accumulation. From this area down-welling begins which can be traced on latitude sections of 35—45° N as an almost continuous inclined layer of ~1100 km width and ~ 1900 km length. Down-welling submerges from a depth of 450—550 km at Moesian and Aegean micro-plates area to a depth of 1600—1900 km beneath the East Black Sea, Anatolian micro-plates and the northern part of the Arabian plate. The mechanism of the inclined layer formation is discussed with the involvement of global seismic tomography data, and the numerical simulation performed by L. I. Lobkovsky.In the 42—44° N and 34—36° E sections we trace column type vertical structure, which crosses almost the entire mantle at depths of 50—100 to > 2500 km. In the middle of the column on its axis there is a relatively high-velocity anomaly, which reduces in size and values downward. The shape and structure of the mantle column resembles a tornado. We consider two possible alternative mechanisms of its formation: a) steep subduction of the West Black Sea micro plate beneath the Central Black Sea Ridge, wedging of the mantle and the extension stresses occurrence in border zone I and middle mantle; b) rising of the plume from zone D'', formation of extension area in middle and upper mantle, lithosphere pulling inward and the subduction zone formation.

Porphyry deposits of the Urals: Geological framework and metallogeny

Most of the Cu (±Mo,Au) porphyry and porphyry-related deposits of the Urals are located in the Tagil-Magnitogorsk, East-Uralian Volcanic and Trans-Uralian volcanic arc megaterranes. They are related to subduction zones of different ages:(1)Silurian westward subduction: Cu-porphyry deposits of the Birgilda-Tomino ore cluster (Birgilda, Tomino, and Kalinovskoe) and the Zeleny Dol Cu-porphyry deposit;(2)Devonian Magnitogorsk eastward subduction and the subsequent collision with the East European plate: deposits and occurrences are located in the Tagil (skarn-porphyry Gumeshevskoe etc.) and Magnitogorsk terranes (Cu-porphyry Salavat and Voznesenskoe, Mo-porphyry Verkhne-Uralskoe, Au-porphyry Yubileinoe etc.), and probably in the Alapaevsk-Techa terrane (occurrences of the Alapayevsk-Sukhoy Log cluster);(3)Late-Devonian to Carboniferous subduction: deposits located in the Trans-Uralian megaterrane. This includes Late-Devonian to Early Carboniferous Mikheevskoe Cu-porphyry and Tarutino Cu skarn-porphyry, Carboniferous deposits of the Alexandrov volcanic arc terrane (Bataly, Varvarinskoe) and Early Carboniferous deposits formed dew to eastward subduction under the Kazakh continent (Benkala, etc.).(4)Continent-continent collision in Late Carboniferous produced the Talitsa Mo-porphyry deposit located in the East Uralian megaterrane.Porphyry mineralization of the Magnitogorsk megaterrane shows an evolving relationship from gabbro-diorite and quartz diorite in the Middle Devonian (Gumeshevskoe, Salavat, Voznesenskoe) to granodiorite-plagiogranodiorite in the Late Devonian (Yubileinoe Au-porphyry) and finally to granodiorite in the Carboniferous (Talitsa Mo-porphyry) with a progressive increase in total REE, Rb and Sr contents. This corresponds to the evolution of the Magnitogorsk terrane from a volcanic arc which gave place to an arc-continent collision in the Famennian.

Possible Triggered Seismicity Signatures Associated with the Vrancea Intermediate-Depth Strong Earthquakes (Southeast Carpathians, Romania)

Online Material: Vrancea earthquake catalogs. To date, no generally applicable procedure is available for distinguishing triggered earthquakes from other seismic events that occur, apparently randomly, within a certain region (see discussion in van der Elst and Brodsky, 2010). In particular, it is not habitual to utilize diagrams illustrating the time evolution of the seismic release (e.g., Mantovani et al. , 1987; Husen et al. , 2004) as a diagnostic tool. However, that investigation method has been shown in the present study to be outstandingly useful for highlighting similarities existing between the patterns of seismic activities recorded in two distinct and possibly interacting lithospheric domains associated with the Carpathians orogenic belt in Romania. The main potentially causative earthquakes occurred in the Vrancea seismic zone (hereafter VSZ), located at intermediate depths (60–180 km) beneath the southeast Carpathian Arc bend (Fig. 1), whereas the resulting seismicity enhancements (recorded several months to tens of months afterward) developed at less than 60 km depth in the adjoining Carpathians‐foredeep region. The concerned Carpathians Mountains foreland basement is built up of two distinct lithospheric plates: the east European plate to the north‐northeast and the Moesian plate to the south‐southwest (Fig. 1), which are separated by a regional system of northwest–southeast‐oriented fractures (the so‐called Trotus and Peceneaga‐Camena faults). In coincidence with that contact, a shallow seismicity domain, designated (Raileanu et al. , 2007) as the Marasesti–Galaţi–Braila lineament (hereafter MGBL), has also been delineated. Figure 1. General seismotectonic setting of the considered area (geology after Sandulescu, 1984). The Carpathian Mountains accretionary wedge has overthrust (saw‐tooth boundary) the corresponding foreland, which extended on two major plates (east European and Moesian). The roughly oval, solid contour bounds the epicentral domain of the intermediate‐depth (≥60 km) Vrancea earthquakes. Large black symbols …

Synergetic tectonics. 3. The main tectonic regularity in the structure of continental margins

Tectonic evolution of continental outskirts (CO) is considered as a result of selfdevelopment in relation with periodical orthogonal change of the Earth's proper rotation axis position — tectonic (T) stages. Relation of Tstages with folding, their organizing role in the Wilson cycle and accordingly in KO structure is under investigation. A model of CO evolution is proposed, inherent types of crystalline crust, sedimentary basins, orogenies are under analysis. Important role of horizontal and vertical sets of Tstages in the studies and contemporary CO structure has been shown. Basic provisions of tectonics of the sets of tectonic stages are demonstrated on examples of tectonic development of south and west CO of East European plate.

ГЕОДИНАМІКА

In the paper the deep structure of the Carpathian region of Ukraine from the plate tectonics point of view is illustrated. According to geophysical research on regional sections the kimberlite formation of tectonomagmatic activation and seismofocal zone of Hercynian tectogenesis are found. Contrary to existing views the obtained data indicate that West European microplate came under the East European plate. In the light of the stated the prospects of oil-and-gas presence of the region are analysed.

Age of zircons from chromites in the residual ophiolitic rocks as a reflection of upper mantle magmatic events

It is highly possible that processes related to the injection of melts through mantle are responsible for the formation of new mineral assemblages in mantle residues (for example, zircon, olivine, Cr-spinel, and clinopyroxene). The present paper reports the results of U‐Pb zircon dating on chromite deposits and attempts to infer the timing of magmatic events in residual mantle ultramafic rocks of the Voikar‐Syninsky ophiolite massif. Ophiolite complexes of the Urals were formed during three stages of the Phanerozoic geodynamic evolution of the oceanic lithosphere: Early Ordovician spreading in the southern segment of a common Paleouralian basin; Ordovician rifting of the East European continental margin; and suprasubduction spreading in Early Devonian time, which was distinctly expressed in the polar segment of the Urals [4, 5]. At the same time, detailed studies of the geological structure of the Polar Urals, new isotope datings on the rocks of ophiolite complexes [6], and palinspastic reconstructions testify to the existence of an ancient (pre-Paleozoic) oceanic lithosphere along the margin of the East European plate [7]. Isotope datings on plutonic and dike complexes of

Neogene–Quaternary magmatism and geodynamics in the Carpathian–Pannonian region: a synthesis

In the Carpathian–Pannonian region in Neogene times, westward-dipping subduction in a land-locked basin caused collision of two lithospheric blocks (Alcapa and Tisia) with the southeastern border of the European plate. Calc-alkaline and alkaline magmatism was closely related to subduction, rollback, collision and extension. From the spatial distribution of the magmatic activity, four segments can be defined: Western Segment (magmatism occurring on the Alcapa block), Central Segment (magmatism occurring on both Alcapa and the Tisia blocks), South-Eastern Segment and Interior Segment (both on the Tisia block). Most calc-alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment. Assimilation and fractionation processes at shallow crustal levels occurred in most of the segments, strongly masking the deeper source processes. Long-term subduction, rollback and/or delamination led to contamination of the asthenosphere beneath the Western Segment. Here, large-volume partial melts of the contaminated mantle caused underplating and crustal anatexis, leading to mixing of mantle-derived calc-alkaline magmas with crustal melts. In the Central Segment, calc-alkaline magmas were formed by subduction and rollback, followed by back-arc extension and slab breakoff. A variable mantle source is indicated in the back-arc setting and larger amount of fluid-induced metasomatism, source enrichment and assimilation nearer to the trench. In the Interior Segment, evolution from typical calc-alkaline magmas to adakite-like ones was related to extension due to fast rotations and transtensional tectonics. Here, calc-alkaline magmas formed by decompression melting of a heterogeneous crust–mantle lithosphere, while adakite-like melts resulted from fliud-dominated melting of the lithosphere. Along the South-Eastern Segment, slab breakoff was responsible for the generation of typical calc-alkaline magmas, but in the extreme south of the segment, shallow level tearing of the slab followed breakoff. Strike–slip tectonics allowed the rise of hot asthenosphere and generation of adakite-like magmas, via slab-melting, along the torn edge of the East European Plate. Alkalic basaltic volcanism with an OIB-like asthenosphere source followed the calc-alkaline stage (Western Segment), or was contemporaneous with it (South-Eastern and Interior Segments) mainly in response to local extensional tectonics.

Modelling of Block Structure Dynamics for the Vancea Region: Source Mechanisms of the Synthetic Earthquakes

The main structural elements (blocks) of the Vrancea (Romania)-the East-European plate; the Moesian, the Black Sea, and the Intra-Alpine (Pannonian-Carpathian) subplates-are assumed to be rigid and separated by infinitely thin plane faults. The interaction of the blocks along the fault planes and with the underlying medium is elasto-viscous. The velocity vectors which define the motion of the East-European plate and of the medium underlying the subplates are input model parameters, which are not changed during the numerical simulation. At each time, the displacements of the subplates caused by these motions are defined so that the system is in the quasistatic equilibrium state. When, for some part of a fault plane, the stress exceeds a certain strength level, a stress-drop (a failure) occurs (in accordance with the dry friction model), and it can cause failures in other parts of the fault planes. The failures represent earthquakes and, as a result of the numerical simulation, a synthetic earthquake catalog is produced. PANZA et al. (1997) and SOLOVIEV et al. (1999) have determined the ranges for the values of the motion velocity vectors and of the other parameters of the model for which the space distribution of epicenters and the frequency-magnitude relation in the synthetic earthquake catalog are close to those of the observed seismicity. In this paper we study the variation of the slip angle of the synthetic earthquakes as a function of the variation of the model parameters, and we compare our results with observations.

Teleseismic tomography across the middle Urals: lithospheric trace of an ancient continental collision

The Urals are a major collision belt between two continental plates separated by island arcs: the East European plate and the Siberian plate. Their linear structure is preserved on a length of about 3000 km. A seismic array of 61 stations has been deployed during more than 3 months on a linear profile across the middle Urals, north of Ekaterinburg. P-wave travel-time residuals are inverted and provide a tomographic cross-section of the lithosphere on a 600-km-long profile across the Urals. An east-west asymmetry is observed both in the crust and in the lithosphere: the western limit between these two different lithospheres corresponds to the western front of the Uralian orogen from the surface to a depth greater than 100 km. Several crustal studies were performed by other teams along the same profile, and we compare our teleseismic cross-section to common-depth-point seismics, to deep seismic soundings and to a wide-angle-reflection fan profile. East of the main Uralian fault, the teleseismic inversion shows high-velocity bodies corresponding to well-known volcanic/mafic and ultramafic rocks in the Tagil syncline. These high-velocity bodies do not appear to be rooted in the lower crust. As a whole, the teleseismic tomogram comforts the Moho imbrication model proposed by Juhlin et al. (1995).

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution

During its Riphean to Palaeozoic evolution, the East European Craton was affected by rift phases during Early, Middle and Late Riphean, early Vendian, early Palaeozoic, Early Devonian and Middle-Late Devonian times and again at the transition from the Carboniferous to the Permian and the Permian to the Triassic. These main rifting cycles were separated by phases of intraplate compressional tectonics at the transition from the Early to the Middle Riphean, the Middle to the Late Riphean, the Late Riphean to the Vendian, during the mid-Early Cambrian, at the transition from the Cambrian to the Ordovician, the Silurian to the Early Devonian, the Early to the Middle Devonian, the Carboniferous to Permian and the Triassic to the Jurassic. Main rift cycles are dynamically related to the separation of continental terranes from the margins of the East European Craton and the opening of Atlantic-type palaeo-oceans and/or back-arc basins. Phases of intraplate compression, causing inversion of extensional basins, coincide with the development of collisional belts along the margins of the East European Craton. The origin and evolution of sedimentary basins on the East European Craton was governed by repeatedly changing regional stress fields. Periods of stress field changes coincide with changes in the drift direction, velocity and rotation of the East European plate and its interaction with adjacent plates. Intraplate magmatism was controlled by changes in stress fields and by mantle hot-spot activity. Geodynamically speaking, different types of magmatism occurred simultaneously.

Alpine crustal shear zones and pre-Alpine basement terranes in the Romanian Carpathians and Apuseni Mountains

The Carpathian orocline formed by complex suturing of small continental fragments to the East European (and Moesian) plate. Remnants of continental fragments belong to three pre-Alpine lithotectonic assemblages: a greenstone-granite association and two gneissic assem blages. During Alpine collision, pieces of crust were repeatedly fragmented and welded to accommodate heterogeneous strain along the irregular East European plate boundary. Shallow structural levels of Alpine tectonic discontinuities in which the locus of most intense strain migrated over time are now exposed as wide retrograde greenschist grade belts. Repeated, mainly transpressive deformation resulted in early ductile fabrics being overprinted by local brittle shear strain. Igneous intrusion accompanied different phases of tectonic activity. The age of shearing initiation is probably late Paleozoic, and the configuration of the zones and their Alpine internal structures are consistent with the geometry of the Carpathian arc.

Direction and intensity of the geomagnetic field in the Middle Devonian and Lower Ordovician: southern Mugodjary ophiolites (Urals)

A considerable quantity of petromagnetic and palaeomagnetic measurements in the field has allowed us to obtain reliable palaeomagnetic results for such difficult and complex objects as ophiolites. Eifelian baked sediments, diabases (dyke contacts) and gabbros, and Tremadocian baked sediments were studied. Continuous thermocleaning, conglomerate and fold tests were applied. The palaeointensity was investigated by means of several palaeomagnetic methods: Wilson-Burakov, van Zijl-Shaw and Bagina-Petrova. The mean intensities of the geomagnetic fields are 7 and 16.5 μT, with mean palaeomagnetic pole positions of 9°N, 134°E and 6°S, 83°E, respectively. These data demonstrate that southern Urals (Mugodgary) was located near the northern margin of the East European plate during Ordovician-Devonian time. The allochthonous crustal oceanic plate was thrust upon the edge of the plate and deformed as late as the Permian. Changes in the polarity of the geomagnetic field are recorded in the succession of sheeted dykes, a direct corroboration of the Vine-Mathews hypothesis.