East European Craton Research Articles

Terrestrial heat flow versus crustal thickness and topography – European continental study

The relation between heat flow, topography and Moho depth for recent maps of Europe is presented. Newest heat flow map of Europe is based on updated database of uncorrected heat flow values to which paleoclimatic correction is applied across the continental Europe (Majorowicz and Wybraniec 2010). Correction is depth dependent due to a diffusive thermal transfer of the surface temperature forcing, of which glacial–interglacial history has the largest impact. This explains some very low uncorrected heat flow values of 20–30 mW/m2in shallow boreholes in the shields, shallow basin areas of the cratons, and in other areas including orogenic belts where heat flow was likely underestimated due to small depth of the temperature logs. New integrated map of the European Moho depth (Grad et al 2009) is the first high resolution digital map for European plate, which is understood as an area from Ural Mountains in the east to mid-Atlantic ridge in the west, and Mediterranean Sea in the south to Spitsbergen and Barents Sea in Arctic, in the north. For correlation we used the following: onshore heat flow density data with palaeoclimatic correction (5318 locations), topography map (30x30 arc seconds, by Danielson and Gesch 2011) and Moho map by Grad et al (2009), providing longitude, latitude and Moho depth (with resolution of 0.1 degree). Analysis was limited to locations for which datasets were available. The area of continental Europe has been divided into two large domains: Precambrian East European craton and Palaeozoic Platform of the West Europe. In addition, two smaller areas were considered, corresponding to Scandinavian Caledonides and Anatolia. The results obtained reveal significantly different correlations between Moho depth, elevation and heat flow for these regions. For each region detailed analysis of these relations in different elevation ranges are presented. In general, it is observed that Moho depth is more significant for heat flow than elevation. Depending on the region and elevation range, heat flow value is up to two times larger than Moho depth, while relation of heat flow to elevation has much more variability.

The thermal regime of the southern margin East-European craton

An analysis, a mathematical modelling and interpretation of the thermal field was focused on the southern margin of the East-Eu ropean Craton. The size and characteristics of the heat flow are determined by tectonic conditions, the sequence of geological developments of the investigation region during the Cenozoic. The close correlation between the heat flow anomalies and the localisation of the oil and gas fields are established.

Relative secular variations of the Earth’s magnetic field in the years 1966–2016 along the profile across the main tectonic units of Poland (Zgorzelec-Wiżajny profile)

The paper summarizes 50 years of research on relative local secular variations of the total magnetic intensity (TMI) along Zgorzelec-Wizajny profile (Z-W profile) through the years 1966–2016. The Z-W profile (approximately 650 km length) cuts through Europe’s major tectonic units, including a zone of Variscan folds in the Paleozoic platform (PP), the Trans-European Suture Zone (TESZ) and the Polish part of the East European Craton (EEC). Measurements of TMI were made at 31 sites of the profile and reduced to the base recordings at the Central Geophysical Observatory in Belsk. Based on linear approximations of relative geomagnetic field values changes in time, relative annual changes in time (relative secular variations) expressed in nanoteslas [nT] per year were calculated.The study on relative geomagnetic field values revealed slower secular variations of the geomagnetic field in EEC as compared to those in PP and TESZ. However, they show lower amplitudes of these variations. An interesting phenomenon are rapid changes in the time of the relative values (trends) of TMI starting from the year 2000, also expressed as the relative secular variations per year, particularly visible in PP area. In the qualitative sense, relative secular variations show a correlation with the main geological units in the Polish territory and also important elements in the seismic and geothermal model of the lithosphere.

Burial and thermal history of the Lower Palaeozoic petroleum source rocks at the SW margin of the East European Craton (Poland)

Thermal maturity modelling was carried out in over sixty wells along the SW margin of the East European Craton (EEC). The burial and thermal history modelling of the EEC, using thermochronological data, allowed the construction of burial history maps showing its geological development in the Phanerozoic. These results have proved that the Ordovician and Silurian source rocks occurring at the SW margin of the EEC reached a maximum palaeotemperature in the Palaeozoic, mainly during Devonian–Carboniferous time and at the latest during the Silurian in the most westerly part of this margin, along the Teisseyre-Tornquist Zone. In Mesozoic and Cainozoic time, the Ordovician and Silurian strata generally were subjected to cooling or to very minor heating, certainly below the Variscan level. The maximum burial and maximum temperature of the Ediacaran–Lower Palaeozoic strata were reached during the Early Carboniferous in the Baltic Basin and during the Late Carboniferous in the Lublin area, and even in the Early Permian in the SE corner of the Lublin Basin. Thus, the main period of maturation of organic matter and hydrocarbon generation in the Ordovician and Silurian source rocks was in the Late Palaeozoic (mainly Devonian–Carboniferous) and in the westernmost zone along the Teisseyre-Tornquist line at the end of the Silurian.

Petroleum generation and expulsion in the Lower Palaeozoic petroleum source rocks at the SW margin of the East European Craton (Poland)

In this work, 1-D numerical modelling of petroleum generation and expulsion processes in the Upper Ordovician and Lower Silurian source rocks was carried out in over sixty wells along the SW margin of the East European Craton ( EEC) in Poland. Lower Palaeozoic sediments were subjected to rapid burial in the Palaeozoic and then were uplifted in several phases, but with the predominance of the late Variscan tectonic inversion. The thermal maturity of organic matter in the Lower Palaeozoic strata indicates the advancement of the generation processes from the phase of low-temperature thermogenic processes in the NE part of the Baltic and Podlasie-Lublin basins to the overmature stage along the zone adjacent to the Teisseyre-Tornquist Zone (TTZ). The results of modelling of generation and expulsion show that these processes took place mainly in the Devonian and Carboniferous periods and in the westernmost part (along the TTZ), even in the latest Silurian. The hydrocarbon expulsion took place with a small – delay after generation. During the Mesozoic and Cainozoic, generation processes practically were not resumed or intensified. Nevertheless, it was found that zones with an increased shale gas potential can occur only in a relatively narrow belt on the SW slope of the EEC, parallel to the edge of the TTZ. The most promising seem to be Caradocian, Llandovery and the Wenlock between the Lebork IG-1 and Kościerzyna IG-1 wells in the Baltic Basin, and the Wenlock source rocks in the Podlasie-Lublin Basin between the Okuniew IG-1, Łopiennik IG-1 and Narol IG-1 wells. Most of the hydrocarbons were subjected to expulsion and possible migration. As a result, there was a large dispersion of the hydrocarbons generated. The chance of preservation of these hydrocarbons in the source rocks is small.

What the ca. 1.83 Ga gedrite-cordierite schists in the crystalline basement of Lithuania tell us about the late Palaeoproterozoic accretion of the East European Craton

ABSTRACTIn the western East European Craton (EEC), southern Lithuania, a suite of fine-grained, thinly bedded rocks of unusual composition has been shown to have originally comprised intermediate and felsic volcanic rocks. They extruded at ca. 1.83 Ga and were hydrothermally altered prior to metamorphism, which converted them into garnet-, gedrite-, anthophyllite-, staurolite- and cordierite-bearing schists. After the rocks have experienced a 630°C and 7 kbar metamorphism, they were uplifted to 15 km (5 kbar) probably at ca. 1.73 Ga. They were reheated to 640°C at ca. 1.50 Ga (monazite age). The monazite age of ca. 1.50 Ga is coeval with the emplacement of the neighboring 1.50 Ga Anorthosite-Mangerite-Charnockite-Granite (AMCG) Mazury complex. The ca. 1.83 Ga volcanic suites in Lithuania and northern Poland, together with the Oskarshamn-Jönköping belt (OJB) in south-central Sweden, may belong to the same chain of volcanic island arcs, and thus provide information on the evolution of the entire western EEC. The ca. 1.50 Ga metamorphic reworking and the replacement of the Mazury AMCG suite may have been triggered by the Danopolonian orogeny further west and, at a larger scale, accretion of the continental margin of Columbia.

Grain assemblages and diagenesis in the tarl-dominated Lower Silurian mudrock succession of the western margin of the east European craton in Poland and Lithuania

Detrital grain assemblages in mudrocks establish a key starting condition for the diagenetic pathways that drive the evolution of rock properties in unconventional petroleum systems. This case study is based on petrographic examination (light microscopy, elemental mapping, and cathodoluminescence imaging) of 41 subsurface samples of Silurian mudrocks from the western margin of the East European Craton (EEC) in Poland. About 2/3 of the samples have grain assemblages composed by >90% of grains of quartz, feldspar, mica, and clay of extrabasinal derivation. Mechanical compaction is the principal cause of porosity decline in these terrigenous-argillaceous mudrocks (tarls). Where thermal maturation has reached a level sufficient to induce smectite illitization, minute amounts of authigenic silica (≪1 vol%) are observed in the small (~100 nm) primary intergranular pores that survived compaction. Organic-rich mudrocks in this succession also display prominent compaction and contain little organic-matter-hosted porosity. Although these organic-rich tarls may have served as effective source rocks as unimpeded compaction drove expulsion of generated hydrocarbons, they do not in general have sufficient porosity and stiffness to serve as effective reservoirs.Around 27% of the sample set has grain assemblages that include biogenic grains in amounts over 10%. Most of these are calcareous tarls (calcareous-terrigenous argillaceous mudrocks), but do not display discernible carbonate cements. Only three of the studied samples contain grain assemblages that originally included a significant component of biogenic silica. These three samples contain microquartz cement (up to 30% of rock volume) and migrated pore-filling organic matter that has developed secondary porosity. Where thermally mature and sufficiently thick, these local intervals of silica-cemented mudrocks may offer interesting targets for development of unconventional gas.

Application of two-dimensional gravity models as input parameters to balanced cross-sections across the margin of the East European Craton in SE Poland

Our paper demonstrates how two-dimensional density models can deliver critical constraints that permit construction and validation of geological models in an underconstrained subcropped fold-and-thrust belt. As a case study, we use a newly discovered thrust-and-fold belt developed above the margin of the East European Craton (EEC) in SE Poland. A geological model constructed using gravity data resolved the basement-cover interface and a top-Cambrian horizon. This model was used as a framework for cross-section construction employing at this step also borehole and seismic evidence. Two cross-sections were created to address a source of uncertainty related to non-uniqueness of gravity modelling with different emphasis on gravimetric vs geological evidence. Model 1 strictly obeys the top-Cambrian derived from gravity modelling that was treated as an envelope of deeper structures. Model 2 allowed for local departures from the gravity model, especially in the case of conflicts with formation thicknesses. The comparison between the present structure and restorations allowed for separating effects of Caledonian and Variscan shortening. Although the fit of both models to the gravity data is satisfactory, model 2 better complies to geological constraints, resolving the long-discussed problem concerning the distribution and intensity of Caledonian tectonics across the SW periphery of the EEC.

3D MODEL OF THE DEEP STRUCTURE OF THE SVECOFENNIAN ACCRETIONARY OROGEN: A GEODYNAMIC INTERPRETATION

The results of this study are reported in two related successive publications. The article “3D model of the deep structure of the Svecofennian accretionary orogen based on data from CDP seismic reflection method, MT sounding and density modeling” (M. V. Mints, E. Yu. Sokolova, LADOGA Working Group) presented a 3D model of the deep structure of the Late Paleoproterozoic Svecofennian accretionary orogen. The model is based on harmonized data of geological mapping, FIRE-2-2a-1 and FIRE-3-3a seismic reflection profiling, using sections of the 3D crustal density model, results of magnetotelluric surveys along the Vyborg-Suojarvi profile in the Northern Ladoga area and materials from MT surveys previously carried out by Finnish specialists in Southern Finland. In this paper these results were used as the baseline for the construction of the evolutionary model and determination of the position of the Svecofennian orogen in the structure and history of the Paleoproterozoic Lauro-Russian intracontinental orogen. This Paleoproterozoic orogeny swept the predominant part of Lauroscandia, a paleocontinent that united the North American and the East European cratons. Interpretation of the structural features and evolution of the Lauro-Russian orogen leads to the conclusion that its onset and evolution had a causative relation to the development of the Paleoproterozoic superplume which, in turn, initiated plate tectonic events. The evolution of the Lauro-Russian orogen included three intensive development periods (~2.5; 2.2–2.1 and 1.95–1.87 Ga). In the axial zone of the intracontinental orogen there appeared the Svecofennian Pre-Labrador Ocean, and the accretionary Svecofennian and Pre-Labrador orogens formed along its continental margins after its closure.

Relative secular variations of the geomagnetic field along the Zgorzelec-Wiżajny profile, Poland

The paper presents results of the study on relative secular variations of total magnetic intensity (TMI) of the geomagnetic field along the 700 km long profile crossing the area of Poland. Surveys were carried out at annual intervals between 1966 and 2016 (50 measurement series), in 31 survey sites (secular points) separated by about 22 km. The studied profile of the SW-NE direction, called Zgorzelec-Wiżajny (Z-W), crosses large parts of the main tectonic units of Europe, namely the Palaeozoic Platform of Central and Western Europe (PLZ) and the East European Craton (EEC), connected by the Teisseyre-Tornquist Zone (TTZ). Using the original methodology of analysis of measured data, reduced to the values of geomagnetic field recorded at the Central Geophysical Observatory in Belsk, the relative secular variations of TMI with the magnetic anomalies (ΔT) and the terrestrial heat flow density (Q) were graphically presented.

APPLICATION OF THE MAGNETIC ANOMALIES IN IDENTIFICATION THE STRUCTURE OF THE CRYSTALLINE BASEMENT OF THE SOUTH–EASTERN POLAND

South-eastern Poland is situated between the East European Craton (EEC), the Paleozoic and Mezosoic of Western Europe and the Carpathians. Complex geological structure of the area is reflected on the maps of potential fields anomalies. The analyses of the total magnetic intensity anomaly map ∆T and the vertical derivatives of these anomalies in relation to geological data provide many information concerning the structure and magnetic properties of rocks of the crystalline basement. These analyses indirectly reveal the degree of the petrologic diversification and the tectonics of the basement in comparison with the adjoining blocks of the Paleozoic and Variscan orogens and their basement as well as those located in the area of the Trans–European Suture Zone (TESZ). Two dimensional (2D) magnetic models of the basement along the seismic profiles (CEL 01, CEL 05) and corresponding three dimensional (3D) model have been constructed. This interpretation is based on spectral analysis of the magnetic anomalies and their quantitative interpretation which includes data from the CELEBRATION 2000 project, as well as information concerning the magnetic properties of rocks made available through drilling. The comparative analysis of maps showing magnetic and gravity anomalies have revealed the architecture of the crystalline basement in the area where the East European Craton (EEC) is in contact with the Paleozoic and Mezosoic of Western Europe, as well as its impact on the image of residual gravity anomalies within the area of the craton.

Paleoproterozoic Rock Metamorphism of the Nyartin Complex, the Subpolar Urals

In the Urals, Archean and Paleoproterozoic formations are revealed as a part of some polymetamorphic complexes which crop out onto the day surface in relatively small tectonic blocks (up to the first thousand square kilometres in area). Belonging of rocks composing polymetamorphic complexes within the Western tectonic zone of the Urals, which located west of the Main Ural Fault, to the Archean-Paleoproterozoic section is most reliable. These complexes are interpreted as fragments of the heterogeneous crystalline basement of the Ural part of the East European craton. Nevertheless, belonging of only two South Ural complexes: the Taratash and Aleksandrov to the Archean-Paleoproterozoic section causes no special disputes due to the relatively weak geochronological study of the polymetamorphic formations. They are framed by the weakly metamorphosed Lower Riphean deposits; reliable geochronological data are obtained on them, which unambiguously indicate the early Precambrian age of rock metamorphism. The existing Early Precambrian dates (with the prevalence of Late Precambrian and Paleozoic ages) for other Ural polymetamorphic complexes are interpreted in different ways. Therefore, their attachment to the Lower Precambrian section is disputed by many researchers. Taking into account the already available data and the first results of mass U-Pb dating of metamorphogenic zircons from gneisses of the Nyartin polymetamorphic complex in the Subpolar Urals, the Paleoproterozoic age of the earliest stage of rock metamorphism is substantiated in the paper. This gives grounds for the conclusion that this geological object belongs, as well as the Taratash and Alexandrov complexes in the Southern Urals, to the Lower Precambrian formations involved into the Uralides’ structure.

Variscan deformation along the Teisseyre-Tornquist Zone in SE Poland: Thick-skinned structural inheritance or thin-skinned thrusting?

Recently acquired seismic reflection data provide better insight in the structural style of extensive sedimentary series overlying the SW slope of the East European Craton (EEC) in Poland. The two main seismic datasets – the POLCRUST-01 profile and PolandSPAN survey – yielded contrasting thick – and thin-skinned structural models for the same structural units in SE Poland. We reattempt an interpretation of the POLCRUST-01 profile using techniques of cross-section balancing and restoration aided by 2D forward seismic modelling. An outcome is the thin-skinned structural model is. This solution relies on a continuous top of the EEC crystalline basement well represented in the seismic data as well as on fragmentary, yet conclusive seismic geometries in shallow depth intervals proving the Ediacaran-Palaeozoic series to be thrust and folded. A Variscan (late Carboniferous) compressional regime is consequently invoked to explain thin-skinned structuring of the pre-Permian sedimentary pile and >20km of calculated shortening. We demonstrate an ambiguous nature of the top-basement irregularities previously used as indicators of basement-rooted vertical faulting. The tilt and abrupt increase of the top-basement taper under the thin-skinned belt are attributed to pre-Ordovician tectonic processes operating along the SW margin of the EEC. Post-rift subsidence and/or flexural loading giving rise to a broken foreland plate are invoked.

Highly Siderophile Elements distribution, Os-S isotope systematics and U-Pb dating of mafic-ultramafic-hosted massive sulphide deposits (Southern Urals) – Implications on the sources of metals

The behaviour of Highly Siderophile Elements (HSEs), including the Platinum Group Elements (PGEs), Re and Au, is still poorly known in hydrothermal systems due to their low concentrations in hydrothermal fluids and related ore deposits. In this work, HSE abundances were determined by fire assay and ICP-MS analyses in the Devonian Dergamysh and Ivanovka massive sulphide deposits from the Southern Urals, Russia. These deposits occur within mafic-ultramafic rocks of the Main Urals Fault suture zone, where the East-European continental unit comes into contact with the Magnitogorsk island arc system. Despite mafic-ultramafic host-rock compositions, the measured Pt and Pd contents are lower than those in island arc-hosted massive sulphide deposits from the same metallogenic province. In Dergamysh massive sulphides, the PGEs and Au positively correlate with Cu, whereas Pt also correlates with Co. For Ivanovka mainly disseminated ores and host rocks, two trends can be observed: (a) low to high PGE at low Au in rocks, with negative Ni-Pd correlation; and (b) both PGE and Au are variable in ores with significant correlation between Au and Pd. The Os-Pb-S isotope systematics in the seafloor Dergamysh hydrothermal system was mainly controlled by mixing of hydrothermal fluid with isotopic signature inherited from mafic host-rocks, and Devonian seawater. A possible additional contribution from more radiogenic Os component was attributed to older Precambrian rocks, which acquired radiogenic Os composition since their formation. Possible presence of such old rocks in serpentinitic melange was evidenced by U-Pb ages of zircons from Dergamysh deposit host rocks, ranging from 3.3Ga to 507Ma. These Archaean to Proterozoic zircons are consistent with source from the Volga-Uralia block of the East-European craton, adjacent to the Urals orogenic belt. Light sulphur isotopic composition in Dergamysh ores was attributed to bacterial reduction processes, which was also observed for modern serpentinite-hosted seafloor systems. Disproportionation of magmatic fluid however cannot be completely ruled out.

Detection of a new sub-lithospheric discontinuity in Central Europe with S-receiver functions

We used S-receiver functions (i.e. S-to-P converted signals) to study seismic discontinuities in the upper mantle between the Moho and the 410km discontinuity beneath central Europe. This was done by using c. 49,000 S-receiver functions from c. 700 permanent and temporary broadband stations made available by the open EIDA Archives. Below Phanerozoic Europe we observed expected discontinuities like the Moho, the lithosphere-asthenosphere boundary (LAB), the Lehmann discontinuity and the 410km discontinuity with an additional overlying low velocity zone. Below the East European Craton (EEC), we observed the Mid-Lithospheric Discontinuity (MLD) at c. 100km depth as well as the controversial cratonic LAB at c. 200km depth. At the boundary of the EEC but still below the Phanerozoic surface, we observed downward velocity reductions below the LAB in the following regions: the North German-Polish Plain at about 200km depth; the Bohemian Massive, north-west dipping from 200 to 300km depth; the Pannonian Basin, north-east dipping from 150 to 200km depth underneath the western Carpathians and the EEC. We named this newly observed structure Sub-Lithospheric Discontinuity (SLD). At the northern edge of the Bohemian Massive, we see a sharp vertical step of about 100km between the SLD below the Bohemian Massive and the North German-Polish Plain. This step follows the surface trace of the Rheic Suture between the continental Saxo-Thuringian and Rheno-Herzynian zones of the Variscan orogen. A preliminary interpretation of these features is that a prong of the cratonic mantle lithosphere penetrated the Phanerozoic asthenosphere during the continental collision at the western and south-western edges of the EEC.

Upper mantle structure across the Trans-European Suture Zone imaged by S-receiver functions

We present a high-resolution study of the upper mantle structure of Central Europe, including the western part of the East European Platform, based on S-receiver functions of 345 stations. A distinct contrast is found between Phanerozoic Europe and the East European Craton across the Trans-European Suture Zone. To the west, a pronounced velocity reduction with depth interpreted as lithosphere–asthenosphere boundary (LAB) is found at an average depth of 90 km. Beneath the craton, no strong and continuous LAB conversion is observed. Instead we find a distinct velocity reduction within the lithosphere, at 80–120 km depth. This mid-lithospheric discontinuity (MLD) is attributed to a compositional boundary between depleted and more fertile lithosphere created by late Proterozoic metasomatism. A potential LAB phase beneath the craton is very weak and varies in depth between 180 and 250 km, consistent with a reduced velocity contrast between the lower lithosphere and the asthenosphere. Within the Trans-European Suture Zone, lithospheric structure is characterized by strong heterogeneity. A dipping or step-wise increase to LAB depth of 150 km is imaged from Phanerozoic Europe to 20–22° E, whereas no direct connection to the cratonic LAB or MLD to the east is apparent. At larger depths, a positive conversion associated with the lower boundary of the asthenosphere is imaged at 210–250 km depth beneath Phanerozoic Europe, continuing down to 300 km depth beneath the craton. Conversions from both 410 km and 660 km discontinuities are found at their nominal depth beneath Phanerozoic Europe, and the discontinuity at 410 km depth can also be traced into the craton. A potential negative conversion on top of the 410 km discontinuity found in migrated images is analyzed by modeling and attributed to interference with other converted phases.

3D density model of the upper mantle of Asia based on inversion of gravity and seismic tomography data

AbstractWe construct a new‐generation 3D density model of the upper mantle of Asia and its surrounding areas based on a joint interpretation of several data sets. A recent model of the crust combining nearly all available seismic data is employed to calculate the impact of the crust on the gravity anomalies and observed topography and to estimate the residual mantle anomalies and residual topography. These fields are jointly inverted to calculate the density variations in the lithosphere and upper mantle down to 325 km. As an initial approximation, we estimate density variations using a seismic tomography model. Seismic velocity variations are converted into temperatures and then to density variations based on mineral physics constraints. In the Occam‐type inversion, we fit both the residual mantle gravity anomalies and residual topography by finding deviations to the initial model. The obtained corrections improve the resolution of the initial model and reflect important features of the mantle structure that are not well resolved by the seismic tomography. The most significant negative corrections of the upper mantle density, found in the Siberian and East European cratons, can be associated with depleted mantle material. The most pronounced positive density anomalies are found beneath the Tarim and South Caspian basins, Barents Sea, and Bay of Bengal. We attribute these anomalies to eclogites in the uppermost mantle, which have substantially affected the evolution of the basins. Furthermore, the obtained results provide evidence for the presence of eclogites in the oceanic subducting mantle lithosphere.

Tectonics of the junction region between the East European craton and West Arctic platform

The region of the junction and interaction between the East European Craton (EEC) and the West Arctic Craton (WAC) is regarded as a complexly built zone or assembly of both the volumetric and dividing linear tectonic elements: the Trollfjord–Rybachi–Kanin (TRK) Lineament, the pericratonic subsidence zone of the EEC, the Karpinskii Lineament, the Murmansk Block of the Fennoscandian (Baltic) Shield, and the Kolmozero–Voronya Zone, which are briefly characterized in this paper. Evidences of thrusting have been established not only in the TRK Suture Zone and on the Rybachi Peninsula, which represent a fragment of the Timanides fold–thrust belt, but also to the southwest, in the Upper Riphean and Vendian terrigenous sequences making up the Sredni Peninsula and related to the pericratonic trough of the VEC. Two phases of fold–thrust deformations with elements of left-lateral strike-slip offset pertaining to the activity and evolution of the lineament suture dividing the Sredni and Rybachi peninsulas have been recorded. The variously oriented fault–fold systems within this fault zone are evidence for multistage deformation and can be explained by an at least twostage change in the kinematics that control displacement along the fault. The disintegrated granitic massifs of the Archean crystalline basement tectonically squeezed out in the upper crust as protrusions are localized within TRK Fault Zone. Plagiogranitic bodies, which underwent superposed fault-fold deformations of both kinematic stages, are an evidence of the vigorous tectonic event that predated folding and two-stage strike-slip displacement along the TRK Fault—by thrusting of Riphean sequences from north to south toward the Archean craton. The nappe–thrust regional structure was formed at this stage; elements of it have been recognized in the Sredni, Rybachi, and Kanin peninsulas. The main stages of tectonic evolution in the junction zone between the EEC and the WAP have been revealed and substantiated.

3-D Inversion of MT Data for Imaging Deformation Fronts in NW Poland

The Pomerania region (northwest part of Poland) occupies a significant position, where the largest European tectonic boundary is situated. This is the area of the contact between the East European Craton (EEC) and the Paleozoic Platform (PP) and it is known as the Trans-European Suture Zone (TESZ). The TESZ was formed during Paleozoic time as a consequence of the collision of several crustal units and it extends from the Black Sea in the southeast to the British Isles in the northwest. It is a region of key importance for our understanding of the tectonic history of Europe. Previous magnetotelluric (MT) results, based on 2-D inverse modeling, show that the contact zone is of lithospheric discontinuity character and there are distinct differences in geoelectric structures between the Precambrian EEC, transitional zone (TESZ), and the younger PP. The presence of a significant conductor at mid and lower crustal depths was also shown. Thus, the main aim of the research presented here was to obtain detailed, 3-D images of electrical conductivity in the crust and upper mantle and its regional distribution below the TESZ in the northwest part of Poland. To accomplish this task we applied the latest 3-D inversion codes, which allowed us to get more realistic model geometries. Additionally, to confirm and complement the study, the Horizontal Magnetic Tensor (HMT) analysis was realized. This method gives us an opportunity to efficiently locate the position of well-conducting structures. As a result we obtain a clearer, three-dimensional model of conductivity distribution, where highly conductive rock complexes appear which we tentatively connected to deformation fronts.

Peri-Amazonian provenance of the Euxinic Craton components in Dobrogea and of the North Dobrogean Orogen components (Romania): A detrital zircon study

The Romanian South Carpathians foreland is located southwards of the East European Craton (EEC) and consists of three major tectonic units: the Scythian Platform, the North Dobrogean Orogen and the Euxinic Craton. The Euxinic Craton is represented in the Dobrogea area by two components: (i) Central Dobrogean Shield and (ii) East Moesia. In central-northern Dobrogea, the Trans European Suture Zone (TESZ), including the Teisseyre–Tornquist Zone, presumably strikes below the surface. Because the paleogeographic provenance of the above tectonic units was poorly documented until present, a systematic sampling for detrital zircon has been conducted in all tectonic units except for the Scythian Platform basement which is entirely covered by the Danube Delta. In all, this totals 26 samples and around 1833 analyzed zircon grains. The distribution of zircon grains dates along the time scale for all the sampled terranes suggests that the sampled components of the Euxinic Craton in Dobrogea and the constitutive terranes of the North Dobrogean Orogen have a peri-Gondwanan, peri-Amazonian provenance. Their ages are Neoproterozoic or younger. In addition, the Euxinic Craton can be depicted as a paleo-Amazonian crustal fragment that was marginally affected by the Avalonian–Cadomian orogenic events. Along with its margin, the Avalonian type terranes accreted or Ganderian type terranes have evolved. Primary relationships between the Amazonian derived terranes and EEC are obscured due to an intricate geologic history exhibited by the North Dobrogean Orogen involving Caledonian, Variscan and Cimmerian orogenic events, while the geologic history of the Scythian Platform is also poorly established. The general distribution diagram of U–Pb detrital zircon ages shows some major zircon sources, shared with those detected at a global scale. They are episodic and coincident along with the time scale, such as those at the end of Archean or those from the Pan-African orogens. Finally, among these discussed tectonic components, only the Scythian Platform can possibly have an EEC provenance.