Geodynamic Interpretation Research Articles

The East Variscan Shear Zone (EVSZ) and Its Regional Mylonitic Complex: A New Geodynamic Interpretation of the Variscan Axial Zone in Sardinia (Italy)?

Sardinia (Italy) represents one of the most comprehensive cross-sections of the Variscan orogen. The metamorphic and structural complexity characterizing its axial zone still presents many unresolved issues in the current state of knowledge. The data presented from the structural study of the entire axial zone of this area have allowed the authors to propose a subdivision into two new structural complexes. In particular, a younger complex is identified as the New Gneiss Complex, containing remnants of an older and higher-grade metamorphic complex defined as the Old Gneiss Complex. The structural and geometric relationships between the two complexes suggest the redefinition of the axial zone of Sardinia as part of the intracontinental East Variscan Shear Zone/medium-temperature Regional Mylonitic Complex. Comparable relationships are also highlighted in many other areas of the Variscan chain (e.g., Morocco, Corsica, Maures Massif, and Argentera Massif). Extending this new structural interpretation to other axial zones of the South European Variscan orogen could provide new hints for reconstructing the collision boundaries between Gondwana and Laurussia in the late Carboniferous to the early Permian periods.

Brittle faulting and tectonic stress history on the western margin of the Congo Basin between Kinshasa and Brazzaville: Implications for the evolution of the Malebo Pool and the Congo River

The history of brittle faulting and associated paleostress states has been investigated in the rapids of the Congo River at the outlet of the Malebo Pool between Kinshasa (Democratic Republic of the Congo) and Brazzaville (Republic of the Congo). The aim of this study was to unravel the Meso-Cenozoic tectonic evolution of the western margin of Central Africa, as well as to investigate the dynamic evolution of the Pool and the capture of the Congo Basin drainage system by the Lower Congo River through the Central African Atlantic swell that formed between the Congo Basin and the Atlantic Ocean. We reviewed the geological evolution of the Pool area using recent data and new field observations to develop a consistent stratigraphic model for both sides of the Congo River. We collected a significant amount of data faults and fractures in the early Paleozoic Inkisi arkosic sandstones, identified four successive data subsets and determined their related paleostress tensors trough an iterative process utilizing relative chronological indications. All paleostress states exhibit a a strike-slip faulting regime, with varying orientation of horizontal principal compression. The timing of faulting was constrained by indirect observations based on the updated understanding of the Pool's evolution. The geodynamic interpretation of the brittle stages considered potential sources of compressional stress arising from plate boundaries and from the oceanic ridge push. A polyphase brittle tectonic history was identified, characterized by the gradual appearance of newly formed faults and reactivation of the existing ones, leading to the gradual saturation of the host rock with fractures. The most recent event let to a significant imprint on the current landscape and is believed to have facilitated the connection of the drainage system of the Congo Basin to the Atlantic coast in the Oligocene period. The current stress state, determined from earthquake focal mechanisms, aligns with the most recent paleostress state identified determined from fault-slip data, displaying similar stress axis orientations but with consistent with a transpressional stress regime instead of a strike-slip one.

Comment on ‘The Generation of Eocene Mafic Dike Swarms During the Exhumation of a Core Complex, Biarjmand Area, NE Iran’ by Azizi et al. (2023), Journal of Petrology, 64, 1–18

Abstract Azizi, H., Daneshvar, N., Asahara, Y., Minami, M. & Anma, R. (2023). The generation of Eocene mafic dike swarms during the exhumation of a Core complex, Biarjmand area, NE Iran. Journal of Petrology64, 1–18 have attributed the E–W-oriented mafic dike swarm in the Biarjmand metamorphic core complex to an Eocene extensional event which is much younger than a previously suggested Late Jurassic–Early Cretaceous age. They proposed that the emplacement of these dikes occurred in a rapid extensional regime coeval with the exhumation of the core complex after gravitational instability in the Central Iran/Eurasia collision zone. I appreciate the opportunity this article provides to shed light on specific aspects of the Late Mesozoic–Early Cenozoic continental extension within the Eurasian sector of the Neotethys subduction system. However, I here bring to attention certain discrepancies within Azizi et al.'s publication. Specifically, the assignment of an Eocene age to the emplacement of the E–W-oriented dike swarm, even though purportedly supported by U–Pb zircon dating, appears to be at odds with field observations and previously published geochronological data. Furthermore, the article contains internal contradictions in its presentation of the core complex model for the study area. It is important to note that Malekpour-Alamdari, A., Axen, G. J., Heizler, M. T. & Hassanzadeh, J. (2017). Large-magnitude continental extension in the northeastern Iranian plateau: insight from K-feldspar 40Ar/39Ar thermochronology from the Shotor Kuh-Biarjmand metamorphic core complex. Geosphere13, 1207–1233 previously documented the geochronological-based metamorphic core complex model of the area. Regrettably, despite its direct relevance, these earlier works have not been acknowledged in Azizi et al.'s paper. In this comment, I outline the problems with the structural and regional geology, the zircon U–Pb age of the dike samples, the age of the dike swarm, and the geodynamic interpretations in Azizi et al.'s work.

Artificial age-independent seismic anisotropy, slab thickening and shallowing due to limited resolving power of (an)isotropic tomography

SUMMARY Seismic anisotropy is key to constrain mantle flow, but it is challenging to image and interpret it. Existing large-scale tomography models of seismic anisotropy typically show large discrepancies, which can lead to completely distinct geodynamical interpretations. To better quantify the robustness of anisotropy tomography, we create a 2-D ridge-to-slab geodynamic model and compute the associated fabrics. Using the resulting 21 elastic constants, we compute seismic full waveforms, which are inverted for isotropic and radially anisotropic structure. We test the effects of different data coverage and levels of regularization on the resulting images and on their geodynamical interpretation. Within the context of our specific imposed conditions and source–receiver configuration, the retrieved isotropic images exhibit substantial artificial slab thickening and loss of the slab’s high-velocity signature below ∼100 km depth. Our results also show that the first-order features of radial anisotropy are well retrieved despite strong azimuthal anisotropy (up to 2.7 per cent) in the input model. On the other hand, regularization and data coverage strongly control the detailed characteristics of the retrieved anisotropy, notably the depth–age dependency of anisotropy, leading to an artificial flat depth–age trend shown in existing anisotropy tomography models. Greater data coverage and additional complementary data types are needed to improve the resolution of (an)isotropic tomography models.

Determination of horizontal deformation of the Earth`s crust on the territory of Ukraine based on GNSS measurements

The purpose of research is to identify horizontal deformation of the Ukraine territory, using only proven and suitable for geodynamic interpretation GNSS stations. The initial data are observations from 30 GNSS stations for 2017 to 2020. Methodology. The methodology includes the analysis of modern Earth's crust deformations of Ukraine. As a result, for the first time the impact of the coordinates time series created by two different methods: Precise Point Positioning (PPP) and the classical differential method, on determining deformation processes was analysed. It was established that nowadays for the tasks of monitoring, including geodynamic, it is necessary to use the Precise Point Positioning (PPP) method, because the accuracy of determined velocities of the GNSS stations by this method was higher than in the classical differential method. Results. A map of horizontal Earth's crust deformations on the territory of Ukraine was created according to the coordinates time series of GNSS stations. The extension areas of Shepetivka-Starokostiantyniv Khmelnytsky region, Boryspil- Pryluky-Pereyaslav-Khmelnitsky Kyiv and Chernihiv region, as well as a compression area of the Earth's crust in Nizhyn - Stepovi Khutory - Kozelets of Chernihiv region was identified. Additionally, a map of horizontal displacements of the GNSS-stations was created, where the diverse of these displacements was observed, which is likely to be caused by the presence of modern subvertical and sub-horizontal faults and fault areas. For better interpretation of the obtained results, it is necessary to involve geological and geophysical data of tectonic activity of the Ukraine territory.

NEW DATA ON THE GEOLOGICAL STRUCTURE AND PRECAMBRIAN EVOLUTION OF THE DENMAN GLACIER WEST SIDE MOUNTAIN FRAME (EAST ANTARCTICA): FIRST PALEOARCHEAN AGE FOR PLAGIOGNEISES

Mountain frame of the Denman Glacier is a little explored and at the same time an most essential region of East Antarctica in the context of studying the Precambrian geological history and geodynamic evolution of the Archean protocratons of East Antarctica. Present paper provides original U–Pb isotope geochronology data from zircons of metamorphic and intrusive rocks sampled from the Denman Glacier western flank outcrops. Geodynamic interpretation of geochronology data are also presented. For the first time, for such East Antarctic location, crystallization time (3355 ± 5.4 Ma) for plagiogneisses magmatic protolith was obtained. The Davis Paleoarchean protocraton in the Archean time interval of evolution was subject to multistage polymetamorphism in the intervals ~3100–3000, 2900–2800 Ma ago. The late stage is associated with crustal extension, which is marked by syntectonic intrusion of ultramafic dikes and pyroxenite sills (2827 ± 6 Ma). The formation time of granite veins and subalkaline granitoid pluthons corresponds to the time of tectono-thermal activisation in the interval of 550–510 Ma traced also along significant part of East Antarctic (the Pan-African tectono-thermal event). The Davis terrane shows a significant similarity in the time of formation and evolution of geodynamic processes with the Paleo-Mesoarchean protocratons of East Antarctica, as well as India and Australia.

Spreading in the Northern Part of the Eurasian Lithospheric Plate from GPS Measurements and Its Possible Geodynamic Interpretation

Spreading in the Northern Part of the Eurasian Lithospheric Plate from GPS Measurements and Its Possible Geodynamic Interpretation

Lithospheric structural dynamics and geothermal modeling of the Western Arabian Shield

Understanding the dynamics of suturing and cratonisation and their implications are vital in estimating the link between the lithospheric mantle architecture and geothermal resources. We propose new interpretations of the Western Arabian Shield’s geodynamic styles and geothermal anomalies. In this work, features of the crust and mantle were interpreted from geophysical modeling to unravel the structural dynamics between the Arabian Shield and the Red Sea rift, as well as the influence of these mechanisms on the uplift of the Cenozoic basalts. Estimates of the lower crust thermal properties were also achieved. Spectral properties of the potential field were used to define the Curie isotherm, heat fluxes, geothermal gradients, radiogenic heat production, Moho configuration, and lithosphere-asthenosphere boundary. Results show new structural styles, micro-sutures, and significant thermal anomalies. The defined geothermal patterns were inferred to be due to localized initiation of tectonic and asthenospheric disequilibrium during the rifting episodes within the Red Sea. Also, magma mixing is initiated by the northward migration of magma from the Afar plume towards the Western Arabian Shield which drives local mantle melts beneath the western Arabia, thereby providing the pressure field required for magma ascent. The ascendant magma flow provides the heating source of geothermal reservoirs within the Western Arabian Shield. However, there are indications that during the episodes of rifting within the Red Sea and/or ancient Pan-African activities, the mixing process may have been altered resulting in crustal thinning and creating pathways of ascendant magma flow along the MMN volcanic line. Integrating geophysical and geothermal models indicated new zones of suturing and extensional tectonics between the amalgamated terranes. The geodynamic interpretation shows a new redistribution of terranes and continuous compressional and transtentional movements within the Arabian Shield.

Spreading in the Northern Part of the Eurasian Lithospheric Plate from GPS Measurements and Its Possible Geodynamic Interpretation

Over the whole area of the Eurasian lithospheric plate considered in the paper —rom the Atlantic to the Pacific Ocean—the velocity vectors of the horizontal eastward displacements of GPS sites form a gentle, smooth, huge arc, convex towards the north. Three relatively narrow bow-shaped bands can be distinguished within the arc. The southernmost band, most provided with measurement data (bow-shaped band A in this paper) is discussed in detail in (Shevchenko et al., 2021). The direct, real results of the published geodetic measurements have shown that the length of this band increases by 5 to 10 mm annually. The arc is lengthening. In the cited paper, we considered and rejected five interpretations of this lengthening, which are based on the idea of external action of the above bow-shaped band on the rocks of the Earth’s crust/lithosphere. The most probable cause of the elongation seems to be the internal process of the increase in the volume of these rocks within the band due to the supply of the additional mineral material into these rocks by the deep fluids and its subsequent crystallization. In this paper, we present the results of similar geodetic measurements in other two bow-shaped bands, B and C. It turns out that bow-shaped band C located to the north of the other bands, is lengthening (and at a similar rate) as band A located to the south of the other bands. At the same time, bow-shaped band B, which has an intermediate position between bands A and C, is moving eastward without lengthening. Geodetic measurements in the axial part of the Mid-Atlantic Ridge in the Iceland island suggest that the general expansion of the Atlantic Ocean and the corresponding eastward motion of the Eurasian lithospheric plate are related to the injection of plastic magmatic wedges (of basic composition) in the axial, rift zone of the ridge. Against the background of this general eastward motiont of the lithospheric plate, its constituent parts (the bow-shaped bands A and C are markers of these parts) are moving in the same eastward direction with a velocity increasing from west to east. We attribute this increase in the velocity and the corresponding lengthening of the two bands to the above inflow of the additional mineral material and its subsequent crystallization.

ГЕОДИНАМІКА

The work analyzes the current horizontal and vertical displacement territory of Western Ukraine according to GNSS data, including the creation of special maps of modern displacements and the allocation of deformation zones of the upper crust. The object of study is the horizontal and vertical deformations of the upper crust. The aim is to identify and analyze deformation zones in Western Ukraine. The initial data are horizontal and vertical velocities of 48 continuous GNSS stations from 2018 to 2021 of Geoterrace network, known tectonic maps of the territory and descriptive materials. The methods include comparison and analysis of modern Earth crust deformations of the region with its known tectonic structure. As a result, for the first time it was possible to create the maps of horizontal velocities of continuous GNSS stations and deformations as well as vertical velocities of GNSS stations of the upper crust of Western Ukraine as a whole region. It is established that the deformations of the territory of Western Ukraine are complex and only partially correlate with the known tectonic structure in the region. Most continuous GNSS stations subside in vertical components, possible due to denudation processes. The Galicia–Volyn depression, however, practically does not subside. On the slopes of the Ukrainian Shield there is a noticeable correlation of vertical displacements and the depth of the surface of crystalline rocks. Zones of compression are identified in Zakarpattia, which corresponds to the Zakarpathian (Transcarpathian) deep fault, and in the north-west of the region. It is necessary to mark the zone around the city of Khmelnytskyi, where abnormal vertical and horizontal displacements are observed. Geodynamic interpretation of anomalous deformation zones is given. Determined velocities of continuous GNSS stations with the increasing observation time interval will make it possible to establish the features of the spatial distribution of Western Ukraine crustal movement as well as create an appropriate regional geodynamic model in the future.

Late Cenozoic Evolution and Present Tectonic Setting of the Aegean–Hellenic Arc

The Aegean–Hellenic arc is a deformed sector of a long heterogeneous orogenic system (Tethyan belt), constituted by an inner old metamorphic crystalline core flanked by younger chains of European and African affinity, running from the Anatolian to the Pelagonian zones. Due to the convergence between the Arabian promontory and the Eurasian continental domain, the Anatolian sector of that belt has undergone a westward extrusion, accommodated by oroclinal bending, at the expense of the surrounding low buoyancy domains. Since the late Miocene, when the Aegean Tethyan belt collided with the Adriatic continental promontory, the southward bowing of the Aegean–Hellenic sector accelerated, leading to the consumption of the Levantine and Ionian oceanic domains and to the formation of the Mediterranean Ridge accretionary complex. The peculiar distribution of extensional and compressional deformation in the Aegean zone has mainly been influenced by the different rheological behaviours of the mainly ductile inner core (Cyclades arc) and of the mainly brittle outer belt (Hellenic arc). The bowing of the inner belt developed without involving any major fragmentation, whereas the outer brittle belt underwent a major break in its most curved sector, which led to the separation of the eastern (Crete–Rhodes) and western (Peloponnesus) Hellenic sectors. After separation, these structures underwent different shortening patterns, respectively driven by the convergence between southwestern Anatolia and the Libyan continental promontory (Crete–Rhodes) and by the convergence between the Cycladic Arc and the Adriatic continental domain (Peloponnesus). A discussion is given about the compatibility of the observed deformation pattern with the main alternative geodynamic interpretations and with the Nubia–Eurasia relative motions so far proposed.

Geodynamic interpretation of modern geodynamic Movements in the southern part of the Yenisei Ridge (in application to the problems of underground isolation of radioactive waste)

The results of geodynamic interpretation of the results of GNSS observations of presentday movements and modeling of the stress-strain state of the upper part of the Earth’s crust in the area of the construction of an underground research laboratory to substantiate the safety of disposal of high-level long-lived radioactive waste in granite-gneiss rocks of the Nizhne-Kansk massif are presented. The kinematic model of the area made it possible to assess the directions of block movements of large structural blocks. The greatest movement gradients were noted in the west, between the underground research laboratory site and the contact between the Siberian Platform and the West Siberian Plate along the Atamanovsky Fault. Local zones of stress concentration have been identified, in which destruction of the rock mass in the near-contour zone of underground workings is most likely. Analysis of models and results of GNSS observations showed that the structural-tectonic block, in which the construction of the underground research laboratory is planned, is in relatively calm geodynamic conditions. Present-day movements determine the regime of sublatitudinal compression in azimuth close to 100–1100 at the underground research laboratory construction site. A systematic analysis of geological and geophysical data made it possible to obtain new knowledge about the kinematics and stress-strain state of the rock mass in the southern part of the Yenisei Ridge, necessary to ensure the geoecological safety of isolation of high-level radioactive waste in the granite-gneiss rocks of the Nizhne-Kansk massif. This work was funded by the Russian Science Foundation (project No. 18-17-00241).

ГЕОДЕЗІЯ, КАРТОГРАФІЯ І АЕРОФОТОЗНІМАННЯ

The aim of the research is to diagnose the metrological characteristics of high-precision GNSS-observations by methods of non-classical error theory of measurements (NETM) based on Ukrainian reference stations. Methodology. We selected 72 GNSS reference stations, downloaded daily observation files from the LPI analysis center server, and created time series in the topocentric coordinate system. The duration of the time series is almost two years (March 24, 2019 - January 2, 2021). Using a specialized software package, the time series have been cleaned of offsets and breaks, seasonal effects, and the trend component has been removed. Verification of empirical distributions of errors was provided by the procedure of NETM on the recommendations offered by G. Jeffries and on the principles of hypothesis tests the theory according to Pearson's criterion. The main result of the research. It is established that the obtained time series of coordinates of reference GNSS stations do not confirm the hypothesis of their conformity to the normal Gaussian distribution law. NETM diagnostics of the accuracy of high-precision GNSS measurements, which is based on the use of confidence intervals for assessing the asymmetry and kurtosis of a significant sample, followed by the Pearson test, confirms the presence of weak, not removed from GNSS-processing, sources of systematic errors. Scientific novelty. The authors use the possibility of NETM to improve the processing of high-precision GNSS measurements and the need to take into account the sources of systematic errors. Failure to take into account certain factors creates the effect of shifting the time coordinate series, which, in turn, leads to subjective estimates of station velocity, i.e. their geodynamic interpretation. Practical significance. Research of the reasons for deviations of errors distribution from the established norms provides metrological literacy of carrying out high-precision GNSS measurements of large samples.

Temporal and Spatial Variations of Enriched Source Components in Linzizong Volcanic Succession, Tibet, and Implications for the India–Asia Collision

Abstract The temporal and spatial distribution of enriched source components at sites of continent–continent collision provides critical insights into mantle dynamic processes associated with subduction- and collision-related events. However, determining the origin of such enriched components remains a significant challenge. We report a comprehensive dataset of the Linzizong volcanic succession (LVS) from four locations with varying distance across-strike to the Indus–Yarlung suture in southern Tibet, which marks the exposed surface expression of the India–Asia collision zone. The LVS rocks in this study can be divided into two groups: a calc-alkaline Group 1 (69–55 Ma), mainly including basaltic–andesitic varieties, and a shoshonitic Group 2 (52–50 Ma), consisting predominantly of silicic rocks with minor mafic compositions. Group 1 samples are likely derived from the fractional crystallization of primitive basaltic melts as a result of the partial melting of a metasomatized mantle wedge. These samples are decoupled in Nd–Hf isotopic compositions, suggesting an incorporation of subducting sediment-derived melts into the mantle wedge. The influence of sediment-derived melt on the mantle source increases away from the suture zone toward Asia (i.e., from the south to the north) as indicated by the more enriched Sr, Nd, Pb, and Hf isotopic compositions, as well as elevated Th/La and La/Sm ratios. The heavy δ26Mg values, and high Ba/Th and Sr/Th ratios of samples close to the suture coincide with the dehydration of the subducting Neo-Tethyan slab. Group 2 mafic samples have depleted and coupled εNd–εHf isotopic compositions and are characterized by elevated (La/Yb)N and Dy/Yb ratios as well as low Zr/Nb ratios, indicating an origin of enriched garnet-bearing lithospheric mantle with contributions from asthenosphere-derived materials. Group 2 silicic samples are isotopically enriched both near and far away from the suture, which can be attributed to the involvement of ancient lower crust-derived melt from Tethyan Himalaya and central Lhasa subterrane basement, respectively. Our results show that the LVS are the magmatic response to late subduction (Group 1), and to initial India–Asia collision and slab breakoff (Group 2). Negative trends in the whole-rock Nd and zircon Hf isotopic compositions at ~51 Ma should be treated with caution for geodynamic interpretations, depending on the distance between the samples and the India–Asia suture.

GPS Kinematics of the Northern Part of the Eurasian Continent and Its Possible Geodynamic Interpretation

GPS Kinematics of the Northern Part of the Eurasian Continent and Its Possible Geodynamic Interpretation

Mantle temperature and density anomalies: The influence of thermodynamic formulation, melt, and anelasticity

Deriving a quantitative geodynamical interpretation from tomography models is a difficult task. It is also a timely task, particularly given the many high-resolution tomography models published in recent years. It is important to assess mantle structure in terms of density and temperature anomalies. Here, we provide a new estimation of the conversion factors between seismic velocity anomalies and density anomalies, Rρ/v, and between seismic velocity anomalies and temperature anomalies, RT/v. These conversion factors are found by considering the constraints provided by thermodynamics, the influence of melt, and anelasticity. To determine the elastic component, we performed thermodynamic simulations by considering several compositions representative of normal or plume-enriched mantle. We also explore the effects of the presence of melt on seismic velocity and consider a radial attenuation profile to account for anelasticity. We provide an envelope of acceptable models, by combining the range of possible solutions combining the elastic, anelastic, and melt relationships used in deriving the conversion factors. Several of the frequently used velocity-density scaling relationships are encompassed in this envelope. We assess the validity of our result by calculating temperature anomalies from the tomographic models using our scaling relationships—these anomalies lie within the range constrained by melting temperatures registered in volcanic rocks (±300 K). Further, we show that the geoid model computed through our velocity-density scaling from the S40RTS tomography provides a good fit to the observed geoid.

Deep subduction, melting, and fast cooling of metapelites from the Cima Lunga Unit, Central Alps

AbstractThe Cima Lunga unit in the Central Alps is dominated by quartzofeldspathic gneisses with subordinate mafic, ultramafic, and metacarbonate rocks. Only mafic and ultramafic lithologies were thought to preserve clear evidence of Alpine high‐P metamorphism. This led to the questions of whether the different rock types were subducted and exhumed as a coherent unit or underwent different pressure–temperature (P–T) histories. New petrological and geochemical data from a metapelite associated with garnet peridotite from Cima di Gagnone (Cima Lunga unit, Switzerland) were obtained using major and trace element mapping. Complex zoning patterns in garnet and white mica are observed. In particular, high Ti content in phengite and increasing P, Zr, and HREE contents in pyrope‐rich garnet indicate that this metapelite underwent high‐P and high‐T (HP–HT) metamorphism involving fluid‐fluxed partial melting. A P–T path is reconstructed by combining textural analysis with petrological–geochemical data and thermodynamic simulations. We show that the mineral record preserves an evolution from prograde to HP–HT peak conditions (2.7 ± 0.1 GPa and 800℃) followed by near‐isobaric cooling (~2.5 GPa and 700–750℃) prior to decompression (1.0 GPa and ~620℃). The reconstructed P–T path suggests that the studied metapelites were subducted to depths where the slab gets heated by proximity to asthenospheric mantle related to slab break‐off. This heating resulted in the dehydration of chlorite‐ to garnet peridotite and the liberated fluids triggered partial melting in the associated metapelites, which might have favoured the fast exhumation of the entire Cima Lunga unit. Metapelites and garnet peridotite from Cima di Gagnone underwent a common prograde to peak and retrograde P–T path without significant tectonic pressure difference between the different lithologies, and deviation from lithostatic pressure is excluded. Lastly, the peak metamorphic conditions of metapelite from Cima di Gagnone are comparable with P–T estimates of ultramafic lithologies from the southern Adula nappe and the Dascio Bellinzona zone, thus opening new scenarios for the geodynamic interpretation of the Central Alps.

COMPARATIVE ANALYSIS OF GEODYNAMIC PARAMETERS OBTAINED FROM ASTRONOMIC AND GPS OBSERVATIONS IN POLTAVA

The functioning of the GPS station and regular astrometric observations with a prismatic astrolabe in Poltava provides series of local displacements of the earth's crust and plumb line in time, characterizing the changes in the gravitational field. The analysis of the N-component of the earth's crust movement and the displacement of the meridional projection of the plumb line was carried out on the basis of GPS data and from observations on the astrolabe, respectively, for the period 2002-2020. Comparison of the trends of these series showed that their shifts occur in opposite directions. It is noted that the movement of the point occurs in the northern direction at a speed of +0.3mm/yr, and the displacement of the plumb line - to the south, at a speed of -2.6mas/year. Similarly, an abrupt displacement of the N-component to the north by + 2mm at the turn of 2014 was accompanied by a displacement of the plumb line to the south by approximately -50 mas. These facts can be explained within the framework of the hypothesis of the existence of a deep structure in the vicinity of Poltava, in which a significant change in mass occurs. The spectra of both series show the presence of cyclicities with close periods: about 3.2, 2.8, 1.0, 0.5, and 0.3 yr. It is known that harmonics with those periods are present in many astrometric series. The geodynamic interpretation of the presented facts requires additional confirmation in observations of neighboring GPS stations, as well as a theoretical explanation and justification.

Determination of the correlation degree between GNSS stations of Ukraine based on time series

Using GNSS for many years is the most common technology for the collection, processing, and interpretation of Earth observation data, in particular for the high-precision study of plate tectonics. The results of GNSS observations, such as coordinate time series, allow us to do continuous monitoring of stations, and modern methods of satellite observation processing provide high-precision results for geodynamic interpretation. The aim of our study is to process the results of observations by DD and PPP methods and determine the degree of correlation between GNSS stations based on coordinate time series. For our study, we selected 10 GNSS stations, which merged into two networks - Lviv (SAMB, STOY, STRY, SULP та ZLRS) and Ukrainian (BCRV, CHTK, CNIV, CRNI, GLSV та SULP). The duration of observations on each of them is about 1.5 years (2019-2020). The downloaded observation files were processed in two software packages: Gamit and GipsyX. After applying the «cleaned» procedures based on the iGPS software package, the residual time series were obtained and the coefficients of the interstation correlation matrices were calculated. After the procedure of "cleaning" the time series, we obtained the RMS value decrease for all components of the coordinates by an average of 7-30%, and some stations by 55%. Based on the obtained RMS values, we can conclude that the influence of unextracted or incorrectly modeled errors can significantly affect the results of satellite observations. The obtained interstation correlation coefficients for both networks show different results depending on the used method for processing satellite observations. The larger correlation values of the DD method can be explained by the fact that the effect of errors is distributed evenly to all network stations, whereas in the PPP method errors for each station are individual. The obtained graphs of the common-mode errors values, after their removal from the residual time series, confirm the more uniform nature of the DD method. The results of our study indicate the feasibility of using the PPP method, as the autonomous processing of stations allows you to see the real geodynamic picture of the studied region.

Geodynamic interpretation of the Late Cretaceous syn-depositional magmatism in central Serbia: Inferences from biostratigraphic and petrographical investigations

Geodynamic interpretation of the Late Cretaceous syn-depositional magmatism in central Serbia: Inferences from biostratigraphic and petrographical investigations