Crustal Layer Research Articles

Fluid upwelling across the Hikurangi subduction thrust during deep slow-slip earthquakes

AbstractSlow-slip events at global subduction zones relieve tectonic stress over days to years. Through slow-slip cycles, high fluid pressures observed at the top of subducting plates are thought to fluctuate, potentially due to the valving action of an impermeable layer near the plate interface. We model teleseismic scattering data at the Manawatu deep slow-slip patch at the Hikurangi margin in New Zealand and find high seismic P-to-S wave velocity ratios, VP/VS, in the upper ~5 km of the subducting Pacific Plate, reflecting sustained elevated fluid pressures that decrease during slow-slip and increase during inter-slow-slip periods. Within a ~ 3 km thick lower crustal layer of the overriding Australian Plate, decreasing VP/VS during inter-slow-slip periods reflects permeability reduction due to mineral precipitation. Increasing VP/VS during slow-slip reflects increasing permeability and crack density, facilitating upward fluid transfer through this layer. Our results suggest it acts as a valve to relieve high fluid pressures in the subducting slab.

Multiple Upward Residual Gravity and Magnetic Maps to Estimate the Deep Crustal Layers and Moho Discontinuity in Eastern Iraq

The upward continuation technique was applied to the gravity and magnetic data to obtain the residual anomalies maps in eastern Iraq. A new processing method is introduced to calculate the crustal layers depending on the relation between the total range of the residual anomalies of gravity, magnetic data and the upward continuation, with multi-elevations. The significant relationship shows slope variations, which may reflect the maximum contrast in the physical properties (density and/or susceptibility) and the intersection point representing the depth of layer contacts. This method was applied to the eastern central part of Iraq, adjacent to the Iranian borders. It is found that the average depth range to the Jurassic formations, top basement rocks, transition layer (Curie point), and Moho discontinuity are 3.1- 4.8 km, 8-12.9 km, 20.9-22.4 km and 43.6 km, respectively. The Sedimentary cover in the study area ranges from 8 to 13 km. The maximum depth to the Moho discontinuity obtained by gravity data in the study area is 43.6 km. The radially average power spectrum technique was applied in the study area to calculate the gravity depth and magnetic sources' depth. Three depth levels of sources from gravity and magnetic data were obtained. These depths are shallow sources, average basement rock and deep sources (Moho) at 3km, 13.2-12.1 km, and 32.2-34km, respectively. The obtained results concerning the main layers in the crust were compared between the two methods, and the new method shows more reliable results. The detected depth levels refer to top Jurassic, basement rocks, and Moho discontinuity. The new method is believed to be used to detect the crustal layers depth with good results.

Crustal melting and continent uplift by mafic underplating at convergent boundaries.

The thick crust of the southern Tibetan and central Andean plateaus includes high-conductivity, low-velocity zones ascribed to partial melt. The melt origin and effect on plateau uplift remain speculative, in particular if plateau uplift happens before continental collision. The East Anatolian Plateau (EAP) has experienced similar, more recent uplift but its structure is largely unknown. Here we present an 80 km deep geophysical model across EAP, constrained by seismic receiver functions integrated with interpretation of gravity data and seismic tomographic, magnetotelluric, geothermal, and geochemical models. The results indicate a 20 km thick lower crustal layer and a 10 km thick mid-crustal layer, which both contain pockets of partial melt. We explain plateau uplift by isostatic equilibration following magmatism associated with roll-back and break-off of the Neo-Tethys slab. Our results suggest that crustal thickening by felsic melt and mafic underplate are important for plateau uplift in the EAP, Andes and Tibet.

Insight into intracontinental deformation and crustal reworking of ancient continents implied by crustal structure imaging of the Yangtze Craton

The crustal imprints from multistage tectonic activities in cratons offer valuable insights into continental evolution. Utilizing seismic data from two densely deployed, nearly perpendicular linear arrays, and a newly developed stepwise joint inversion of depth-domain receiver function and surface wave dispersion, we constructed a detailed crustal layering model for the Yangtze Craton. Our analysis revealed elongated double velocity reversal zones as salient features of the crust, which likely record ancient crustal reworking and juvenile crustal growth associated with Neoproterozoic rift-related magmatic processes. The interlayering of low- and high-velocity structures may contribute to the enduring stability of the Yangtze Craton. Additionally, superimposed layers separated by east-dipping interfaces and abrupt changes in crustal thickness in the boundary belts surrounding the Yangtze Craton document the crust's structural responses to intracontinental deformation during continent assembly.

GEOGRAPHICAL CROSS AND BIOSPHERE: RELATIONSHIPS, SIMILARITIES AND DIFFERENCES

This article explores the doctrine of the geographic crust and the biosphere, their relationship, similarities and differences, as well as A.A. Grigoriev's theory, landscape crust and epigeosphere, geographic crust and geographic environment, landscape crust, recommendation by I.B. Zabelin replace the concept of the geographic crust with the concept of the biogenosphere, since the origin and development of life took place in the geographic crust, the upper and lower layers of the earth's crust. upper part of the geographic crust Among scientists here are different opinions about the lower limits of the earth's crust, the presence of substances in three states in the geographic crust, that the Biosphere is the outer crust of the Earth, about the composition, structure and boundaries of the biosphere, and the cycle of substances in nature.

GEOGRAPHICAL CROSS AND BIOSPHERE: RELATIONSHIPS, SIMILARITIES AND DIFFERENCES

This article explores the doctrine of the geographic crust and the biosphere, their relationship, similarities and differences, as well as A.A. Grigoriev's theory, landscape crust and epigeosphere, geographic crust and geographic environment, landscape crust, recommendation by I.B. Zabelin replace the concept of the geographic crust with the concept of the biogenosphere, since the origin and development of life took place in the geographic crust, the upper and lower layers of the earth's crust. upper part of the geographic crust Among scientists here are different opinions about the lower limits of the earth's crust, the presence of substances in three states in the geographic crust, that the Biosphere is the outer crust of the Earth, about the composition, structure and boundaries of the biosphere, and the cycle of substances in nature.

Rapid Impact Crater Relaxation Caused by an Insulating Methane Clathrate Crust on Titan

Titan’s impact craters are hundreds of meters shallower than expected, compared to similar-sized craters on Ganymede. Only 90 crater candidates have been identified, the majority of which have low certainty of an impact origin. Many processes have been suggested to shallow, modify, and remove Titan’s craters, including fluvial erosion by liquid from rainfall, aeolian sand infill, and topographic relaxation induced by insulating sand infill. Here we propose an additional mechanism: topographic relaxation due to an insulating methane clathrate crustal layer in Titan’s upper ice shell. We use finite element modeling to test whether a clathrate crust 5, 10, 15, or 20 km thick could warm the ice shell and relax craters to their currently observed depths or remove them completely. We model the viscoelastic evolution of crater diameters 120, 100, 85, and 40 km, with two initial depths based on depth−diameter trends of Ganymede’s craters. We find that all clathrate crustal thicknesses result in rapid topographic relaxation, despite Titan’s cold surface temperature. The 5 km thick clathrate crust can reproduce nearly all of the observed shallow depths, many in under 1000 yr. A 10 km thick crust can reproduce the observed depths of the larger craters over geologic timescales. If relaxation is the primary cause of the shallow craters, then the clathrate thickness is likely 5–10 km thick. Topographic relaxation alone cannot remove craters; crater rims and flexural moats remain. To completely remove craters and reproduce the observed biased crater distribution, multiple modification processes must act together.

Effects of phosphatization on the mineralogical and geochemical composition of marine ferromanganese crusts from the JiaXie Guyot in the Western Pacific: Constraints from high resolution analysis

The marine crusts comprise ferromanganese sediments formed through the precipitation of dissolved elements in seawater. These crusts serve as a record elements signal from paleo-ocean and are extensively utilized in paleo-oceanography. Previous researches have examined the chemical composition of the phosphatized crust layers using powder chemistry and leaching experiments. However, there exist divergent viewpoints regarding the influence of phosphatization on element behavior. In this study, we employed a combination of analytical techniques including scanning electron microscope (SEM), powder X-ray diffractometer (XRD), TESCAN Integrated Mineral Analyzer (TIMA), laser ablation and inductively coupled plasma time of flight mass spectrometry combined system (LA-ICP-TOF), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These methods were utilized to achieve mineral phase quantification, precise depiction of element distribution, and in-situ profile analysis of elements within the phosphatized crust layers from the JiaXie Guyot in the Western Pacific. The mineral phase analysis shows enormous carbonate fluorapatite (CFA) precipitate, which replace calcite in the old phosphatized layer. Additionally, vernadite experiences partial dissolution. Furthermore, a small amount of hematite, goethite, todorokite, zeolite, barite, as well as trace amounts chalcopyrite, sphalerite, galena, ilmenite, and pyrite are formed. The element distributions suggest potential outward migration of Fe, V, Zr, Zn and Cu, while Ce and Pb are locally enriched. In the phosphatized crust, some elements exhibit depletion in the old crust layer compared to the young crust layer, with Fe > Si > V>Zn > Ti ≥ Pb, while others are enriched in the order crust layer, such as Y>Pd > Ce > Pt. The study proposes that FeOOH·nH2O and associated adsorbed elements like Si, Ce, Y, V, Zn, Ti and Pb dissolve in vernadite and migrate outward during phosphatization, with weak phosphatization influence on Mn oxide. In addition, the phosphate-rich seawater might contribute additional elements such as Y, Ce and Pd to the crust layers. Thus, this study highlights the elemental distributions, migration patterns observed, and significance of presence for critical metals between old and young crust layers from the influence of phosphatization based on high resolution analysis. Particularly, it acknowledges the contribution of phosphate-rich seawater to the elemental composition of crust layers.

Enhancing biocementation performance in low permeability clayey soil through sand column strategy

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeability-clayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.

Pre-shortening reconstruction of the adria microplate: Balanced and restored cross-sections through the Southern Apennines–Dinarides (Central Mediterranean Sea)

The Adria plate and/or microplate has accommodated the differential eastward motion of Africa, Europe-Iberia, since the Jurassic times, and the subsequent convergence between Africa and Eurasia from Middle Cretaceous onwards. Its complex tectonic deformation, responsible of the development of the opposing Apennines and Dinarides thin- and thick-skinned fold and thrust belts, remains poorly constrained, fueling an ongoing debate on the original position of Adria, its pre-compressional continental width, and crustal structure. Here we tackle these uncertainties by analyzing and integrating published structural cross-sections, subsurface data and 2D lithospheric numerical models to build a 758 km long regional balanced and restored cross-sections along a SW-NE transect through the Southern Apennines and Southern Dinarides. Employing the line length method for the sedimentary cover and assuming the preservation of the pre-Triassic continental crustal area, we reconstruct the pre-compressional continental width of Adria. The unfolding of the sedimentary cover along the SW-NE cross-section results in an undeformed continental Adria microplate width of approximately 1050 km, slightly under previous estimations (1175 to 1670 km). The minimum total shortening results in 291 km: 148 km across the Southern Apennines and 143 km across the Southern Dinarides. We then calculate the Adria microplate continental crustal thickness during Middle-Late Jurassic time assuming local isostatic balance, obtaining 23 km for the eastern and central Adria sectors, based on shallow water carbonate sequences. In contrast, the western Adria sector at the Southern Apennines results in a restored pre-Triassic continental crustal thickness of only 7 km, suggesting that the middle and lower crustal layers in this sector may have been partially removed, possibly by mantle delamination during Neogene to Quaternary collisional processes. The results strongly support that the Adria microplate was located to the east of the Pelagian Basin and formed part of the African Plate around the Permian–Triassic boundary interval.

Deep structure of the Wulong goldfield, Liaodong Peninsula, China, revealed by receiver functions: implications for the tectonic and mineralization dynamics

During the Mesozoic, the North China Craton experienced intense tectonic movements that resulted in the formation of numerous gold deposits on the Liaodong and Jiaodong Peninsulas in northeastern China. To investigate the relationship between deep crustal structure and gold mineralization in the Liaodong Peninsula, we deployed 334 dense seismic stations in the Wulong goldfield (WLGF) with the idea of analysing numerous receiver functions at different array stations. The purpose focused on knowing the potential for gold mineralization in the area. The study revealed the following: (1) The WLGF is characterized by a crustal thickness of approximately 32 km and an average Vp/Vs ratio of 1.76. The high value of the Vp/Vs ratio near the Wulong gold deposit suggests that mantle materials have penetrated into the crust and contributed to the mineralization process. (2) A low-velocity layer located at a depth of 10–18 km below the WLGF seems to support the existence of a potentially brittle-ductile transition zone. Also, hydrothermal magma upwelling channels are observed in the upper crust beneath the Wulong gold deposit. (3) The presence of a discontinuous low-velocity layer in the middle crust beneath the Liaodong Peninsula suggests promising prospects for gold ore exploration. The receiver functions method based on a dense seismic array employed in this study can offer valuable references and guidance for the fine exploration and research of ore deposits in other regions globally.

A fresh look at the Gulf of St. Lawrence, Eastern Canada: Geophysical imaging of salt bodies and volcanic rocks in the upper Paleozoic Magdalen Basin

In the Gulf of St. Lawrence, the late Middle Devonian to early Permian Magdalen Basin hosts numerous salt bodies, but their number and geometry remained poorly constrained due to the poor quality of industry-seismic data. Salt originates from the Middle Mississippian (Visean) Windsor Group, which includes marine carbonates and evaporites. In this study, we use multibeam bathymetry as well as unpublished aerogravity and aeromagnetic data to better characterize the geometry of salt bodies. These datasets show a high degree of coherency and illustrate deformation on the seafloor, gravity lows and magnetic highs, all associated with salt bodies and overlying volcanic rocks. In map view, the geometry of individual salt bodies varies from nearly circular to ovoid and strongly elongated. Some salt bodies coalesce in complex-shaped salt walls elongated NNE, parallel to some of the faults that controlled the early stages of the Magdalen Basin development. Forward modeling indicates that low density salt bodies overlain by a 100–300 m thick volcanic pile may account for both gravity and magnetic signals. The ubiquity of mafic volcanic rocks indicates that the late Visean to Serpukhovian volcanic episode is more voluminous than previously thought. This episode is possibly associated with a series of dykes continuous for up to 225 km and with a period of underplating now recorded by a lower crustal layer with high seismic velocity.

К оценке геодинамической устойчивости геосфер Земли

The Earth, as a system, is characterized by certain average state parameters (density, temperature). These parameters cannot but depend on similar states of internal geospheres (subsystems), which follow the unified law of increasing entropy of the cooling Earth from the center in the direction of the Earth's radius. As a model for assessing the dynamic stability of the Earth's internal geospheres relative to each other, the principle of the golden proportion (golden section) was used with the given parameters of density, temperature, power of the geospheres to the extreme ratios of their states at points (0.618; 1.618; 2.618), which determine the conditions for the stable dynamic equilibrium of the compared parameters of geospheres. And if these relations satisfied the known theoretical, model, geophysical data, then the conclusion was made that the geospheres in the compared parameter relations were in a state close to a stable dynamic equilibrium of the exchange of matter and energy between them. Otherwise, it was recognized that the compared geospheres of the Earth were in a state of either unstable dynamic equilibrium with an assessment of the level of this deviation from the golden numbers, or the known values of the density and temperature of the geospheres, as well as their structure, should be subject to clarification. Average model estimates of the parameters of the Earth's internal geospheres reach a stable dynamic equilibrium at a level of deviation from the golden numbers of up to 2.72 %. This allows estimating the model duration of the modern geological activity of the Earth for another 124 million years until the formation of a new state of the existing continents. The instability of the dynamic equilibrium of density and temperature of matter is established at the boundaries: continental and oceanic crust; oceanic crust and Golitsin layer; at the boundary between the outer part of the Earth's core and the lower mantle; inside the Earth's core at the level of identified transition zones in the four-layer core model. The presence of spheres with a high core density from 16.05 to 26.45 g/cm3 suggests the stratification of its central part into essentially gold and platinoid. The presence of instability boundaries in the dynamic state of geospheres is in good agreement with the concept of plate tectonics and with the depths of plume origin. It can be assumed that the relative equilibrium of the internal structure of the Earth will continue for about 124 million years until the beginning of the formation of a new Pangea Proxima, which, according to Cristofor Scotese, will arise in 200 million years.

A rapid analysis of aftershock processes after a moderate magnitude earthquake with ML methods

SUMMARY Moderate magnitude earthquakes and seismic sequences frequently develop on fault systems, but whether they are linked to future major ruptures is always ambiguous. In this study, we investigated a seismic sequence that has developed within a portion of the stretching region of the Apennines in Italy where moderate to large earthquakes are likely to occur. We captured a total of 2039 aftershocks of the 2023 September 18, Mw 4.9 earthquake occurred during the first week, by using machine-learning (ML) based algorithms. Aftershocks align on two 5–7 km long parallel faults, from a length that exceeds what is expected from the main shock magnitude. The segments are ramping at about 6 km depth on closely spaced N100 striking 70 N dipping planes, at a distance of some kilometres from the main shock hypocentre. Our results indicate that even moderate magnitude events trigger seismicity on a spread set of fault segments around the main shock hypocentre, revealing processes of interaction within the crustal layer. The possibility that larger earthquakes develop during seismicity spread is favoured by pore pressure diffusion, in relation with the closeness to criticality of fault segments. Based on the very rapid activation of seismicity on the entire system and a back-front signal from the hypocentre of the main event, we infer that fluid pressure, initially high within the crustal layer, rapidly dropped after the main shock. Our study reinforces the importance of timely extracting information on fault geometry and seismicity distribution on faults. ML-based methods represent a viable tool for semi-real-time application, yielding constraints on short-time forecasts.

Continuous distribution pattern and the origin of the high‐velocity layer in the Pearl River Mouth Basin in the northern South China Sea: Constraints by gravity modelling

The high‐velocity layer in the lower crust is widely distributed in the northern continental margin of the South China Sea. A detailed anatomy of the high‐velocity layer is crucial for understanding the continental rifting and crustal thinning. Based on three seismic reflection profiles across the Pearl River Mouth Basin (PRMB) and the global free‐air gravity anomaly data in this study, by the gravity modelling we construct the crustal structure along three seismic reflection profiles across the depression and uplift zones. The free‐air gravity anomaly data within the uplift and depression zones indicates the distinct zonation, and the high and low values of free‐air gravity anomalies in the basin show the northeastward trend. Based on the gravity modelling along the three seismic profiles, the crustal thickness is of 12–23 km beneath the basin and thickness of the crust is gradually thinning from the continental shelf to the continental slope. The high‐velocity layer extends eastward to the Dongsha Uplift and terminates westward beneath the Baiyun Sag. The average thickness of the high‐velocity layer is 4–6 km and the maximum thickness is about 8 km at the Dongsha Uplift. The thickness variation of the high‐velocity layer suggests the continuous distribution of mantle underplating and intense magma activity. According to the isolated distribution and the continuous distribution of the high‐velocity layer found by previous studies in the northern South China Sea, we use gravity modelling to test which models of the high‐velocity layer within the PRMB are reasonable. According to testing models and preferred models of the crustal structure by gravity modelling, we propose that the continuous distribution pattern of the high‐velocity layer is the best model to interpret the crustal thinning characteristics and the gravity anomaly responses of the high‐velocity layer in the basin. We propose that the high‐velocity layer in the Pearl River Mouth Basin was formed by the long‐term underplating of the high‐temperature melted mantle.

Full waveform inversion of ocean bottom seismometer data from the oceanic Pacific Plate of the Japan trench

SUMMARY The geometrical and seismic structure of the Pacific oceanic Plate of the Japan Trench is essential for the understanding of earthquake activity in the area. Ocean Bottom Seismometer (OBS) data can be used, via ray-based tomography, to obtain estimates of properties such as crust thickness and structure, hydration and depth to the Moho boundary. The spatial resolution of these properties can be substantially improved by using the full waveform inversion (FWI) method. Most OBS data in this area are acquired with a sparse receiver spacing of 5–6 km, whereas FWI is assumed to work best with denser (1–2 km) receiver spacing. We show that FWI can be adapted to sparsely sampled data with better resolution than traveltime tomography. Using a 500 km long OBS longitudinal profile from the Japan Trench we obtain a detailed velocity structure of the crust, a better definition of the Moho boundary, a well-defined low-velocity layer in the lower crust and a clear spatial definition of areas with velocity inversions.

Crustal structure beneath the Western Dharwar Craton segment of Western Ghats: Insights from ambient noise correlation technique

The Western Ghats (WG) comprise three major tectonic blocks: the Deccan Volcanic Province (DVP), Western Dharwar Craton (WDC) and Southern Granulite Terrain (SGT) from north to south. Among these, the WDC region encompasses the oldest basement rocks, including greenstone belts and calc-alkaline plutons dating back to ∼3.0 to 3.4 Ga. While the crustal structure of the DVP and SGT segments of the WG has been extensively studied, knowledge regarding the crustal structure beneath the WDC segment of the WG is limited due to the scarcity of seismic stations. To address this gap, we utilized continuous waveform data from a newly established network of seismic stations by the National Centre for Earth Science Studies (NCESS), in addition to other available stations and deciphered the shallow crustal shear-wave velocity structure along a profile beneath the WDC segment of the WG using ambient noise cross-correlation and surface wave dispersion. The results reveal a continuous upper layer characterized by a high shear wave velocity of ∼3.6 km/s with notable variation in thickness along the profile. Furthermore, a thick middle layer with velocities reaching up to ∼3.9 km/s and a lower layer with velocities of ≥4.2 km/s are observed. Intriguingly, variations in the thickness of the upper layer, ranging from 5 km to 20 km, are noted beneath the study region. The thickness of this layer exhibits changes in relation to topographical variations, with this dependency diminishing for deeper layers. Notably, high shear wave velocity perturbations (∼10 %) are observed in the upper layer beneath low-elevation regions, possibly indicating the presence of Tonalite–Trondhjemite–Granodiorite (TTG)-type gneiss − a significant rock type in the WDC region, alongside greenstone belts and late calc-alkaline to potassic plutons. These findings suggest that the uneven topography of the WG may result from long-term erosion, exposing deeper and higher-density rocks and leading to higher shear wave velocities at shallow depths. This study serves as a foundation for further exploration into the influence of the upper crustal layer and its correlation with the evolution of the WG.

Глубинное строение Северо-Востока России, закономерности размещения и прогноз рудного золота

The principal gold-bearing zone of the Kolyma-Chukotka fold belt is controlled by the Yana-Kolyma downfold of the earth's crust identified on the basis of gravity prospection data; it involves thick (25 km) terrigenous formations and their underlying migmatites as well as the lower layers of the earth's crust and asthenosphere. The Yana-Kolyma downfold is formed under the influence of the protogenic asthenospheric ultramafic magma chamber. According to the analysis of the most important ore-controlling factor (the thickness of the erosion cut), the structures of the deep Yano-Kolyma downfold are the least eroded, and, consequently, the rich placers of the principal gold bearing zone might have been formed from very rich gold motherlodes. This conclusion determines inferred resources in the principal zone and conforms with the calculated ratio of motherlode reserves exceeding placer reserves. The gold ore ratio of 2.6 is used for the prognostic evaluation of the ore gold mineragenic potential of the Kolyma-Chukotka fold belt, which makes 6 000 t.

On the Crustal Sources of Magnetic Anomalies in the Middle Urals

The 800×500 sq km area of the the Middle Urals, Russia, lying between 56 to 60° northern latitude and 54 to 66° eastern longitude, was studied in terms of the deep crustal structure. The study was based on three-dimensional modeling of the sources of magnetic anomalies in three layers of the Earth’s crust. The studied area covers the folded region of the Urals and adjacent structures of the East European Platform and the West Siberian Plate. The sources modeled in the near-surface layer down to a depth of 5 km make it possible to clarify the position of magnetized massifs, mainly consisting of mafic-ultrabasic rocks, and to trace their connection with mafic-ultrabasic belts in the granite layer and root blocks in the lower basaltic layer of the Earth’s crust. When the sources in the upper crustal layer are compared with those in the lower crustal layer, it is apparent that many belts on the platform have deep-seated roots and are located above the basalt layer protrusions, while most of the massifs in the Urals do not have deep-seated roots. The springs located under the western slope of the Urals allow reliably determining the depth to the basement of the ancient platform and the location of the eastern border of the East European Platform in the lower layer of the Earth’s crust. There were found extended zones of subsidence of the roof of the lower magnetized layer, which probably mark the boundaries of various terrains forming the paleo-island arc sector of the Ural fold system. The most extensive subsidence of the roof of the lower layer occurs to the west of the Tyumen-Chudinovsky fault and is perhaps the eastern deep-seated dividing line between the Ural fold system and the West Siberian Plate.

Глубинное строение Среднего Урала по гравитационным и магнитным данным

For the Middle Urals and adjacent territories of the East European and West Siberian platforms within geographic coordinates from 56º to 60º northern latitude and from 54º to 66º east longitude, the structural features of the anomalous magnetic and gravitational fields were studied and maps of separated anomalies were constructed for three layers of the earth's crust. Using original parallel algorithms for solving forward and inverse problems of gravimetry and magnetometry, a density model of the lithosphere and sources of magnetic anomalies in the earth's crust were constructed. The results of modeling the sources of magnetic anomalies in the Earth's crust are compared with the density model in order to study the differences in the deep structure of the western paleocontinental and eastern paleo-island arc sectors of the Ural fold system, as well as the zones of junction of the orogen with the East European and West Siberian platforms.