Crustal structure at the Trans-European Suture Zone in 

northwest Poland based on gravity data

A new gravity model of the crustal structure of the Trans-European Suture Zone in the northwestern Poland has been constructed. The Bouguer anomaly map, obtained after stripping off the three-dimensional gravity effect of the sedimentary cover down to the Zechstein formations, is characterized by a 50 mGal gravity anomaly. We have assumed that the short-wavelength components derive from upper crustal intrusions and the long-wavelength components reflect crustal thickness and lateral heterogeneity which are strongly supported by the new seismic data along the LT-7 geotraverse. Quantitative modelling of gravity data along three profiles crossing the area indicate the presence of anomalous masses within the Lower Palaeozoic sequence, mainly along the Teisseyre-Tornquist Zone. Two of the profiles crossing the long-wavelength ‘stripped’ gravity high suggest the existence of a zone of 35 km crust above a dense upper mantle along the Teisseyre-Tornquist Zone. The extent of the zone can be determined based on the Bouguer anomalies interpretation.

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Structural cross sections based on a gravity survey of parts of the Quetico and Wawa subprovinces near Thunder Bay, Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e90-019 ◽

1990 ◽

Vol 27 (2) ◽

pp. 187-199 ◽

Cited By ~ 3

Author(s):

M. M. Kehlenbeck ◽

S. P. Cheadle

Keyword(s):

Cross Sections ◽

Gravity Data ◽

Bouguer Anomaly ◽

Gravity Models ◽

Low Grade ◽

Thunder Bay ◽

Metavolcanic Rocks ◽

Dimensional Gravity ◽

Anomaly Map ◽

Bouguer Anomaly Map

In this study, gravity data from 350 new gravity stations are combined with those from 50 previously surveyed stations in a detailed Bouguer anomaly map of a portion of the Quetico and Wawa subprovinces north and west of Thunder Bay, Ontario.In general, high gravity values characterize the southern and southwestern part of the area where metavolcanic rocks of the Wawa subprovince dominate. Much of the Quetico subprovince forms a broad gravitational low, reflecting extensive exposures of gneisses, schists, and migmatites. Well-defined gravity lows are associated with several granitic intrusive bodies.Three- and [Formula: see text]-dimensional gravity models of subsurface configuration of the density contrasts, representative of major rock units, indicate a trough-like structure for the metavolcanic rocks of the Wawa subprovince. This trough-like structure is flanked by a domical feature in the granitoid rocks to the south. North of the metavolcanic rocks, a succession of low-grade greywackes and slates occupies a basinal structure. These structures form the principal subsurface elements of the Wawa subprovince in this area.The gneisses, schists, and migmatites of the Quetico subprovince form a thick, southward-dipping, wedge-shaped structure that may extend under the structures of the Wawa subprovince. This wedge-shaped structure is underlain by a model unit of greater density representative of mafic gneisses and amphibolites. The denser substratum is modelled with local abrupt changes in dip corresponding in position with the Quetico and Hawkeye Lake faults.

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Crustal architecture of a metallogenic belt and ophiolite belt: implications for mineral genesis and emplacement from 3-D electrical resistivity models (Bayankhongor area, Mongolia)

Earth Planets and Space ◽

10.1186/s40623-021-01400-9 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Matthew J. Comeau ◽

Michael Becken ◽

Alexey V. Kuvshinov ◽

Sodnomsambuu Demberel

Keyword(s):

Electrical Resistivity ◽

Crustal Structure ◽

Three Dimensional ◽

Suture Zone ◽

Fault System ◽

Magnetotelluric Data ◽

Low Resistivity ◽

Ophiolite Belt ◽

Geological Processes ◽

Metallogenic Belt

AbstractCrustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust (< 25 km) is found to be generally highly resistive (> 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture—including the major crustal boundary—acts as a first‐order control on the location of the metallogenic belt.

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Geometrical Characterisation of the Mamfe Basin, Cameroon, from the Earth, Gravitational Model (EGM 2008)

Earth Science Research ◽

10.5539/esr.v7n1p94 ◽

2018 ◽

Vol 7 (1) ◽

pp. 94

Author(s):

Anatole Eugene Djieto Lordon ◽

Mbohlieu YOSSA ◽

Christopher M Agyingi ◽

Yves Shandini ◽

Thierry Stephane Kuisseu

Keyword(s):

Average Length ◽

Gravity Data ◽

Bouguer Anomaly ◽

Igneous Rocks ◽

Average Depth ◽

The Earth ◽

Gravitational Model ◽

Petroleum Generation ◽

Anomaly Map ◽

Bouguer Anomaly Map

Gravimetric studies using the ETOPO1-corrected high resolution satellite-based EGM2008 gravity data was used to define the surface extent, depth to basement and shape of the Mamfe basin. The Bouguer anomaly map was produced in Surfer 11.0. The Fast Fourier Transformed data was analyzed by spectral analysis to remove the effect of the regional bodies in the study area. The residual anomaly map obtained was compared with the known geology of the study area, and this showed that the gravity highs correspond to the metamorphic and igneous rocks while the gravity lows match with Cretaceous sediments. Three profiles were drawn on the residual anomaly map along which 2D models of the Mamfe basin were drawn. The modeling was completed in Grav2dc v2.06 software which uses the Talwini’s algorithm and the resulting models gave the depth to basement and the shape of the basement along the profiles. After processing and interpretation, it was deduced that the Mamfe basin has an average length and width of 77.6 km and 29.2 km respectively, an average depth to basement of 5 km and an overall U-shape basement. These dimensions (especially the depth) theoretically create the depth and temperature conditions for petroleum generation.

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3D Gravity modeling of the volcanic island of Surtsey, Iceland

10.5194/egusphere-egu21-15769 ◽

2021 ◽

Author(s):

sara sayyadi ◽

Magnús T. Gudmundsson ◽

Thórdís Högnadóttir ◽

James White ◽

Joaquín M.C. Belart ◽

...

Keyword(s):

Sea Level ◽

Gravity Data ◽

Bouguer Anomaly ◽

Gravity Modeling ◽

Gravity Station ◽

Effusive Activity ◽

3D Gravity ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Drill Cores

The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones. &#160;Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35&#176; from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019).&#160;We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme. &#160;Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m-3 was found between the lapilli tuffs of the diatreme and the seafloor sediments.&#160; Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.&#160; The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores.&#160;A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.&#160; Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.

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Upper crustal structure of Deception Island area (Bransfield Strait, Antarctica) from gravity and magnetic modelling

Antarctic Science ◽

10.1017/s0954102005002622 ◽

2005 ◽

Vol 17 (2) ◽

pp. 213-224 ◽

Cited By ~ 27

Author(s):

A. MUÑOZ-MARTÍN ◽

M. CATALÁN ◽

J. MARTÍN-DÁVILA ◽

A. CARBÓ

Keyword(s):

Crustal Structure ◽

Gravity Data ◽

Bouguer Anomaly ◽

Active Volcano ◽

Magnetic Data ◽

Deception Island ◽

Intrusive Body ◽

The South ◽

Bransfield Strait ◽

Gravity And Magnetic

Deception Island is a young, active volcano located in the south-western part of Bransfield Strait, between the Antarctic Peninsula and the South Shetland archipelago. New gravity and magnetic data, from a marine geophysical cruise (DECVOL-99), were analysed. Forty-eight survey lines were processed and mapped around Deception Island to obtain Bouguer and magnetic anomaly maps. These maps show well- defined groups of gravity and magnetic anomalies, as well as their gradients. To constrain the upper crustal structure, we have performed 2+1/2D forward modelling on three profiles perpendicular to the main anomalies of the area, and taking into account previously published seismic information. From the gravity and magnetic models, two types of crust were identified. These were interpreted as continental crust (located north of Deception Island) and more basic crust (south of Deception Island). The transition between these crustal types is evident in the Bouguer anomaly map as a high gradient area trending NE–SW. Both magnetic and gravity data show a wide minimum at the eastern part of Deception Island, which suggests a very low bulk susceptibility and low density intrusive body. With historical recorded eruptions and thermal and fumarolic fields, we interpret this anomaly as a partially melted intrusive body. Its top has been estimated to be at 1.7 km depth using Euler deconvolution techniques.

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Gravity ideal bodies

Geophysics ◽

10.1190/1.1442387 ◽

1987 ◽

Vol 52 (9) ◽

pp. 1265-1278 ◽

Cited By ~ 16

Author(s):

Mark E. Ander ◽

Stephen P. Huestis

Keyword(s):

Gravity Data ◽

Three Dimensional ◽

Computer Code ◽

Solution Set ◽

Rio Grande Rift ◽

Positive Anomaly ◽

Dimensional Gravity ◽

Exploration Tool ◽

Ideal Body ◽

Rigorous Bounds

The interpretation of gravity anomaly data suffers from a fundamental nonuniqueness, even when the solution set is bounded by physical or geologic constraints. Therefore, constructing a single solution that fits or approximately fits the data is of limited value. Consequently, much effort has been applied in recent years to developing inverse techniques for rigorous deduction of properties common to all possible solutions. To this end, Parker developed the theory of an ideal body, which characterizes the extremal solution with the smallest possible maximum density. Gravity ideal‐body analysis is an excellent reconaissance exploration tool because it is especially well suited for handling sparse data contaminated with noise, for finding useful, rigorous bounds on the infinite solution set, and for predicting accurately what data need to be collected in order to tighten those bounds. We present a practical three‐ dimensional gravity ideal‐body computer code, IDB, that can optimize a mesh with over [Formula: see text] cells when used on a CRAY computer. Using actual gravity data, we use IDB to produce ideal‐body tradeoff curves that bound the solution set and show how to restrict the bound on the solution further by applying geologic and geophysical data to the tradeoff curves. As an example, we compare two‐dimensional and three‐dimensional ideal‐body results from a study of a positive anomaly associated with the Lucero uplift located on the western flank of the Rio Grande rift in New Mexico.

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Three-dimensional gravity modelling applied to the exploration of uranium unconformity-related basement-hosted deposits: the Contact prospect case study, Kiggavik, northeast Thelon region (Nunavut, Canada)

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2016-0225 ◽

2017 ◽

Vol 54 (8) ◽

pp. 869-882 ◽

Cited By ~ 5

Author(s):

Régis Roy ◽

Antonio Benedicto ◽

Alexis Grare ◽

Mickaël Béhaegel ◽

Yoann Richard ◽

...

Keyword(s):

Gravity Data ◽

Three Dimensional ◽

Gravity Anomalies ◽

3D Models ◽

Low Density ◽

Uranium Deposits ◽

Geological Interpretation ◽

Thelon Basin ◽

Dimensional Gravity ◽

Density Values

In unconformity-related uranium deposits, mineralization is associated with hydrothermal clay-rich alteration haloes that decrease the density of the host rock. In the Kiggavik uranium project, located in the eastern Thelon Basin, Nunavut (Canada), basement-hosted shallow deposits were discovered by drilling geophysical anomalies in the 1970s. In 2014, gravity data were inverted for the first time using the Geosoft VOXI Earth ModellingTM system to generate three-dimensional (3D) models to assist exploration in the Contact prospect, the most recent discovery at Kiggavik. A 3D unconstrained inversion model was calculated before drilling, and a model constrained by petrophysical data was computed after drilling. The unconstrained inversion provided a first approximation of the geometry and depth of a low-density body and helped to collar the discovery holes of the Contact mineralization. The constrained inversion was computed using density values measured on 315 core samples collected from 21 drill holes completed between 2014 and 2015. The constrained modelling highlights three shallower and smaller low-density bodies that match the geological interpretation and refines the footprint of the gravity anomalies in relation to the current understanding of the deposit. The 3D inversion of gravity data is a valuable tool to guide geologists in exploration of shallow basement-hosted uranium deposits associated with alteration haloes and to assess the deposit gravity geometry.

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SHEAR ZONES IN NORTH EGYPT INTERPRETED FROM GRAVITY DATA

Geophysics ◽

10.1190/1.1440785 ◽

1977 ◽

Vol 42 (6) ◽

pp. 1207-1214 ◽

Cited By ~ 24

Author(s):

S. Riad

Keyword(s):

Gravity Data ◽

Bouguer Anomaly ◽

Shear Zones ◽

Gulf Of Suez ◽

Eastern Side ◽

Fault Systems ◽

Anomaly Map ◽

Bouguer Anomaly Map ◽

Transcurrent Faults

The Bouguer anomaly map for the northern part of Egypt was used for determining fault systems which are probably present in the area. These systems show the presence of a number of almost parallel shear zones, striking in a northwest‐southeast direction. Extrapolation of some of these zones is suggested in the Gulf of Suez area. The movement of the eastern side of each zone is thought to be right‐lateral to the southeast. The shear zones are probably related to the interaction between the European and African plates. They probably started developing in the Oligocene and are presently still active. The opening of the Gulf of Suez is thought to be mainly due to the action of these transcurrent faults.

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Processing steps for the compiling AAGRG gravity maps

10.5194/egusphere-egu2020-16484 ◽

2020 ◽

Author(s):

Pavol Zahorec ◽

Juraj Papčo ◽

Roman Pašteka ◽

Keyword(s):

Gravity Data ◽

Atmospheric Correction ◽

Bouguer Anomaly ◽

Taylor Series Expansion ◽

Methodological Innovation ◽

Atmospheric Effect ◽

Free Air ◽

Point Data ◽

Anomaly Map ◽

Bouguer Anomaly Map

First unified complete Bouguer anomaly map of AlpArray area compiled from terrestrial gravity data is in preparation. The following steps to calculate the first version of the map were performed: 1. unification of different spatial, height and gravity systems, 2. getting available detailed (mainly LiDAR-based) elevation models and their transformation from physical to ellipsoidal heights, 3. calculation of mass corrections (gravity effect of the topography between the surface and ellipsoid level) with density 2 670 kg/m3, 4. calculation of bathymetric corrections for water masses below the ellipsoid (correction density -1&#160;640 kg/m3), 5. calculation of lake correction for great alpine lakes (correction density -1&#160;670 kg/m3), 6. calculation of the final complete Bouguer anomalies based on normal field (Somigliana formula with GRS80 parameters, free-air correction using Taylor series expansion to the 2nd order) and particular corrections including also the atmospheric correction.The quality control of input data was performed based on the height differences between the point data and particular elevation models. Several thousand points with height residuals higher than chosen threshold (&#177;50 m) were excluded. The available detailed local elevation models (resolution 10 &#8211; 20 m) were compared with global model MERIT (resolution 25 m).The most significant methodological innovation is the ellipsoidal heights concept using straightforward calculation of mass/bathymetric corrections in respect to the ellipsoid instead of using the geophysical indirect effect computation. Our specially developed program Toposk was used for mass/bathymetric correction calculation (the standard distance of 166.7 km was used for the first version of the map) as well as for the calculation of lake corrections. Mass corrections amount to hundreds of mGal, while the lake corrections reach more than 5 mGal locally. Atmospheric effect taking into account topography was also calculated and compared with standard atmospheric correction.&#160;

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The transition of the East European cratonic lithosphere to that of the Palaeozoic collage of the Trans-European Suture Zone as depicted on the TTZ-South deep seismic profile (SE Poland to NW Ukraine)

10.5194/egusphere-egu2020-7687 ◽

2020 ◽

Author(s):

Tomasz Janik ◽

Vitaly Starostenko ◽

Paweł Aleksandrowski ◽

Tamara Yegorova ◽

Wojciech Czuba ◽

...

Keyword(s):

Crustal Structure ◽

Lower Crust ◽

Seismic Velocity ◽

Sedimentary Cover ◽

Suture Zone ◽

Crystalline Basement ◽

Moho Depth ◽

Crustal Layer ◽

Velocity Inversion ◽

East European

Crustal and uppermost mantle structure along the Teisseyre-Tornquist Zone (TTZ)&#160; was explored along the ~550 km long, NW-SE-trending TTZ-South profile, using seismic wide-angle reflection/refraction (WARR) method. The profile line was intended to follow the border between the East European Craton (EEC) and the so called Palaeozoic Platform (PP) of north-central Europe, believed to contain a number of crustal blocks that were accreted to the craton during pre-late Carboniferous times, defining the Trans-European Suture Zone (TESZ).The seismic velocity model of the TTZ-South profile shows lateral variations in crustal structure. Its Ukrainian segment crosses the interior of the Sarmatian segment of the EEC, where the crystalline basement gradually dips from ~2 km depth in the SE to ~12 km at the Ukrainian-Polish border. This part of the model shows a four-layered crustal structure, with an up to 15 km-thick sedimentary cover, an underlying crystalline upper crust, a 10-15 km-thick middle crust and a ~15 km thick lower crust. In Poland, the profile passes along the TESZ/EEC transition zone of complex crustal structure. The crystalline basement, whose top occurs at depths of 10-17 km, separates the sedimentary cover from the ~10 km thick mid-crustal layer (Vp=6.5-6.6 km/s), which, in turn, overlies a block of 10-15 km thickness with upper crustal velocities (Vp~6.2 km/s). The latter is underlain by a ~10-15 km-thick lower crust. Along most of the model one can see conspicuous velocity inversion zones occuring at various depths. At intersections of the TTZ-South profile with some previous deep seismic profiles (e.g. CEL02, CEL05, CEL14, PANCAKE) such inversions document complex wedging relationships between the EEC and PP crustal units. These may have resulted from tectonic compression and thick-skinned thrusting due to either Neoproterozoic EEC collision with accreting terranes or intense Variscan orogenic events. Five high velocity bodies (HVB; Vp = 6.85-7.2 km/s) were detected in the middle and lower crust at 15-37 km depth. The Moho depth varies substantially along the profile. It is at ~42 km depth in the NW and deepens SE-ward to ~50 km at ~685 km. Subsequently, it rises abruptly to ~43 km at the border of the Sarmatian segment of the EEC and sinks again to ~50 km beneath the Lviv Paleozoic trough at ~785 km. From this point until the SE end of the profile, the Moho gently shallows, up to a depth of ~37 km, including a step-like jump of 2 km at ~875 km. Such abrupt Moho steps may be related to crust-scale strike-slip faults. Along the whole profile, sub-Moho velocities are ~8.05-8.1 km/s, and at depths of 57-63 km Vp values reach 8.2-8.25 km/s. Four reflectors/refractors were modelled in the upper mantle at ~57-65 km and ~80 km depths.

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