Tectonic significance of potential-field anomalies in western Canada: results from the Lithoprobe SNORCLE transect

2005 ◽  
Vol 42 (6) ◽  
pp. 1239-1255 ◽  
Author(s):  
C Elissa Lynn ◽  
Frederick A Cook ◽  
Kevin W Hall
Keyword(s):  
Cross Sections ◽  
Upper Mantle ◽  
Potential Field ◽  
Precambrian Rocks ◽  
Reflection And Refraction ◽  
Gravity And Magnetic ◽  
Tectonic Significance ◽  
Geometrical Constraints ◽  
Subsurface Geometry ◽  
Local Anomalies

Potential-field anomalies within the Lithoprobe SNORCLE (Slave – Northern Cordillera Lithospheric Evolution) transect area provide geometrical constraints for regional crustal and lithospheric structures, as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles. Areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections, and forward modelling provides tests of different interpretations of deep (crustal and upper mantle) density structures. In a key result from modelling, a Paleoproterozoic subduction zone beneath the Wopmay orogen probably consists of high-density rocks, such as eclogite, within the upper mantle. This result supports the concept of moderate- to low-angle intra-lithospheric sutures. On an even larger scale, applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus provide means to track patterns across structural grain. For example, gravity and magnetic trends that are associated with Precambrian rocks of the Canadian Shield can, in some cases, be followed across much of the Cordillera. This result is consistent with North American Precambrian rocks composing much of the crust in the Cordillera and thus that the addition of "new" lithosphere during Mesozoic – early Tertiary accretion has been relatively minor.

Overview of regional geophysical studies in Manitoba and northwestern Ontario

1982 ◽  
Vol 19 (11) ◽  
pp. 2049-2059 ◽  
Author(s):  
D. H. Hall ◽  
W. C. Brisbin
Keyword(s):  
Greenstone Belt ◽  
Seismic Velocities ◽  
Crustal Layer ◽  
Northwestern Ontario ◽  
Reflection And Refraction ◽  
Gravity And Magnetic ◽  
Winnipeg River ◽  
Lower Crustal ◽  
Gravity And Magnetic Anomaly

This paper presents an overview of six geophysical projects (seismic reflection and refraction, gravity and magnetic anomaly interpretation, specific gravity and magnetic property measurements) carried out in an area in Manitoba and northwestern Ontario bounded by 93 and 96°W longitude, and 49 and 51°N latitude.The purpose of the surveys was to define crustal structure in the Kenora–Wabigoon greenstone belt, the Winnipeg River batholithic belt, the Ear Falls – Manigotagan gneiss belt, and the Uchi greenstone belt. The following conclusions emerge.In all of the belts, a major discontinuity divides the crust into the commonly found upper and lower crustal sections. At the top of the lower crust, a seismically distinct layer (the mid-crustal layer) occurs. Seismic velocities in this layer suggest either intermediate to basic igneous rocks or metamorphic rocks of the amphibolite facies.Crustal geophysical characteristics vary sufficiently among the four belts to justify the classification of all four as distinct subprovinces of the Superior Province.Cet article présente une vue générale sur six projets de géophysique (réflexion et réfraction sismique, interprétation d'anomalies de gravité et magnétiques, déterminations de densité et de propriétés magnétiques) réalisés dans une région du Manitoba et du nord-ouest de l'Ontario encadrée par les longitudes 93 et 96°O et les latitudes 49 et 51°N.

scholarly journals Crustal structure in the Campanian region (Southern Apennines, Italy) from potential field modelling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Y. Kelemework ◽  
M. Milano ◽  
M. La Manna ◽  
G. de Alteriis ◽  
M. Iorio ◽  
...  
Keyword(s):  
Potential Field ◽  
Carbonate Platform ◽  
Vertical Gradient ◽  
Magnetic Data ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Significant Depression ◽  
Mountain Chain ◽  
Surrounding Areas ◽  
Gravity And Magnetic Data

AbstractWe present a 3D model of the main crustal boundaries beneath the Campanian region and the onshore and offshore surrounding areas, based on high-resolution potential field data. Our main objective is the definition of the main structural interfaces in the whole Campanian region from gravity and magnetic data, thanks to their ability to define them on a regional and continuous way. The complex morphology of the Mesozoic carbonate platform, which is fundamental to constrain the top of geothermal reservoir, was reconstructed by inverting the vertical gradient of gravity. We assumed local information from seismic models and boreholes to improve the model. We modeled the deep crustal structures by spectral analysis of Bouguer gravity and magnetic data. The inferred depth estimates indicate a shallow crystalline basement below the Tyrrhenian crust and the Apulian foreland and a significant depression beneath the Bradanic foredeep. The map of the Moho boundary shows a NE-SE verging trough below the Southern Apennine chain and two pronounced uplifts beneath the foreland and the Tyrrhenian crust. We also estimated the depth to the magnetic bottom, showing a thick magnetic crust below the mountain chain and shallow depths where the crustal heat flow is high. The models were compared with seismic sections along selected profiles; a good agreement was observed, despite of some inherent lower resolution for the gravity modelling from spectral methods. The regional covering and the continuity of our estimated crustal interfaces make it a new and valid reference for further geological, geophysical and geothermal studies, especially in areas such as northern and eastern Campania, where there is an incomplete geophysical and geological information.

Three-dimensional depth-to-basement modelling based on seismic and potential field data – basement configuration in the westernmost Polish Outer Carpathians

2020 ◽  
Author(s):  
Mateusz Mikołajczak ◽  
Jan Barmuta ◽  
Małgorzata Ponikowska ◽  
Stanislaw Mazur ◽  
Krzysztof Starzec
Keyword(s):  
Qualitative Analysis ◽  
Cross Sections ◽  
Potential Field ◽  
Field Data ◽  
Gravity Data ◽  
Three Dimensional ◽  
Magnetic Data ◽  
Gravity Inversion ◽  
Potential Field Data ◽  
Outer Carpathians

<p>The Silesian Nappe in the westernmost part of the Polish Outer Carpathians Fold and Thrust Belt exhibits simple, almost homoclinal character. Based on the field observations, a total stratigraphic thickness of this sequence equals to at least 5400 m. On the other hand, the published maps of the sub-Carpathian basement show its top at depths no greater than 3000 m b.s.l. or even 2000 m b.s.l. in the southern part of the Silesian Nappe. Assuming no drastic thickness variations within the sedimentary sequence of the Silesian Nappe, such estimates of the basement depth are inconsistent with the known thickness of the Silesian sedimentary succession. The rationale behind our work was to resolve this inconsistency and verify the actual depth and structure of the sub-Carpathian crystalline basement along two regional cross-sections. In order to achieve this goal, a joint 2D quantitative interpretation of gravity and magnetic data was performed along these regional cross-sections. The interpretation was supported by the qualitative analysis of magnetic and gravity maps and their derivatives to recognize structural features in the sub-Carpathian basement. The study was concluded with the 3D residual gravity inversion for the top of basement. The cross-sections along with the borehole data available from the area were applied to calibrate the inversion.</p><p>In the westernmost part of the Polish Outer Carpathians, the sub-Carpathian basement comprises part of the Brunovistulian Terrane. Because of great depths, the basement structure was investigated mainly by geophysical, usually non-seismic, methods. However, some deep boreholes managed to penetrate the basement that is composed of Neoproterozoic metamorphic and igneous rocks. The study area is located within the Upper Silesian block along the border between Poland and Czechia. There is a basement uplift as known mainly from boreholes, but the boundaries and architecture of this uplift are poorly recognized. Farther to the south, the top of the Neoproterozoic is buried under a thick cover of lower Palaeozoic sediments and Carpathian nappes.</p><p>Our integrative study allowed to construct a three-dimensional map for the top of basement the depth of which increases from about 1000 m to over 7000 m b.s.l. in the north and south of the study area, respectively. Qualitative analysis of magnetic and gravity data revealed the presence of some  basement-rooted faults delimiting the extent of the uplifted basement. The interpreted faults are oriented mainly towards NW-SE and NE-SW. Potential field data also document the correlation between the main basement steps and important thrust faults.</p><p> </p><p>This work has been funded by the Polish National Science Centre grant no UMO-2017/25/B/ST10/01348</p>

Gravity and magnetic data analysis based on Poisson wavelet-transforms

2020 ◽  
Author(s):  
Kirill Kuznetsov ◽  
Bulychev Andrey ◽  
Ivan Lygin
Keyword(s):  
Data Analysis ◽  
Magnetic Fields ◽  
Potential Field ◽  
Wavelet Transforms ◽  
Geophysical Methods ◽  
Magnetic Data ◽  
Potential Field Data ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Data ◽  
Poisson Wavelets

<p>Studies of the Earth’s interior structure are one of the most complex topics in modern science. Integration of different geophysical methods plays a key role in effectively tackling the problem. In the last decade capabilities of potential field geophysical methods have been increasing due to development of advanced digital technologies. Improved resolution and accuracy of gravity and magnetic fields measurements made by modern equipment makes it possible to build more detailed geological models. Different tectonic and structural elements being interpreted in such models produce potential field signals with different spectral characteristics. Like any geophysical signals, potential fields can be described as a spatially non-stationary signal. This means its frequency content may change depending on a given signal sample, in particular with different spatial location of a sample. In this case, approaches of gravity and magnetic fields analysis based on Fourier transform or signal decomposition into a number of harmonic functions can lead to incorrect results. One of the ways to solve this challenge involves using wavelet transform based algorithms, since these transforms do not assume stationary signals and each function of a wavelet-based basis is localized in space domain.</p><p>In gravity and magnetic data analysis it is beneficial to use wavelets based on partial derivatives of the Poisson kernel, which correspond to derivatives of a point source gravity potential. Application of Poisson wavelets in potential field data analysis has begun in the 1990's and is predominantly aimed at studying gravity and magnetic fields singularity points during data interpretation.</p><p>Similar to Fourier-based potential field techniques, it is possible to construct a number of data filtering algorithms based on Poisson wavelets. Current work demonstrates that it is possible to construct algorithms based on Poisson wavelets for transforming profile and spatially gridded gravity and magnetic data, e.g. for calculation of equivalent density and magnetization distributions, upward and downward continuations, reduction to pole and many other filters that take into account spatial distribution of the signal.</p><p>Wavelet-transforms allow to account for spatially non-stationary nature of geophysical signals. Use of wavelet based techniques allows to effectively carry out potential field data interpretation in a variety of different geologic and tectonic settings in a consistent fashion.</p>

A simple derivation of Cordell’s stripping filter

Geophysics ◽  
1994 ◽  
Vol 59 (3) ◽  
pp. 488-490 ◽  
Author(s):  
Adebayo Aina
Keyword(s):  
Frequency Domain ◽  
Potential Field ◽  
Simple Derivation ◽  
Regional Background ◽  
Deep Source ◽  
Local Anomalies

The presence of a strong regional (deep source) anomaly often makes the identification of local (shallow source) anomalies difficult. It may become necessary to either separate the regional and the residual, or carry out an operation on the observed map that enhances the local anomalies at the expense of the regional background. The problem of separation of deep and shallow‐source potential field anomalies is one of the oldest problems in geophysics. Various authors (Griffin, 1949; Nettleton, 1954; Abdelrahman et. al., 1985, for example) have presented details and schemes for separating residual and background anomalies. More recently, Cordell (1985) through Green’s equivalent stratum theorem obtained a filter in the frequency domain that may be used for separating shallow and deep‐source potential field anomalies.

Gravity and magnetic interpretation of the Deer Lake basin, Newfoundland

1984 ◽  
Vol 21 (1) ◽  
pp. 10-18 ◽  
Author(s):  
H. G. Miller ◽  
J. A. Wright
Keyword(s):  
Magnetic Data ◽  
Lake Basin ◽  
Magnetic Interpretation ◽  
Seismic Surveys ◽  
Reflection And Refraction ◽  
Gravity And Magnetic ◽  
Refraction Seismic ◽  
Gravity And Magnetic Data ◽  
Gravity And Magnetic Interpretation ◽  
Total Sediment

Detailed reconnaissance gravity surveys in the Deer Lake Carboniferous basin have been conducted using a station spacing of 2.5 km. The digitized aeromagnetic data for the basin were reduced to a 1:253 440 scale composite map. These two data bases were used to determine the configuration of major features and the total sediment thickness at various locations in the basin. Preliminary seismic results from reflection and refraction seismic surveys planned on the basis of these results are discussed. Modelling of gravity and magnetic data indicates that the Humber syncline contains approximately 1.2 km of sediments underlain on the west by rocks similar to the Long Range Complex. The eastern limb of the syncline is underlain by rocks similar to the Gull Pond Igneous Suite. The Howley Formation is deduced to be approximately 1.5 km thick and floored by rocks similar to the Topsails Igneous Suite.

COMPLEX GEOPHYSICAL STUDIES OF THE IVANO-FRANKIVSK NATIONAL TECHNICAL UNIVERSITY OF OIL AND GAS TERRITORY

2019 ◽  
pp. 7-17
Author(s):  
M. V. Shtogryn ◽  
S. G. Anikeyev ◽  
O. O. Synytska
Keyword(s):  
Oil And Gas ◽  
Magnetic Anomalies ◽  
Research Area ◽  
Geological Interpretation ◽  
Gravity And Magnetic ◽  
Small Intensity ◽  
National University ◽  
Electrical Sounding ◽  
Electrical Prospecting ◽  
Local Anomalies

The results of high-precision integrated geophysical studies of the Ivano-Frankivsk National University territory are presented. Research methods used are electrical prospecting and gravity and magnetic prospecting. According to the results of geodetic measurements and field geophysical observations, heights maps of the territory, regional components and detailed maps of local anomalies of the gravitational and magnetic fields, and also, according to the data of vertical electrical sounding, geoelectric sections along interpretation profiles were constructed. For the construction data on the geological and tectonic structure of the section to the depths of the first hundred meters were used, as well as geophysical materials obtained in previous years through of the Ivano-Frankivsk city territory. The analysis of the general behavior of the regional components of the gravimagnetic fields and morphology of geophysical anomalies was performed. The geological interpretation of the identified individual local gravitational and magnetic anomalies is presented. A regional field of gravity tends to increase in the direction of increasing heights in the study area and the regional magnetic field has an insignificant, but inverse relationship. A series of positive small intensity local anomalies of the field of gravity is probably due to the rocks of the Kosovska and Tyraska suite, for example, compacted carbonates or anhydrites. Local magnetic anomalies have a relatively small intensity ranging from -100 nTl to 500 nTl and due mainly to university facilities and communications. According to the results of the analysis of the intensity of geophysical fields, a general forecast estimate of the ecological state of the research area is presented. The obtained field intensity values are much lower than the sanitary norms.

3D geophysical modeling of the Alberton-Mathinna section of the “Main Slide,” northeast Tasmania

2020 ◽  
Vol 8 (3) ◽  
pp. T525-T540
Author(s):  
Daniel Bombardieri ◽  
Mark Duffett ◽  
Andrew McNeill ◽  
Mike Vicary ◽  
Rod Paterson
Keyword(s):  
Cross Sections ◽  
3D Model ◽  
Physical Property ◽  
Magnetic Survey ◽  
Geophysical Modeling ◽  
New Synthesis ◽  
Gravity And Magnetic ◽  
Rock Physical Property ◽  
Geological Units ◽  
Fault Network

We have developed a high-resolution 3D model of the Alberton-Mathinna section of the “Main Slide,” northeast Tasmania. This geological model expresses a new synthesis based on mapping and structural interpretation on multiple cross sections. We have refined this model by 3D geophysical inversion constrained by gravity and magnetic survey data coupled with drilling and rock physical property databases. Our modeling incorporates statistically generated sensitivity characterization metrics into 3D model products that map confidence in the geometry of geological units at depth. The results include a granitoid surface that is considerably more detailed than earlier versions based on 2D modeling. Among the new features to emerge is a cupola 1.6 km below and slightly west of the Mathinna goldfield. At the Ringarooma United deposit located within the Alberton goldfield, we seethat the fault network underpinning the deposit was intruded by granite to a depth of approximately 400 m. Ore-forming solutions for both deposits have been interpreted as metamorphic in origin, but our results suggest the possibility of a role for magmatic fluids (i.e., granite related) in the gold-mineralizing system, particularly for the Ringarooma United deposit.

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