A geological interpretation of the Bouguer anomalies adjacent to the Churchill–Superior boundary in northern Manitoba

1968 ◽  
Vol 5 (3) ◽  
pp. 439-453 ◽  
Author(s):  
R. A. Gibb
Keyword(s):  
Bouguer Anomaly ◽  
Gravity Gradient ◽  
Southern Limit ◽  
Near Surface ◽  
Surface Mass ◽  
Geological Interpretation ◽  
Bouguer Anomalies ◽  
Mass Distributions ◽  
Gravity Effects ◽  
Anomaly Map

The Bouguer anomaly map of nothern Manitoba and part of northeastern Saskatchewan was updated by a gravity survey in 1965. Density determinations of some 2000 Precambrian rock samples provide a sound basis for interpretation of the Bouguer anomalies in terms of relatively near-surface mass distributions in the upper crust. In some parts of the area there is excellent correlation between the surface rocks, their densities, and the Bouguer anomalies. The Nelson River gravity high outlines a belt of dense granulites. To the northwest three gravity lows are interpreted as the gravity effects of granitic intrusions, of which one is exposed at Split Lake and the others are largely subjacent, although their presence is supported by the occurrence of numerous mappable stocks of granite within the gravity lows. The Nelson River gravity high is separated from these lows by a steep gravity gradient, which marks a boundary between rocks of predominantly different ages (Hudsonian and Kenoran) between latitudes 54 °N and 56 °N. Age determinations are consistent with an interpretation of the Pikwitonei subprovince as an inlier of Kenoran age within the Churchill Province. The main Churchill–Superior boundary may then be moved south to what is at present the southern limit of the Cross Lake subprovince, which is a return to approximately the position originally selected by M. E. Wilson.

A Gravity Investigation of the Pickwell Down Sandstone, North Devon

1967 ◽  
Vol 104 (1) ◽  
pp. 63-72 ◽  
Author(s):  
Hamid Nassar Al-Sadi
Keyword(s):  
Bouguer Anomaly ◽  
Gravity Gradient ◽  
Near Surface ◽  
Red Sandstone ◽  
Residual Gravity ◽  
The North ◽  
Thrust Plane ◽  
Residual Gravity Anomaly ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

AbstractThe area to the north of Barnstaple (North Devon) was covered by a detailed gravity survey. The main gravity gradient of the Bouguer anomaly map (estimated to be 1·2 mgals per mile) confirmed the conclusions drawn by Bott et al. (1958), who attributed it to a basin of possibly Carboniferous sediments and/or Old Red Sandstone, about 4 miles thick, separated from the outcropping Devonian rocks by an assumed thrust plane.A negative residual gravity anomaly is located over the outcrop of the Pickwell Down Sandstone. Analyses of the anomaly show that it is caused by the southwards dipping belt of sandstone and that the angle of dip of the formation decreases with depth. At a depth of about 2 miles the formation becomes nearly horizontal. Alternatively, it may terminate against an assumed thrust plane underlying the whole outcropping Devonian.The aeromagnetic map of the area shows an elongated magnetic “high” following the outcrop of the Morte Slates. The anomaly is probably caused by near surface, highly magnetized rocks in association with the Morte Slates.

AEROMAGNETIC AND GEOLOGICAL INTERPRETATION OF A SECTION OF THE APPALACHIAN BELT IN CANADA

1967 ◽  
Vol 4 (6) ◽  
pp. 1015-1037 ◽  
Author(s):  
B. K. Bhattacharyya ◽  
B. Raychaudhuri
Keyword(s):  
Prince Edward Island ◽  
Bouguer Anomaly ◽  
Polarization Vector ◽  
Fault System ◽  
Aeromagnetic Data ◽  
Eastern Canada ◽  
Geological Interpretation ◽  
Vertical Displacements ◽  
Regional Tectonic ◽  
Anomaly Map

Studies were made of total field aeromagnetic data over an area covering a section of the Appalachian belt in eastern Canada. This area is bounded by latitudes 45 °N and 47°40′ N and longitudes 62°30′ W and 67 °W. The residual magnetic values were filtered analytically in order to accentuate the effects of regional tectonic trends in the area. The second vertical derivative values were evaluated for outlining the contacts of magnetized geological formations with a reasonable degree of accuracy. Results of the analysis of the Bouguer anomaly map for the area seemed to correspond well with the tectonic trends indicated by the aeromagnetic data. Sixty-five anomalies were chosen from the residual and filtered maps to determine the following parameters of the causative bodies: (1) intensity of polarization; (2) direction-cosines of the polarization vector; and (3) depths to the top and bottom of the bodies.The picture of the pre-Carboniferous basement, as inferred from aeromagnetic data, is that of a valley and ridge configuration characterized by a series of subparallel, elongated basement blocks with relative vertical displacements. The basement blocks are bounded by major fault systems, known or inferred, mostly of pre-Carboniferous age. These blocks are aligned mostly in the direction of major tectonic trend in the area. The details of subsurface Basement topography are discussed on the basis of the results of interpretation of aeromagnetic data. Most interesting of all is a belt of high magnetic intensity running roughly in a NW–SE direction over the Gulf of St. Lawrence and Prince Edward Island. It has been suggested that this belt is caused by a pre-Taconic topographic high, or alternatively, by a pre-Carboniferous basement high bounded by fault zones subparallel with the fault system under the Cabot Strait.

A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques

1993 ◽  
Vol 130 (5) ◽  
pp. 583-591 ◽  
Author(s):  
B. C. Chacksfield ◽  
W. De Vos ◽  
L. D'Hooge ◽  
M. Dusar ◽  
M. K. Lee ◽  
...  
Keyword(s):  
Large Scale ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Digital Processing ◽  
Integrated Modelling ◽  
Magnetic Data ◽  
Gravity Gradient ◽  
The North ◽  
Anomaly Map ◽  
Shaded Relief

AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.

Applying laterally varying density corrections to ground gravity and airborne gravity gradiometry data: a case study from the Bathurst Mining Camp

2019 ◽  
Vol 56 (5) ◽  
pp. 493-503 ◽  
Author(s):  
Peter Tschirhart ◽  
William A. Morris ◽  
John Mims ◽  
Hernan Ugalde
Keyword(s):  
Variable Density ◽  
Airborne Gravity ◽  
Surface Sampling ◽  
Gravity Gradiometry ◽  
Near Surface ◽  
Surface Mass ◽  
Geological Interpretation ◽  
Density Correction ◽  
Bathurst Mining Camp ◽  
Airborne Gravity Gradiometry

The influence of topography on gravity and gravity gradiometry measurements is profound and should be minimized prior to geological interpretation. The standard way of minimizing these effects is through the computation of a terrain correction. Terrain corrections require two inputs: topography and density. Often, geology and topography are inextricably intertwined: topography is caused by a change in geology. In geologic environments where there is a structural and (or) stratigraphic control on the near-surface mass distribution, using a single density value in the corrections leads to removal of the topographic effect of rocks having the chosen density. Any remaining gravity signal that correlates with topography is providing geological information. If the objective is to produce a gravity map with minimal topographic signal, then a regionally variable density correction is a means of compensating for this effect. In this paper, we demonstrate how to apply a spatially variable density correction using ground gravity and airborne gravity gradiometry data for the geologically complex Bathurst Mining Camp, northern New Brunswick, Canada. Ground gravity and airborne full tensor gravity gradiometry measurements are subdivided into a series of domains on the basis of the underlying tectonostratigraphic group. Terrain and Bouguer corrections are calculated for each domain using representative density values obtained from drill core and surface sampling throughout the Bathurst Mining Camp. The output from the spatially variable density correction is then compared with previous maps. Overall, the differences are subtle, but the spatially variably density allows for isolated anomalies to be better resolved.

scholarly journals The use of microgravity technique in archaeology: A case study from the St. Nicolas Church in Pukanec, Slovakia

2009 ◽  
Vol 39 (3) ◽  
pp. 237-254 ◽  
Author(s):  
Jaroslava Pánisová ◽  
Roman Pašteka
Keyword(s):  
Local Density ◽  
Measurement Techniques ◽  
Bouguer Anomaly ◽  
Roman Catholic Church ◽  
Gravity Measurement ◽  
Gravity Gradient ◽  
Near Surface ◽  
Vertical Gravity Gradient ◽  
Vertical Gravity

The use of microgravity technique in archaeology: A case study from the St. Nicolas Church in Pukanec, SlovakiaThe detection of subsurface cavities, such as crypts, cellars and tunnels, in churches and castles belongs to successful applications of the employment of surface gravity measurement techniques in archaeo-prospecting. The old historic building exploration requires using of non-invasive methods, and hence the microgravity technique is a proper candidate for this task. On a case study from the Roman-Catholic Church of St. Nicolas in the town Pukanec the results of using microgravity for detection and delineation of local density variations caused by a near-surface void are shown. The acquired negative anomaly in the residual Bouguer anomalies field suggested the presence of a possible void feature. Euler deconvolution and 3D modelling were used to estimate the depth and shape of the anomalous source. Additionally, measurements of the vertical gravity gradient on several stations were performed. We tested how the use of a downward continuation of gravity, utilizing the real vertical gravity gradient, influences the shape and amplitude of the final Bouguer anomaly map.

scholarly journals Análise e interpretação de dados gravimétricos nas porções terrestre e marítima do Brasil Meridional

1997 ◽  
Vol 20 ◽  
pp. 201-214
Author(s):  
Paula Lúcia Ferrucio da Rocha ◽  
Luiz Fernando Santana Braga
Keyword(s):  
Bouguer Anomaly ◽  
Two Dimensional ◽  
Gravity Modelling ◽  
Bouguer Anomalies ◽  
Dimensional Gravity ◽  
Marine Data ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Geological Constraints ◽  
South Brazil

We have interpreted the Bouguer anomaly map from South Brazil and its adjoining oceanic areas, using the land data from the SAGP Project (1990), and the marine data derived from GEOSAT. With the aid of the vertical derivatives and the maximum horizontal gradientes of the Bouguer anomalies we have mapped the boundaries between the major lithospheric compartments, here characterized by their gravity signatures. Two dimensional gravity modelling with available geological constraints have also been performed aiming to estimate the crustal thicknesses within each individual compartment. We show that the gravity responses of the continental, transitional and oceanic lithospheres are well distinguished.

scholarly journals High resolution Slovak Bouguer gravity anomaly map and its enhanced derivative transformations: new possibilities for interpretation of anomalous gravity fields

2017 ◽  
Vol 47 (2) ◽  
pp. 81-94 ◽  
Author(s):  
Roman Pašteka ◽  
Pavol Zahorec ◽  
David Kušnirák ◽  
Marián Bošanský ◽  
Juraj Papčo ◽  
...  
Keyword(s):  
Gravity Field ◽  
Slovak Republic ◽  
Bouguer Anomaly ◽  
Gradient Field ◽  
Horizontal Gradient ◽  
Lateral Direction ◽  
Geological Interpretation ◽  
Gravity Fields ◽  
Anomalous Gravity ◽  
Anomaly Map

AbstractThe paper deals with the revision and enrichment of the present gravimetric database of the Slovak Republic. The output of this process is a new version of the complete Bouguer anomaly (CBA) field on our territory. Thanks to the taking into account of more accurate terrain corrections, this field has significantly higher quality and higher resolution capabilities. The excellent features of this map will allow us to re-evaluate and improve the qualitative interpretation of the gravity field when researching the structural and tectonic geology of the Western Carpathian lithosphere. In the contribution we also analyse the field of the newCBAbased on the properties of various transformed fields – in particular the horizontal gradient, which by its local maximums defines important density boundaries in the lateral direction. All original and new transformed maps make a significant contribution to improving the geological interpretation of theCBAfield. Except for the horizontal gradient field, we are also interested in a new special transformation ofTDXAS, which excellently separates various detected anomalies of gravity field and improves their lateral delimitation.

Interpretation of the gravity anomaly field in the Noranda – Val d'Or region, Abitibi Greenstone Belt, Canadian Shield

1992 ◽  
Vol 29 (5) ◽  
pp. 962-971 ◽  
Author(s):  
Pierre Keating
Keyword(s):  
Apparent Density ◽  
Cross Sections ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Geological Interpretation ◽  
Vertical Derivative ◽  
Generalized Inversion ◽  
Density Map ◽  
Anomaly Map ◽  
First Vertical Derivative

Gravity data from the Noranda – Val d'Or region have been reprocessed: the Bouguer anomaly map, the first vertical derivative map, and an apparent density map have been used for geological interpretation of the gravity field in this region. It is found that variations in the Bouguer anomaly can be mainly explained by density structures located within the uppermost 5 km of the crust. The vertical derivative map helps to better locate some geological contacts, and the apparent density map allows the easy distinction between thin and thick batholiths. Generalized inversion was used to calculate density cross sections from the Bouguer anomaly values, and measured surface formation densities were used as constraints. Analysis of a detailed profile in the Rouyn–Noranda area shows that steep north-dipping reflectors observed in a seismic reflection survey are associated with a north-dipping density structure.

Microgravity Methods to Characterize the karst structures in north-western Algeria

2020 ◽  
Author(s):  
Fatma Khaldaoui ◽  
Abdesslam ABTOUT Abtout ◽  
Hayet Bouguerra ◽  
Ibtissem Hedjazi
Keyword(s):  
Visual Inspection ◽  
Residential Buildings ◽  
Bouguer Anomaly ◽  
Surface Mass ◽  
Western Algeria ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
The Stability ◽  
A Site ◽  
North Western

<p>A gravimetric study was conducted on a site located at Tlemcen, a city of western Algeria, where it was intended to build residential buildings. During the excavation for the preparation of foundations, cavities were discovered. This is confirmed by visual inspection. The study area is geologically composed of dolomitic limestone jurrassique, characterized by strong pérméabilité caused by cracking and karstic formation.</p><p>The geophysical method more appropriate in this case is the microgravimetric. The gravimetric campaign which lasted 15 days is composed of more than 1000 stations measures and was realized on several zones at the site with a step of 2.5 m. All these stations have been identified topographically.</p><p>            The Bouguer anomaly map presents a short-wavelength gravity low which reaches a minimum value up of - 33.190 mGal. A qualitative analysis of this map showed that the relative gravity lows is related to the mass deficit. Some of the anomalies detected by microgravimetric are well correlated with cavities observed on the surface. Mass deficits have been assimilated as underground cavities and that can present a danger to the stability of buildings.</p><p>The 3D modelling has been realized using software based on the algorithm of Talwani (Talwani & all 1960), it has allowed us to determinate location and dimensions of the cavities detected.</p><p><strong>Key words</strong>: Cavities, karst, Microgravimetic, Anomalies, Talwani, Tlemcen, Algeria.</p>

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