Dissertations / Theses: 'Aeromagnetics'

1

Bontenakel, Alexander P. "Three dimensional modelling of the Truro-Sandleton area using aeromagnetics and gravity /." Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09S.B/09s.bb722.pdf.

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Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1993.
On title page: "National Grid reference: Adelaide sheet S1 54-9 (1:250 000). Map in pocket inside back cover. Includes bibliographical references (leaves 23-25).

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Sahu, Bijay Kumar. "Aeromagnetics of selected continental areas flanking the Indian Ocean : with implications for geological correlation and reassembly of Central Gondwana." Doctoral thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/10718.

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Reassembling continental fragments of Gondwana has been a subject of interest to many since almost the beginning of the last century. As a result, the broad relative position of the major continental fragments and their dispersal history is well understood using marine magnetic anomalies, coastline geometry, surface geology and limited geophysics. Uncertainty still prevails in reassembly of central Gondwana fragments flanking the Indian Ocean. This thesis aims at utilising geophysical constraints to corroborate an fine-tune the reconstruction of these fragments supported by geological evidence.

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Thomson, G. F. "Palaeomagnetic and aeromagnetic studies of some sulphide deposits." Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383983.

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4

Whiting, Thomas H. "A study of the lithology and structure of the eastern Arunta Inlier based on aeromagnetic interpretation : a lithological subdivision and structural history of the eastern Arunta Inlier, with particular emphasis on the relationship between magnetic mineral petrogenesis, rock magnetism and aeromagnetic signature /." Title page, contents and abstract only, 1987. http://web4.library.adelaide.edu.au/theses/09PH/09phw6125.pdf.

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5

Casto, Daniel W. "Calculating depths to shallow magnetic sources using aeromagnetic data from the Tucson Basin." Tucson, Ariz. : U.S. Dept. of the Interior, U.S. Geological Survey, 2001. http://geopubs.wr.usgs.gov/open-file/of01-505/.

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6

Naudé, Corus. "Target selection from airborne magnetic and radiometric data in Steinhausen area, Namibia." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1001520.

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The eastern branch of the late Proterozoic Damara Orogenic Belt of central Namibia hosts various copper, gold, manganese and uranium deposits, but in the vicinity of Steinhausen, approximately 145 km northeast of Windhoek, the Damara Belt becomes increasingly covered by recent Kalahari cover sediments resulting in little known geology and subsequent lack of discovered economic mineral deposits. Airborne magnetic and radiometric data over the Steinhausen Study Area was enhanced through image processing and filtering to accentuate characteristics of subsurface geology that, by comparing these characteristics to known geology, aided in the interpretive mapping of lithology, structure and targets for follow-up exploration. As a result, some important observations regarding the regional lithology can be drawn. An arenaceous stratigraphic unit that includes a coarse grained, glassy quartzite below the Kuiseb Formation equates to either the eastern Damaran equivalent of the Nosib Group subjected to high grade metamorphism or, alternatively, the upper part of the pre-Damaran sequence, immediately underlying the Damara. The Kuiseb Formation within the study area is uncharacteristically varied as compared to the same formation further west along the Damaran Orogen and can be subdivided into 5 separate units based on geophysical signature. Structural features evident within the study area include the prominent Kudu and Okahandja Lineaments and straddle an area of inferred uplifted stratigraphy of possibly pre-Damara age. The Ekuja Dome (Kibaran age and host to the Omitiomire copper deposit) is also clearly discernible on the airborne magnetic data and is cross-cut by an east-northeast structural zone. Direct targets for follow-up exploration include the Rodenbeck intrusion, anomalous magnetic bodies and numerous radiometric anomalies present within the study area. Identified dome-like features are considered prospective for Omitiomire-style deposits and the Okatjuru Layered Complex is considered a possible source of copper, chromite, magnetite, ilmenite, nickel and the platinum group elements.

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Johnson, Ashley Charles. "A geophysical investigation of crustal structure and segmentation of the central Antarctic Peninsula." Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266417.

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Garrett, S. W. "Interpretation of regional gravity and aeromagnetic surveys of the Antarctic Peninsula." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373905.

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9

Lucius, Jeffrey E. "Crustal geology of Ohio inferred from aeromagnetic and gravity anomaly analysis." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1318868502.

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10

Magaia, Luis. "Processing Techniques of Aeromagnetic Data. Case Studies from the Precambrian of Mozambique." Thesis, Uppsala universitet, Geofysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183714.

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During 2002-2006 geological field work were carried out in Mozambique. The purpose was to check the preliminary geological interpretations and also to resolve the problems that arose during the compilation of preliminary geological maps and collect samples for laboratory studies. In parallel, airborne geophysical data were collected in many parts of the country to support the geological interpretation and compilation of geophysical maps. In the present work the aeromagnetic data collected in 2004 and 2005 in two small areas northwest of Niassa province and another one in eastern part of Tete province is analysed using GeosoftTM. The processing of aeromagnetic data began with the removal of diurnal variations and corrections for IGRF model of the Earth in the data set. The study of the effect of height variations on recorded magnetic field, levelling and interpolation techniques were also studied. La Porte interpolation showed to be a good tool for interpolation of aeromagnetic data using measured horizontal gradient. Depth estimation techniques are also used to obtain semi-quantitative interpretation of geological bodies. It was showed that many features in the study areas are located at shallow depth (less than 500 m) and few geological features are located at depths greater than 1000 m. This interpretation could be used to draw conclusions about the geology or be incorporated into further investigations in these areas.

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Leblanc, G. "Wavelet analysis denoising of aeromagnetic data, application to hydrocarbon and mineral exploration." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0035/NQ66216.pdf.

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12

Ukaigwe, Nnaemeka Francis. "Interpretation of aeromagnetic data of the Olary province, South Australia and the development of interpretation methods /." Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phu34.pdf.

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13

Keating, Pierre B. "The inversion of time-domain airborne electromagnetic data using the plate model /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75772.

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Airborne electromagnetic methods were developed in the early 1950's, mostly by Canadian mining exploration companies as a means of economically and successfully searching large areas for conductive massive sulfide mineralisations. As new technologies developed they have become more and more sophisticated. They can detect conductors at depths in excess of 200 m and are routinely used for overburden mapping. The data is digitally recorded and processed. One of the most successful methods is the time domain airborne INPUT$ sp1$ system, for numerous mineral deposits were found by this system in the Canadian Shield.
Present interpretation techniques are based on the use of nomograms (i.e. families of pre-computed characteristic responses) and the method is easily amenable to digital processing as it is easy to program and economic to use. For high accuracy interpretation however it is necessary to develop quantitative interpretation techniques that can make full use of all the data available. Inverse theory has been used with great success in all branches of geophysics, but to date in mining exploration it has been used for the interpretation of airborne E.M. data using only the one layer earth model. Use of inverse theory for the plate model has been limited by the high cost of numerically solving the forward problem.
In this thesis we show how to use inverse theory to interpret time domain E.M. data with the rectangular thin plate model by introducing some economies. It is then possible to estimate parameter errors, the correlation matrix and to assess the validity of the model. This is extended to the joint inversion of magnetic and aeromagnetic data a case that often arises in mining problems. It is finally shown that under some assumptions the late time channels can be used to interpret time domain E.M. data in the presence of conductive overburden. ftn$ sp1$Registered trademark of Barringer Research Ltd.

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Kennedy, Roger J. "A 3-D gravity and aeromagnetic interpretation of the Black Hill - Cambrai region /." Title page, contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09SB/09sbk36.pdf.

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15

Chan, Mei-ki. "Gravity and aeromagnetic modelling of the Longmenshan Fold-and-Thrust Belt, SW China." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/b4020330x.

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Chan, Mei-ki, and 陳美琪. "Gravity and aeromagnetic modelling of the Longmenshan Fold-and-Thrust Belt, SW China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4020330X.

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17

Martin, J. E. "Spectral analysis of aeromagnetic data and investigation of errors in spherical harmonic models." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376255.

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18

Ström, Tobias. "A geophysical study of the Mertainen area : Modelling and interpretation of primarily aeromagnetic data." Thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-63850.

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Nautanen Deformation Zone, is a prominent deformation zone in the Malmfälten area, which is of importance to understand for mineral exploration purposes. In spite of diverse geophysical data being available in Malmfälten and the good correlation between airborne measurements and geological observations, the area has not been fully investigated in detail using the aforementioned available data. A geological feature in connection with the Mertainen magnetite-breccia apatite iron ore deposit has been studied. Methods include the study of geological maps, the study of analytic signals of magnetic and gravity data, data processing, potential field- and 3D modelling and the interpretation of aforementioned models. Based on the observed and modelled data a fold structure has been detected in connection with Mertainen, and several mineralizations are believed to be structurally related to this fold. Furthermore, a potential mineralization structurally related with the fold has been detected, though it is quite likely that it isn't economically viable.
Nautanen Deformation Zone, är en framträdande deformationszon i Malmfälten området, vilken är av betydelse att förstå för mineral prospekterings ändåmål. Trotts att det finns ett stort utbud av geofysiska data i Malmfälten och att det finns en god korrelation mellan de flyggeofysiska mätningarna och geologiska observationer, så har området inte undersökts fullständigt med den tillgängliga datan. En geologisk struktur i koppling till apatit järn malms fyndigheten Mertainen has studerats. Bland metoder ingår studie av geologiska kartor, studie av de analytiska signlar hos magnetiska och gravimetriska data, data processering, potential fält- och 3D modellering samt tolkningen av ovannämnda modeller. Baserat på den observerade samt modellerade datan har en veck strucktur upptäckts i koppling till Mertainen, och flertalet mineraliseringar tros vara strukturellt relaterade till detta veck. Dessutom har en potentiell mineralisering strukturellt relaterad till vecket upptäckts, dock är det väldigt troligt att den inte är ekonomiskt brytbar.

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19

Miles, Warner Frederick. "An interpretation of high resolution aeromagnetic data over the Manitouwadge greenstone belt, Ontario, Canada." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0005/MQ36726.pdf.

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20

Reynolds, Scott. "A gravity and aeromagnetic investigation of sub-surface granitoids in the Pine Creek geosyncline /." Abstract and contents only, 1997. http://web4.library.adelaide.edu.au/theses/09SB/09sbr465.pdf.

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21

Taib, Samsudin Hj. "Interpretation of the aeromagnetic anomalies of mainland Scotland using pseudogravimetric transformation and other methods." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6076/.

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A procedure to upward continue magnetic anomalies observed on an irregular surface onto a horizontal plane has been developed and applied to the aeromagnetic map of Great Britain. Pseudogravimetric transformation was then carried out on this reduced anomaly and both data sets have been used for analysis and interpretation of several prominent anomalies in Scotland along the Great Glen fault and over the Midland Valley. A prominent linear positive magnetic anomaly occurring along the Great Glen fault has been modelled as due to a locally magnetized outward dipping body almost symmetrical about its apex beneath the fault line, together with a magnetized crustal slab to the northwest of the fault. The outward dipping body has its top lying within the upper crust, a magnetization of greater than about 1.0 A/m, a half-width of about 40 km at its base and a thickness of the order of 7-18 km. The origin of the outward dipping magnetized body may possibly be explained by metamorphism produced by frictional heating resulting from the transcurrent fault movement. Alternatively the metamorphism may be associated with some other fault related process such as crustal fluid flow. Thermal modelling has been used to demonstrate this. The magnetization contrast across the fault may be the direct result of blocks of differing magnetization on opposite side, juxtaposed as a result of transcurrent movement. The modelling along a profile over the Clyde Plateau (Midland Valley of Scotland) using a well-constrained lava body reveals the presence of a long wavelength anomaly component due to a deeper crustal source. The basement anomaly is conspicuous on the pseudogravimetric map but not on the aeromagnetic map. A near circular magnetic anomaly near Bathgate in the Midland Valley can be explained by an unexposed intrusive body superimposed on the deep crustal source as above.

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22

Vallejos, Luis E. Santamaria. "Three-dimensional analysis of aeromagnetic and gravimetric data of sedimentary basins from Panama, Central America." Licentiate thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18258.

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The knowledge of the geology of the sedimentary basins from the Gulf of Panama is still quite limited. There is a lack of data from the basin geometry, the thickness, the continuity and connection between the basins, and from the characteristics of the crystalline basement rocks beneath the sedimentary basins. Geological maps have been published without evidence from geophysical studies; i.e. marine faults patters are showed only as the continuation of fault pattern on land and in some cases faults are showed only to adjust geodynamics models. In the marines areas the geophysical surveys so far carried out, like seismic reflection and well logging, have not given information about the nature of and depth to the crystalline basement rock and interpretations of aeromagnetic and gravity data are still missing. Many of the geophysical surveys like aeromagnetic and marine gravity data have been published as contour maps. However, different data processing techniques and various references levels have been used, which do not permit an integral regional analysis. Here we present composite regional aeromagnetic and gravity maps and integral interpretations with reference to source parameters such as; depths to the top of basement rock, faults patters, locations of magnetic boundaries, susceptibility contrasts, geometry and connection between the basins. The interpretations are based on regional aeromagnetic maps and on marine and land gravity data compiled from several sources and integrated with reference to a fixed level. Various techniques have been applied for the interpretation e.g. enhancement of the aeromagnetic anomalies maps by sun shading technique, applying band pass filtering and upward analytic continuation. Maps have also been transformed into images called 3D analytic signal amplitude and local wave number maps. The depth estimates resulting from the analyses of these maps are compared and the location of interpreted contacts are combined into a map showing the dip direction for contacts. The Bouguer gravity data from the Gulf of Panama are transformed into a residual anomaly map using a filtering technique. This residual anomaly map have been analyzed in order to estimate depths to the top of the basement rocks.

Godkänd; 2008; 20080602 (ysko)

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23

Markham, Stephen L. "The application of high resolution aeromagnetic surveys to petroleum exploration in the Western Otway Basin /." Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09SM/09smm345.pdf.

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Thesis (M. Sc.)--University of Adelaide, Dept. of Geology and Geophysics, 1999.
One compact disc in pocket on back end paper. System requirements for accompanying computer CD-ROM: Mackintosh or IBM-compatible computer. Other requirements: Microsoft Word 6 or compatible Word Processor, or Postscript file viewer. Includes bibliographical references (leaves 183-197).

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24

Santamaria, Vallejos Luis E. "Three-dimensional analysis of aeromagnetic and gravimetric data of sedimentary basins from Panama, Central America /." Luleå : Luleå University of Technology, 2008. http://epubl.ltu.se/1402-1757/2008/24/.

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25

Haidarian, Mohammad Reza. "Aeromagnetic interpretation of a section of the Willyama Inliers in the Curnamona Craton, South Australia /." Title page, contents and abstract only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phh149.pdf.

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26

Leonard, Mark. "Interpretation of an aeromagnetic survey over a shallow sedimentary basin with particular emphasis on spectral analysis /." Title page, contents and abstract only, 1986. http://web4.library.adelaide.edu.au/theses/09SB/09sbl581.pdf.

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27

Beinke, Lynelle Marie. "Applications of three component aeromagnetic data to iron ore exploration in the Hamersley Basin, Western Australia /." Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09SB/09sbb4228.pdf.

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Thesis (B.Sc.(Hons.)) -- University of Adelaide, Dept. of Geology and Geophysics, 1997.
"November 1997" The potential applications of three component aeromagnetic data in iron ore exploration have been investigated through forward model study and the interpretation of real data from the Hamersley Basin. The use of three component aeromagnetic data for iron ore exploration in the future has been recommended.

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28

Barker, Kelly. "Improved application of remote referencing data in aeromagnetic processing : insights and applications from global geomagnetic modelling." Thesis, University of Liverpool, 2016. http://livrepository.liverpool.ac.uk/3002173/.

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Magnetic surveys are an important method of understanding subsurface geology, however there are several reasons why correction by remote referencing may fail, including local induced effects, activity levels of the field, and simple distance between survey and base station. We look for ways to improve correction by remote referencing using insights from global field models and comparisons of data from a wide range of observatories. We investigate the conditions in which the behaviour of nearby observatories differ from each other, and where the CM4 comprehensive model fails to match the observed behaviour of the local geomagnetic field. The misfits are separated by cause: those due to the activity level of the geomagnetic field, and the location of the observatory. We see that CM4 is a good match to observatories in the conditions it was designed for (mid-latitudes and Kp up to 2), but also that it can produce a good fit to stations out of this range (up to Kp of 3 or 4). The correlation of misfits to CM4 allows us to separate effects due to latitude, and location on the coast. Further investigation allows us to suggest some corrections that may improve the quality and extent of magnetic data gained by surveys in these locations. High latitude stations show changes in behaviour which fall into latitudinally split groups, most likely due to the presence of induced fields from ionospheric currents. Ensuring base station and survey fall into the same grouping would eliminate many of the problems this causes. Geomagnetic storms often lead to survey data being unusable due to their effects. We find that while X component data contains mostly storm signal, the Y and Z components at many stations contain retrievable data. The recovery period of the storm can, for most stations, be used after a regression is applied. We also consider the effects of induced fields due to the tides and the coast effect -well-known effects that can be seen at many stations. We find a correction for the dominant M2 tidal effect using cosine waves. We also find an approximate correction for the coast effect, using cosine or sine waves of the Sq period as appropriate for the station pair chosen. It is also noted that small differences in location can have a large effect on the induced fields, as seen at GUI and TAM, where storms seem to have a smaller than expected effect.

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Harvey, Leslie M. "Examination of an aeromagnetic anomaly over the Talisker Mine area on the southern Fleurieu Peninsula, South Australia /." Title page, contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09SB/09sbh342.pdf.

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30

Branch, Thomas Cameron. "Electrical conductivity experiments on carbon-rich Karoo shales and forward modelling of aeromagnetic data across the Beattie Anomaly." Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/d1014544.

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The Beattie Magnetic Anomaly is the world’s longest terrestrial magnetic anomaly with a strike length of over 1000 km and a wavelength in excess of 100 km. Collinear with this is a large belt of elevated crustal conductivities called the Southern Cape Conductive Belt. Historical crustal interpretations proposed a common source of serpentinized ophiolite as an explanation for both the anomalous crustal magnetic susceptibility and electrical conductivities. Spreading between the Western and Eastern Cape of South Africa the mid- to lower crust that hosts these anomalies is obscured by the overlying Cape and Karoo Supergroups. Between 2003 and 2006, three high resolution geophysical experiments were completed across the surface maximum of the Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB). These included a magnetotelluric (MT) survey and near vertical reflection and wide angle refraction seismic profiles. Within the MT inversion model the SCCB appeared as a composite anomaly, which included a mid-crustal conductor which is spatially associated with the BMA and a laterally continuous upper crustal conductor which is located at depths equivalent to the lower Karoo Supergroup. Subsequently; the upper crustal conductor was identified in northern and eastern extensions of the magnetotelluric profile; a distance in excess of 400 km. Historical magnetometer and Schlumberger Sounding experiments have previously identified elevated conductivities in the Karoo sequences which were attributed to the Whitehill and Prince Albert formations. These carboniferous, transgressive sediments are known to be conductive from borehole conductivity surveys and direct measurements at surface. In order to constrain the conductive properties of these sediments, impedance spectroscopy (IS) experiments were completed on core samples collected from a historical borehole drilled near to the MT profile. Part One of this thesis presents the results of these experiments, which support the proposition that the Whitehill and Prince Albert Formations are responsible for the laterally continuous, sub-horizontal, upper crustal conductor visible in the MT inversion model. Vitrinite reflectance studies were performed on the same samples by the Montanuniversität, in Leoben, these results corroborate the proposition that elevated organic carbon, of meta-anthracite rank, is the primary conductive phase for the Whitehill and Prince Albert formations. Part two of this thesis completed forward modelling exercises using historical aeromagnetic data previously collected across the Beattie Magnetic Anomaly. Preliminary models were unable to fit the geometry of any single magnetic model with conductors present in the MT inversion model discounting the proposition that the SCCB and BMA arise from a single crustal unit. Two constrained models were arrived at through an iterative process that sought a best fit between the measured data and the NVR crustal interpretations. The first model, proposes a largely resistive unit which incorporates portions of elevated crustal conductivity; these conductors are spatially correlated to crustal portions also characterised by high seismic reflectivity. The size of this modelled body suggest the likely host of the BMA is an intermediate plutonic terrane, analogous with the Natal sector of the Namaqua Natal Mobile Belt as well as the Heimefrontfjella in Dronning Maud Land, Antarctica, with magnetite hosted within shear zones. This is in agreement with previous studies. The second model proposes a lower crustal sliver imaged in the NVR data at depths proximal to the Curie Isotherm for magnetite and hematite as the source of the BMA. At these depths geomagnetic properties such as burial magnetisation or thermo-viscous remanent magnetism (TVRM) can potentially be linked to regional scale tectonic processes and can theoretically elevate a body’s net magnetic susceptibility. TVRM has been proposed for long wavelength crustal anomalies elsewhere.

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Anderson, Eric D. "Aeromagnetic signature of the geology and mineral resources near the pebble porphyry cu-au-mo deposit, southwest Alaska." Thesis, Colorado School of Mines, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602616.

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Aeromagnetic data are used to better understand the geology and mineral resources near the Late Cretaceous Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska. The reduced-to-pole (RTP) transformation of regional-scale aeromagnetic data show that the Pebble deposit is within a cluster of magnetic anomaly highs. Similar to Pebble, the Iliamna, Kijik, and Neacola porphyry copper occurrences are in magnetic highs that trend northeast along the crustal-scale Lake Clark fault. A high-amplitude, short- to moderate-wavelength anomaly is centered over the Kemuk occurrence, an Alaska-type ultramafic complex. Similar anomalies are found west and north of Kemuk. A moderate-amplitude, moderate-wavelength magnetic low surrounded by a moderate-amplitude, short-wavelength magnetic high is associated with the gold-bearing Shotgun intrusive complex. The RTP transformation of the district-scale aeromagnetic data acquired over Pebble permits differentiation of a variety of Jurassic to Tertiary magmatic rock suites. Jura-Cretaceous basalt and gabbro units and Late Cretaceous biotite pyroxenite and granodiorite rocks produce magnetic highs. Tertiary basalt units also produce magnetic highs, but appear to be volumetrically minor. Eocene monzonite units have associated magnetic lows. The RTP data do not suggest a magnetite-rich hydrothermal system at the Pebble deposit. The 10 km upward continuation transformation of the regional-scale data shows a linear northeast trend of magnetic anomaly highs. These anomalies are spatially correlated with Late Cretaceous igneous rocks and in the Pebble district are centered over the granodiorite rocks genetically related to porphyry copper systems. The spacing of these anomalies is similar to patterns shown by the numerous porphyry copper deposits in northern Chile. These anomalies are interpreted to reflect a Late Cretaceous magmatic arc that is favorable for additional discoveries of Late Cretaceous porphyry copper systems in southwestern Alaska. Aeromagnetic data help to understand the three-dimensional distribution of plutonic rocks near the Pebble porphyry copper deposit. Magnetic susceptibility measurements show that rocks in the Pebble district are more magnetic than rocks of comparable compositions in the Pike Creek-Stuyahok Hills volcano-plutonic complex. The reduced-to-pole transformation of the aeromagnetic data demonstrates that the older rocks in the Pebble district produce strong magnetic anomaly highs. The tilt derivative transformation highlights a strong, northeast-trending structural grain attributed to Tertiary volcanic rocks. Multiscale edge detection maps near-surface magnetic sources that are mostly outward dipping and coalesce at depth in the Pebble district. The total horizontal gradient of the 10 km upward continued magnetic data map a circular, deep magnetic contact along which the porphyry deposits occur. Forward and inverse magnetic modeling show that the magnetic rocks in the Pebble district extend to depths greater than 9 km. The magnetic inversion is constrained by a near-surface, three-dimensional geologic model that is attributed with measured magnetic susceptibilities from various rock types in the region. The inversion results indicate that several near-surface magnetic features with moderate susceptibilities converge with depth into magnetic bodies with higher susceptibilities. This deep magnetic source appears to rise towards the surface in several areas. An isosurface value of 0.02 SI is used to depict the magnetic contact between outcropping granodiorite and non-magnetic sedimentary host rocks. The contact is shown to be outward dipping. At depths around 5 km nearly the entire model exceeds the isosurface value indicating the limits of non-magnetic host material. The inversion results show the presence of a relatively deep, northeast trending magnetic low that parallels lineaments mapped by the tilt derivative. This deep low represents a strand of the Lake Clark fault. The geodynamic setting of an accreted island-arc terrane represent a region in which several types of mineral resources may occur. The mineral resources from southwest Alaska are classified into greenstone-hosted, oxidized intrusion-related, reduced intrusion-related, and epithermal. Aeromagnetic data are related to the classified mineral resource and outcropping geology to better understand the distribution of gold-rich mineral resources. Three magnetic domains are defined by the reduced-to-pole, upward continue, and tilt derivative transforms. The greenstone-hosted mineral resources that include VMS are mapped along magnetic lineaments mostly landward of the accreted island-arc. The oxidized intrusion-related mineral resources that include porphyry copper, skarn, and Alaska-type ultramafic-mafic complexes occur along magnetic anomaly highs in the Peninsular and Kahiltna domains. Characteristic short wavelength, high amplitude magnetic anomalies suggest additional Alaska-type ultramafic-mafic complexes and skarn resources in the Kahiltna and Kuskokwim domain. Magnetic depth estimates indicate potential greenstone-hosted and oxidized intrusion-related resources occur beneath 100 m of glacial deposits. Reduced intrusion-related resources are best imaged in the more landward, Kuskokwim magnetic domain. Epithermal resources are not well imaged. The mineral potential map highlights areas most favorable for additional mineral resources.

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32

Stokes, Terence Michael. "An investigation of ground based and aeromagnetic data over the Cairngorm and other Caledonian granites in the UK." Thesis, Open University, 1994. http://oro.open.ac.uk/57502/.

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The aeromagnetic map of Great Britain shows a number of granites associated with magnetic anomalies. One of the largest of these granites, the Cairngorm pluton, has a complex overlying aeromagnetic anomaly, yet measurements show that the surface rocks have a magnetic susceptibility too low to account for this aeromagnetic field. The purpose of this investigation was to determine the likely reasons for this discrepancy employing a range of computer based techniques, and using new land-based data. Potential field data for the Cairngorm area, together with a region of the Southern Uplands, was subjected to frequency domain reduction and filtering. Hand specimens from the granite and host rock were collected for susceptibility measurements. The results have been integrated with profile models to explain the variations observed in the aeromagnetic and ground based magnetic field. The Cairngorm granites appear to be zoned at depth, with a variable thickness cap of low density, low magnetic susceptibility granite. The presence of intermediate composition rock in the upper reaches of the granite mass provides evidence for stoping, whilst the presence of intermediate composition rock at deeper levels is thought to be due to multiple magma pulses and/or differentiation. The Loch Doon granite has a low magnetic susceptibility subsurface core extending off its eastern flank. A number of correlations between the geophysics and geochemistry of the granites investigated were noted. The concept of gravrnag space has been developed and applied as a framework in which to explore the relationships between the granites of Scotland and northern England. Relationships between the background geophysics and the geochemistry of granites in the area of the proposed Iapetus Subduction zone have also been investigated.

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33

Dutra, Alanna Costa. "\"Estudo de anomalias gravimétricas e aeromagnéticas das alcalinas morro de engenho e A2, sudoeste de Goiás\"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/14/14132/tde-12032007-164243/.

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A Província Alcalina Rio Verde - Iporá, na borda norte da Bacia do Paraná é caracterizada pela presença de intrusões alcalinas com forte assinatura aeromagnética e gravimétrica, apresentando-se como anomalias quase circulares. O trabalho refinou o levantamento gravimétrico na região sudoeste de Goiás, incluindo um levantamento de detalhe sobre as intrusões de Morro do Engenho (ME) e uma intrusão a poucos quilômetros a NE de Morro de Engenho (A2), com informações gravimétricas e aeromagnéticas, e sobre a anomalia gravimétrica próxima à cidade de Britânia, sem informação de anomalia aeromagnética. As anomalias gravimétricas variam de 15 a 30 mGal com relação ao campo gravimétrico regional, enquanto que as anomalias aeromagnéticas são da ordem de ±3000nT. Foram feitas também medidas das propriedades petrofísicas de amostras da área. Os resultados da inversão 2D e 3D dos dados gravimétricos e 3D dos dados magnéticos indicam que os corpos alongam-se dentro da crosta superior até a profundidade máxima de 10 km e diâmetro da ordem de 8 km, com geometria aproximadamente cilíndrica. Os dados gravimétricos e aeromagnéticos de ME foram tratados de forma conjunta por modelamento direto (2,5D) onde foi incluída a magnetização remanescente, os resultados obtidos indicam que o volume do corpo anômalo é da ordem de 980 km3.
The Alkaline Province Rio Verde - Iporá, in the north border of the Paraná Basin is characterized by the presence of alkaline intrusions with strong gravity and magnetic signature. This project implemented a gravity survey in the Southwest of Goiás, including a detail one on Morro do Engenho Complex (ME), and one a few kilometers towards NE from ME over an aeromagnetic anomaly known as A2, and over a gravity anomaly close to Britânia city. ME and A2 have magnetic anomaly. The gravity anomalies vary from 15 to 30 mGal in relation to the regional gravity field, while the magnetic anomalies are of the order ±3000nT. Measurements of petrophysical properties of samples from the area were also done. The results present the inversion of the gravity and magnetic data, suggesting that the bodies are inside of the superior crust until the maximum depth of 10 km, in a cylindrical form with 8 to 10 km in diameter. 2.5D direct modeling was also done for ME including remanent magnetization and was performed at the two data sets together, the obtained results indicate that the close volume of the anomalous body it is 980 km3.

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Basford, Paul W. "Investigation of isolated aeromagnetic anomalies in the Kimba region of South Australia, using magnetic, gravity and induced polarization methods /." Title page, contents and abstract only, 1992. http://web4.library.adelaide.edu.au/theses/09SB/09sbb299.pdf.

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Thesis (B. SC.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1993.
On title page : "National Grid reference : Kimba Sheet s1 53-7(1:250 000) Whyalla Sheet S153-8(1:250 000) Yardea Sheet S153-3(1:250 000)." Includes bibliographical references (leaves 22-24).

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35

Nnange, Joseph Metuk. "The crustal structure of the Cameroon Volcanic Line and the Foumban Shear Zone based on gravity and aeromagnetic data." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305782.

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36

Samson, Esuene M. A. "A critical evaluation of the "Tilt-Depth" method of magnetic data interpretation : application to aeromagnetic data from North Eastern (NE) Nigeria." Thesis, University of Leeds, 2012. http://etheses.whiterose.ac.uk/4925/.

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To simplify the complex total magnetic field intensity (T) on datasets obtained from locations close to the geomagnetic Equator (inclinations |α| ≤ 20°) such datasets are routinely reduced-to-equator (RTE), since they cannot be stably reduced-to-pole (RTP). RTE anomalies tend to have small amplitudes and exhibit azimuth-based anisotropy, unlike RTP anomalies. Anisotropy describes the dependence of the amplitude and shape of an RTE anomaly on the strike direction of its source. For example, an East-West striking contact/fault will generate a strong RTE anomaly response whereas a North-South striking equivalent will not. Where adjacent sources occur, anisotropy causes interference between anomalies, displacing anomalies relative to their sources. This makes using magnetic data to map structures in regions that are close to the geomagnetic equator difficult or potentially of limited value. This thesis develops a strategy to interpret RTE datasets and applies it to determine the basement structure in NE Nigeria where |α| ≤ 8°. This area has >50% of the basement concealed beneath Cretaceous and Quaternary sediments of the Benue Trough and Chad basin, respectively. The aim of the study is to structurally map the basement underlying the Benue and Chad rifted basins in NE Nigeria, by tracing and determining the depths of basement faults and associated structures. The first-order derivative-based "Tilt-Depth" method has been evaluated to determine its effectiveness when applied to RTE datasets to determine the location and depth of structures. The method was tested first using RTE and RTP equivalents of synthetic  datasets obtained from profiles across East-West striking, 2D contacts at various depths, inclinations of effective magnetisation (ϕ), and dips (d). RTP datasets were used throughout as reference models. Errors in "Tilt-Depth" method estimates were invariant to changes in depth, but sensitive to changes in ϕ and d of sources. At error limits of 0-20%, the method effectively estimates locations and depths of 2D contacts when dip is within the 75 ≤ d° ≤ 105 range, inclination of remanent magnetisation relative to induced magnetisation is within the 155 ≤ β° ≤ 205 range (magnetisations are collinear), and Koenigsberger ratio (Q) of remanent to induced magnetisation amplitudes ≤ 1. Relationships between Q, α , β and ϕ suggests that the simplification of remanence-laden anomalies due to magnetisations being collinear results from deviations of ϕ from α of ≤12° when Q≤1. Similar deviations occur between ϕ and α , for all β values, when Q≤0.2. Hence, remanent magnetisation is negligible for RTP or RTE datasets when a priori information suggests Q≤0.2. The "Tilt-Depth" method was further tested for anisotropy-induced anomaly interference effects using RTP or RTE of the Complex “Bishop” Model (CBM) and Tanzania grids. The CBM grid contains 2D contacts of various strikes and three-dimensional (3D) sources with non-2D contacts at various depths (all precisely known), and satisfy the d, ϕ and Q requirements above. The Tanzania grid presented a real dataset from a Karoo rift basin, where more randomly striking 2D contacts occur at unknown depths. For comparison, the second vertical derivative, analytic signal amplitude, local wavenumber, and the horizontal gradient magnitudes of Ѳ (HGM(Ѳ)) and  (HGM()) methods were also tested using these grids. Locations estimated from all these methods show that: (1) Sources of all shapes and strikes are correctly imaged on RTP grids; (2) North-South striking 2D contacts are not imaged at all on RTE datasets, but can be inferred from linear alignments of stacked short wavelength East-West striking anomalies; (3) 2D contacts with strikes ranging from N045 to N135° are correctly imaged on RTE datasets; (4) Anomalies from poorly isolated 2D contacts with N±020° strikes interfere to further complicate RTE datasets, making it difficult to correctly image these sources; and (5) RTE anomalies from 3D sources tend to smear in an East-West direction, extending such anomalies well past edges of their sources along this direction. These North-South striking non-2D edges are not imaged at all, whilst their East-West striking non 2D (Northern and Southern edges are correctly imaged. Depths estimated for 2D and non-2D contacts with strikes ranging from N045 toN135° from RTP and RTE of the CBM grids, using the local wavenumber, analytic signal amplitude and |Ѳ| = 27°- based “Tilt-Depth" methods show that: (1) "Tilt-Depth” and local wavenumber methods underestimate the actual depth of sources, while the analytic signal amplitude method provided both severely underestimated and overestimated depths. Thus, “Tilt-Depth” and local wavenumber estimates were easier to utilise and interpret; (2) "Tilt-Depth" and local wavenumber methods underestimate 2D contacts from RTP and RTE grids by up to 25 and 35% of their actual depths, respectively; (3) 'Tilt-Depth" and local wavenumber methods, respectively, underestimate depths of East-West striking non-2D edges of 3D sources by about 35 and 30% from the RTP grid; and (4) "Tiit-Depth" method consistently underestimates non-2D contacts from RTE grids by up to 40%. Using knowledge gained from the above tests, all the methods were applied to a NE Nigeria  (RTE) dataset, to delineate basement structures in the area. The dataset was a 1 km upward-continued grid with 1 km x 1 km cell size, and extended well beyond NE Nigeria into Niger, Chad and Cameroon Republics. While basement depths were estimated from the dataset using the "Tilt-Depth" and local wavenumber methods only, these methods and the second vertical derivative, analytic signal amplitude, local wavenumber, as well as the horizontal gradient magnitudes of Ѳ (HGM(Ѳ)) and  (HGM()) methods, were used to map source edge locations. A basement structure map of NE Nigeria was obtained using the above methods and found not to be dominated by North-South striking faults. Instead the basement is dissected mainly by near vertical, NE-SW trending faults against which NW-SE or E-W trending faults terminate. The relationship between these inferred faults, basement horsts, volcanic plugs, and basement depressions, and outcrop information suggests that rifting was episodic as the mainly NorthEast directed rift propagation direction was occasionally deflected by transcurrent faults to relieve differential stresses built up from wall rock and/or crustal resistance. Apparent stress relief features include the Yola basin, flood basalts, Lamurde Anticline and Kaltungo Inlier. A number of isolated depocenters, mainly half grabens, with sediment thickness exceeding 11km seem to occur in NE Nigeria. Outside these depocenters, basement occur at depths generally shallower than 0.5 km, except where intra-basinal horsts occur, at depths shallower than 2.5 km. These depths agree well with well information and seismic data interpretation, and show the SW Chad basin depocenter to be isolated from adjoining basins in Cameroon, Chad and Niger Republics.

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37

Sunderland, Andrew. "Characterising and improving a magnetic gradiometer for geophysical exploration." University of Western Australia. School of Physics, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0111.

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[Truncated abstract] Magnetic gradiometers are powerful tools for mineral exploration. The magnetic field contains valuable information about the mineral content of the surveyed terrain. The magnetic gradient specifies the amount of spatial variation in the direction and magnitude of the magnetic field. Surveys that measure the magnetic gradient provide vastly more information about geological targets than the magnetic field alone. This technology could have enormous benefits in terms of new discoveries and lower exploration costs. The magnetic gradient is normally calculated by subtracting the outputs of two total field magnetometers which are separated by a baseline. In 1997, a direct string magnetic gradiometer (DSMG) was developed that directly measures magnetic gradients using only a single string as its sensing element. This thesis describes research conducted to improve the sensitivity and performance of the DSMG. The main advantage of the DSMG is that only gradients can induce second harmonic vibrations in the string. Thus, the DSMG is insensitive to uniform magnetic fields that we are not interested in, such as the global magnetic field of the Earth. By using inductive electronics to measure second harmonic string vibrations, we can select to measure the magnetic gradient of nearby targets. Recent work has shown that a magnetic gradiometer with a noise floor of 0.01 nT/m/ v Hz should be sufficiently sensitive for geophysical exploration. In order to reach this goal, this thesis presents an investigation of all noise sources affecting the DSMG. ... Gas damping is negligible in high vacuum and no vibration isolation is required. This means that longer strings with low resonant frequencies can be used. Using theoretical modelling, I show that a space borne DSMG should be able to match the white noise level of SQuID based magnetic gradiometers and have a lower 1/f noise corner. Deployment in space could be the most viable application of the DSMG because of the ease of operation and enhancement of sensitivity. If the thermal noise level is reduced then other sources of noise will start to become more important. When rotated in the Earth's magnetic field, the DSMG detects a pseudo magnetic gradient despite the field being almost uniform. A possible cause is magnetically susceptible parts which are magnetically aligning with the Earth's field. I have conducted a thorough investigation of magnetic susceptible parts in the DSMG and reported the results in this thesis. In the DSMG, a pair of inductive pickup coils are used to measure the string's displacement with a root mean square accuracy of 1011 m/ v Hz. This is adequate at present but the inductive electronics may not be sensitive enough after other improvements in the DSMG are implemented. Here, I present a new capacitive displacement readout with a high sensitivity of 1013 m/ v Hz. The thesis also presents some magnetic gradient measurements in the lab and the results of a ground survey in the field. These trial measurements are used to characterise the DSMG and demonstrate its effectiveness for airborne surveying.

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Pereira, Janaína Gattermann. "Contribuição ao estudo geológico da Bacia do Camaquã – RS, através de modelagem aeromagnética 2,5D." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/56294.

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A Bacia do Camaquã (BC) é uma unidade geológica fundamental no esclarecimento da evolução geotectônica do Rio Grande do Sul. Ela agrupa e preserva, em parte, diferentes associações vulcano-sedimentares representativas do estágio de transição da Plataforma Sul-Americana. Depositada sobre os terrenos ígneos e metamórficos do Escudo Sul-riograndense, sua evolução estratigráfica e geocronológica tem sido pesquisada por diversos autores. Por outro lado, a geofísica tem contribuído pouco nestes estudos, apesar de seu grande potencial como ferramenta exploratória. Por esse motivo, e mediante o avanço das técnicas de processamento de dados, uma nova abordagem foi aplicada ao levantamento aeromagnético realizado em 1972 pelo Serviço Geológico do Brasil, com o objetivo de contribuir para o conhecimento geológico e tectônico da área. O reprocessamento destas variáveis permitiu a reinterpretação da BC e a geração de uma proposta de modelo para o seu arcabouço estrutural. Foram gerados mapas temáticos da BC e realizada a modelagem 2,5D de dados aeromagnéticos de um perfil NW-SE, com 40Km de extensão, localizado ao sul da área. Os mapas temáticos aeromagnéticos, além de delimitar os principais corpos e estruturas da região, permitiram dividir a área de estudo em três grandes domínios geofísicos: Oeste, Central e Leste, separados pela Anomalia Magnética de Caçapava do Sul e pela Zona de Cisalhamento Dorsal de Canguçu, respectivamente. A modelagem aeromagnética 2,5D ilustrou anomalias entre -40 e -110nT associadas às rochas vulcânicas e metamórficas aflorantes e à ocorrência do embasamento cristalino em subsuperfície, modelado a uma profundidade máxima de 7000m na parte NW do perfil. Em termos geotectônicos, o modelo obtido para o perfil evidenciou falhas extensionais, sugerindo uma configuração que se assemelha a um arranjo composto por horsts e grábens, característico de um sistema de riftes, atribuindo um regime distensivo para evolução da BC. O modelo também ilustrou dois altos do embasamento nas bordas do perfil, relacionados aos altos de Caçapava do Sul e da Serra das Encantadas. Esse soerguimento do embasamento nos flancos do perfil e o comportamento flexural que o mesmo assume na porção central, podem ser indicativos de um regime compressivo ocorrido anteriormente ao processo de rifteamento e à deposição da BC. A baixa susceptibilidade dos sedimentos que preenchem a bacia é um indicativo de que as áreas fonte podem ser os altos de Caçapava do Sul e da Serra das Encantadas, compostos por rochas graníticas e gnáissicas de baixa susceptibilidade magnética. O reprocessamento das variáveis geofísicas, os filtros aplicados no perfil estudado e a modelagem geofísica, mostraram-se técnicas eficientes para mapeamento geológico e delimitação do arcabouço estrutural, gerando um modelo geológico representante de uma porção da BC e permitindo assim, um avanço no entendimento de sua arquitetura e evolução geotectônica.
The Camaquã Basin (CB) is an important geologic unit and the knowledge of these rocks helps to clarify the geotectonic evolution of Rio Grande do Sul State. It has partially preserved different volcano-sedimentary associations representing the transition stage of South American Platform. The rocks of the basin overlays the igneous and metamorphic terrains of the Sul-riograndense Shield and its stratigraphic and geochronologic evolution have been widely studied by several authors. On the other hand, the geophysics has a small contribution to these studies, in despite of its great potential as an exploratory tool. Therefore, with the improvement of the data processing techniques, a new approach was applied in the aeromagnetic survey, acquired in 1972 by Brazilian Geological Survey. In this context, this research aims to contributes to the geologic and tectonic knowledge of the basin. The reprocessing of these variables led to the reinterpretation of the CB and to the production of a suggested model for its structural framework. Thematic maps and a 2,5D model of the CB were made from aeromagnetic data of a NW-SE section, with 40 km long, located in the south of the basin. These thematic aeromagnetic maps set out the main bodies and structures inside the basin and also provide a division of the study area into three main geophysics domains: West, Central and East, separated by the Magnetic Anomaly of Caçapava do Sul and the Dorsal de Canguçu Shear Zone, respectively. The 2,5D aeromagnetic modeling shows anomalies between -40 e -110nT, associated with volcanic and metamorphic outcropping rocks and the crystalline basement in subsurface, modeled at a maximum deep of 7000m in the NW portion of the section. In terms of geotectonic, the model obtained for this section revealed extensional faults, suggesting a sketch that resembles a horst and graben structure. This structure is typical for a rift system, assigning a distensive strain event in the evolution of the CB. The model also displayed two basement uplifts on the section borders, related with Caçapava do Sul and Serra das Encantadas uplifts. This uplift of the basement on section borders and its flexural behavior in the central portion can be an evidence of a compressive regime that occurred before the rift process and the sedimentation of the Camaquã Basin. The low susceptibility of the sediments that fill the basin is an indicative that the source areas can be the highs of Caçapava do Sul and Serra das Encantadas, composed mainly by low susceptibility granitic and gneissic rocks. The reprocessing of the geophysical variables, together with the frequency filters applied and the geophysical modeling, proved to be an efficient technique to the geologic mapping and to define the structural framework of the area. Based on this, a geologic model was created, which represents a specific portion of the basin and introduced an important knowledge of the structural framework and geotectonic evolution of the Camaquã Basin.

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Baptiste, Julien. "Cartographie structurale et lithologique du substratum du Bassin parisien et sa place dans la chaîne varisque de l’Europe de l’Ouest : approches combinées géophysiques, pétrophysiques, géochronologiques et modélisations 2D." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2052/document.

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Nous avons mené cet exercice au travers d’une étude pluridisciplinaire combinant des couvertures géophysiques (gravimétrie et aéromagnétisme) réactualisées ou nouvelles, des informations géologiques acquises sur le terrain ou sur carottes de forages pétroliers et un catalogage de propriétés pétrophysiques des roches. Sur une large moitié sud du Bassin parisien, du Massif armoricain aux Vosges, nous avons : i) réalisé un schéma structural du substratum du Bassin parisien, ii) proposé une carte géologique détaillée, sous couverture, iii) réactualisé la carte de zonation de la chaîne varisque en France, intégrant de nouvelles datations sur carottes de forages ayant atteint le substratum. D’après ces résultats, la suture éo-varisque se poursuit d’ouest en est, de la partie sud-armoricaine jusqu’au nord des Vosges, le domaine nord-armoricain se prolonge jusqu’à la faille de Bray et la zone saxothuringienne est continue d’est (Vosges) en ouest (Manche). Egalement, à l’aide de modélisations conjointes de gravimétrie et magnétisme, intégrant l’information recueillie dans le forage de Couy, la nature du substratum environnant désormais mieux connu, ainsi que les contraintes pétrophysiques nouvelles, nous proposons que la source de l’AMBP soit un corps plutonique intermédiaire à acide. Pour finir, en compilant la bibliographie et nos résultats, nous proposons que ce corps se soit mis en place entre le Viséen inférieur et le Viséen supérieur, dans une ouverture NNE-SSW selon un raccourcissement maximal NNW-SSE
Mapping the cadomian/variscan basement buried beneath the Paris basin is a key objective to improve the geological knowledge of the Variscan belt in West Europe. We address this objective using a combination of new and updated potential field data (aeromagnetic and gravity), as well as information provided by field studies and drill cores, and a library of petrophysical characteristics measured on field samples. On a large southern half of the Paris basin, from the Armorican Massif to the Vosges: i) we made a new interpretative structural sketch map under the sedimentary cover, ii) we proposed a detailed geological map of the Paris basin substratum, iii) we updated the tectonic sketch of the Variscan belt in France, supported by new geochronological determinations on deep drill cores. Altogether, these results show that the eo-Variscan suture is extended from the southern part of the Armorican Massif to the northern Vosges. Eastwards, the North-Armorican domain reaches the Bray fault; and the Saxothuringian zone is extended from the Vosges to the English Channel. In addition, based on combined aeromagnetic and gravity 2D modelling constrained by Couy deep borehole data, the PBMA source is interpreted as a deep intermediate-alkaline plutonic body. Finally, compiling bibliographic information together with our new results, we hypothesize that this magmatic body could have been emplaced in the early to late Visean period, during a NNE-SSW opening under a NNW-SSE shortening

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Le, Maire Pauline. "Caractérisation des anomalies magnétiques, approches théoriques et expérimentales : applications à des objets anthropiques et géologiques." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAH006/document.

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L’objectif de ce travail est d’améliorer la caractérisation des sources à l’origine d’anomalies magnétiques, par le biais de développements théoriques et expérimentaux. Pour des structures invariantes dans une direction horizontale (structures à 2D), l’idée de Nabighian (1972) a été généralisée, ce qui implique une nouvelle façon d’étudier les méthodes potentielles à 2D. Ces développements ont permis de proposer une nouvelle approche théorique et de nouvelles représentations dans le plan complexe des fonctions magnétiques. La deuxième approche de ce travail est expérimentale. Une étude y est faite par le biais de données et de cas synthétiques, afin d’estimer l’apport d’acquisitions magnétiques à différentes altitudes pour caractériser une source. Dans un troisième temps, les développements théoriques et expérimentaux sont mis en œuvre pour deux exemples : des anomalies magnétiques en domaine océanique de type Vine et Mathews et une cartographie pour l’archéologie
Magnetic anomalies recorded outside bodies provide high quality information relative to buried structures. By using theoretical and experimental developments, this thesis aims to improve the characterization of the source inducing the magnetic anomaly. Firstly, some properties of three dimensional magnetic functions are presented, for example the presence of several maxima of the analytic signal operator (3D) is demonstrated. The Nabighian (1972) equation is generalized, which imply a new process to study potential method in two dimensions. These developments enable a new visualization of the anomaly in the complex field. The second approach is experimental. Synthetic cases are used to estimate the contribution of different configurations of magnetic data acquisitions at different altitudes to characterize the magnetic source. Theoretical and experimental developments are finally applied to two field examples: oceanic magnetic anomalies and archaeological magnetic prospection

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Hahne, Kai. "Detektion eines mesozoischen Gangschwarmes in NW Namibia und Rekonstruktion regionaler Spannungszustände während der Südatlantiköffnung." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/177/.

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Gangschwärme nehmen eine bedeutende Stellung im Verständnis zur kontinentalen Fragmentierung ein. Einerseits markieren sie das Paläo-Spannungsfeld und helfen bei der Rekonstruktion der strukturellen Entwicklung der gedehnten Lithosphäre, andererseits gibt ihre petrologische Beschaffenheit Aufschluß über die Entstehung des Magmas, Aufstieg und Platznahme und schließlich erlaubt ihre Altersbestimmung die Rekonstruktion einer chronologischen Reihenfolge magmatischer und struktureller Ereignisse.

Das Arbeitsgebiet im namibianischen Henties Bay-Outjo Dike swarm (HOD) war zur Zeit der Unterkreide einem Rifting mit intensiver Platznahme von überwiegend mafischen Gängen unterworfen. Geochemische Signaturen weisen die Gänge als erodierte Förderkanäle der Etendeka Plateaubasalte aus. Durch den Einsatz von hochauflösenden Aeromagnetik- und Satellitendaten war es möglich, die Geometrie des Gangschwarmes erstmals detailliert synoptisch zu erfassen. Viele zu den Schichten des Grundgebirges foliationsparallel verlaufende magnetische Anomalien können unaufgeschlossenen kretazischen Intrusionen zugeordnet werden.

Bei der nach Norden propagierenden Südatlantiköffnung spielte die unterschiedliche strukturelle Vorzeichnung durch die neoproterozoischen Faltengürtel sowie Lithologie und Spannungsfeld des Angola Kratons eine bedeutende Rolle. Im küstennahen zentralen Bereich war dank der Vorzeichnung des Nordost streichenden Damara-Faltengürtels ein Rifting in Nordwest-Südost-Richtung dominierend, bis das Angola Kraton ein weiteres Fortscheiten nach Nordosten hemmte und die Vorzeichnung des Nordwest streichenden Kaoko-Faltengürtels an der Westgrenze den weiteren Riftverlauf und die letztendlich erfolgreiche Öffnung des Südatlantiks bestimmte. Aus diesem Grund kann das Gebiet des HOD als ein failed rift betrachtet werden.

Die Entwicklung des Spannungsfeldes im HOD kann folgendermaßen skizziert werden:

1. Platznahme von Gängen bei gleichzeitig hoher Dehnungsrate und hohem Magmenfluß.
2. Platznahme von Zentralvulkanen entlang reaktivierter paläozoischer Lineamente bei Abnahme der Dehnungsrate und fortbestehendem hohen Magmenfluß.
3. Abnahme/Versiegen des Magmenflusses und neotektonische Bewegungen führen zur Bildung von Halbgräben.
Dike swarms play a fundamental role in understanding continental breakup. On the one hand they represent strain markers of the paleo-deformation field and help to reconstruct the structural evolution of the rifted lithosphere. On the other hand their magmatic infill contains information about the conditions of magma generation, ascent and emplacement. Finally, dating of dikes allows reconstructing a chronological order of magmatic and structural events. The study area of the Namibian Henties Bay-Outjo Dike swarm (HOD) underwent tectonic extension in the Lower Cretaceous associated with the widespread emplacement of predominantly mafic dikes and intrusive ring complexes representing the remnants of volcanic centres. Geochemical signatures of the dikes prove them to be the feeder structures of the Etendeka Plateau Basalts. The application of recent high resolution aeromagnetic surveys and satellite imaging revealed the dike swarm's extent and geometry for the first time. The distribution and geometry of the dikes shown in the aeromagnetics reflect the propagation of the South Atlantic opening from south to north by their relative-ages.

Northwest-southeast-directed rifting was dominant in the central coastal area, due to the structural control of the northeast striking basement structures until further propagation was hampered by the Angola Craton. Subsequently the structural control of the coast-parallel Kaoko Belt became dominant and determined the successful opening of the South Atlantic. Hence, the area of the HOD can be considered as a failed rift.

The stress field evolution within the HOD can be outlined as follows:

1. Intrusion of dikes when extension rates as well as magma supply were high.
2. Intrusion of volcanic ring complexes along reactivated Panafrican lineaments when extension rates decreased and magma supply remained high.
3. Neotectonic movements create half-grabens after the termination of magmatism.

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42

Potie, Gilbert. "Contribution à l'étude géologique de la frontière SE de la plaque caraibe : la serrania del interior oriental sur le transect Cumana-Urica et le bassin de Maturin (Vénézuela) : application de données géophysiques et géologiques à une interpretation structurale." Brest, 1989. http://www.theses.fr/1989BRES2005.

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L'analyse des donnees stratigraphiques et structurales de la serrania del interior confirme l'existence de 2 cycles sedimentaires cretace moyen-miocene. L'interpretation des profils sismique montre que la partie enfouie de l'edifice est structuree par des accidents suggerant la presence d'un decollement. L'interpretation gravimetrique et aeromagnetique confirme que la serrania est un exemple de chaine d'avant pays decollee et mise en place dans un contexte particulier associant une composante principale en coulissage dextre avec une collision oblique

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43

Inkster, D. H. "Filtering aeromagnetic data to reduce the masking effect of near-surface basalt." Thesis, 1995. http://hdl.handle.net/2440/88300.

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This item is only available electronically.
This project investigated two areas in northern Queensland where Tertiary basalt covers igneous and metamorphic rocks considered prospective for gold. The moderate to high magnetic susceptibility of the basalt, combined with variations in its thickness, give a high degree of variability to the aeromagnetic data which impedes interpretation of deeper structures. Low-pass filters of the Butterworth, averaging-window and median-window types were used initially, because the near-surface signals tends to be higher in spatial frequency. Upward continuation was also used. All were able to remove high frequencies but none showed a clear superiority at simultaneously resolving detail. The best results eventually were obtained from a differencing method in which the high-frequency signals were first emphasised by downward continuation and then subtracted from the original signal. This enabled identification of several features which had not been visible in either the original, or low-pass-filtered data. The differencing method is shown to be equivalent to subtracting the first vertical derivative (multiplied by a scaling factor) from the total magnetic intensity. The generality of this approach was then tested by applying it to another dataset with different sampling and geological parameters. The resolution available in the second case is limited by the 400m flight line spacing, instead of the 200m of the first dataset. The results were less successful but there is evidence that the approach is still valid.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 1995

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44

Harvey, L. M. "Examination of an aeromagnetic anomaly over the Talisker Mine area on the southern Fleurieu Peninsula, South Australia." Thesis, 1989. http://hdl.handle.net/2440/119293.

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A N-E striking elongate aeromagnetic anomaly is observed over the Talisker Mine area, on the southern Fleurieu Peninsula, which has character and amplitude similar to an anomaly observed at Delamere (several kilometres to the north) found to be caused by magnetic Brachina Formation. Geological and geophysical techniques have been used to determine if the rock type at Talisker is also magnetic Brachina Formation, why there is a gap between the two anomalies, and why the anomaly at Talisker ends near the south coast. Geological mapping, microscopy and petrologic studies have been used in conjunction with local ground magnetic surveys and modelling procedures, to reveal magnetic Brachina Formation as the cause of the anomaly at Talisker. Mapping has shown the anomaly to be the result of a sliver of magnetic Brachina Formation caught up within a local zone of intense deformation that extends for at least 1500m across strike, and which outcrops on the coast. The Brachina Formation is sheared out against Cambrian Backstairs Passage Formation to the south, forming the southern end to the anomaly. To the north, the Brachina Formation suffered deeper erosion during Permian times, and is covered by a greater thickness of non-magnetic cover which causes the apparent gap in the aeromagnetic anomaly.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 1989

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45

Odwar, Henry Dilah. "Combined MAGSAT and aeromagnetic investigation of the Alpha Ridge crust." 1993. http://hdl.handle.net/1993/17767.

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46

Rajagopalan, Shanti. "Aeromagnetic interpretation of the Kanmantoo Group, South Australia / Shanti Rajagopalan." 1989. http://hdl.handle.net/2440/19036.

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Processed.
Bibliography: leaves 115-128.
xi, 128 leaves : ill., maps (some col.), 1 folded ; 30 cm. + 2 microfiche, 5 maps (folded), appendix and errata in pocket inside back cover.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--Dept. of Geology and Geophysics, University of Adelaide, 1989

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47

Hitchman, Adrian P. "Interactions between aeromagnetic data and electromagnetic induction in the earth." Phd thesis, 1999. http://hdl.handle.net/1885/147975.

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48

Rajagopalan, Shanti. "Aeromagnetic interpretation of the Kanmantoo Group, South Australia / Shanti Rajagopalan." Thesis, 1989. http://hdl.handle.net/2440/19036.

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Bibliography: leaves 115-128.
xi, 128 leaves : ill., maps (some col.), 1 folded ; 30 cm. + 2 microfiche, 5 maps (folded), appendix and errata in pocket inside back cover.
Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1989

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49

Dhu, Trevor. "The use of fractal dimension for texture-based enhancement of aeromagnetic data." 2008. http://hdl.handle.net/2440/49982.

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This thesis investigates the potential of fractal dimension (FD) as a tool for enhancing airborne magnetic data. More specifically, this thesis investigates the potential of FD-based texture transform images as tools for aiding in the interpretation of airborne magnetic data. A series of different methods of estimating FD are investigated, specifically: • geometric methods (1D and 2D variation methods and 1D line divider method); • stochastic methods (1D and 2D Hurst methods and 1D and 2D semi-variogram methods), and; • spectral methods (1D and 2D wavelet methods and 1D and 2D Gabor methods). All of these methods are able to differentiate between varying theoretical FD in synthetic profiles. Moreover, these methods are able to differentiate between theoretical FDs when applied to entire profiles or in a moving window along the profile. Generally, the accuracy of the estimated FD improves when window size is increased. Similarly, the standard deviation of estimated FD decreases as window size increases. This result implied that the use of moving window FD estimates will require a trade off between the quality of the FD estimates and the need to use small windows to allow better spatial resolution. Application of the FD estimation methods to synthetic datasets containing simple ramps, ridges and point anomalies demonstrates that all of the 2D methods and most of the 1D methods are able to detect and enhance these features in the presence of up to 20% Gaussian noise. In contrast, the 1D Hurst and line divider methods can not clearly detect these features in as little as 10% Gaussian noise. Consequently, it is concluded that the 1D Hurst and line divider methods are inappropriate for enhancing airborne magnetic data. The application of these methods to simple synthetic airborne magnetic datasets highlights the methods’ sensitivity to very small variations in the data. All of the methods responded strongly to field lines some distance from the causative magnetic bodies. This effect was eliminated through the use of a variety of tolerances that essentially required a minimum level of difference between data points in order for FD to be calculated. Whilst this use of tolerances was required for synthetic datasets, its use was not required for noise corrupted versions of the synthetic magnetic data. The results from applying the FD estimation techniques to the synthetic airborne magnetic data suggested that these methods are more effective when applied to data from the pole. Whilst all of the methods were able to enhance the magnetic anomalies both at the pole and in the Southern hemisphere, the responses of the FD estimation techniques were notably simpler for the polar data. With the exception of the 1D Hurst and line divider methods, all of the methods were also able to enhance the synthetic magnetic data in the presence of 10% Gaussian noise. Application of the FD estimation methods to an airborne magnetic dataset from the Merlinleigh Sub-basin in Western Australia demonstrated their ability to enhance subtle structural features in relatively smooth airborne magnetic data. Moreover, the FD-based enhancements were able to enhance some features of this dataset better than any of the conventional enhancements considered (i.e. an analytic signal, vertical and total horizontal derivatives, and automatic gain control). Most of the FD estimation techniques enhanced similar features to each other. However, the 2D methods generally produced clearer results than their associated 1D methods. In contrast to this result, application of the FD-based enhancements to more variable airborne magnetic data from the Tanami region in the Northern Territory demonstrated that these methods are not as well suited to this style of data. The main conclusion from this work is that FD-based enhancement of relatively smooth airborne magnetic data can provide valuable input into an interpretation process. This suggests that these methods are particularly useful for aiding in the interpretation of airborne magnetic data from regions such as sedimentary basins where the distribution of magnetic sources is relatively smooth and simple.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1339560
Thesis (Ph.D.) - University of Adelaide, Australian School of Petroleum, 2008

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50

Dhu, Trevor. "The use of fractal dimension for texture-based enhancement of aeromagnetic data." Thesis, 2008. http://hdl.handle.net/2440/49982.

Full text

Abstract:

This thesis investigates the potential of fractal dimension (FD) as a tool for enhancing airborne magnetic data. More specifically, this thesis investigates the potential of FD-based texture transform images as tools for aiding in the interpretation of airborne magnetic data. A series of different methods of estimating FD are investigated, specifically: • geometric methods (1D and 2D variation methods and 1D line divider method); • stochastic methods (1D and 2D Hurst methods and 1D and 2D semi-variogram methods), and; • spectral methods (1D and 2D wavelet methods and 1D and 2D Gabor methods). All of these methods are able to differentiate between varying theoretical FD in synthetic profiles. Moreover, these methods are able to differentiate between theoretical FDs when applied to entire profiles or in a moving window along the profile. Generally, the accuracy of the estimated FD improves when window size is increased. Similarly, the standard deviation of estimated FD decreases as window size increases. This result implied that the use of moving window FD estimates will require a trade off between the quality of the FD estimates and the need to use small windows to allow better spatial resolution. Application of the FD estimation methods to synthetic datasets containing simple ramps, ridges and point anomalies demonstrates that all of the 2D methods and most of the 1D methods are able to detect and enhance these features in the presence of up to 20% Gaussian noise. In contrast, the 1D Hurst and line divider methods can not clearly detect these features in as little as 10% Gaussian noise. Consequently, it is concluded that the 1D Hurst and line divider methods are inappropriate for enhancing airborne magnetic data. The application of these methods to simple synthetic airborne magnetic datasets highlights the methods’ sensitivity to very small variations in the data. All of the methods responded strongly to field lines some distance from the causative magnetic bodies. This effect was eliminated through the use of a variety of tolerances that essentially required a minimum level of difference between data points in order for FD to be calculated. Whilst this use of tolerances was required for synthetic datasets, its use was not required for noise corrupted versions of the synthetic magnetic data. The results from applying the FD estimation techniques to the synthetic airborne magnetic data suggested that these methods are more effective when applied to data from the pole. Whilst all of the methods were able to enhance the magnetic anomalies both at the pole and in the Southern hemisphere, the responses of the FD estimation techniques were notably simpler for the polar data. With the exception of the 1D Hurst and line divider methods, all of the methods were also able to enhance the synthetic magnetic data in the presence of 10% Gaussian noise. Application of the FD estimation methods to an airborne magnetic dataset from the Merlinleigh Sub-basin in Western Australia demonstrated their ability to enhance subtle structural features in relatively smooth airborne magnetic data. Moreover, the FD-based enhancements were able to enhance some features of this dataset better than any of the conventional enhancements considered (i.e. an analytic signal, vertical and total horizontal derivatives, and automatic gain control). Most of the FD estimation techniques enhanced similar features to each other. However, the 2D methods generally produced clearer results than their associated 1D methods. In contrast to this result, application of the FD-based enhancements to more variable airborne magnetic data from the Tanami region in the Northern Territory demonstrated that these methods are not as well suited to this style of data. The main conclusion from this work is that FD-based enhancement of relatively smooth airborne magnetic data can provide valuable input into an interpretation process. This suggests that these methods are particularly useful for aiding in the interpretation of airborne magnetic data from regions such as sedimentary basins where the distribution of magnetic sources is relatively smooth and simple.
Thesis (Ph.D.) - University of Adelaide, Australian School of Petroleum, 2008

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