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

Mapping anomalies in the Earth’s magnetic field is one method used in applied geophysics, for exploring buried structures and objects. Magnetic surveys can be ground-based or made airborne, onboard airplanes, helicopters, or unmanned aerial vehicles (UAV), also known as drones. The measurements in this project were made as part of a mapping project by the Swedish Geological Survey (SGU) in the Enåsen area in Hälsingland, central Sweden. The magnetic data were collected by SGU in the field summer of 2021. The aim of this project is to model the data from UAV-borne surveys and validate them by checking the response with the measure ground-based data collected by SGU and compare several different profiles to investigate the different results from ground-based vs. UAV-borne surveys. Two models from two different UAV flight lines were made using the software Potent, to show anomalies in the magnetic field intensity. The modelling results show a relatively good correlation between the response from the model and ground-based data. However, there are detailed variations in the ground-based data that are not resolved by the UAV data. This is partly because of the height difference and partly different sampling. The magnetic anomalies in the project area were interpreted, with the help of the modelled profiles, as being caused mainly by geological units consisting of metasedimentary rock/migmatite. These units generally dip with 30-50°, some of them containing Cuand Au-mineralizations. The dip, rock type, and magnetic susceptbilities of these units match the field data from SGU relatively well and are also backed up by SGU models of electrical resistivity from the same area. / Kartläggning av avvikelser i jordens magnetfält är en metod som används inom tillämpad geofysik för att upptäcka underjordiska strukturer och objekt. Magnetiska undersökningar kan utföras på marken eller från luften, med hjälp av flygplan, helikopter eller drönare. De geofysiska mätningarna i detta projekt gjordes som en del av ett karteringsprojekt av Sveriges geologiska undersökning (SGU) i Enåsen, Hälsingland. Dessa magnetiska data insamlades av SGU under sommaren 2021. Syftet med projektet är att modellera magnetiska data insamlade med hjälp av drönare, för att sedan kontrollera modellerna med magnetiska markdata insamlade av SGU i samma område. Dessa profiler jämfördes för att undersöka hur insamlad data från drönare respektive markmätningar skiljer sig. Modellerna gjordes i programvaran Potent, där anomalierna i magnetfältets intensitet. Resultaten från modelleringen visar en relativt tydlig korrelation mellan hur modellen (från insamlade drönardata) svarar mot markdata. Det förekommer dock små variationer i profilerna från markdata, som inte syns i modellerna från drönardata. Detta beror delvis på att mätningarna gjordes på olika höjd, och delvis på att proverna skiljer sig åt i viss mån. De magnetiska anomalierna i projektområdet tolkades med hjälp av de modellerade profilerna, och förmodas vara orsakade av enheter av metasedimentär bergart/migmatit. Dessa enheter stupar mestadels med 30-50°, och på vissa platser förekommer Cu- och Au-mineraliseringar. Stupningen, bergarter och den magnetiska susceptibiliteten stämmer relativt väl överens med SGU:s information från fältundersökningar, och tolkningen styrks ytterligare av SGU:s modeller av den elektriska resistiviteten i samma område.

The State Farm Antiform is a major structural feature of the eastern Piedmont of Virginia. Exposed in the core of this structure is the easternmost known outcrop of Grenville basement, the State Farm Gneiss. The eastern limb of the antiform coincides with a zone of late Paleozoic mylonitization, the Hylas Zone, and the western border fault of the Richmond Triassic Basin. The crest of a major gravity anomaly, the Piedmont gravity high, is coincident with the hinge of the State Farm Antiform. In addition, this region is in the eastern portion of the Central Virginia Seismic Zone. Detailed geologic mapping and potential field modeling shows that the character of the Piedmont gravity high is a result of both crustal thickness variation and density contrasts between the surficially exposed lithologies. Geologic, gravity and magnetic field modeling has determined the structure of the antiform and the Triassic basin to a depth of 5 km. Microearthquake activity is shown to be concentrated along a planar zone that extends to a depth of 20 km, which is concordant to regional structure. This concordancy implies that any major sole thrust in the crust is either very shallow or deeper than 20 kilometers. / M.S.

Thesis (PhD)--Macquarie University, Division of Environmental & Life Sciences, Department of Earth and Planetary Sciences, 2005. / Bibliography: leaves 202-224. / Introduction -- Geological setting of the New England Fold Belt -- Regional geophysical investigation -- Data acquisition and reduction -- Modelling and interpretation of magnetic data over the Peel Fault -- Modelling and interpretation of magnetic data over the Mooki Fault -- Gravity modelling of the Tamworth Belt and Gunnedah Basin -- Interpretation and discussion -- Conclusions. / This thesis presents new magnetic and gravity data for the Southern New England Fold Belt (SNEFB) and the Gunnedah Basin that adjoins to the west along the Mooki Fault in New South Wales. The SNEFB consists of the Tamworth Belt and Tablelands Complex that are separated by the Peel Fault. The Tablelands Complex to the east of the Peel Fault represents an accretionary wedge, and the Tamworth Belt to the west corresponds to the forearc basin. A total of five east-north-east trending gravity profiles with around 450 readings were conducted across the Tamworth Belt and Gunnedah Basin. Seven ground magnetic traverses of a total length of 60 km were surveyed across the bounding faults of the Tamworth belt, of which five were across the Peel Fault and two were across the Mooki Fault. The gravity data shows two distinct large positive anomalies, one over the Tamworth Belt, known as the Namoi Gravity High and another within the Gunnedah Basin, known as the Meandarra Gravity Ridge. All gravity profiles show similarity to each other. The magnetic data displays one distinct anomaly associated with the Peel Fault and an anomaly immediately east of the Mooki Fault. These new potential field data are used to better constrain the orientation of the Peel and Mooki Faults as well as the subsurface geometry of the Tamworth Belt and Gunnedah Basin, integrating with the published seismic data, geologic observations and new physical properties data. --Magnetic anomalies produced by the serpentinite associated with the Peel Fault were used to determine the orientation of the Peel fault. Five ground magnetic traverses were modelled to get the subsurface geometry of the serpentinite body. Modelling results of the magnetic anomalies across the Peel Fault indicate that the serpentinite body can be mostly modelled as subvertical to steeply eastward dipping tabular bodies with a minimum depth extent of 1-3 km, although the modelling does not constrain the vertical extent. This is consistent with the modelling of the magnetic traverses extracted from aeromagnetic data. Sensitivity analysis of a tabular magnetic body reveals that a minimum susceptibility of 4000x10⁻⁶cgs is needed to generate the observed high amplitude anomalies of around 2000 nT, which is consistent with the susceptibility measurements of serpentinite samples along the Peel Fault ranging from 2000 to 9000 x 10⁻⁶ cgs. Rock magnetic study indicates that the serpentinite retains a strong remanence at some locations. This remanence is a viscous remanent magnetisation (VRM) which is parallel to the present Earth's magnetic field, and explains the large anomaly amplitude over the Peel fault at these locations. The remanence of serpentinite at other localities is not consistent enough to contribute to the observed magnetic anomalies. A much greater depth extent of the Peel Fault was inferred from gravity models. It is proposed that the serpentinite along the Peel Fault was emplaced as a slice of oceanic floor that has been accreted to the front of the arc, or as diapirs rising off the serpentinised part of the mantle wedge above the supra subduction zone. / Magnetic anomalies immediately east of the Mooki Fault once suggested to be produced by a dyke-like body emplaced along the fault were modelled along two ground magnetic traverses and three extracted aeromagnetic lines. Modelling results indicate that the anomalies can be modelled as an east-dipping overturned western limb of an anticline formed as a result of a fault-propagation fold with a shallow thrust step-up angle from the décollement. Interpretation of aeromagnetic data and modelling of the magnetic traverses indicate that the anomalies along the Mooki Fault are produced by the susceptibility contrast between the high magnetic Late Carboniferous Currabubula Formation and/or Early Permian volcanic rocks of the Tamworth Belt and the less magnetic Late Permian-Triassic Sydney-Gunnedah Basin rocks. Gravity modelling indicates that the Mooki Fault has a shallow dip ( ̃25°) to the east. Modelling of the five gravity profiles shows that the Tamworth Belt is thrust westward over the Sydney-Gunnedah Basin for 15-30 km. --The Meandarra Gravity Ridge within the Gunnedah Basin was modelled as a high density volcanic rock unit with a density contrast of 0.25 tm⁻³, compared to the rocks of the Lachlan Fold Belt in all profiles. The volcanic rock unit has a steep western margin and a gently dipping eastern margin with a thickness ranging from 4.5-6 km, and has been generally agreed to have formed within an extensional basin. --The Tamworth Belt, being mainly the product of volcanism of mafic character and thus has high density units, together with the high density Woolomin Association, which is composed chiefly of chert/jasper, basalt, dolerite and metabasalt, produces the Namoi Gravity High. Gravity modelling results indicate that the anomaly over the Tamworth Belt can be modelled as either a configuration where the Tablelands Complex extends westward underthrusting the Tamworth Belt, or a configuration where the Tablelands Complex has been thrust over the Tamworth Belt. When the gravity profiles were modelled with the first configuration, the Peel Fault with a depth extent of around 1 km can only be modelled for the Manilla and Quirindi profiles, modelling of the rest of the gravity profiles indicates that the Tablelands Complex underthrust beneath the Tamworth belt at a much deeper location. / Mode of access: World Wide Web. / xi, 242 leaves ill., maps

Thesis (M.A.)--University of Tennessee, Knoxville, 2009. / Title from title page screen (viewed on Oct. 22, 2009). Thesis advisor: Gerald F. Schroedl. Vita. Includes bibliographical references.

Cette thèse concerne l’étude du message magnétique de la lithosphère océanique. Nous nous sommes, dans un premier temps, intéressés à l’évolution du signal magnétique à travers une section de croûte océanique complète et continue des basaltes jusqu’aux gabbros. Le but était de comprendre comment les propriétés magnétiques des roches peuvent nous renseigner sur les conditions d’altération dans la croûte océanique. Nous avons donc établi un jeu de données magnétiques (température de Curie, paramètres d’hystérésis, mesures magnétiques basse température) sur l’ensemble de la section de croûte océanique forée au site IODP 1256D, dans l’océan Pacifique. Ces données sont confrontées aux températures d’altération, établies par thermo barométrie et mettent en évidence une étroite relation entre l’altération des phases magnétiques et les températures d’altération. De plus, des analyses semi-quantitatives et des observations microscopiques (optique, MEB et MET) mettent en évidence un changement de structure cristalline, associée à une perte de titane, permettant la formation d’une phase secondaire, l’hydroschorlomite, dans un intervalle de forte altération des phases magnétiques (entre 670 et 1028 mbsf (meters below sea floor)). Dans un second temps, l’acquisition de profils d’anomalies magnétiques marines de surface et d’un profil d’anomalies de fond « deep tow » à travers le superchron du Crétacé (entre 83 et 120 Ma) nous a permis de tester la stabilité de polarité du champ géomagnétique durant cette période. Nous mettons en évidence la présence d’anomalies magnétiques : des anomalies de courtes longueurs d’onde ou « tiny-wiggles » à travers l’ensemble du superchron et des anomalies magnétiques de plus grande longueur d’onde, assimilables à de courts intervalles de polarité inverse. Nos mesures montrent que le comportement du champ magnétique durant le superchron n’est pas différent des périodes qui le précèdent (chrons M0-M1-M2) et le suivent (chrons 33n et 33r). La définition de superchron doit être remise en question. / So we, in a first part, studied the evolution of the magnetic signal through a section of a, complete and continuous, oceanic crust, from basalts to gabbros. In order to understand how the magnetic properties of rocks can tell us about the conditions of alteration in the oceanic lithosphere, we established a set of magnetic data (Curie temperature, hysteresis parameters, low temperature magnetic measurements) through the entire section of the oceanic crust, drilled at IODP Site 1256D, in the Equatorial Pacific Ocean. These magnetic data are compared to alteration temperatures, determined by thermobarometry (Alt et al., 2010) and show a close relationship between the alteration of the magnetic phases and the alteration temperatures, including the identification of an interval of strong alteration of the titanomagnetites (between 670 and 1028 mbsf (meters below sea floor). In addition, semi quantitative chemical analysis and microscopic observations (optical, SEM and TEM), performed on titanomagnetites, show a change in crystalline structure and a loss of titanium element (Ti4 +) in titanomagnetites to form a secondary phase rich in titanium, in this same interval of strong alteration. In a second part, the acquisition of numerous sea-surface magnetic profiles and a high resolution magnetic profile ("deep tow") through the Cretaceous Normal Superchron (83-120 Ma), allowed us to test the stability of the geomagnetic polarity of the superchron and to highlight the presence of numerous magnetic anomalies: anomalies of short wavelength or "tiny-wiggles” through the entire period and magnetic anomalies of greater length wave, similar to short intervals of reverse polarity. Our measurements show that the behavior of the magnetic field during the superchron is no different from previous periods (chrons M0-M1-M2) and the following magnetic period (chrons 33n and 33R) and the definition of ‘superchron’, long geomagnetic event without inversions, must be questioned