Interpretation of Las Salinas sedimentary basin - Argentina, based on integration of geological and geophysical data

La cuenca sedimentaria de las Salinas está ubicada en aproximadamente 31º de latitud sur y 67º de longitud oeste de Argentina, tiene algo más de 100 km de largo, unos 50 km de ancho y una altitud media de 500 m sobre el n.m.m. La cuenca, de rumbo NNW-SSE, está encajada entre las Sierras de la Huerta, las Guayaguas y las Quijadas al oeste, y las Sierras de Chepes, Ulapes y San Luis al este. Ella abarca un área aproximada de 5,700 km2 con una profundidad media de 5 km que crece hacia el norte. Por el sur está separada de la cuenca de Beazley por la dorsal de San Pedro. Nuevos datos de gravedad y valores de archivo, datos de densidades (de pozo) y reinterpretaciones sísmicas permitieron obtener un modelo integrado que involucra: a) un basamento técnico a profundidad de 3.5 km obtenido a partir de reinterpretaciones sísmicas; b) un basamento cristalino con una profundidad media de 5 km obtenido desde datos de gravedad invertidos; c) un fallamiento perimetral e interno que alcanza los 11 km de profundidad que insinúa una disposición lístrica profunda en un estilo de piel gruesa, obtenido desde reinterpretaciones sísmicas 2D, desde técnicas espectrales y desde los alineamientos obtenidos a partir de las soluciones gravimétricas de Euler; d) una sucesión de densidades extraídas desde datos de pozo que permitieron realizar una inversión desde las anomalías de Bouguer operando con densidad variable; y e) un sistemas de tres anticlinales asimétricos cortado por tres sistemas de fallas inversas. f) Una estructura regional que evidencia y dimensiona el esquema compresivo al que ha sido sometida la región. Esperamos que nuestro modelo integrado, con excelente definición, contribuya a la búsqueda de estructuras geológicas de interés económico.Las Salinas sedimentary basin is located at 31º S and 67º W approximately, in the central-western part of Argentina. Its dimensions are 100 km long, about 50 km wide, plus an average altitude of 500 m above sea level. The basin is situated among the mountain ranges of De la Huerta, Guayaguas and Las Quijadas to the west, and the ranges of Chepes, Ulapes and San Luis to the east, with a NW-SE orientation. Its surface is approximately 5,700 km2 with an average depth of 5 km increasing in a northerly direction. The southern part of the basin is separated from the Beazley basin by the buried San Pedro ridge. New gravimetric information and archive file data, density data (from wells) and seismic reinterpretation allowed us to obtain an integrated model, which involved: a) seismic basement situated at a depth of 3.5 km obtained from seismic reinterpretation; b) crystalline basement with an average depth of 5 km obtained from inverted gravimetric data; c) perimeter and internal faults system reaching 11 km in depth suggesting a listric type disposition in depth, thick-skinned type, obtained from 2-D seismic reinterpretation, spectral analysis technique and alignments obtained from Euler’s technique; d) succession of density data extracted from wells allowing us to perform a gravimetric inversion from Bouguer’s anomalies operating with variable density; e) a system of three asymmetric breached anticlines crossed by three systems of inverse faults and f) regional structure serving as evidence, permitting us to dimension the compressive framework to which the region has been subjected. Our purpose is that this well-defined integrated model will contribute to the search for further geological structures of economic interest.Fil: Azeglio, Edgardo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; ArgentinaFil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Introcaso, Antonio. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Interpretation of Las Salinas sedimentary basin - Argentina, based on integration of geological and geophysical data

La cuenca sedimentaria de las Salinas está ubicada en aproximadamente 31º de latitud sur y 67º de longitud oeste de Argentina, tiene algo más de 100 km de largo, unos 50 km de ancho y una altitud media de 500 m sobre el n.m.m. La cuenca, de rumbo NNW-SSE, está encajada entre las Sierras de la Huerta, las Guayaguas y las Quijadas al oeste, y las Sierras de Chepes, Ulapes y San Luis al este. Ella abarca un área aproximada de 5,700 km2 con una profundidad media de 5 km que crece hacia el norte. Por el sur está separada de la cuenca de Beazley por la dorsal de San Pedro. Nuevos datos de gravedad y valores de archivo, datos de densidades (de pozo) y reinterpretaciones sísmicas permitieron obtener un modelo integrado que involucra: a) un basamento técnico a profundidad de 3.5 km obtenido a partir de reinterpretaciones sísmicas; b) un basamento cristalino con una profundidad media de 5 km obtenido desde datos de gravedad invertidos; c) un fallamiento perimetral e interno que alcanza los 11 km de profundidad que insinúa una disposición lístrica profunda en un estilo de piel gruesa, obtenido desde reinterpretaciones sísmicas 2D, desde técnicas espectrales y desde los alineamientos obtenidos a partir de las soluciones gravimétricas de Euler; d) una sucesión de densidades extraídas desde datos de pozo que permitieron realizar una inversión desde las anomalías de Bouguer operando con densidad variable; y e) un sistemas de tres anticlinales asimétricos cortado por tres sistemas de fallas inversas. f) Una estructura regional que evidencia y dimensiona el esquema compresivo al que ha sido sometida la región. Esperamos que nuestro modelo integrado, con excelente definición, contribuya a la búsqueda de estructuras geológicas de interés económico.Las Salinas sedimentary basin is located at 31º S and 67º W approximately, in the central-western part of Argentina. Its dimensions are 100 km long, about 50 km wide, plus an average altitude of 500 m above sea level. The basin is situated among the mountain ranges of De la Huerta, Guayaguas and Las Quijadas to the west, and the ranges of Chepes, Ulapes and San Luis to the east, with a NW-SE orientation. Its surface is approximately 5,700 km2 with an average depth of 5 km increasing in a northerly direction. The southern part of the basin is separated from the Beazley basin by the buried San Pedro ridge. New gravimetric information and archive file data, density data (from wells) and seismic reinterpretation allowed us to obtain an integrated model, which involved: a) seismic basement situated at a depth of 3.5 km obtained from seismic reinterpretation; b) crystalline basement with an average depth of 5 km obtained from inverted gravimetric data; c) perimeter and internal faults system reaching 11 km in depth suggesting a listric type disposition in depth, thick-skinned type, obtained from 2-D seismic reinterpretation, spectral analysis technique and alignments obtained from Euler’s technique; d) succession of density data extracted from wells allowing us to perform a gravimetric inversion from Bouguer’s anomalies operating with variable density; e) a system of three asymmetric breached anticlines crossed by three systems of inverse faults and f) regional structure serving as evidence, permitting us to dimension the compressive framework to which the region has been subjected. Our purpose is that this well-defined integrated model will contribute to the search for further geological structures of economic interest.Fil: Azeglio, Edgardo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; ArgentinaFil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Introcaso, Antonio. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Influence of pre-Andean history over Andean foreland deformation: structural styles in the Malargüe fold-and-thrust belt at 35ºS, Andes of Argentina

We present the first complete balanced cross-section of the Argentinean Andes at 35ºS. Based on an extensive field survey and limited sub-surface information, we constructed a structural model in which both the tectonic inversion of Mesozoic normal faults and the formation of Cenozoic Andean thrusts play a role in the deformation. We obtained a shortening of 26.2 km, equivalent to 22% of the initial length. This value is lower than previous estimates obtained from partial cross-sections using non-inversion structural models. Comparison of our results with a geophysical model of the crust indicates that: (i) crustal thickness was not constant across the orogen before Andean shortening, but a thick (~45 km) crustal block was interpreted? in the west as a remnant of a Late Paleozoic orogeny, and a thinner sector (~32 km) was located in the east as a result of Mesozoic stretching; and (ii) the structural model presented in this work is more consistent with the regional shortening and crustal thickness trends than models which do not take into account tectonic inversion.Fil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Tassara Oddo, Andres Humberto. Universidad de Concepción; ChileFil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

Gravity modelling in the western Bushveld Complex, South Africa, using integrated geophysical data

A 10 km x 10 km study area in the western Bushveld Complex, south of the Pilanesberg Complex, was selected for testing the inversion of vertical component gravity (Gz) data to determine the geometry of the Bushveld Complex/Transvaal Supergroup contact. This contact has a density contrast of ~0.350 g.cm-3 making it a suitable target for gravity inversion. The resulting 3D gravity model agrees well with the 3D seismic interpretation, indicating that the depths determined from the seismic data are appropriate. The gravity inversion could be extended laterally to investigate regions without seismic data coverage. This methodology may prove useful where upwellings in the floor of the Bushveld Complex distort seismic data, but can be imaged by gravity inversions. The Gz dataset was created from converted Airborne Gradient Gravity (AGG) data, combined with upward continued ground Gz gravity data, providing extensive coverage. This combined dataset was used in an interactive, iterative 3D gravity inversion methodology used to model the geometry of the Bushveld Complex/Transvaal Supergroup contact and densities of the Bushveld Complex, Transvaal Supergroup and Iron-Rich Ultramafic Pegmatoids (IRUPs). The resulting 3D gravity model provides an acceptable first-pass model of the Bushveld Complex/Transvaal Supergroup contact. In the shallow south-west region of the study area, the steeply dipping contact was determined from borehole intersections. 3D seismic data was the only constraint towards the north-east, where the contact flattens out to a sub-parallel contact, at ~2 000 m depth. In the north-western section, the Bushveld Complex/Transvaal Supergroup contact is fault-bounded by a conjugate set of the Rustenburg Fault, causing the Bushveld to onlap the Transvaal sediments. In the southern region, the contact changes as the conjugate fault dies out, and the Bushveld Complex becomes layered/sub-parallel to Transvaal sediments. This, and other geological features (e.g. faulting, folding, dykes), can be explained in relation to the regional tectonic history, relating to motion along the Thabazimbi-Murchison Lineament (TML). Pre-Bushveld emplacement NW-SE far-field stress caused NW trending extensional features in the region (e.g. Rustenburg Fault). Re-orientation of the compressive force to NE-SW, in syn- to post-emplacement, caused compressive features in the region (e.g. open folds with axes trending NW). Ground gravity data (100 m x 100 m station- and line-spacing) were also inverted to obtain a 3D model of the overburden, constrained by borehole data. However, the inversion failed to satisfy the gravity data and borehole data simultaneously, relating to difficulties in modelling the regional gravity field and the gradational nature of the weathered contact. Several rapid variations in overburden thickness were mapped, with particular success in the high frequency ground gravity survey (30 m x 30 m station- and line-spacing) with the identification of a deeply weathered (~10 m deep) channel relating to an mapped fault

Geophysical analysis of the Copahue volcano region and surrounding areas

El Complejo volcánico Caviahue-Copahue se localiza entre los 37° y 38.5°S sobre los Andes Neuquinos en la región NO de la Patagonia Argentina. El Complejo volcánico Caviahue-Copahue constituye el recurso geotermal más importante de la provincia de Neuquén y desde la década de los 90 ha sido estudiado en forma continua hasta la actualidad debido a sus frecuentes erupciones. En este trabajo integramos información gravimétrica, aeromagnética y sismológica con el fin de caracterizar la estructura en profundidad del volcán Copahue y su entorno. A partir de datos gravimétricos satelitales y utilizando un programa de inversión se obtuvo un modelo 3D de distribución de densidades. Se procesaron datos aeromagnéticos para la obtención de la anomalía magnética y se calculó la correspondiente reducción al Polo. El estudio sismológico fue realizado a partir de una red de 20 estaciones de banda ancha, 19 de la red de AÑELO y 1 de la red de la Federation of Digital Seismograph Network, y 1 de período corto del Instituto Nacional de Prevención Sísmica. Se localizaron 55 sismos ocurridos en el periodo de un año, con magnitudes que varían entre 1.7 y 3.4. Del total de la sismicidad localizada, en este trabajo solo se reporta la sismicidad con error en parámetros de localización menor a 10 km. Para este conjunto de sismos, las incertezas en latitud y longitud (mediana) son de 5.45 y 6.15 km, respectivamente. La incerteza en el hipocentro es de 3.2 km.The Caviahue-Copahue volcanic Complex is located between 37°S and 38.5°S on the Andes Neuquinos, on the NW region of the Argentinean Patagonia. The Caviahue-Copahue volcanic Complex constitutes the main geothermal resource of the Neuquén province, and has been heavily studied since 1990 due to its frequent eruptions. For this contribution, we correlate gravimetric, aeromagnetic, and seismologic data with the aim of characterizing the in-depth structure of the Copahue volcano and its surroundings. From satellite gravimetric data and using an inversion software, a 3D density distribution model was obtained. In order to compare magnetic and gravimetric data magnetic anomalies and their corresponding Reduction to the Pole corrections were computed from the aeromagnetic data. The seismological study was conducted using a network composed of 20 broad band stations, 19 of which belong to a local network that belongs to the IGSV (AÑELO network) and 1 from the Federation of Digital Seismograph Network, and 1 additional short period station from the Instituto Nacional de Prevención Sísmica. We registered and located 55 seismic events over the course of one year, with magnitudes (Ml) ranging from 1.7 to 3.4. From the total seismicity located, we only report events with less than 10 km in error in their location parameters, which are concentrated on the Copahue caldera. For said events, the median latitude and longitude uncertainties are 5.45 and 6.15 km, respectively and 3.2 km for the hypocenter.Fil: Pechuan Canet, Stefanie Nadia. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Godoy, Laura Beatriz. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Nacif Suvire, Silvina Valeria. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Alvarez Pontoriero, Orlando. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Correa Otto, Sebastian Ariel. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentin

Tectono-sedimentary evolution of the San Pedro basin (Dominican Republic) and its hydrocarbon potential

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Geológicas, leída el 16-12-2020La Cuenca de San Pedro (CSP) se define como una depresión batimétrica con tendencia E-O y una extensión aproximada de 6000 km2, situada en el margen sureste de la isla de La Española (República Dominicana y Haití). Estructuralmente, el SPB está ubicada en la parte trasera del Cinturón Deformado de los Muertos (CDM). Considerada tradicionalmente como una cuenca de edad Mioceno medio, cuyo relleno ha sido depositado en el espacio de configuración generado por la progresiva deformación del CDM. El área de estudio pertenece al límite norte entre las Placas Norteamericana y Caribe, habiendo registrado la compleja interacción entre ambas. Aun-que la CSP se encuentra próxima a un sistema petrolero confirmado (los descubrimientos de Ma-leno e Higuerito en la región de Azua recuperaron 50,000 brls de petróleo), podría considerarse como poco explorada y los diferentes intentos de correlaciones estructurales y estratigráficas con la región de San Cristóbal (tradicionalmente considerada como la extensión en tierra de la CSP) y la cuenca de Azua han puesto de manifiesto importantes discrepancias. En consecuencia, tanto la evolución de la CSP como su potencial de hidrocarburos siguen sin estar claramente definidos...The San Pedro Basin (SPB) consists of an E-W bathymetric depression with an extension of 6000 km2, located in the south-eastern margin of Hispaniola Island (Dominican Republic and Haiti). Structurally, the SPB is situated at the rear zone of the Muertos Thrust Belt (MTB). The basin has been dated as middle Miocene in the bibliography, with the infill deposited in the configuration space generated by the progressive deformation of the MTB. The study area belongs to the north-ern limit of the Caribbean Plate, having recorded the complex interaction with the North Ameri-can Plate. Although the SPB is located close to a confirmed petroleum system (the discoveries of Maleno and Higuerito in the Azua region recovered 50,000 brls of oil), it remains almost unex-plored and the different attempts of onshore-offshore structural and stratigraphic correlations with the nearby San Cristóbal (traditionally considered as the onshore extension of SPB) and Azua Basins have shown strong discrepancies. Therefore, the SPB evolution and its hydrocarbon po-tential remains unclear...Fac. de Ciencias GeológicasTRUEunpu

New Global Perspectives on Archaeological Prospection

This volume is a product of the 13th International Conference on Archaeological Prospection 2019, which was hosted by the Department of Environmental Science in the Faculty of Science at the Institute of Technology Sligo. The conference is held every two years under the banner of the International Society for Archaeological Prospection and this was the first time that the conference was held in Ireland. New Global Perspectives on Archaeological Prospection draws together over 90 papers addressing archaeological prospection techniques, methodologies and case studies from 33 countries across Africa, Asia, Australasia, Europe and North America, reflecting current and global trends in archaeological prospection. At this particular ICAP meeting, specific consideration was given to the development and use of archaeological prospection in Ireland, archaeological feedback for the prospector, applications of prospection technology in the urban environment and the use of legacy data. Papers include novel research areas such as magnetometry near the equator, drone-mounted radar, microgravity assessment of tombs, marine electrical resistivity tomography, convolutional neural networks, data processing, automated interpretive workflows and modelling as well as recent improvements in remote sensing, multispectral imaging and visualisation

an interdisciplinary research project to study the Dead Sea Transform

repor

Electrical conductivity experiments on carbon-rich Karoo shales and forward modelling of aeromagnetic data across the Beattie Anomaly

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

Electrical conductivity experiments on carbon-rich Karoo shales and forward modelling of aeromagnetic data across the Beattie Anomaly

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