Ademola Adetunji - Academia.edu (original) (raw)
Papers by Ademola Adetunji
Geology, Feb 10, 2023
A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, ... more A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, Canada, images a 50-km-long north-dipping conductor (<20 Ω•m) at 20-25 km depth and subvertical conductors spatially correlated with crustal-scale shear zones and large orogenic gold deposits. The conductors are interpreted to be the conductivity signature of the deep crustal source of the auriferous fluids and pathways of the orogenic gold system. The geophysical results, supported by existing geochemical and fluid inclusion studies, suggest that the Au-and CO 2-rich fluids responsible for gold mineralization were released by devolatilization of supracrustal rocks underthrust to mid-to lower-crustal levels during subduction. This MT study links shallow gold mineralization to a deep crustal source region, demonstrating the connection between a crustal suture zone and the formation of orogenic gold deposits in an Archean greenstone belt.
The leading edge, Apr 1, 2023
GEO 2010, 2010
UMI, ProQuest ® Dissertations &amp;amp;amp; Theses. The world&amp;amp;#x27;s most... more UMI, ProQuest ® Dissertations &amp;amp;amp; Theses. The world&amp;amp;#x27;s most comprehensive collection of dissertations and theses. Learn more... ProQuest, Mapping the internal structure of sand dunes in the Jafurah Sand Sea of Eastern Saudi Arabia using Ground Penetrating Radar. ...
The Leading Edge, 2008
Quick Search: All GSW Journals, GSW + GeoRef. advanced search. ...
Geological Society of America Abstracts with Programs, 2020
Precambrian Research, 2021
Abstract The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supe... more Abstract The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supergroup near the southern margin of Archean Superior craton, along strike from the Temagami Greenstone Belt, 50 km northeast of world-class metal endowment in the Sudbury Igneous Complex. It has been attributed to coincidental geophysical responses from Neoarchean iron formation and a Paleoproterozoic mafic–ultramafic intrusion. The TGA is investigated using integrated magnetotelluric, magnetic, gravity and seismic reflection datasets to further define the geometry of its sources; to define structures in overlying Huronian Supergroup rocks; and to examine the geometrical relationship of Archean basement structure, the Proterozoic mafic–ultramafic intrusion, and Proterozoic rift structures. Geophysical results reveal a strong conductor, interpreted to be iron formation, extending downwards from the Archean basement surface and enveloping the upper northern margin of a large magnetic, dense body at 5 km depth. The geometry of the features indicates mafic–ultramafic intrusion adjacent to greenstone rocks. Alignment of the long-axis of the intrusion with the greenstone belt suggests control on the intrusion process by the Neoarchean structures. The 60x10x10 km TGA intrusion lies within the mantle-plume, rift-related Huron-Nipissing magmatic belt and interpreted to be a member of the 2.491–2.475 Ga East Bull Lake intrusive suite. Based on this genetic relationship, the intrusion probably contributes significantly to Ni-Cu-PGE endowment of the Sudbury region. The spatial correlation of the intrusion with an overlying 20 km wide, 4.5 km deep, fault-bounded rift basin is attributed to crustal subsidence triggered by the intrusion. Seismic reflection and magnetotelluric results show younger Huronian Supergroup rocks record the transition to sedimentation on a laterally-extensive passive margin. An electrically-anisotropic, moderately-conductive layer in the Gowganda Formation is related to alteration during intrusion of the 2.200 Nipissing Diabase.
Precambrian Research, 2021
Abstract The Neoarchean is considered as a pivotal era during the Earth’s evolution in terms of c... more Abstract The Neoarchean is considered as a pivotal era during the Earth’s evolution in terms of cratonization and development of plate tectonics. The supporting crustal processes, however, remain elusive due in part to limited comprehensive imaging of crustal structures underlying Neoarchean terranes. This study uses new seismic, magnetotelluric, and geologic data from the Metal Earth Sturgeon transect (70 km) and existing seismic and aeromagnetic data to investigate the Neoarchean crustal architecture underlying the greenstone-dominated western Wabigoon terrane (WWT) and the tonalite-trondhjemite-granodiorite-dominated Winnipeg River terrane (WRT) of the Superior craton. The results suggest that (1) the Sturgeon Lake greenstone belt of the WWT is 5–10 km thick and separated by a thrust fault from the underlying basement, (2) the basement is characterized by gneissic fabrics from the mid- to lower-crust of probable Paleo to Mesoarchean WRT rocks, and that (3) the crust was extensively reworked by Neoarchean post-tectonic magmatism that was characterized by carbon- and/or hydrogen-rich silicates and likely caused by partial melting of mantle/crustal rocks triggered by subduction-related fluids/melts. With the reprocessed Lithoprobe seismic data from the same region, a 3D crustal architecture is reconstructed and reveals a convergent belt between the main WRT to the north and a continental margin promontory of the WRT to the south. This Neoarchean convergent belt is characterized by an allochthonous greenstone belt as a thrust sheet in the upper crust, a collision zone in the mid- to lower-crust, an apparent crustal root of 3–5 km relief, and subcreted crustal rocks beneath a mantle wedge. Published data suggest that an outboard, north-dipping subduction zone associated with the Wawa terrane provided the fluids/melts for the post-tectonic magmatism in the WRT-WWT crust. This study favors a model of subduction followed by collision over a collision-only model, which indicates that multiple subduction zones were operative synchronously in a period during the assembly of the western Superior craton. Cratonization by accretionary orogenesis due to plate tectonics in the Neoarchean, therefore, is imaged and characterized in this study using a 3D crustal architecture.
Precambrian Research, 2021
Abstract Our understanding of crustal architecture and tectonic evolution has advanced due to int... more Abstract Our understanding of crustal architecture and tectonic evolution has advanced due to integrated geological and geophysical research on Precambrian cratons. However, it is still a heated debate whether Archean crust structure developed by an allochthonous model similar to modern plate tectonics or autochthonous model emphasizing in-situ evolution of supracrustal belts. The ca. 2696 Ma) deformation event, which is expressed by internally foliated clasts in conglomerate. The Chicobi belt was regionally folded and cut by shear zones during a second (D2) deformation event, and was re-folded by Z-shaped folds during a third (D3) dextral shearing event. The D2 event is constrained between ca. 2696 Ma, the pre-existing age of detrital zircon in the Scapa Group along strike of the Chicobi belt, and ca. 2681 Ma, the new age of the cross-cutting syenitic Gemini-Saint-Eloi Pluton. New high-resolution seismic reflection and magnetotelluric surveys were conducted along the same transect across the Chicobi belt. The seismic reflection survey imaged subhorizontal to shallowly north-dipping reflective bands at depths of 3–7 km. Regional-scale inversion of new and pre-existing gravity data indicates that these reflective bands are linked to the Beauchamp Fault south of the Amos Group. Magnetotelluric inversion model shows high resistivity (>1000 Ω·m) zones under metasedimentary rocks, as well as a synform defined by low resistivity (10–100 Ω·m) zones, which aligns with folded metavolcanic rocks south of the Chicobi belt. Integration of the geophysical data with surface mapping suggests that the upper-middle crustal architecture of the Chicobi belt is dominated by D2 upright folds overlying a fault zone. We suggest that deformation of the Chicobi belt is dominated by thrusting and folding, a deformation style compatible with allochthonous growth of the Abitibi Subprovince.
Geophysical Journal International, 2015
The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province i... more The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province in southern Ontario, Canada is investigated using 84 magnetotelluric (MT) sites divided into four profiles. Depth-based regional geoelectric dimensionality analyses of the MT responses indicate that the mantle lithosphere north of Lake Ontario can be subdivided into upper (45-150 km) and deeper (>200 km) lithospheric mantle layers with regional strike azimuths of N85 • E (±5 •) and N65 • E (±5 •), respectively. MT responses from the Grenville Front and the northwest part of the Central Gneiss Belt are compatible with the presence of 2-D resistivity structures but farther to the southeast, in the southeast part of the Central Gneiss Belt and Central Metasedimentary Belt, they suggest the presence of localized 3-D structures. 2-D inversion of distortion-free MT responses images a large scale very resistive (>20 000 m) region that extends 300 km southeast of the Grenville Front and for at least 800 km alongstrike in the lithospheric mantle beneath the Grenville Province. This feature is interpreted to be Superior Province lithosphere and the corresponding N85 • E geoelectric strike to be associated with the fabric of the Superior Province. The base of the resistor reaches depths of 280 km on two of the three MT profiles north of Lake Ontario and this depth is interpreted to be the base of the lithosphere. A large region of enhanced conductivity in the lower lithosphere, spatially correlated with decreased seismic velocity, is bounded to the northwest by a subvertical resistivity anomaly located near the Kirkland Lake and Cobalt kimberlite fields. The enhanced conductivity in the lower lithosphere is attributed to refertilization by fluids associated with Cretaceous kimberlite magmatism and can be explained by water content in olivine of 50 wt ppm in background areas with higher values in a localized anomaly beneath the kimberlite fields. Farther to the southeast the resistivity models include a lithospheric conductor between 100 and 150 km depth beneath the Central Metasedimentary Belt. The enhanced conductivity is attributed to grain boundary graphite films, associated with the Cretaceous kimberlitic magmatic process, or to water and carbon, introduced into the mantle during the pre-Grenvillian tectonism.
Tectonophysics, 2014
The lithosphere beneath the margin of the Archean Superior and Proterozoic Grenville provinces wa... more The lithosphere beneath the margin of the Archean Superior and Proterozoic Grenville provinces was investigated with a northwest-southeast oriented, 650-km-long profile of 40 magnetotelluric stations. Dominant geoelectric strike azimuths of N45°E and N85°E were defined for the crust and the lithospheric mantle respectively. A 2-D isotropic resistivity model derived using the crustal strike images resistive Laurentian margin rocks dipping southeast to the base of the crust, bounded to the northwest by the Grenville Front, and to the southeast by the Central Metasedimentary Belt Boundary Zone. The observation is in contrast to conductive mid to lower crust elsewhere in the region. A 2-D isotropic resistivity model determined using the lithospheric mantle strike azimuth reveals an extremely resistive region in the upper 100 km of the mantle lithosphere of the northern Grenville Province. The geometry of this body, which includes a well-defined base and southeast dip, suggests that it is Superior lithosphere. A sub-vertical conductor, located approximately 50 km along strike from the Mesozoic Kirkland Lake and Cobalt kimberlite fields, is interpreted to be due to re-fertilization of an older mantle scar. The resistivity model includes a horizontal conductor at 160 km depth beneath the southern Superior Province that is possibly the resistivity signature of the lithospheric-asthenospheric boundary.
Three-Dimensional Ground Penetrating Radar (GPR) surveys were conducted in two locations to map t... more Three-Dimensional Ground Penetrating Radar (GPR) surveys were conducted in two locations to map the internal structure of sand dunes in eastern Saudi Arabia. The 400 MHz antenna that was used achieved a 4 m to 6 m penetration depth. The excellent spatial resolution of about 8 cm made it possible to identify the major internal features, such as cross-stratification and bounding surfaces. The recorded radargrams proved useful in understanding the dune's growth and migration in this area. Results suggest that GPR is an important tool in any study of recent sand dunes as analogues of hydrocarbon sandstone reservoirs of aeolian origin. Laboratory analyses showed the presence of elevated amounts of iron-oxide-bearing minerals in some dark layers of the sand in the study area. These changes in iron content might be the reason behind the strong electromagnetic impedance contrasts that ultimately generate reflections on the GPR images. Master of Science Degree King Fahd University of Pet...
Journal of Geophysical Research: Solid Earth, 2015
Magnetotelluric (MT) responses at the Proterozoic Grenville Front in Canada have been interpreted... more Magnetotelluric (MT) responses at the Proterozoic Grenville Front in Canada have been interpreted as being caused by lithospheric electrical anisotropy, and the area is often noted as a classic example of lithospheric anisotropy. This study reevaluates evidence for the electrical anisotropy using 56 MT stations. The spatially uniform MT responses noted at the Grenville Front extend to~200 km southeast and for at least 400 km along strike and are associated with rocks at less than 150 km depth. Examination of induction arrows at longer periods shows arrows at high angle to the MT conductive direction consistent with the presence of macroscopic resistivity structures. New 2-D anisotropic inversions show that electrical anisotropy is not required to fit the MT data. The results indicate that in the resistive mantle lithosphere beneath the Grenville Front, and in conductive lithosphere in adjacent areas, the maximum horizontal resistivity anisotropy is <10%, much less than the factor of 15 determined in earlier 1-D studies. The results suggest that the upper lithospheric mantle in the area is devoid of significant electrical anisotropy and that the observed MT response directionality is due to large-scale resistivity structure. We interpret the spatially consistent MT responses observed at the Grenville Front as being associated with the resistive Archean lithosphere extending southeast beneath the Grenville Front. The obliquity between seismic and MT responses arises because the Superior fabric is oblique to the seismic fast direction. If dextral shearing occurred, it appears to have not caused any significant shape preferred electrical anisotropy.
Journal of Environmental & Engineering Geophysics, 2016
Ground-penetrating radar (GPR) measures the velocity (VG) of electromagnetic waves in a subsurfac... more Ground-penetrating radar (GPR) measures the velocity (VG) of electromagnetic waves in a subsurface material. In a low-loss material, VG depends primarily on the porosity (φ) and water saturation (Sw) of the material. Therefore, it is impossible to estimate φ and Sw uniquely from VG without additional information. The seismic P-wave velocity (VP) in the same material can provide the extra information required for the inversion. In this study, an approach is described for a closed-form solution of VG and VP to invert for φ and Sw in shallow sediments. The complex refractive index model (CRIM) for VG and Gassmann-Biot model for VP are used to relate these velocities to φ and Sw. Each model presents a nonlinear equation in φ and Sw. The two equations are solved simultaneously to estimate φ and Sw from VG-VP measurements. Testing of the inversion procedure in the presence of errors in assuming the properties of the soil matrix showed that these errors can drastically affect the inverted ...
Geology, Feb 10, 2023
A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, ... more A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, Canada, images a 50-km-long north-dipping conductor (<20 Ω•m) at 20-25 km depth and subvertical conductors spatially correlated with crustal-scale shear zones and large orogenic gold deposits. The conductors are interpreted to be the conductivity signature of the deep crustal source of the auriferous fluids and pathways of the orogenic gold system. The geophysical results, supported by existing geochemical and fluid inclusion studies, suggest that the Au-and CO 2-rich fluids responsible for gold mineralization were released by devolatilization of supracrustal rocks underthrust to mid-to lower-crustal levels during subduction. This MT study links shallow gold mineralization to a deep crustal source region, demonstrating the connection between a crustal suture zone and the formation of orogenic gold deposits in an Archean greenstone belt.
The leading edge, Apr 1, 2023
GEO 2010, 2010
UMI, ProQuest ® Dissertations &amp;amp;amp; Theses. The world&amp;amp;#x27;s most... more UMI, ProQuest ® Dissertations &amp;amp;amp; Theses. The world&amp;amp;#x27;s most comprehensive collection of dissertations and theses. Learn more... ProQuest, Mapping the internal structure of sand dunes in the Jafurah Sand Sea of Eastern Saudi Arabia using Ground Penetrating Radar. ...
The Leading Edge, 2008
Quick Search: All GSW Journals, GSW + GeoRef. advanced search. ...
Geological Society of America Abstracts with Programs, 2020
Precambrian Research, 2021
Abstract The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supe... more Abstract The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supergroup near the southern margin of Archean Superior craton, along strike from the Temagami Greenstone Belt, 50 km northeast of world-class metal endowment in the Sudbury Igneous Complex. It has been attributed to coincidental geophysical responses from Neoarchean iron formation and a Paleoproterozoic mafic–ultramafic intrusion. The TGA is investigated using integrated magnetotelluric, magnetic, gravity and seismic reflection datasets to further define the geometry of its sources; to define structures in overlying Huronian Supergroup rocks; and to examine the geometrical relationship of Archean basement structure, the Proterozoic mafic–ultramafic intrusion, and Proterozoic rift structures. Geophysical results reveal a strong conductor, interpreted to be iron formation, extending downwards from the Archean basement surface and enveloping the upper northern margin of a large magnetic, dense body at 5 km depth. The geometry of the features indicates mafic–ultramafic intrusion adjacent to greenstone rocks. Alignment of the long-axis of the intrusion with the greenstone belt suggests control on the intrusion process by the Neoarchean structures. The 60x10x10 km TGA intrusion lies within the mantle-plume, rift-related Huron-Nipissing magmatic belt and interpreted to be a member of the 2.491–2.475 Ga East Bull Lake intrusive suite. Based on this genetic relationship, the intrusion probably contributes significantly to Ni-Cu-PGE endowment of the Sudbury region. The spatial correlation of the intrusion with an overlying 20 km wide, 4.5 km deep, fault-bounded rift basin is attributed to crustal subsidence triggered by the intrusion. Seismic reflection and magnetotelluric results show younger Huronian Supergroup rocks record the transition to sedimentation on a laterally-extensive passive margin. An electrically-anisotropic, moderately-conductive layer in the Gowganda Formation is related to alteration during intrusion of the 2.200 Nipissing Diabase.
Precambrian Research, 2021
Abstract The Neoarchean is considered as a pivotal era during the Earth’s evolution in terms of c... more Abstract The Neoarchean is considered as a pivotal era during the Earth’s evolution in terms of cratonization and development of plate tectonics. The supporting crustal processes, however, remain elusive due in part to limited comprehensive imaging of crustal structures underlying Neoarchean terranes. This study uses new seismic, magnetotelluric, and geologic data from the Metal Earth Sturgeon transect (70 km) and existing seismic and aeromagnetic data to investigate the Neoarchean crustal architecture underlying the greenstone-dominated western Wabigoon terrane (WWT) and the tonalite-trondhjemite-granodiorite-dominated Winnipeg River terrane (WRT) of the Superior craton. The results suggest that (1) the Sturgeon Lake greenstone belt of the WWT is 5–10 km thick and separated by a thrust fault from the underlying basement, (2) the basement is characterized by gneissic fabrics from the mid- to lower-crust of probable Paleo to Mesoarchean WRT rocks, and that (3) the crust was extensively reworked by Neoarchean post-tectonic magmatism that was characterized by carbon- and/or hydrogen-rich silicates and likely caused by partial melting of mantle/crustal rocks triggered by subduction-related fluids/melts. With the reprocessed Lithoprobe seismic data from the same region, a 3D crustal architecture is reconstructed and reveals a convergent belt between the main WRT to the north and a continental margin promontory of the WRT to the south. This Neoarchean convergent belt is characterized by an allochthonous greenstone belt as a thrust sheet in the upper crust, a collision zone in the mid- to lower-crust, an apparent crustal root of 3–5 km relief, and subcreted crustal rocks beneath a mantle wedge. Published data suggest that an outboard, north-dipping subduction zone associated with the Wawa terrane provided the fluids/melts for the post-tectonic magmatism in the WRT-WWT crust. This study favors a model of subduction followed by collision over a collision-only model, which indicates that multiple subduction zones were operative synchronously in a period during the assembly of the western Superior craton. Cratonization by accretionary orogenesis due to plate tectonics in the Neoarchean, therefore, is imaged and characterized in this study using a 3D crustal architecture.
Precambrian Research, 2021
Abstract Our understanding of crustal architecture and tectonic evolution has advanced due to int... more Abstract Our understanding of crustal architecture and tectonic evolution has advanced due to integrated geological and geophysical research on Precambrian cratons. However, it is still a heated debate whether Archean crust structure developed by an allochthonous model similar to modern plate tectonics or autochthonous model emphasizing in-situ evolution of supracrustal belts. The ca. 2696 Ma) deformation event, which is expressed by internally foliated clasts in conglomerate. The Chicobi belt was regionally folded and cut by shear zones during a second (D2) deformation event, and was re-folded by Z-shaped folds during a third (D3) dextral shearing event. The D2 event is constrained between ca. 2696 Ma, the pre-existing age of detrital zircon in the Scapa Group along strike of the Chicobi belt, and ca. 2681 Ma, the new age of the cross-cutting syenitic Gemini-Saint-Eloi Pluton. New high-resolution seismic reflection and magnetotelluric surveys were conducted along the same transect across the Chicobi belt. The seismic reflection survey imaged subhorizontal to shallowly north-dipping reflective bands at depths of 3–7 km. Regional-scale inversion of new and pre-existing gravity data indicates that these reflective bands are linked to the Beauchamp Fault south of the Amos Group. Magnetotelluric inversion model shows high resistivity (>1000 Ω·m) zones under metasedimentary rocks, as well as a synform defined by low resistivity (10–100 Ω·m) zones, which aligns with folded metavolcanic rocks south of the Chicobi belt. Integration of the geophysical data with surface mapping suggests that the upper-middle crustal architecture of the Chicobi belt is dominated by D2 upright folds overlying a fault zone. We suggest that deformation of the Chicobi belt is dominated by thrusting and folding, a deformation style compatible with allochthonous growth of the Abitibi Subprovince.
Geophysical Journal International, 2015
The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province i... more The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province in southern Ontario, Canada is investigated using 84 magnetotelluric (MT) sites divided into four profiles. Depth-based regional geoelectric dimensionality analyses of the MT responses indicate that the mantle lithosphere north of Lake Ontario can be subdivided into upper (45-150 km) and deeper (>200 km) lithospheric mantle layers with regional strike azimuths of N85 • E (±5 •) and N65 • E (±5 •), respectively. MT responses from the Grenville Front and the northwest part of the Central Gneiss Belt are compatible with the presence of 2-D resistivity structures but farther to the southeast, in the southeast part of the Central Gneiss Belt and Central Metasedimentary Belt, they suggest the presence of localized 3-D structures. 2-D inversion of distortion-free MT responses images a large scale very resistive (>20 000 m) region that extends 300 km southeast of the Grenville Front and for at least 800 km alongstrike in the lithospheric mantle beneath the Grenville Province. This feature is interpreted to be Superior Province lithosphere and the corresponding N85 • E geoelectric strike to be associated with the fabric of the Superior Province. The base of the resistor reaches depths of 280 km on two of the three MT profiles north of Lake Ontario and this depth is interpreted to be the base of the lithosphere. A large region of enhanced conductivity in the lower lithosphere, spatially correlated with decreased seismic velocity, is bounded to the northwest by a subvertical resistivity anomaly located near the Kirkland Lake and Cobalt kimberlite fields. The enhanced conductivity in the lower lithosphere is attributed to refertilization by fluids associated with Cretaceous kimberlite magmatism and can be explained by water content in olivine of 50 wt ppm in background areas with higher values in a localized anomaly beneath the kimberlite fields. Farther to the southeast the resistivity models include a lithospheric conductor between 100 and 150 km depth beneath the Central Metasedimentary Belt. The enhanced conductivity is attributed to grain boundary graphite films, associated with the Cretaceous kimberlitic magmatic process, or to water and carbon, introduced into the mantle during the pre-Grenvillian tectonism.
Tectonophysics, 2014
The lithosphere beneath the margin of the Archean Superior and Proterozoic Grenville provinces wa... more The lithosphere beneath the margin of the Archean Superior and Proterozoic Grenville provinces was investigated with a northwest-southeast oriented, 650-km-long profile of 40 magnetotelluric stations. Dominant geoelectric strike azimuths of N45°E and N85°E were defined for the crust and the lithospheric mantle respectively. A 2-D isotropic resistivity model derived using the crustal strike images resistive Laurentian margin rocks dipping southeast to the base of the crust, bounded to the northwest by the Grenville Front, and to the southeast by the Central Metasedimentary Belt Boundary Zone. The observation is in contrast to conductive mid to lower crust elsewhere in the region. A 2-D isotropic resistivity model determined using the lithospheric mantle strike azimuth reveals an extremely resistive region in the upper 100 km of the mantle lithosphere of the northern Grenville Province. The geometry of this body, which includes a well-defined base and southeast dip, suggests that it is Superior lithosphere. A sub-vertical conductor, located approximately 50 km along strike from the Mesozoic Kirkland Lake and Cobalt kimberlite fields, is interpreted to be due to re-fertilization of an older mantle scar. The resistivity model includes a horizontal conductor at 160 km depth beneath the southern Superior Province that is possibly the resistivity signature of the lithospheric-asthenospheric boundary.
Three-Dimensional Ground Penetrating Radar (GPR) surveys were conducted in two locations to map t... more Three-Dimensional Ground Penetrating Radar (GPR) surveys were conducted in two locations to map the internal structure of sand dunes in eastern Saudi Arabia. The 400 MHz antenna that was used achieved a 4 m to 6 m penetration depth. The excellent spatial resolution of about 8 cm made it possible to identify the major internal features, such as cross-stratification and bounding surfaces. The recorded radargrams proved useful in understanding the dune's growth and migration in this area. Results suggest that GPR is an important tool in any study of recent sand dunes as analogues of hydrocarbon sandstone reservoirs of aeolian origin. Laboratory analyses showed the presence of elevated amounts of iron-oxide-bearing minerals in some dark layers of the sand in the study area. These changes in iron content might be the reason behind the strong electromagnetic impedance contrasts that ultimately generate reflections on the GPR images. Master of Science Degree King Fahd University of Pet...
Journal of Geophysical Research: Solid Earth, 2015
Magnetotelluric (MT) responses at the Proterozoic Grenville Front in Canada have been interpreted... more Magnetotelluric (MT) responses at the Proterozoic Grenville Front in Canada have been interpreted as being caused by lithospheric electrical anisotropy, and the area is often noted as a classic example of lithospheric anisotropy. This study reevaluates evidence for the electrical anisotropy using 56 MT stations. The spatially uniform MT responses noted at the Grenville Front extend to~200 km southeast and for at least 400 km along strike and are associated with rocks at less than 150 km depth. Examination of induction arrows at longer periods shows arrows at high angle to the MT conductive direction consistent with the presence of macroscopic resistivity structures. New 2-D anisotropic inversions show that electrical anisotropy is not required to fit the MT data. The results indicate that in the resistive mantle lithosphere beneath the Grenville Front, and in conductive lithosphere in adjacent areas, the maximum horizontal resistivity anisotropy is <10%, much less than the factor of 15 determined in earlier 1-D studies. The results suggest that the upper lithospheric mantle in the area is devoid of significant electrical anisotropy and that the observed MT response directionality is due to large-scale resistivity structure. We interpret the spatially consistent MT responses observed at the Grenville Front as being associated with the resistive Archean lithosphere extending southeast beneath the Grenville Front. The obliquity between seismic and MT responses arises because the Superior fabric is oblique to the seismic fast direction. If dextral shearing occurred, it appears to have not caused any significant shape preferred electrical anisotropy.
Journal of Environmental & Engineering Geophysics, 2016
Ground-penetrating radar (GPR) measures the velocity (VG) of electromagnetic waves in a subsurfac... more Ground-penetrating radar (GPR) measures the velocity (VG) of electromagnetic waves in a subsurface material. In a low-loss material, VG depends primarily on the porosity (φ) and water saturation (Sw) of the material. Therefore, it is impossible to estimate φ and Sw uniquely from VG without additional information. The seismic P-wave velocity (VP) in the same material can provide the extra information required for the inversion. In this study, an approach is described for a closed-form solution of VG and VP to invert for φ and Sw in shallow sediments. The complex refractive index model (CRIM) for VG and Gassmann-Biot model for VP are used to relate these velocities to φ and Sw. Each model presents a nonlinear equation in φ and Sw. The two equations are solved simultaneously to estimate φ and Sw from VG-VP measurements. Testing of the inversion procedure in the presence of errors in assuming the properties of the soil matrix showed that these errors can drastically affect the inverted ...