scholarly journals Shallow crustal structure in the Meadowbank River - Tehek Lake area: insights from gravity and magnetic modelling

2012 ◽  
Author(s):  
M D Thomas
Keyword(s):  
Crustal Structure ◽  
Lake Area ◽  
Gravity And Magnetic ◽  
Magnetic Modelling

Crustal structure beneath the Western Canada Sedimentary Basin: constraints from gravity and magnetic modelling

2002 ◽  
Vol 39 (3) ◽  
pp. 291-312 ◽  
Author(s):  
Jacqueline Hope ◽  
David Eaton
Keyword(s):  
Magnetic Anomaly ◽  
Crustal Structure ◽  
Potential Field ◽  
Red Deer ◽  
Sedimentary Basin ◽  
Western Canada ◽  
Western Canada Sedimentary Basin ◽  
Gravity And Magnetic ◽  
Magnetic Modelling ◽  
Canada Sedimentary Basin

Regional gravity and magnetic anomalies that originate from crystalline basement rocks extend over many parts of the Western Canada Sedimentary Basin. Although these potential-field anomalies provide a basis for tectonic subdivisions of the basement crust, most previous interpretations of these features have been largely qualitative in nature. This study focuses on numerical simulation and quantitative interpretation of five regional potential-field anomalies in Alberta, Canada, for which independent constraints on crustal structure are available from Lithoprobe seismic and electromagnetic studies. The Kimiwan High (~55°N, 116°W) is a roughly 250 km long linear magnetic high. Seismic profiles across this anomaly provide evidence for a crustal-scale extensional fault system that offsets the Winagami reflection sequence, a series of mid-crustal sills. We find that the magnetic anomaly can be modelled as either a 15–40 km wide zone of moderate positive susceptibility (4.5 × 10–3 SI units) in the hanging wall of the detachment (5–17 km depth), or as a narrower (5–10 km), steeply dipping zone of high susceptibility (2.5 × 10–2 SI units) in the footwall (16–32 km depth). We interpret the former scenario as indicative of an extensive zone of alteration above the fault, whereas the latter could represent a decapitated granitic pluton that correlates with magmatic rocks farther north. To the southeast, the Thorsby Low (~53°N, 114°W) is a sinuous, 400 km long magnetic low and gravity gradient trend that appears to be a splay of the much more extensive Snowbird tectonic zone. Previous seismic interpretations across the Thorsby Low indicate that it coincides with a 10 km offset in the Moho. Our results show that this abrupt change in crustal thickness is consistent with, but not required by, the gravity signature of this feature. The northeast-striking Red Deer High (~53°N, 112°W) is a narrow magnetic anomaly in central Alberta with variable intensity along strike. Previous magnetotelluric studies suggest that the Red Deer anomaly is closely associated with a linear, highly conductive body in the upper basement. Our modelling results confirm the shallow depth of the causative body and suggest an eastward dip that is consistent with published seismic interpretations. Near the eastern border of Alberta, the 300 km long Eyehill High (~52°N, 110°W) is a prominent north-striking magnetic anomaly adjacent to the western hinterland of the Trans-Hudson Orogen. Combined gravity and magnetic modelling show that this feature occurs near the western boundary of a large block of dense material in the lower crust. The magnetic anomaly can be simulated by a near-vertical dyke-like body in the upper crust. Lastly, the Vulcan structure (~50.5°N, 112°W) forms the ~400 km long, northern boundary of the Archean Medicine Hat block. It is defined by a sinuous east-trending magnetic anomaly and gravity low. The wavelength and polarity of the magnetic anomaly (positive in the north), coupled with the coincident gravity low, are most simply explained by a mid-crustal low-density body with significant remanent magnetization oriented antiparallel to the present-day field.

Crustal structure and kinematic framework of the northwestern Pontiac Subprovince, Quebec: an integrated structural and geophysical study

1994 ◽  
Vol 31 (2) ◽  
pp. 271-281 ◽  
Author(s):  
Keith Benn ◽  
Warner Miles ◽  
Mohammad R. Ghassemi ◽  
John Gillett
Keyword(s):  
Crustal Structure ◽  
Shear Zones ◽  
Seismic Profile ◽  
Crustal Thickening ◽  
Structural Development ◽  
Seismic Reflection Profile ◽  
Gravity And Magnetic ◽  
Magnetic Model ◽  
Geophysical Study ◽  
Magnetic Modelling

Structural mapping, gravity and magnetic modelling, and interpretation of a deep-seismic profile in the northwestern Pontiac Subprovince outline the crustal structure and early structural development of the region. Penetrative D1 fabrics in the Pontiac Group and in the underlying Opasatica Gneiss may record south-vergent thrusting of a high-grade nappe. D2 and D3 structures record southeast-vergent folding and thrusting within the Pontiac Group. Steeply dipping northeast-trending ductile shear zones may represent oblique ramps initiated during D1. Gravity and magnetic model profiles are consistent with north-dipping structures in the shallow crust, and indicate that the Pontiac Group is a wedge underlain by north-dipping slabs of different densities and magnetic susceptibilities. Interpretation of a seismic reflection profile shows mid-crustal duplex structures overlying a deeper thrust between 16 and 24 km. From the surface to the deep crust, the structure of the northwestern Pontiac Subprovince records south- to southeast-directed thrusting and important crustal thickening during a collisional event. In light of field observations, available isotopic ages suggest that D1 deformation began no earlier than 2694 Ma, and that deformation continued until at least 2668 Ma.

scholarly journals Gravity and Magnetic Constraints on the Crustal Structure and Evolution of the Horeki Seamount in the Izu-Bonin Arc

2006 ◽  
Vol 4 (0) ◽  
pp. 55-65 ◽  
Author(s):  
Toshiya Fujiwara ◽  
Yukari Kido ◽  
Yoshihiko Tamura ◽  
Osamu Ishizuka
Keyword(s):  
Crustal Structure ◽  
Gravity And Magnetic

3D Gravity/Magnetic Modelling of Crustal Structure on the UK Atlantic Margin

1997 ◽  
Author(s):  
M.K. Lee ◽  
R.M. Carruthers ◽  
Z.K. Dabek ◽  
I.F. Smith ◽  
J.W.f. Edwards ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Magnetic Modelling ◽  
3D Gravity ◽  
The Uk ◽  
Atlantic Margin

scholarly journals Crustal structure of Mesozoic rifting in the northeastern Gulf of Mexico from integration of seismic and potential fields data

2019 ◽  
Vol 7 (4) ◽  
pp. T857-T867 ◽  
Author(s):  
Mei Liu ◽  
Irina Filina ◽  
Paul Mann
Keyword(s):  
Gulf Of Mexico ◽  
Crustal Structure ◽  
Late Jurassic ◽  
Phase 1 ◽  
Integrated Approach ◽  
High Density ◽  
Magnetic Data ◽  
Data Sets ◽  
Gravity And Magnetic ◽  
Northeastern Gulf Of Mexico

We have investigated the crustal structure of a 400 km wide zone of thinned continental crust in the northeastern Gulf of Mexico (GOM) using gravity and magnetic modeling along two deeply penetrated seismic transects. Using this approach, we identify two zones of prominent, southward-dipping reflectors associated with 7–10 km thick, dense, and highly magnetic material. Previous workers have interpreted the zones as either coarse clastic redbeds of Mesozoic age that are tilted within half-grabens or seaward-dipping reflectors of magmatic origin. Both seismic reflection lines reveal a 10 km thick and 67 km wide northern zone of high density near the Florida coastline beneath the Apalachicola rift (AR). The southern zone of high density occurs 70 km to the south in the deepwater central GOM along the northern flank of the marginal rift, a 48 km wide, southeast-trending structure of inferred Late Jurassic age that is filled by 3 km of low-density and low-magnetic susceptibility sediments including complexly deformed salt deposits. We propose that these two subparallel rifts and their associated magmatic belts formed in the following sequence: (1) AR formed during Triassic-early Jurassic (210–163 Ma) phase 1 of diffuse continental stretching and was partially infilled on its northern edge by southward-dipping volcanic flows; and (2) the similarly southward-dipping southern magmatic zone formed adjacent to the marginal rift during the early phase 2 of late Jurassic (161–153 Ma) rifting of the GOM continental extension; this southern area of SDR formation immediately preceded the formation of the adjacent oceanic crust that separated the rift-related evaporates into the northern and southern GOM. Our integrated approach combining 2D seismic, gravity, and magnetic data sets results in a more confident delineation of these deep crustal features than from seismic data alone.

scholarly journals Upper crustal structure of Deception Island area (Bransfield Strait, Antarctica) from gravity and magnetic modelling

2005 ◽  
Vol 17 (2) ◽  
pp. 213-224 ◽  
Author(s):  
A. MUÑOZ-MARTÍN ◽  
M. CATALÁN ◽  
J. MARTÍN-DÁVILA ◽  
A. CARBÓ
Keyword(s):  
Crustal Structure ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Active Volcano ◽  
Magnetic Data ◽  
Deception Island ◽  
Intrusive Body ◽  
The South ◽  
Bransfield Strait ◽  
Gravity And Magnetic

Deception Island is a young, active volcano located in the south-western part of Bransfield Strait, between the Antarctic Peninsula and the South Shetland archipelago. New gravity and magnetic data, from a marine geophysical cruise (DECVOL-99), were analysed. Forty-eight survey lines were processed and mapped around Deception Island to obtain Bouguer and magnetic anomaly maps. These maps show well- defined groups of gravity and magnetic anomalies, as well as their gradients. To constrain the upper crustal structure, we have performed 2+1/2D forward modelling on three profiles perpendicular to the main anomalies of the area, and taking into account previously published seismic information. From the gravity and magnetic models, two types of crust were identified. These were interpreted as continental crust (located north of Deception Island) and more basic crust (south of Deception Island). The transition between these crustal types is evident in the Bouguer anomaly map as a high gradient area trending NE–SW. Both magnetic and gravity data show a wide minimum at the eastern part of Deception Island, which suggests a very low bulk susceptibility and low density intrusive body. With historical recorded eruptions and thermal and fumarolic fields, we interpret this anomaly as a partially melted intrusive body. Its top has been estimated to be at 1.7 km depth using Euler deconvolution techniques.

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