scholarly journals Electromagnetic images of crustal structures in southern and central Canadian Cordillera

1995 ◽  
Vol 32 (10) ◽  
pp. 1541-1563 ◽  
Author(s):  
Alan Q. Jones ◽  
D. Ian Gough
Keyword(s):  
Seismic Refraction ◽  
Three Dimensional ◽  
Compressional Wave ◽  
Canadian Cordillera ◽  
Fracture Density ◽  
Magnetotelluric Data ◽  
Juan De Fuca Plate ◽  
The North ◽  
Reflection And Refraction ◽  
Dimensional Variation

Data from more than 400 magnetotelluric soundings, made since the early 1980's in the Canadian Cordillera over a 300 000 km2 area between 49 and 53.5°N, are used to image qualitatively regional three-dimensional crustal variation in electrical conductivity by means of phase maps, phase–frequency sections, and maps of resistivity at depth. Two hundred of the soundings were acquired as part of Lithoprobe Southern Canadian Cordillera Transect activities, and their locations were coordinated with the seismic reflection and refraction experiments. The lower crust has a generally pervasive, low resistivity (1–100 Ω·m) throughout the Cordillera west of the Foreland Belt. Within this "Canadian Cordilleran Regional" conductor, the magnetotelluric data reveal both two-dimensional structures, with highest conductivities along the Coast Belt and Omineca Belt, and three-dimensional variation along geological strike. This conductor, mapped over a volume in excess of 106 km3, is most probably caused by fluids–saline waters and silicate melts–in fractures and along interconnected grain boundaries. The observed lateral variations in conductivity may result from variations in fracture density, temperature, and the sources of hot fluid, such as the subducting Juan de Fuca plate under the Coast Belt, and mantle upflow under the Omineca Belt. In addition, we report a major east–west-trending geophysical discontinuity in the upper and middle crust of the Omineca Belt at a latitude of 50°N, with highly resistive rocks (>1000 Ω·m) to the south and more conductive rocks to the north (30–300 Ω·m). Seismic refraction models, residual gravity, and filtered magnetic maps correlate changes in compressional-wave velocity, density, and magnetization along this cross-strike discontinuity.

Geophysical measurements in the region of the Explorer ridge off western Canada

1978 ◽  
Vol 15 (9) ◽  
pp. 1508-1525 ◽  
Author(s):  
R. D. Hyndman ◽  
G. C. Rogers ◽  
M. N. Bone ◽  
C. R. B. Lister ◽  
U. S. Wade ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Low Velocity ◽  
Geothermal Heat ◽  
Juan De Fuca Plate ◽  
The North ◽  
The Pacific ◽  
Ocean Bottom Seismometers ◽  
Seismic Reflection Profiles

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.

Broadside wide-angle seismic studies and three-dimensional structure of the crust in the southeast Canadian Cordillera

1997 ◽  
Vol 34 (8) ◽  
pp. 1156-1166 ◽  
Author(s):  
M. J. A. Burianyk ◽  
E. R. Kanasewich ◽  
N. Udey
Keyword(s):  
Signal To Noise Ratio ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
High Signal ◽  
Canadian Cordillera ◽  
Wide Angle ◽  
Low Velocity ◽  
Seismic Properties ◽  
High Degree

Broadside, or fan, recordings of a Lithoprobe seismic refraction – wide-angle reflection experiment in the southeastern Canadian Cordillera show several features further illuminating the crustal structure beyond that previously derived from SCoRE '90 (Southern Cordillera Refraction Experiment of 1990) in-line data. Analysis of a nearly in-line profile centred on Castlegar, British Columbia, shows lower velocities in the upper crust associated with the Purcell Anticlinorium as well as velocity variations that may have some association with the Purcell fault zone. The depth to Moho is almost 38 km, somewhat deeper and on trend with the structure that has been established farther north. The broadside records show high signal-to-noise ratio PmP arrivals (i.e., reflections from the bottom of the crust). These PmP fan picks were analysed in regions away from in-line profiles, providing further measurements of the depth to Moho in the southeastern Cordillera. The analysis of the broadside records combined with the earlier in-line interpretations as well as older crustal seismic measurements make up a relatively high resolution database, compared with most other regions in Canada, from which we have generated maps of depth to Moho and average crustal velocity in the southeastern Cordillera of Canada. The maps show thin, low-velocity crust over much of the region and indicate a high degree of correlation between current crustal seismic properties and regional isotherms.

Three-dimensional inversion of controlled-source audio-frequency magnetotelluric data based on unstructured finite-element method

2020 ◽  
Vol 17 (3) ◽  
pp. 349-360
Author(s):  
Xiang-Zhong Chen ◽  
Yun-He Liu ◽  
Chang-Chun Yin ◽  
Chang-Kai Qiu ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Three Dimensional ◽  
Audio Frequency ◽  
Magnetotelluric Data ◽  
Controlled Source ◽  
Element Method

scholarly journals Three-dimensional deformation time series of glacier motion from multiple-aperture DInSAR observation

2019 ◽  
Vol 93 (12) ◽  
pp. 2651-2660 ◽  
Author(s):  
Sergey Samsonov
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Ground Deformation ◽  
Three Dimensional ◽  
Data Sets ◽  
Ice Flow ◽  
The North ◽  
Glacier Ice ◽  
Deformation Component ◽  
3D Deformation

AbstractThe previously presented Multidimensional Small Baseline Subset (MSBAS-2D) technique computes two-dimensional (2D), east and vertical, ground deformation time series from two or more ascending and descending Differential Interferometric Synthetic Aperture Radar (DInSAR) data sets by assuming that the contribution of the north deformation component is negligible. DInSAR data sets can be acquired with different temporal and spatial resolutions, viewing geometries and wavelengths. The MSBAS-2D technique has previously been used for mapping deformation due to mining, urban development, carbon sequestration, permafrost aggradation and pingo growth, and volcanic activities. In the case of glacier ice flow, the north deformation component is often too large to be negligible. Historically, the surface-parallel flow (SPF) constraint was used to compute the static three-dimensional (3D) velocity field at various glaciers. A novel MSBAS-3D technique has been developed for computing 3D deformation time series where the SPF constraint is utilized. This technique is used for mapping 3D deformation at the Barnes Ice Cap, Baffin Island, Nunavut, Canada, during January–March 2015, and the MSBAS-2D and MSBAS-3D solutions are compared. The MSBAS-3D technique can be used for studying glacier ice flow at other glaciers and other surface deformation processes with large north deformation component, such as landslides. The software implementation of MSBAS-3D technique can be downloaded from http://insar.ca/.

scholarly journals Crustal architecture of a metallogenic belt and ophiolite belt: implications for mineral genesis and emplacement from 3-D electrical resistivity models (Bayankhongor area, Mongolia)

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Matthew J. Comeau ◽  
Michael Becken ◽  
Alexey V. Kuvshinov ◽  
Sodnomsambuu Demberel
Keyword(s):  
Electrical Resistivity ◽  
Crustal Structure ◽  
Three Dimensional ◽  
Suture Zone ◽  
Fault System ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
Ophiolite Belt ◽  
Geological Processes ◽  
Metallogenic Belt

AbstractCrustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust (< 25 km) is found to be generally highly resistive (> 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture—including the major crustal boundary—acts as a first‐order control on the location of the metallogenic belt.

scholarly journals Haemoglobin polymorphisms affect the oxygen-binding properties in Atlantic cod populations

2008 ◽  
Vol 276 (1658) ◽  
pp. 833-841 ◽  
Author(s):  
Øivind Andersen ◽  
Ola Frang Wetten ◽  
Maria Cristina De Rosa ◽  
Carl Andre ◽  
Cristiana Carelli Alinovi ◽  
...  
Keyword(s):  
Evolutionary Biology ◽  
Quaternary Structure ◽  
Atlantic Cod ◽  
Three Dimensional ◽  
Oxygen Affinity ◽  
Oxygen Binding ◽  
Low Oxygen ◽  
Binding Properties ◽  
Important Species ◽  
The North

A major challenge in evolutionary biology is to identify the genes underlying adaptation. The oxygen-transporting haemoglobins directly link external conditions with metabolic needs and therefore represent a unique system for studying environmental effects on molecular evolution. We have discovered two haemoglobin polymorphisms in Atlantic cod populations inhabiting varying temperature and oxygen regimes in the North Atlantic. Three-dimensional modelling of the tetrameric haemoglobin structure demonstrated that the two amino acid replacements Met55β 1 Val and Lys62β 1 Ala are located at crucial positions of the α 1 β 1 subunit interface and haem pocket, respectively. The replacements are proposed to affect the oxygen-binding properties by modifying the haemoglobin quaternary structure and electrostatic feature. Intriguingly, the same molecular mechanism for facilitating oxygen binding is found in avian species adapted to high altitudes, illustrating convergent evolution in water- and air-breathing vertebrates to reduction in environmental oxygen availability. Cod populations inhabiting the cold Arctic waters and the low-oxygen Baltic Sea seem well adapted to these conditions by possessing the high oxygen affinity Val55–Ala62 haplotype, while the temperature-insensitive Met55–Lys62 haplotype predominates in the southern populations. The distinct distributions of the functionally different haemoglobin variants indicate that the present biogeography of this ecologically and economically important species might be seriously affected by global warming.

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