Conductive structures under the Canadian Rocky Mountains

1985 ◽  
Vol 22 (3) ◽  
pp. 384-398 ◽  
Author(s):  
D. K. Bingham ◽  
D. I. Gough ◽  
M. R. Ingham
Keyword(s):  
Rocky Mountains ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Vertical Component ◽  
Rocky Mountain ◽  
Auroral Zone ◽  
Event Analysis ◽  
Canadian Rocky Mountains ◽  
Period Range ◽  
Single Station

The paper reports results from an array of 33 three-component magnetometers that recorded time-varying fields in 1981 over an area of some 56 000 km2 in the Canadian Cordillera. The array was centred at Tête Jaune Cache in the Rocky Mountain Trench, where a large magnetovariation anomaly had been located in an earlier array study. It was bisected by the trench and extended to the northeast across the Rocky Mountains to the Alberta Foothills and to the southwest across the Cariboo and Monashee mountains. Magnetograms and Fourier transform maps covering the period range 10–91 min show strong attenuation of the vertical component, Z, southwest of the Rocky Mountain Trench, with very large Z amplitudes in the Main Ranges of the Rockies. The horizontal components show an elongated anomaly along the Rocky Mountains Main Ranges and Trench, with three-dimensional features superimposed. The conductive structures include a highly conductive layer, probably in the lower crust, southwest of the trench and a conductive ridge rising into the upper crust near the edge of that layer. Current models have been fitted to observed vertical -and horizontal-component anomalies and show that both layer and ridge are necessary for a fit and that the ridge is 50–80 km wide. Single-station transfer functions at periods of 10 and 22 min have been calculated from a number of variation events of various polarizations, to reduce any displacement of the anomalies by auroral-zone source currents. Artificial-event analysis, with these transfer functions, shows that the conductive ridge lies under the Main Ranges of the Rockies and not under the trench. Its great width indicates a structure of major tectonic significance, which will be considered in another paper.

A Transfer Function Analysis of a Geomagnetic Depth Sounding-Profile across Central British Columbia

1973 ◽  
Vol 10 (7) ◽  
pp. 1089-1098 ◽  
Author(s):  
H. Dragert
Keyword(s):  
British Columbia ◽  
Transfer Functions ◽  
Function Analysis ◽  
Three Dimensional ◽  
Vertical Component ◽  
Rocky Mountain ◽  
Three Dimensional Model ◽  
Transfer Function Analysis ◽  
Single Station ◽  
Depth Sounding

Time variations of the geomagnetic field observed across British Columbia at a mean latitude of 54 °N are analyzed using 'single-station' and 'paired-station' optimum transfer functions. The frequency and spatial dependence of both coastal and inland geomagnetic anomalies are estimated with the following results. (1) The normal coast effect is strongly perturbed by lateral conductivity inhomogeneities both north and south of the profile. (2) A simple, single NW–SE striking conductivity contrast between the Cordillera and plains cannot account for the total geomagnetic anomaly in the area of the Rocky Mountain Trench; a three-dimensional model is required, incorporating (i) a lateral inhomogeneity striking east–west and located to the south of the profile, (ii) the effect of induction by the vertical component of source or secondary fields.

Conductive structures in southwestern Canada: a regional magnetometer array study

1982 ◽  
Vol 19 (8) ◽  
pp. 1680-1690 ◽  
Author(s):  
D. I. Gough ◽  
D. K. Bingham ◽  
M. R. Ingham ◽  
A. O. Alabi
Keyword(s):  
British Columbia ◽  
Lower Crust ◽  
Transfer Functions ◽  
Vertical Component ◽  
Rocky Mountain ◽  
Event Analysis ◽  
Response Curves ◽  
Model Studies ◽  
Single Station ◽  
Induced Currents

An array of 33 three-component recording magnetometers was operated in June and July 1980 in Alberta and British Columbia south of the Edmonton – Prince Rupert highway. This very large array, with its stations dispersed through 550 000 km2 and on average 150 km apart, had limited resolution and was designed to confirm known conductive structures, discover new ones, and locate them sufficiently for suitable placement of further arrays with closer spaced stations and, therefore, higher resolution. Magnetograms and three sets of Fourier transform anomaly maps are presented. They show the general attenuation of the vertical component of variation fields west of the Rocky Mountain Belt known from previous work and generally attributed to a conductive layer in the lower crust or upper mantle. Two prominent local anomalies are shown by variation fields of periods 15–30 min. The first indicates induced currents near Tête Jaune Cache, west of Jasper. The highly conductive structure carrying the induced currents may include wet sediments in the Rocky Mountain Trench and possibly partial melt at depth associated with recent volcanics. The second local anomaly appears to be associated with a crustal conductive structure that strikes northeast–southwest across southern Alberta and crosses the southeast corner of British Columbia into eastern Washington State. This may be associated with a Precambrian rift in the lower crust discovered by Kanasewich and his colleagues using deep crustal seismic reflections some 15 years ago. Both of these anomalies are under further investigation by means of arrays operated in 1981 in locations indicated by the results of the array reported here. The regional westward attenuation of the vertical fields has been quantified by means of single-station transfer functions and artificial event analysis, as developed by Bailey and others, to show the Z response to unit southwest–northeast horizontal field at three periods, along a profile from Squamish, near Vancouver, to Edmonton. These response curves will be used in model studies of the regional conductive structure.

Modeling tippers on a sphere

2021 ◽  
Author(s):  
Alexey Kuvshinov ◽  
Mikhail Kruglyakov
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Vertical Component ◽  
Spherical Geometry ◽  
Magnetic Data ◽  
Period Range ◽  
Continental Scale ◽  
Uniform External Magnetic Field

<p>In the past three decades, a huge amount of long-period magnetic data (from weeks to years of measurements) has been collected around the world either inland or at sea bottom. It makes tempting to estimate from these data magnetotelluric (MT) vertical transfer functions - tippers – in as wide  period range as practicable and further probe with them the three-dimensional (3-D) distribution of electrical conductivity in the upper mantle on a global or semi-global/continental scale. Such problem setup requires modelling MT responses in spherical geometry. It is known that MT impedances in spherical coordinates can be modelled using different polarizations of a uniform external magnetic field. As for tippers, one cannot compute them on a sphere using this type of excitation, because the uniform external magnetic field of any polarization contains a non-zero vertical component. To overcome the problem, we elaborate a model of the source, which leads to valid MT tippers on a sphere or a part thereof. To compute tippers in spherical Earth models with 3-D conductivity distribution we use a novel accurate and computationally efficient solver called GEMMIE. The solver is based on nested integral equations, allowing researchers to calculate high-resolution MT tippers globally and regionally taking into account realistic oceans, sediments, and Earth’s conductivity.</p>

THE ROCKY MOUNTAIN TRENCH: A PROBLEM

1964 ◽  
Vol 1 (3) ◽  
pp. 184-205 ◽  
Author(s):  
C. H. Crickmay
Keyword(s):  
Rocky Mountains ◽  
Rocky Mountain ◽  
Canadian Rocky Mountains ◽  
The West ◽  
West Side ◽  
Combined Action ◽  
Headward Erosion

The Rocky Mountain Trench is defined as the 1 000-mile valley which marks the west side of the Canadian Rocky Mountains. The background of the Trench as a problem is examined, and descriptions, geographical and geological, are given. Previous work on Trench origin is reviewed and note is taken of the seeming inapplicability of accepted erosion theories to the making of the erosion-made Trench. An hypothesis is offered in which the combined action of drainage hemmed in by bordering uplifts, guided headward erosion, lateral corrasion, and streams repeatedly reversed by continuing diastrophism is suggested as the excavator of the Trench, a valley characterized by the puzzling peculiarity of continuous depth without a consistent gradient.

scholarly journals Exploring effects in tippers at island geomagnetic observatories due to realistic depth- and time-varying oceanic electrical conductivity

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Rafael Rigaud ◽  
Mikhail Kruglyakov ◽  
Alexey Kuvshinov ◽  
Katia J. Pinheiro ◽  
Johannes Petereit ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Sea Water ◽  
Three Dimensional ◽  
Oceanic Lithosphere ◽  
Induction Effect ◽  
Electromagnetic Modeling ◽  
Period Range ◽  
Model Studies ◽  
Magnetic Transfer ◽  
The One

AbstractVertical magnetic transfer functions (tippers) estimated at island observatories can constrain the one-dimensional (1-D) conductivity distribution of the oceanic lithosphere and upper mantle. This is feasible due to the bathymetry-dependent ocean induction effect (OIE), which originates from lateral conductivity contrasts between ocean and land and leads to non-zero tippers even for 1-D conductivity distributions below the ocean. Proper analysis of island tippers requires accurate three-dimensional (3-D) modeling of the OIE, for which so far was performed assuming constant sea water electric conductivity with depth. In this study, we explore—using rigorous 3-D electromagnetic modeling—to what extent realistic, depth-dependent, oceanic conductivity affects island tippers. The modeling is performed for 11 island observatories around the world in the period range $$10^{-1}$$ 10 - 1 to $$10^{4}$$ 10 4 s. We also investigate the effect of seasonal variations of the oceanic conductivity and to which extent this could explain the observed systematic seasonal variation of tippers. Our model studies suggest that for most of the considered island observatories the effect from depth-varying oceanic conductivity is tangible and exceeds the error floor of 0.025, which usually is assigned to tippers during their inversion. The effect varies significantly with location, depending on regional bathymetry. Contrarily, the effects from seasonally varying oceanic conductivity were found to be too small to be worth consideration.

Distribution and Life History of the Lodgepole Needle Miner (Recurvaria sp.) (Lepidoptera: Gelechiidae) in Canadian Rocky Mountain Parks

1954 ◽  
Vol 86 (1) ◽  
pp. 1-12 ◽  
Author(s):  
R. W. Stark
Keyword(s):  
Life History ◽  
Rocky Mountains ◽  
National Park ◽  
Life Histories ◽  
Rocky Mountain ◽  
Yosemite National Park ◽  
Canadian Rocky Mountains ◽  
History Of

General. The life history of the lodgepole needle miner in Yosemite National Park, California, has been described (24). The Canadian outbreak was discovered in 1942 but intensive investigations were not commenced until 1948. Many differences have been noted between the Canadian and Californian life histories since the discovery of the outbreak.It is the purpose of this paper to bring together all information collected by the author and staff of the Laboratory of Forest Zoology at Calgary, Alberta, concerning the life history of the lodgepole needle miner in the Canadian Rocky mountains.

scholarly journals Parameterization of lateral drag in flowline models of glacier dynamics

2012 ◽  
Vol 58 (212) ◽  
pp. 1119-1132 ◽  
Author(s):  
Surendra Adhikari ◽  
Shawn J. Marshall
Keyword(s):  
Rocky Mountains ◽  
Three Dimensional ◽  
Correction Factors ◽  
Canadian Rocky Mountains ◽  
Horizontal Shear ◽  
Cross Sectional ◽  
Shape Factors ◽  
Bed Topography ◽  
Valley Glacier ◽  
Basal Flow

Given the cross-sectional geometry of a valley glacier, effects of lateral drag can be parameterized in flowline models through the introduction of Nye shape factors. Lateral drag also arises due to lateral variability in bed topography and basal flow, which induce horizontal shear stress and differential ice motion. For glaciers with various geometric and basal conditions, we compare three-dimensional Stokes solutions to flowline model solutions to examine both sources of lateral drag. We calculate associated correction factors that help flowline models to capture the effects of lateraldrag. Such parameterizations provide improved simulations of the dynamics of narrow, channelized, fast-flowing glacial systems. We present an example application for Athabasca Glacier in the Canadian Rocky Mountains.

scholarly journals The Quaternary Geologic History of the Canadian Rocky Mountains

2007 ◽  
Vol 46 (1) ◽  
pp. 5-50 ◽  
Author(s):  
Peter Bobrowsky ◽  
Nathaniel W. Rutter
Keyword(s):  
Central Region ◽  
Rocky Mountains ◽  
Ice Sheet ◽  
Rocky Mountain ◽  
Canadian Rocky Mountains ◽  
Geologic History ◽  
Physical Form ◽  
History Of ◽  
Central Rocky Mountains ◽  
Late Wisconsinan

ABSTRACT The Canadian Rocky Mountains figured prominently during the glacial history of western Canada. First as a western limit or boundary to the Laurentide Ice Sheet, second as an eastern margin of the Cordilleran Ice Sheet, and finally as a centre of local Montane ice. Throughout the Quaternary, complex interactions of glacier ice from these three ice sources markedly changed the physical form of the Rocky Mountains, Trench and Foothills areas. Investigations into the Quaternary history of this region have been ongoing since the beginning of the last century. Since about 1950, the number of studies performed in this area have increased significantly. This paper briefly reviews the historical accomplishments of Quaternary work in the region up to the period of about 1950. From this time to the present, individual study efforts are examined in detail according to the three geographic regions: 1) the northern Rocky Mountains (from the Liard Plateau south to the McGregor Plateau), 2) the central Rocky Mountains (from the McGregor Plateau south to the Porcupine Hills) and 3) the southern Rocky Mountains (from the Porcupine Hills south to the international border). In the northern region, geologic data suggest a maximum of two Rocky Mountain glaciations and only one Laurentide glaciation and no ice coalescence. In the central region, three of four Rocky Mountain events, and at least two Laurentide events are known. Only in the central region is there good evidence for ice coalescence, but the timing of this event is not clearly established. In the south, at least three Rocky Mountain episodes and a variable number of Laurentide episodes are recognized. There is no evidence for ice coalescence. A number of facts support the proposal that Cordilleran ice crossed the Continental Divide and joined with local Montane ice at several locations. However, this expansion of western ice occurred before the Late Wisconsinan in all areas but Jasper. In general, the chronological data presented suggest that the Late Wisconsinan glaciation in the Rocky Mountains was a short-lived event which started around or after 20 ka years ago and ended before 12 ka ago.

scholarly journals Exploring Effects in Tippers at Island Geomagnetic Observatories Due to Realistic Depth- and Time-varying Oceanic Electrical Conductivity

2020 ◽  
Author(s):  
Rafael Rigaud ◽  
Mikhail Kruglyakov ◽  
Alexey Kuvshinov ◽  
Katia J Pinheiro ◽  
Johannes Petereit ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Sea Water ◽  
Three Dimensional ◽  
Oceanic Lithosphere ◽  
Induction Effect ◽  
Electromagnetic Modeling ◽  
Period Range ◽  
Model Studies ◽  
Magnetic Transfer ◽  
The One

Abstract Vertical magnetic transfer functions (tippers) estimated at island observatories can constrain the one-dimensional (1-D) conductivity distribution of the oceanic lithosphere and upper mantle. This is feasible due to the bathymetry-dependent ocean induction effect (OIE), which originates from lateral conductivity contrasts between ocean and land and leads to non-zero tippers even for 1-D conductivity distributions below the ocean. Proper analysis of island tippers requires accurate three-dimensional (3-D) modeling of the OIE, for which so far was performed assuming constant sea water electric conductivity with depth. In this study we explore using rigorous 3-D electromagnetic modeling - to what extent realistic, depth-dependent, oceanic conductivity affects island tippers. The modeling is performed for eleven island observatories around the world in the period range 10-1 to 104 sec. We also investigate the effect of seasonal variations of the oceanic conductivity and to which extent this could explain the observed systematic seasonal variation of tippers. Our model studies suggest that for most of the considered island observatories the effect from depth-varying oceanic conductivity is tangible and exceeds the error floor of 0:025, which usually is assigned to tippers during their inversion. The effect varies significantly with location, depending on regional bathymetry. Contrarily, the effects from seasonally varying oceanic conductivity were found to be too small to be worth consideration.

Paleomagnetism and age of three Canadian Rocky Mountain diatremes

1992 ◽  
Vol 29 (1) ◽  
pp. 35-47 ◽  
Author(s):  
P. Jane Wynne ◽  
E. Irving ◽  
Daniel J. Schulze ◽  
Douglas C. Hall ◽  
Hewart H. Helmstaedt
Keyword(s):  
North America ◽  
Rocky Mountains ◽  
Rocky Mountain ◽  
Canadian Rocky Mountains ◽  
Early Devonian ◽  
Polar Wander ◽  
Middle Ordovician ◽  
Normal Polarity ◽  
The Cross ◽  
Age Estimates

Paleomagnetic results, and age estimates derived from them, arc presented for three diatremes, using as a basis of comparison the combined apparent polar wander (APW) path for North America and Europe of Van der Voo. The Cross diatreme of the Front Ranges of the Canadian Rocky Mountains has yielded a radiometric age of 241 Ma (earliest Triassic) and is hosted by the flat-lying Pennsylvanian Tunnel Mountain Formation. It has normal polarity magnetization and yields a paleopole correctly placed according to its radiometric age on the APW path. The Blackpool diatreme (for which no radiometric age is available), which is located in the Main Ranges of the Rocky Mountains, is known to be post-Late Ordovician because it is hosted by rocks of that age. It also has magnetization of normal polarity and yields a paleopole that, when calculated with respect to present horizontal, is coincident with the latest Cretaceous to Paleocene paleopole for North America. The paleopole, when calculated with respect to bedding, lies on the Middle Ordovician portion of the combined APW path. A clockwise rotation of 10° brings the paleopole into agreement with the latest Ordovician. Hence, from a paleomagnetic standpoint, a latest Cretaceous to Paleocene or latest Ordovician age is possible. The HP pipe (radiometric age 391 ± 5 Ma or Early Devonian), previously studied by D. T. A. Symons and M. T. Lewchuk, is hosted in limestones of Upper Cambrian to Middle Ordovician age. It has reversed polarity and yields a paleopole that, when compared with the combined APW path, suggests an age of mid-Permian, although errors are such that it could be somewhat younger, roughly coeval with the Cross diatreme. We conclude, therefore, that the radiometric age estimated for the HP pipe could be too old by about 130 million years.

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