Paleomagnetism and U–Pb geochronology of Franklin dykes in High Arctic Canada and Greenland: a revised age and paleomagnetic pole constraining block rotations in the Nares Strait regionThis is a companion paper to Denyszyn, S.W., Davis, D.W., and Halls, H.C. Paleomagnetism and U–Pb geochronology of the Clarence Head dykes, Arctic Canada: orthogonal emplacement of mafic dykes in a large igneous province. Canadian Journal of Earth Sciences, 46(3): 155–167.

2009 ◽  
Vol 46 (9) ◽  
pp. 689-705 ◽  
Author(s):  
Steven W. Denyszyn ◽  
Henry C. Halls ◽  
Don W. Davis ◽  
David A.D. Evans
Keyword(s):  
High Arctic ◽  
Companion Paper ◽  
North American Plate ◽  
Large Igneous Province ◽  
Arctic Canada ◽  
Age Progression ◽  
The North ◽  
Paleomagnetic Poles ◽  
The Difference ◽  
Key Pole

U–Pb baddeleyite ages and paleomagnetic poles obtained for dykes on Devon Island and Ellesmere Island in the Canadian Arctic and the Thule region of Greenland show that they are associated with the Franklin magmatic event. This study is the only one devoted to Franklin igneous rocks where a primary paleomagnetic remanence and U–Pb age have been obtained from the same rocks. Ages from this study range from 721 to 712 Ma, but paleomagnetic directional data show no clear age progression. The paleomagnetic poles from each of the two regional subsets are significantly different at the 95% confidence level from paleomagnetic results previously published for the Franklin event in the Canadian Shield. The difference in the pole locations can be accounted for, to first approximation, by a simple model of early Cenozoic block rotations among the North American plate, Greenland, and a hypothesized ancient microplate comprising Ellesmere, Devon, Cornwallis, and perhaps Somerset islands. A new grand-mean paleopole for the Franklin event, including restoration of Greenland and the proposed “Ellesmere microplate” to North America, is located at (8.4°N, 163.8°E, A95 = 2.8°, N = 78 sites) and is a key pole for Neoproterozoic supercontinent reconstructions.

Paleomagnetism and U–Pb geochronology of the Clarence Head dykes, Arctic Canada: orthogonal emplacement of mafic dykes in a large igneous province

2009 ◽  
Vol 46 (3) ◽  
pp. 155-167 ◽  
Author(s):  
Steven W. Denyszyn ◽  
Don W. Davis ◽  
Henry C. Halls
Keyword(s):  
Remanent Magnetization ◽  
High Arctic ◽  
Large Igneous Province ◽  
Dyke Swarm ◽  
Canadian High Arctic ◽  
The North ◽  
Igneous Province ◽  
The Difference ◽  
Age Range ◽  
Chemical Remanent Magnetization

The north–south-trending Clarence Head dyke swarm, located on Devon and Ellesmere Islands in the Canadian High Arctic, has a trend orthogonal to that of the Neoproterozoic Franklin swarm that surrounds it. The Clarence Head dykes are dated by the U–Pb method on baddeleyite to between 716 ± 1 and 713 ± 1 Ma, ages apparently younger than, but within the published age range of, the Franklin dykes. Alpha recoil in baddeleyite is considered as a possible explanation for the difference in ages, but a comparison of the U–Pb ages of grains of equal size from both swarms suggests that recoil distances in baddeleyite are lower than those in zircon and that the Clarence Head dykes are indeed a distinctly younger event within the period of Franklin magmatism. The Clarence Head dykes represent a large swarm tangential to, and cogenetic with, a giant radiating dyke swarm ∼800 km from the indicated source. The preferred mechanism for the emplacement of the Clarence Head dykes is the exploitation of concentric zones of extension around a depleting and collapsing plume source. While the paleomagnetism of most Clarence Head dykes agrees with that of the Franklin dykes, two dykes have anomalous remanence directions, interpreted to be a chemical remanent magnetization carried by pyrrhotite. The pyrrhotite was likely deposited from fluids mobilized southward from the Devonian Ellesmerian Orogeny to the north that used the interiors of the dykes as conduits and precipitated pyrrhotite en route.

scholarly journals ESTIMATING EULER POLE PARAMETERS FOR EASTERN CANADA USING GPS VELOCITIES

2015 ◽  
Vol 41 (4) ◽  
pp. 162-173
Author(s):  
Mohammad Ali Goudarzi ◽  
Marc Cocard ◽  
Rock Santerre
Keyword(s):  
North American Plate ◽  
Eastern Canada ◽  
Intraplate Earthquakes ◽  
Seismic Region ◽  
Ottawa River ◽  
The North ◽  
Euler Pole ◽  
Saint Lawrence River ◽  
The Difference ◽  
Gps Velocities

Eastern Canada is characterized by many intraplate earthquakes mostly concentrated along the Saint Lawrence River and Ottawa River valleys. After the rigid plate rotation of North America, the glacial isostatic adjustment (GIA) is by far the largest source of geophysical signal in eastern Canada. We estimate a set of Euler pole parameters for this area using a velocity field of 19 continuously operating GPS stations out of 112, and show that they are different from the overall rotation of the North American plate. This difference potentially reflects local stresses in this seismic region, and the difference in intraplate velocities between the two flanks of the Saint Lawrence River valley accumulate stress along the river.

scholarly journals Geochemical database of Cretaceous High Arctic Large Igneous Province magmatic rocks, Arctic Canada

2020 ◽  
Author(s):  
J H Bédard ◽  
B -M Saumur ◽  
M -C Williamson ◽  
C Tegner ◽  
V R Troll ◽  
...  
Keyword(s):  
High Arctic ◽  
Large Igneous Province ◽  
Arctic Canada ◽  
Magmatic Rocks ◽  
Igneous Province

Regionally continuous Miocene rhyolites beneath the eastern Snake River Plain reveal localized flexure at its western margin: Idaho National Laboratory and vicinity

2020 ◽  
Vol 57 (3) ◽  
pp. 241-270
Author(s):  
Kyle L. Schusler ◽  
David M. Pearson ◽  
Michael McCurry ◽  
Roy C. Bartholomay ◽  
Mark H. Anders
Keyword(s):  
Volcanic Rocks ◽  
Snake River Plain ◽  
North American Plate ◽  
Snake River ◽  
Trace Element Geochemistry ◽  
Deep Borehole ◽  
Age Progression ◽  
Western Margin ◽  
Silicic Volcanic ◽  
River Plain

The eastern Snake River Plain (ESRP) is a northeast-trending topographic basin interpreted to be the result of the time-transgressive track of the North American plate above the Yellowstone hotspot. The track is defined by the age progression of silicic volcanic rocks exposed along the margins of the ESRP. However, the bulk of these silicic rocks are buried under 1 to 3 kilometers of younger basalts. Here, silicic volcanic rocks recovered from boreholes that penetrate below the basalts, including INEL-1, WO-2 and new deep borehole USGS-142, are correlated with one another and to surface exposures to assess various models for ESRP subsidence. These correlations are established on U/Pb zircon and 40Ar/39Ar sanidine age determinations, phenocryst assemblages, major and trace element geochemistry, δ18O isotopic data from selected phenocrysts, and initial εHf values of zircon. These data suggest a correlation of: (1) the newly documented 8.1 ± 0.2 Ma rhyolite of Butte Quarry (sample 17KS03), exposed near Arco, Idaho to the upper-most Picabo volcanic field rhyolites found in borehole INEL-1; (2) the 6.73 ± 0.02 Ma East Arco Hills rhyolite (sample 16KS02) to the Blacktail Creek Tuff, which was also encountered at the bottom of borehole WO-2; and (3) the 6.42 ± 0.07 Ma rhyolite of borehole USGS-142 to the Walcott Tuff B encountered in deep borehole WO-2. These results show that rhyolites found along the western margin of the ESRP dip ~20º south-southeast toward the basin axis, and then gradually tilt less steeply in the subsurface as the axis is approached. This subsurface pattern of tilting is consistent with a previously proposed crustal flexural model of subsidence based only on surface exposures, but is inconsistent with subsidence models that require accommodation of ESRP subsidence on either a major normal fault or strike-slip fault.

Fractures in the northern plains, stream patterns, and the midcontinent stress field

1987 ◽  
Vol 24 (6) ◽  
pp. 1086-1097 ◽  
Author(s):  
Mel R. Stauffer ◽  
Don J. Gendzwill
Keyword(s):  
Stress Field ◽  
Horizontal Stress ◽  
The Body ◽  
North American Plate ◽  
Plate Motion ◽  
Viscous Drag ◽  
Near Surface ◽  
The North ◽  
Elastic Rebound ◽  
Western North Dakota

Fractures in Late Cretaceous to Late Pleistocene sediments in Saskatchewan, eastern Montana, and western North Dakota form two vertical, orthogonal sets trending northeast–southwest and northwest–southeast. The pattern is consistent, regardless of rock type or age (except for concretionary sandstone). Both sets appear to be extensional in origin and are similar in character to joints in Alberta. Modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures.Elevation variations on the sub-Mannville (Early Cretaceous) unconformity form a rectilinear pattern also parallel to the fracture sets, suggesting that fracturing was initiated at least as early as Late Jurassic. It may have begun earlier, but there are insufficient data at present to extend the time of initiation.We interpret the fractures as the result of vertical uplift together with plate motion: the westward drift of North America. The northeast–southwest-directed maximum principal horizontal stress of the midcontinent stress field is generated by viscous drag effects between the North American plate and the mantle. Vertical uplift, erosion, or both together produce a horizontal tensile state in near-surface materials, and with the addition of a directed horizontal stress through plate motion, vertical tension cracks are generated parallel to that horizontal stress (northeast–southwest). Nearly instantaneous elastic rebound results in the production of second-order joints (northwest–southeast) perpendicular to the first. In this manner, the body of rock is being subjected with time to complex alternation of northeast–southwest and northwest–southeast horizontal stresses, resulting in the continuous and contemporaneous production of two perpendicular extensional joint sets.

scholarly journals Characteristics of Arctic tides at CANDAC-PEARL (80° N, 86° W) and Svalbard (78° N, 16° E) for 2006–2009: radar observations and comparisons with the model CMAM-DAS

2011 ◽  
Vol 29 (10) ◽  
pp. 1939-1954 ◽  
Author(s):  
A. H. Manson ◽  
C. E. Meek ◽  
X. Xu ◽  
T. Aso ◽  
J. R. Drummond ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Radar Data ◽  
High Arctic ◽  
Wind Component ◽  
Meteor Radar ◽  
The North ◽  
Wave Numbers ◽  
Central Canada ◽  
June July ◽  
Abstract Operation

Abstract. Operation of a Meteor Radar (MWR) at Eureka, Ellesmere Island (80° N, 86° W) began in February 2006: this is the location of the Polar Environmental and Atmospheric Research Laboratory (PEARL), operated by the "Canadian Network for the Detection of Atmospheric Change" (CANDAC). The first 36 months of tidal wind data (82–97 km) are here combined with contemporaneous tides from the Meteor Radar (MWR) at Adventdalen, Svalbard (78° N, 16° E), to provide the first significant evidence for interannual variability (IAV) of the High Arctic's diurnal and semidiurnal migrating (MT) and non-migrating tides (NMT). The three-year monthly means for both diurnal (DT) and semi-diurnal (SDT) winds demonstrate significantly different amplitudes and phases at Eureka and Svalbard. Typically the summer-maximizing DT is much larger (~24 m s−1 at 97 km) at Eureka, while the Svalbard tide (5–24 m s−1 at 97 km)) is almost linear (north-south) rather than circular. Interannual variations are smallest in the summer and autumn months. The High Arctic SDT has maxima centred on August/September, followed in size by the winter features; and is much larger at Svalbard (24 m s−1 at 97 km, versus 14–18 m s−1 in central Canada). Depending on the location, the IAV are largest in spring/winter (Eureka) and summer/autumn (Svalbard). Fitting of wave-numbers for the migrating and non-migrating tides (MT, NMT) determines dominant tides for each month and height. Existence of NMT is consistent with nonlinear interactions between migrating tides and (quasi) stationary planetary wave (SPW) S=1 (SPW1). For the diurnal oscillation, NMT s=0 for the east-west (EW) wind component dominates (largest tide) in the late autumn and winter (November–February); and s=+2 is frequently seen in the north-south (NS) wind component for the same months. The semi-diurnal oscillation's NMT s=+1 dominates from March to June/July. There are patches of s=+3 and +1, in the late fall-winter. These wave numbers are also consistent with SPW1-MT interactions. Comparisons for 2007 of the observed DT and SDT at 78–80° N, with those within the Canadian Middle Atmosphere Model Data Assimilation System CMAM-DAS, are a major feature of this paper. The diurnal tides for the two locations have important similarities as observed and modeled, with seasonal maxima in the mesosphere from April to October, and similar phases with long/evanescent wavelengths. However, differences are also significant: observed Eureka amplitudes are generally larger than the model; and at Svalbard the modeled tide is classically circular, rather than anomalous. For the semi-diurnal tide, the amplitudes and phases differ markedly between Eureka and Svalbard for both MWR-radar data and CMAM-DAS data. The seasonal variations from observed and modeled archives also differ at each location. Tidal NMT-amplitudes and wave-numbers for the model differ substantially from observations.

scholarly journals Barotropic Regeneration of Upper-Level Synoptic Disturbances in Different Configurations of the Zonal Weather Regime

2008 ◽  
Vol 65 (10) ◽  
pp. 3159-3178 ◽  
Author(s):  
Gwendal Rivière
Keyword(s):  
Large Scale ◽  
Deformation Field ◽  
Regeneration Process ◽  
Barotropic Model ◽  
Weather Regime ◽  
The North ◽  
The Difference ◽  
Upper Level ◽  
Composite Maps ◽  
Large Scale Flow

Barotropic dynamics of upper-tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime (i.e., in different zonal-like large-scale flows) were studied using observational analyses and barotropic model experiments. The contraction stage of upper-level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text. This barotropic mechanism is studied through notions of barotropic critical regions (BtCRs) and effective deformation that have been introduced in a previous paper. The effective deformation field is equal to the difference between the square of the large-scale deformation magnitude and the square of the large-scale vorticity. Regions where the effective deformation is positive correspond to regions where the large-scale flow tends to strongly stretch synoptic disturbances. A BtCR is an area separating two large-scale regions of positive effective deformation, one located upstream and on the south side of the jet and the other downstream and on the north side. Such a region presents a discontinuity in the orientation of the dilatation axes and is a potential area where the barotropic regeneration process may occur. Winter days presenting a zonal weather regime in the 40-yr ECMWF Re-Analysis dataset are decomposed, via a partitioning algorithm, into different configurations of the effective deformation field at 300 hPa. A six-cluster partition is obtained. Composite maps of the barotropic generation rate for each cluster exhibit a succession of negative and positive values on both sides of the BtCRs. It confirms statistically that the barotropic regeneration mechanism occurs preferentially about BtCRs. Numerical experiments using a forced barotropic model on the sphere are performed. Each experiment consists of adding a synoptic-scale perturbation to one of the zonal-like jet configurations found in observations, which is kept fixed with time. The combined effects of the effective deformation and nonlinearities are shown to be crucial to reproduce the barotropic regeneration process about BtCRs.

United Front: Partisans of the Leningrad Region and their connections with the Central Asian Soviet Republics

2021 ◽  
Vol 2021 (02) ◽  
pp. 214-225
Author(s):  
Sergey Kulik ◽  
Аnatoliy Kashevarov ◽  
Zamira Ishankhodjaeva
Keyword(s):  
World War Ii ◽  
Weather Conditions ◽  
Leningrad Region ◽  
World War ◽  
North West ◽  
The North ◽  
Occupied Territory ◽  
Central Asian ◽  
The Difference ◽  
Almost All

During World War II, representatives of almost all the Soviet Republics fought in partisan detachments in the occupied territory of the Leningrad Region. Among them were many representatives of the Central Asian republics: Kazakhstan, Kyrgyzstan and Uzbekistan. Many Leningrad citizens, including relatives of partisans, had been evacuated to Central Asia by that time. However, representatives of Asian workers’ collectives came to meet with the partisans. The huge distance, the difference in cultures and even completely different weather conditions did not become an obstacle to those patriots-Turkestanis who joined the resistance forces in the North-West of Russia.

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