Blueschist and eclogite in mylonitic allochthons, Ross River and Watson Lake areas, southeastern Yukon

1987 ◽  
Vol 24 (7) ◽  
pp. 1439-1449 ◽  
Author(s):  
Philippe Erdmer
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
North American ◽  
Leading Edge ◽  
Ultramafic Rocks ◽  
Glaucophane Schist ◽  
The North ◽  
New Occurrences

Two new occurrences of eclogite associated with mylonitic rocks are documented. The first, near Ross River, is in a quartz-rich metasedimentary host that includes glaucophane schist. The host forms part of a belt of high-pressure rocks more than 50 km long and several kilometres wide between Ross River and Faro. In the second occurrence, north of Watson Lake, eclogite is associated with mafic and ultramafic rocks occurring in a klippe more than 100 km2 in area that rests on unmetamorphosed Triassic rocks of the North American miogeocline. Geothermobarometry shows that the eclogites were metamorphosed at 10–15 kb (1 kb = 100 MPa), between 470 and 750 °C. These peak conditions are comparable to those for other eclogites in the Yukon and adjacent Alaska. The age of metamorphism and mylonitization is Triassic or older.The high-pressure rocks occur at the leading edge of the most inboard accreted terrane, along its boundary with North American miogeoclinal strata, over a length of several hundred kilometres. Their extensive distribution makes these rocks regionally mappable units. This supports other evidence that both the Yukon–Tanana terrane and mylonite sheets obducted on North American foreland rocks are composed in part of trench and subduction-zone material.

Eclogitic rocks in the St. Cyr klippe, Yukon, and their tectonic significance

1992 ◽  
Vol 29 (6) ◽  
pp. 1296-1304 ◽  
Author(s):  
Philippe Erdmer
Keyword(s):  
High Pressure ◽  
Oceanic Crust ◽  
North American ◽  
Suture Zone ◽  
Late Paleozoic ◽  
The North ◽  
Tectonic Significance ◽  
Subducted Oceanic Crust ◽  
Ophiolitic Rocks ◽  
Subducting Slab

Until recently, the Nisutlin allochthonous assemblage, a part of the Yukon–Tanana composite terrane interpreted as trench mélange from a late Paleozoic – Mesozoic arc system, was the only tectonic assemblage known to include subducted material in the northern Cordillera. The discovery of eclogitic rocks in two parts of a klippe of the Anvil allochthonous assemblage, which comprises mafic ophiolitic rocks, above the Cassiar terrane west of the Tintina fault confirms other evidence that subducted oceanic crust was also returned to the surface. The eclogitic rocks have been largely retrograded by postsubduction metamorphism. Their existence is interpreted as additional evidence of the link between nappes above the Cassiar terrane and their inferred root, the Teslin suture zone. The Nisutlin and Anvil allochthonous assemblages can now be interpreted, not simply as crustally metamorphosed assemblages with minor, structurally interleaved high-pressure components, but as deeply metamorphosed and intensely strained slices of continental and oceanic crust switched from subducting slab to overriding plate and returned to the surface during collision of the arc with the North American margin.

Some Aspects of High Performance Jet Aircraft

1953 ◽  
Vol 57 (510) ◽  
pp. 375-390
Author(s):  
W. A. Waterton
Keyword(s):  
High Pressure ◽  
North American ◽  
High Performance ◽  
Aircraft Industry ◽  
The North

Most sections of the Aircraft Industry with something to make, something to describe or something to sell will doubtless find much to take issue with in what is about to be said. No apologies are forthcoming, however, since it is proposed to speak about, and of, aircraft as found and experienced by pilots and operators.Along with Lease-Lend the North American idea of high pressure salesmanship appears to have permeated British aeronautical matters together with all the superlatives ending in " ER." Of all mankind's ingenious devices probably none are more full of compromises than aeroplanes, therefore adjectives describing one or more of their aspects may be noteworthy but, when they tend to overflow, a sceptical eyebrow may well be raised.

Crustal electrical conductivity in north-central Saskatchewan: the North American Central Plains anomaly and its relation to a Proterozoic plate margin

1984 ◽  
Vol 21 (5) ◽  
pp. 533-543 ◽  
Author(s):  
S. Handa ◽  
P. A. Camfield
Keyword(s):  
Electrical Conductivity ◽  
Subduction Zone ◽  
North American ◽  
Central Plains ◽  
Period Range ◽  
Geological Evidence ◽  
North Central ◽  
The North ◽  
Plate Margin ◽  
Lake Zone

Seven recording magnetometers monitored time-varying fields at points on a northwest–southeast line 280 km long in north-central Saskatchewan during July 1981. The experiment was designed to test the hypothesis advanced in 1975 by Alabi, Camfield, and Gough that the electrical conductivity anomaly in the North American Central Plains links with the Wollaston Domain in the exposed Precambrian Shield of Saskatchewan. From clear reversals in the phase of vertical variations, it is evident that the conductor passes between two stations straddling the Rottenstone–La Ronge Magmatic Belt, to the immediate east of the Wollaston Domain. Enhanced horizontal variations transverse to the belt at a third, intermediate, station reinforce this interpretation. Vertical-field response arrows obtained from daytime events in the period range 1–40 min clearly indicate the existence of a major conductor that extends to lower crustal depths beneath the belt. To the northwest across the Cree Lake Zone, reversals in the direction of response arrows at short periods (up to 4 min) imply complex electrical structures in the shallow part of the crust.Lewry termed the Rottenstone–La Ronge Belt a Hudsonian "Cordillera-type" arc massif, and described strong geological evidence for collisional suturing and microplate interaction in this part of the Churchill Province. A similar scenario seems to apply in Wyoming, from the work of Hills and Houston. Thus the conductor appears to trace a Proterozoic plate margin 1500 km from a subduction zone in Wyoming along a transform fault to a subduction zone in northern Saskatchewan.

scholarly journals Analysis of the 13–14 July Gulf Surge Event during the 2004 North American Monsoon Experiment

2007 ◽  
Vol 135 (9) ◽  
pp. 3098-3117 ◽  
Author(s):  
Peter J. Rogers ◽  
Richard H. Johnson
Keyword(s):  
North American ◽  
Gulf Of California ◽  
Leading Edge ◽  
North American Monsoon ◽  
Strong Wind ◽  
Kelvin Wave ◽  
High Resolution Data ◽  
Low Level ◽  
Second Stage ◽  
The North

Abstract Gulf surges are disturbances that move northward along the Gulf of California (GOC), frequently advecting cool, moist air from the GOC or eastern tropical Pacific Ocean into the deserts of the southwest United States and northwest Mexico during the North American Monsoon (NAM). Little attention has been given to the dynamics of these disturbances because of the lack of reliable high-resolution data across the NAM region. High temporal and spatial observations collected during the 2004 North American Monsoon Experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13–14 July 2004. Integrated Sounding Systems deployed along the east coast of the GOC and an enhanced network of rawinsonde sites across the NAM region are used in this study. Observations show that the 13–14 July gulf surge occurred in two primary stages. The first stage was preceded by anomalous low-level warming along the northern GOC on 13 July. Sharp cooling, moistening, and increased low-level south-southeasterly flow followed over a 12–18-h period. Over the northern gulf, the wind reached ∼20 m s−1 at 750 m AGL. Then there was a brief respite followed by the second stage—a similar, but deeper acceleration of the southerly flow associated with the passage of Tropical Storm (TS) Blas on 14 July. The initial surge disturbance traversed the GOC at a speed of ∼17–25 m s−1 and resulted in a deepening of the mixed layer along the northern gulf. Dramatic surface pressure rises also accompanied the surge. The weight of the evidence suggests that the first stage of the overall surge itself consisted of two parts. The initial part resembled borelike disturbances initiated by convective downdrafts impinging on the low-level stable layer over the region. The secondary part was characteristic of a Kelvin wave–type disturbance, as evident in the deeper layer of sharp cooling and strong wind that ensued. Another possible explanation for the first part is that the leading edge of this Kelvin wave steepened nonlinearly into a borelike disturbance. The second stage of the surge was associated with the increased circulation around TS Blas.

Paleomagnetism of Mesozoic plutons in the westernmost Coast Complex of British Columbia

1977 ◽  
Vol 14 (9) ◽  
pp. 2127-2139 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
North American ◽  
Leading Edge ◽  
Upper Jurassic ◽  
North American Plate ◽  
The North ◽  
Banks Island ◽  
Plutonic Complex ◽  
Normal Polarity ◽  
Coast Plutonic Complex ◽  
North American Craton

The Lower Cretaceous Stephens Island (102 ± 8 Ma) and Captain Cove (109 ± 6 Ma) plutons and the Upper Jurassic Gil Island (136 ± 3 Ma) and Banks Island (144 ± 6 Ma) plutons belong to the western K–Ar age zone of the N 35° W trending Coast plutonic complex southwest of Prince Rupert, B.C. After removal of initial viscous components, AF demagnetization isolates a stable primary remanence at 36 of 49 sites (10 specimens from 5 cores/site) before anhysteretic components are added. All sites have normal polarity which is consistent because their K–Ar ages fall in the predominantly normal Cretaceous and Jurassic Quiet Intervals. The poles for Stephens Island (339° W, 67° N (7°, 10°)), Captain Cove (9° W 72° N (8°, 11°)), and Gil Island (357° N. 70° N (6°, 8°)) lie just north of Britain and are discordant for the North American craton. The tectonic panel including these plutons was tilted [Formula: see text] during the Upper Cretaceous–Paleocene orogeny as the leading edge of the North American plate overrode the subducting oceanic Kula Plate. This interpretation is supported by other arguments including the attitudes of contacts and foliations, plutonic trend directions, distribution of metamorphic grades, and paleomagnetic data from the area to the east. The Banks Island pluton lies in the tectonic panel to the west. Its pole of 210° W, 81° N (33°, 38°) is poorly defined but apparently concordant.

scholarly journals Variations in North American Summer Precipitation Driven by the Atlantic Multidecadal Oscillation

2011 ◽  
Vol 24 (21) ◽  
pp. 5555-5570 ◽  
Author(s):  
Qi Hu ◽  
Song Feng ◽  
Robert J. Oglesby
Keyword(s):  
High Pressure ◽  
North America ◽  
North American ◽  
Lower Troposphere ◽  
Summer Precipitation ◽  
Atlantic Multidecadal Oscillation ◽  
Upper Troposphere ◽  
North American Continent ◽  
The North ◽  
Anomaly Pattern

Abstract Understanding the development and variation of the atmospheric circulation regimes driven by the Atlantic multidecadal oscillation (AMO) is essential because these circulations interact with other forcings on decadal and interannual time scales. Collectively, they determine the summer (June, July, and August) precipitation variations for North America. In this study, a general circulation model (GCM) is used to obtain such understanding, with a focus on physical processes connecting the AMO and the summertime precipitation regime change in North America. Two experimental runs are conducted with sea surface temperature (SST) anomalies imposed in the North Atlantic Ocean that represent the warm and cold phases of the AMO. Climatological SSTs are used elsewhere in the oceans. Model results yield summertime precipitation anomalies in North America closely matching the observed anomaly patterns in North America, suggesting that the AMO provides a fundamental control on summertime precipitation in North America at decadal time scales. The impacts of the AMO are achieved by a chain of events arising from different circulation anomalies during warm and cold phases of the AMO. During the warm phase, the North Atlantic subtropical high pressure system (NASH) weakens, and the North American continent is much less influenced by it. A massive body of warm air develops over the heated land in North America from June–August, associated with high temperature and low pressure anomalies in the lower troposphere and high pressure anomalies in the upper troposphere. In contrast, during the cold phase of the AMO, the North American continent, particularly to the west, is much more influenced by an enhanced NASH. Cooler temperatures and high pressure anomalies prevail in the lower troposphere, and a frontal zone forms in the upper troposphere. These different circulation anomalies further induce a three-cell circulation anomaly pattern over North America in the warm and cold phases of the AMO. In particular, during the cold phase, the three-cell circulation anomaly pattern features a broad region of anomalous low-level southerly flow from the Gulf of Mexico into the U.S. Great Plains. Superimposed with an upper-troposphere front, more frequent summertime storms develop and excess precipitation occurs over most of North America. A nearly reversed condition occurs during the warm phase of the AMO, yielding drier conditions in North America. This new understanding provides a foundation for further study and better prediction of the variations of North American summer precipitation, especially when modulated by other multidecadal variations—for example, the Pacific decadal oscillation and interannual variations associated with the ENSO and the Arctic Oscillation.

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