A Discussion on global tectonics in Proterozoic times - Palaeomagnetic evidence for a Proterozoic super-continent

1976 ◽  
Vol 280 (1298) ◽  
pp. 469-490 ◽  
Keyword(s):  
North American ◽  
Mantle Convection ◽  
Great Circle ◽  
Prominent Feature ◽  
Time Data ◽  
Polar Wander ◽  
Late Precambrian ◽  
Palaeomagnetic Data ◽  
The Baltic ◽  
Global Tectonics

The Precambrian apparent polar wander (a.p.w.) curve for Africa is now defined in a general way from ca . 2700 million years (Ma) to Palaeozoic times, and is compared here with palaeomagnetic results from other Precambrian regions. Loops present in the African and North American a.p.w. curves between 2000 and 1000 Ma can be matched in size and shape, and when superimposed show that the AfroArabian and North American regions were in continuity at this time. Data from other Gondwanaland continents are reviewed and seem to be consistent with the SmithHallam reconstruction to ca . 2100 Ma for South America, to ca . 1800 Ma for India, and possibly for Australia back to ca . 2100 Ma. The a.p.w. curve from the Baltic and Ukrainian Shields can be matched with that from Africa and North America such that there was crustal continuity prior to 1000 Ma with the Gothide and Grenville mobile belts in great-circle alignment. The limited palaeomagnetic data from the Siberian Shield do not allow it to be placed uniquely with respect to the other land masses but are consistent with a position in juxtaposition with the Baltic-Ukrainian Shields such that massive anorthosites and ca . 1000 Ma mobile belts are in alignment with those from elsewhere. The palaeomagnetic evidence is consistent with a model in which the bulk of the Precambrian shields were aggregated together as a single super-continent during much of Proterozoic times, the most prominent feature of which is a great circle alignment of massive anorthosites (2250-1000 Ma) along a belt which also became a concentrated zone of igneous intrusion by rapakivi granites and alkaline intrusions, and culminated in generation of long linear mobile belts at 1150 ± 200 Ma and thick graben sedimentation. The predominance of this feature during much of the Proterozoic suggests that a simple mantle convection system pertained during this time. The proposed super-continent is not greatly different in form from the later shortlived super-continent Pangaea, formation of which may have involved relatively minor redistribution of the sialic regions in late Precambrian (probably post-800 Ma) and Palaeozoic times.

Paleomagnetism of the upper Keweenawan sediments: the Nonesuch Shale and Freda Sandstone

1977 ◽  
Vol 14 (5) ◽  
pp. 1128-1138 ◽  
Author(s):  
Steven G. Henry ◽  
Frederick J. Mauk ◽  
Rob Van der Voo
Keyword(s):  
North American ◽  
Natural Remanent Magnetization ◽  
North American Plate ◽  
Virtual Geomagnetic Pole ◽  
General Direction ◽  
Polar Wander ◽  
Late Precambrian ◽  
The North ◽  
Copper Mineralization ◽  
Geomagnetic Pole

The natural remanent magnetization of the upper Keweenawan Nonesuch Shale and Freda Sandstone has been analyzed with thermal, alternating field, and chemical demagnetization techniques. The results of this study are in good agreement with previously published works by DuBois and by Vincenz and Yaskawa, but place a tighter constraint on the North American apparent polar wander path. Fifty-eight samples, representing nearly 900 m of section, have been collected from the flanks of the Porcupine Mountain uplift. From principally thermal demagnetization analyses, a mean direction of primary magnetization has been calculated for the Nonesuch Shale, with declination 279.8°, inclination +9.8°, yielding a virtual geomagnetic pole position at 176.5° E, 10.3° N, and for the Freda Sandstone, with declination 271.3° inclination + 0.7°, yielding a virtual geomagnetic pole at 179.5° E, 1.2° N. A group of intermediate (secondary) components of magnetization is removed between temperatures of 350 °C and 550 °C, yielding well clustered directions. Its mean direction with declination 280.6°, inclination −9.5°, resulted in a virtual geomagnetic pole at 169.2° E, 3.7° N. This secondary magnetization is assumed to be of chemical origin and is most likely associated with the late Precambrian copper mineralization of the Nonesuch Shale. By thorough sampling of the stratigraphic column it is possible to infer the general direction of motion of a plate as the sediments were deposited. The motion of the North American plate as observed in the upper Keweenawan magnetizations is in agreement with the previously published polar wander paths for the late Precambrian.

Reinterpretation of the North American apparent polar wander curve for the interval 800–1500 Ma

1980 ◽  
Vol 17 (9) ◽  
pp. 1229-1235 ◽  
Author(s):  
Glenn W. Berger ◽  
Derek York
Keyword(s):  
North America ◽  
North American ◽  
Baltic Shield ◽  
Drift Rate ◽  
El Paso ◽  
Continental Drift ◽  
Polar Wander ◽  
The North ◽  
The Pacific ◽  
The Baltic

We have reviewed the geochronology of rocks having paleopoles in the interval 800–1500 Ma from North America, Greenland, and the Baltic Shield. The present uncertainties in the acquisition times of the remanent magnitizations allow the construction of a simplified apparent polar wander curve for North America that incorporates Sveconorwegian paleopoles in a Grenville Loop, and that places poles from the El Paso, Stoer Group, and Aillik Bay rocks on the Logan Loop. Furthermore, the sense of motion through poles older than ~ 1.3 Ga is reversed to permit the shortest connection to poles older than 1.6 Ga. As well, the timing and shape of the Hadrynian Track are modified so that it begins in the Atlantic hemisphere at ~ 800 Ma and terminates in the Pacific at ~ 650 Ma, representing a minimum average continental drift rate of ~ 10 cm/year for this interval.

scholarly journals FLIGHT TRAJECTORIES COMPARISON IN THE BALTIC FAB / BALTIJOS FUNKCINIO ORO ERDVĖS BLOKO SKRYDŽIŲ TRAJEKTORIJŲ PALYGINIMAS

2018 ◽  
Vol 10 (0) ◽  
pp. 1-6
Author(s):  
Anrieta Dudoit ◽  
Jonas Stankūnas
Keyword(s):  
Service Providers ◽  
Great Circle ◽  
Flight Distance ◽  
Optimal Trajectories ◽  
Entry And Exit ◽  
Fuel Burn ◽  
The Us ◽  
Navigation Service ◽  
The Baltic ◽  
National Borders

Aviation is one of the types of transport which has a crucial role in the modern world and develops with unprecedent speed. As the number of flights tends to increase, the Air Traffic Management (ATM) system has to ensure the safety of these flights and effectiveness of them. The design and use of the European routes and use of the air route network are considered to be a major causal factor of flight inefficiencies in the continent. The present ATM system needs to be reorganised to satisfy airspace operator needs and maintain safety levels, because of the recent and future predicted traffic growth and not always satisfactory indicators of the efficiency of the ATM system.The airspace is currently fragmented along national borders that is why the efficiency of flights is not assured i.e. to perform flights along optimal trajectories avoiding delays, excessive fuel burn and emissions. One of the conditions for ATM system to be more effective is connection of the airspace blocks, into Functional Airspace Blocks (FAB), within which more efficient flight could be conducted based on more direct routes connecting entry and exit points of the FAB. According to the analysis on European and US ATM systems, where the European ATM system is the sum total of a large number of separate Air Navigation Service Providers (ANSP) whereas the US system is operated by a single ANSP, it was analysed and stated that the less fragmentation there is, the more efficient flights are.The focus of this paper is to show the differences between fixed routes and direct trajectories (Great Circle) in the Baltic FAB in terms of flight distance, fuel burn and emission. The airspace is currently fragmented along national borders that is why the efficiency of flights is not assured i.e. to perform flights along optimal trajectories avoiding delays, excessive fuel burn and emissions. One of the conditions for ATM system to be more effective is connection of the airspace blocks, into Functional Airspace Blocks (FAB), within which more efficient flight could be conducted based on more direct routes connecting entry and exit points of the FAB. According to the analysis on European and US ATM systems, where the European ATM system is the sum total of a large number of separate Air Navigation Service Providers (ANSP) whereas the US system is operated by a single ANSP, it was analysed and stated that the less fragmentation there is, the more efficient flights are. The focus of this paper is to show the differences between fixed routes and direct trajectories (Great Circle) in the Baltic FAB in terms of flight distance, fuel burn and emission. Santrauka Aviacija – viena iš greitai augančių transporto šakų, kuri yra svarbi šiuolaikiniame moderniajame pasaulyje. Kadangi skrydžių nuolatos daugėja, oro eismo valdymo (OEV) sistema turi užtikrinti skrydžių saugą ir efektyvumą. Europos oro maršrutų išdėstymas ir naudojimas laikomi svarbiausiais skrydžių neefektyvumo veiksniais žemyne. Dėl esamo ir numatomo oro eismo augimo ir ne visados patenkinamų OEV sistemos efektyvumo rodiklių esama OEV sistema turi būti reorganizuota, siekiant užtikrinti oro erdvės naudotojų poreikius ir palaikyti reikalingą saugos lygį.Šiuo metu oro erdvė yra sudalyta pagal kiekvienos šalies valstybines ribas, dėl to skrydžių efektyvumas nėra optimalus, t. y. atliekami skrydžiai nevykdomi pagal optimalias trajektorijas vengiant užlaikymų, mažinant naudojamo kuro sąnaudas ir emisijas. Viena sąlyga, siekiant OEV sistemą padaryti efektyvesnę, – sujungti oro erdvės blokus į funkcinius oro erdvės blokus (FOEB), kur skrydžiai būtų vykdomi tiesesniais maršrutais tarp įskridimo ir išskridimo į FOEB taškų.Atlikus Europos OEV ir JAV sistemų analizę matyti, kad Europos OEV sistema susideda iš daugybės atskirtų oro navigacijos paslaugų teikėjų, o JAV sistemą valdo vienas oro navigacijos paslaugų teikėjas. Konstatuota, kad ten, kur fragmentacija mažesnė, skrydžių efektyvumas didesnis.Straipsnio tikslas – parodyti skirtumus tarp fiksuotųjų ir laisvųjų maršrutų Baltijos funkciniame oro erdvės bloke skrydžių atstumo, sunaudojamo kuro ir emisijų faktoriais.

Paleomagnetism of the Great Slave Supergroup, Northwest Territories, Canada: the Stark Formation

1976 ◽  
Vol 13 (4) ◽  
pp. 563-578 ◽  
Author(s):  
D. K. Bingham ◽  
M. E. Evans
Keyword(s):  
Northwest Territories ◽  
North American ◽  
Geomagnetic Field ◽  
Pole Position ◽  
The West ◽  
Stratigraphic Sequence ◽  
Polar Wander ◽  
Early Proterozoic ◽  
The North ◽  
Polarity Reversals

Paleomagnetic results from 55 sampling sites throughout the Stark Formation are reported. The known stratigraphic sequence of these sites enables the behaviour of the geomagnetic field in these remote times (1750 m.y.) to be elucidated. Two polarity reversals are identified and these represent potentially useful correlative features in strata devoid of index fossils. One of these is investigated in detail and indicates that behaviour of the geomagnetic field during polarity reversals was essentially the same in the early Proterozoic as it has been over the last few million years. The pole position (145°W, 15°S, dp = 3.5, dm = 6.9) lies far to the west of that anticipated from earlier results, implying further complexity of the North American polar wander curve. Possible alternatives to this added complexity are discussed.

Paleomagnetism of the Lawrenceton Formation volcanic rocks, Silurian Botwood Group, Change Islands, Newfoundland

1989 ◽  
Vol 26 (2) ◽  
pp. 296-304 ◽  
Author(s):  
Julie E. Gales ◽  
Ben A. van der Pluijm ◽  
Rob Van der Voo
Keyword(s):  
North American ◽  
Volcanic Rocks ◽  
Mobile Belt ◽  
Structural Mapping ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
North American Craton

Paleomagnetic sampling of the Lawrenceton Formation of the Silurian Botwood Group in northeastern Newfoundland was combined with detailed structural mapping of the area in order to determine the deformation history and make adequate structural corrections to the paleomagnetic data.Structural analysis indicates that the Lawrenceton Formation experienced at least two folding events: (i) a regional northeast–southwest-trending, Siluro-Devonian folding episode that produced a well-developed axial-plane cleavage; and (ii) an episode of local north-trending folding. Bedding – regional cleavage relationships indicate that the latter event is older than the regional folding.Thermal demagnetization of the Lawrenceton Formation yielded univectorial southerly and shallow directions (in situ). A fold test on an early mesoscale fold indicates that the magnetization of the Botwood postdates this folding event. However, our results, combined with an earlier paleomagnetic study of nearby Lawrenceton Formation rocks, demonstrate that the magnetization predates the regional folding. Therefore, we conclude that the magnetization occurred subsequent to the local folding but prior to the period of regional folding.While a tectonic origin for local folding cannot be entirely excluded, the subaerial nature of these volcanics, the isolated occurrence of these folds, and the absence of similar north-trending folds in other areas of eastern Notre Dame Bay suggest a syndepositional origin. Consequently, the magnetization may be nearly primary. Our study yields a characteristic direction of D = 175°, I = +43°, with a paleopole (16°N, 131 °E) that plots near the mid-Silurian track of the North American apparent polar wander path. This result is consistent with an early origin for the magnetization and supports the notion that the Central Mobile Belt of Newfoundland was adjacent to the North American craton, in its present-day position, since the Silurian.

Paleomagnetism of the komatiitic basalts of the Ottawa Islands, N.W.T.

1985 ◽  
Vol 22 (4) ◽  
pp. 553-566 ◽  
Author(s):  
K. L. Buchan ◽  
W. R. A. Baragar
Keyword(s):  
North American ◽  
Hudson Bay ◽  
The West ◽  
Magnetization Direction ◽  
Polar Wander ◽  
The North ◽  
Dominant Component ◽  
Apparent Polar Wander Path

The komatiitic basalts of the Ottawa Islands in eastern Hudson Bay are on strike with and believed to form a continuation of similar units of the Cape Smith Belt 150 km to the northeast. Units sampled in the Ottawa Islands all dip gently to the west and hence are not suitable for an internal fold test of their age of magnetization. However, before correcting for the tilt of the lavas, the dominant magnetization direction (D = 207.6°, I = 61.9°, k = 168, α95 = 3.7°) does not differ significantly from the uncorrected magnetization direction reported from the steeply dipping, northwest-facing units at Cape Smith (D = 218°, I = 60°, k = 47, α95 = 4°). This negative fold test suggests that the remanence at both locations was acquired after folding. Comparison with the North American Precambrian apparent polar wander path implies that overprinting is related to the Hudsonian Orogeny.A second stable magnetization directed to the west with a shallow inclination is superimposed on the dominant component at a number of sampling sites. Its direction is poorly defined and no fold test is possible. However, magnetic evidence suggests that this component was probably acquired as an overprint after the dominant magnetization, perhaps during a mild reheating associated with the Elsonian Orogeny.

Palaeomagnetic constraints on the distribution of continents in the late Silurian and early Devonian

1985 ◽  
Vol 309 (1138) ◽  
pp. 29-56 ◽  
Keyword(s):  
North American ◽  
Large Scale ◽  
Igneous Rocks ◽  
Red Beds ◽  
Early Devonian ◽  
Palaeomagnetic Data ◽  
Subsequent Deformation ◽  
Boundary Reconstruction

Silurian and Devonian palaeomagnetic data are reviewed and used to orient continental fragments in a global map-frame. In some cases longitude separations have been estimated from palaeontological data. The resulting maps show a possible evolution of the continents in Silurian and Devonian time. A 10° present-day latitude-longitude grid has been rotated to past positions and the extent of areas involved in subsequent deformation are shown. Two internally consistent alternatives are presented for the Silurian-Devonian boundary reconstruction. The first draws on North American and Baltic data, mostly from cratonic sediments; the second uses British data obtained mostly from igneous rocks, and admits poles from SE Australia in positioning Gondwanaland. Choosing between these alternatives depends on having better data from Gondwanaland and on evaluating the hypothesis of large-scale remagnetization of red beds

Palaeomagnetic evidence for Proterozoic continental development

1981 ◽  
Vol 301 (1461) ◽  
pp. 265-277 ◽  
Keyword(s):  
North America ◽  
High Latitude ◽  
Baltic Shield ◽  
Continental Drift ◽  
Polar Wander ◽  
Late Proterozoic ◽  
Apparent Polar Wander Path ◽  
Orogenic Uplift ◽  
The Baltic ◽  
Opening And Closing

The palaeomagnetic record of continental drift during the Proterozoic is reasonably complete for North America (including Greenland and the Baltic Shield), less complete for Africa and Australia, and fragmentary elsewhere. Palaeomagnetic poles of similar age from different cratons or structural provinces of any one continent tend to fall on a common apparent polar wander path (a.p.w.p.), indicating no major (> 1000 km) intercratonic movements. On this evidence, Proterozoic orogens and mobile belts are essentially ensialic in origin. However, the palaeomagnetic record has systematic gaps. In highly metamorphosed orogens (amphibolite grade and above), remagnetization dating from post-orogenic uplift and cooling is pervasive. Collisional and ensialic orogenesis cannot then be distinguished. Palaeopoles from different continents do not follow a common a.p.w.p. They record large relative rotations and palaeolatitude shifts. A recurrent pattern appears in the late Proterozoic drift of North America. At approximately 200 Ma intervals (at about 1250, 1050, 850 and 600 Ma B.P .), the continent returned to the same orientation and (equatorial) latitudes from various rotations and high-latitude excursions. Lacking detailed a.p.w.ps. from other continents, it is not possible to say if these motions represent Wilson cycles of ocean opening and closing in the Phanerozoic style, but they do require minimum drift rates of 50—60 mm/a, comparable to the most rapid present-day plate velocities.

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