Displacement of Vancouver Island: paleomagnetic evidence from the Karmutsen Formation

1980 ◽  
Vol 17 (9) ◽  
pp. 1210-1228 ◽  
Author(s):  
R. W. Yole ◽  
E. Irving
Keyword(s):  
North America ◽  
Vancouver Island ◽  
Late Triassic ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Individual Site ◽  
Anticlockwise Rotation ◽  
Oriented Samples ◽  
Geomagnetic Fields ◽  
The Mean

New paleomagnetic results from the Karmutsen Formation (Late Triassic) of Vancouver Island confirm the presence of two families of magnetizations (X and Y), both of which are inconsistent with known Mesozoic and Cenozoic geomagnetic fields of cratonic North America. The X magnetizations have coherent directions with the exception of a subset of five sites (the B subset). We argue that the deviation of the B subset is caused either by a 31 ± 13 °anticlockwise rotation of a small block relative to the main sampling areas or by a short-term excursion of the field. The X magnetization has an overall mean direction 008°, −33 °α95 = 6 °based on results from 147 oriented samples (usually 2 specimens from each) collected at 28 sites spanning about 6000 m stratigraphically. We interpret this as the original Late Triassic magnetization. The corresponding X paleopole (21°N, 44°E A95 = 6°) is strongly far-sided and right-handed with respect to the Mesozoic apparent polar wander path for cratonic North America. The paleolatitude indicated for Vancouver Island in the Late Triassic is either 18°N or 18°S, the latter being preferred on the grounds that it yields a more consistent pattern for Cordilleran magnetizations, but the ambiguity is still not settled. In either case the results show that Vancouver Island was far south of its present position relative to North America in the Late Triassic, thus confirming the previous results of Irving and Yole. The Y magnetizations, with more heterogenous properties, occur at 14 sites (66 oriented cores, usually 2 specimens each). Y magnetizations are generally softer than X and for this and other reasons we regard them as secondary and post-Triassic in age. Individual site poles for the Y magnetization are, with minor exceptions, right-handed and slightly far-sided with respect to the apparent polar wandering path for cratonic North America. The mean paleopole for Y magnetizations is situated at 70°N, 15°W A95 = 11°. Both the X and Y magnetizations are consistent with either northward motion of the westernmost Cordilleran elements accompanied by clockwise rotation, or with oblique translation from the southwest. The northward component of motion derived from X directions would be the same in both instances and amounts to 1300 or 4900 km depending on whether the northern or the southern paleolatitude option is chosen. Our preference is for the latter and we present arguments which suggest that Vancouver Island may have been originally derived from a region near to eastern Gondwana or from a block east of Gondwana that might have included Malaysia. The procedures used for the tectonic analysis of aberrant paleopoles are described in the Appendix.

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.

Paleomagnetism of the Upper Cretaceous Nanaimo Group, southwestern Canadian Cordillera

2001 ◽  
Vol 38 (10) ◽  
pp. 1403-1422 ◽  
Author(s):  
Randolph J Enkin ◽  
Judith Baker ◽  
Peter S Mustard
Keyword(s):  
British Columbia ◽  
North America ◽  
Upper Cretaceous ◽  
Vertical Axis ◽  
Vancouver Island ◽  
Canadian Cordillera ◽  
Paleontological Data ◽  
The Mean ◽  
Prime Target

The Baja B.C. model has the Insular Superterrane and related entities of the Canadian Cordillera subject to >3000 km of northward displacement with respect to cratonic North America from ~90 to ~50 Ma. The Upper Cretaceous Nanaimo Group (on and about Vancouver Island, British Columbia) is a prime target to test the model paleomagnetically because of its locality and age. We have widely sampled the basin (67 sites from seven islands spread over 150 km, Santonian to Maastrichtian age). Most samples have low unblocking temperatures (<450°C) and coercivities (~10 mT) and strong present-field contamination, forcing us to reject three quarters of the collection. Beds are insufficiently tilted to provide a conclusive fold test, and we see evidence of relative vertical axis rotations. However, inclination-only analysis indicates pretilting remanence is preserved for many samples. Both polarities are observed, and reversals correlate well to paleontological data, proving that primary remanence is observed. The mean inclination, 55 ± 3°, is 13 ± 4° steeper than previously published results. Our new paleolatitude, 35.7 ± 2.6° is identical to that determined from the slightly older Silverquick and Powell Creek formations at Mount Tatlow, yet the inferred displacement is smaller (2300 ± 400 km versus 3000 ± 500 km) because North America was drifting southward starting around 90 Ma. The interpreted paleolatitude conflicts with sedimentologic and paleontologic evidence that the Nanaimo Basin was deposited near its present northern position.

Paleomagnetism of igneous rocks from the Belcher Islands, Northwest Territories, Canada

1980 ◽  
Vol 17 (7) ◽  
pp. 807-822 ◽  
Author(s):  
P. W. Schmidt
Keyword(s):  
North America ◽  
Northwest Territories ◽  
Igneous Rock ◽  
Pole Position ◽  
Igneous Rocks ◽  
Hudson Bay ◽  
Plate Model ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Pole

Paleomagnetic results from igneous rock units on the Belcher Islands, Hudson Bay, are described. Fold tests for all units studied, as well as a contact test for the intrusive bodies, indicate that both primary (initial), and secondary (post-folding) magnetizations are present.The paleomagnetic pole position from primary directions of the oldest unit studied, the Eskimo volcanics, is situated at 40°S, 002°E (A95 = 12°) and is similar to that derived from equivalent volcanics on the mainland. The younger volcanic unit studied, the Flaherty volcanics, yielded a pole position from primary directions at 0°, 244°E (A95 = 7°). The Haig intrusions, associated with these younger volcanics, yields an almost identical pole position at 1°N, 247°E (A95 = 6°), being derived from directions which are shown to be not only pre–folding but also date from initial cooling. The Eskimo volcanics, which have been more deeply buried than the Flaherty (upper) volcanics, carry substantial components of secondary (post-folding) magnetization which yield a pole position at 19°N, 243°E (A95 = 15°), about 20° north of the pole positions derived from the youngest units.It is argued that the apparent polar wander path (APWP) constructed for the Belcher Islands is representative of the mainland Ungava Craton. Comparison with the equivalent APWP from elsewhere in North America shows that the two APWP's are at variance. Although a two-plate model could be advanced, perhaps a more conservative interpretation is to extend the existing North American APWP eastward to include the Belcher–Ungava APWP, that is, to favour a one-plate model.

Paleomagntism of Archean rocks from northwestern Ontario: II. Shelley Lake granite, Quetico Subprovince

1984 ◽  
Vol 21 (8) ◽  
pp. 869-878 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Dipole Field ◽  
Polar Wander ◽  
Orthogonal Vector ◽  
Site Type ◽  
Apparent Polar Wander Path ◽  
Northwestern Ontario ◽  
Heating Event ◽  
The Mean

The 2580 ± 20 Ma Shelley Lake granite of the Quetico gneiss belt in northwestern Ontario preserves two distinct natural remanent magnetizations (NRM's) of different ages. Type 1 NRM of either normal (1N) or reverse (1R) polarity was isolated in 43 samples, using three methods: stable end-point directions, orthogonal vector plots, and converging remagnetization circles. The mean direction based on both 1N and 1R results is D = 5.9 °I = +56.4 °(k = 95.4, α95 = 4.4°, N = 12 sites), which is significantly different from both the present Earth's field (PEF) and axial dipole field directions at the site. Type 2 NRM, either normal (2N) or reverse (2R), was successfully separated from 1N/1R in 13 samples. Its mean direction, combining both polarities, is D = 70.3 °I = −27.8 °(k = 20.1, α95 = 9.4°, N = 13 samples).The paleopole SL1 corresponding to 1N/1R falls at 65.8°E, 77.6°N, near track 6 of the Laurentian apparent polar wander path (APWP) around 2600 Ma. This remanence is carried principally by primary multidomain magnetite with blocking temperatures up to 580 °C. If it is a primary thermoremanence, as is argued here, SL1 provides a well dated tie point for the APWP at 2580 ± 20 Ma.Paleopole SL2 corresponding to 2N/2R falls at 157.1°W, 1.3°S, around 1250 Ma on the APWP. The remanence is probably a chemical or thermochemical overprint acquired during a mild heating event (T < 300 °C, t > 1100 Ma) that reset 40Ar/39Ar feldspar ages. An earlier tentative assignment of SL2 to track 6 around 2800 Ma is incorrect.

Reconnaissance paleomagnetic study of igneous rocks from the eastern sector of the Labrador Trough

1985 ◽  
Vol 22 (11) ◽  
pp. 1561-1570
Author(s):  
Maurice K.-Seguin ◽  
Thomas Clark
Keyword(s):  
North America ◽  
Igneous Rocks ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
Eastern Sector ◽  
Paleomagnetic Study ◽  
Component C ◽  
The Mean ◽  
Three Components

A paleomagnetic study has been carried out on 75 samples of metagabbro and metaperidotite from 14 sites in the Labrador Trough. The sites were distributed over a distance of 500 km and are situated in sills intruded into formation near the top of the trough stratigraphic column. Four components (A, B, C, and D) were obtained after alternating field (AF) and thermal demagnetization. The mean directions of magnetization are A. 143°, +33°. α95 = 14.4°. k = 15.4, 8 sites: B, 69°, +51°, α95 = 10.3d, k = 22.9, 10 sites: C. 278°. +15°, α95 = 7.7°, k = 28, 14 sites; and D, 200°, +16°. α95 = 13.3°, k = 16.2, 9 sites. All components are secondary. The fold test is negative, and consequently no primary magnetization has been preserved in the isolated components. Component C may have erased all others in zones of highest metamorphism. The paleopoles obtained for components D, A, and C are, respectively, 270°E. 23°S (δP = 10°. δm = 18°); 327°E, 9°S (δp = 11°. δm = 20°); and I9°E, 11°S (antipole) (δp = 10°. δm = 17°). The paleopole positions obtained for these three components are compared with me existing late Aphebian and early Paleohelikian apparent polar wander (APW) path for North America and fall in the 1750–1850 Ma interval.

Giant Upper Triassic bivalves of Wrangellia, Vancouver Island, Canada

2013 ◽  
Vol 50 (2) ◽  
pp. 142-147
Author(s):  
George D. Stanley ◽  
Thomas E. Yancey ◽  
Hannah M.E. Shepherd
Keyword(s):  
North America ◽  
Vancouver Island ◽  
Upper Triassic ◽  
Warm Water ◽  
Late Triassic ◽  
Fine Grained ◽  
Large Size ◽  
Wallowa Terrane ◽  
Volcanic Islands ◽  
First Time

One of the most distinctive components of the Late Triassic warm-water biota are alatoform, reclining bivalves of the genus Wallowaconcha. Wallowaconcha raylenea was first described from shallow-water, fine-grained Upper Triassic carbonate rocks of the Wallowa terrane, northeastern Oregon, and later found in coeval limestone in the Yukon. Fossils of the family Wallowaconchidae are easily recognized and readily distinguished from other fossil groups by their large size (over a metre in length), alatoform morphology, and especially the chambered wing-like extensions likely associated with photosymbiosis. Several different taxa of Norian age inhabited lagoon and reef-related settings on four separate terranes of western North America (Antimonio terrane, Sonora, Mexico; Wallowa terrane, northeastern Oregon; Stikine terrane in the Yukon; Chulitna terrane of Alaska), which during Triassic time existed as volcanic islands in the eastern Panthalassa Ocean. Outside eastern Panthalassa in the eastern Tethys, two other species of Wallowaconcha come from distant localities in Asia and Arabia. We here report for the first time, in presumed Rhaetian limestone of the upper part of the Parson Bay Formation, Vancouver Island, newly discovered examples of Wallowaconcha. They are from Wrangellia and, based on size and shape of the chambers, are assignable to W. raylenea but unlike other examples they appear to be Rhaetian in age. This species of giant bivalve inhabited warm-water locales outboard of North America during the Late Triassic, and its presence provides possible paleobiogeographic links of Wrangellia with both Stikinia and the Wallowa terrane.

Paleomagnetism of Archean rocks from northwestern Ontario: IV. Burchell Lake granite, Wawa–Shebandowan Subprovince

1984 ◽  
Vol 21 (10) ◽  
pp. 1098-1104 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Natural Remanent Magnetization ◽  
Reverse Polarity ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Northwestern Ontario ◽  
Normal Polarity ◽  
The Mean ◽  
Low K

The late Archean Burchell Lake granite of the Shebandowan greenstone belt in northwestern Ontario has a characteristic natural remanent magnetization (NRM) resembling the type 1 NRM of the nearby Shelley Lake granite of the Quetico gneiss belt. Of 36 stably magnetized samples, 21 had predominantly normal polarity (1N) NRM and 15 had reverse polarity (1R). The mean direction based on stable end-point and vector subtracted directions is D = 2.3 °I = 48.9 °(k = 23.9, α95 = 10.0°, N = 10 sites). Intersecting remagnetization circles gave a similar direction. The corresponding paleopole BL1 lies at 83.2°E, 71.1°N, near track 6 of the Laurentian apparent polar wander path around 2600 Ma. Although the Burchell Lake pluton is not dated radiometrically, neighbouring granites give K/Ar biotite ages of 2550–2600 Ma, and it is reasonable to suppose that the NRM dates from the time of intrusion or shortly thereafter. A type 2 NRM like that of the Shelley Lake granite was isolated in 12 samples. Its mean direction is D = 80.9 °I = −11.1°, but the precision is unacceptably low (k = 7.7).

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