A paleomagnetic study of the lava flows within the Copper Harbor Conglomerate, Michigan: new results and implications

1994 ◽  
Vol 31 (2) ◽  
pp. 369-380 ◽  
Author(s):  
J. F. Diehl ◽  
T. D. Haig
Keyword(s):  
High Temperature ◽  
Entire Range ◽  
Lava Flows ◽  
Polar Wander ◽  
Lake Shore ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Pole ◽  
Complete Section ◽  
Paleomagnetic Study ◽  
Petrographic Analyses

New paleomagnetic data have been obtained from the interbedded lava flows within the Copper Harbor Conglomerate on Michigan's Keweenaw Peninsula. Previous paleomagnetic studies of these lava flows, known collectively as the Lake Shore Traps, have produced contradictory results. To investigate the cause of these conflicting results, 30 sites encompassing the most complete section of lava flows possible were collected and analyzed.Well-defined characteristic directions of magnetization were isolated using either alternating-field or thermal demagnetization or a combination of both. These directions of magnetization are interpreted as primary magnetizations acquired during the original cooling of the lavas. Hysteresis, thermomagnetic, and petrographic analyses suggest the carrier of magnetization is a pseudo-single-domain, titanium-poor magnetite that has undergone some high-temperature oxidation.Site means determined from the 30 lava flows define three distinct directional clusters. Each cluster of directions corresponds to a different stratigraphic package of lava flows with the Copper Harbor Conglomerate. Between-site dispersion for each stratigraphic package or unit is much less than the expected value for Keweenawan-age rocks. Therefore, we suggest that most of the lava flows in each unit were extruded rapidly and that within an individual stratigraphic unit, paleosecular variation has not been adequately sampled. This explains why previous studies on the Lake Shore Traps have produced such different results; each study did not sample the entire range of directions possible in these lava flows.The paleomagnetic pole calculated from the 30 site-mean virtual geomagnetic poles is located at 22.2°N, 180.8°E (k = 35.0; A95 = 6.5°). The new Copper Harbor pole is now located in the appropriate chronological position with respect to the underlying Portage Lake Volcanics and the overlying Nonesuch Shale on the Keweenawan apparent polar wander path. The similarity of our Copper Harbor pole to that of the Portage Lake Volcanics reinforces the idea that the Copper Harbor Conglomerate is more closely related in time to the Portage Lake Volcanics than to the Nonesuch Shale.

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 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.

Paleomagnetism of Archean rocks from northwestern Ontario: Wabigoon gabbro, Wabigoon Subprovince

1983 ◽  
Vol 20 (12) ◽  
pp. 1805-1817 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Blocking Temperature ◽  
Virtual Geomagnetic Pole ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Northwestern Ontario ◽  
Paleomagnetic Pole ◽  
Geomagnetic Pole ◽  
Chemical Remanent Magnetization

The Wabigoon gabbro of the Archean Wabigoon greenstone belt in northwestern Ontario preserves a univectorial natural remanent magnetization (NRM) with D = 246°, I = 12° (k = 19.5, α95 = 10.5°, N = 11 sites). The precision is reduced if sample means are averaged, however (k = 9.3, α95 = 9.2°, N = 29 samples). The paleomagnetic pole falls either at 160°W, 11°S (δp = 5.3°, δm = 10.6°), corresponding to an age of ~1300 Ma on the Laurentian apparent polar wander path, or the reverse of this, 20°E, 11° N, corresponding to a late Archean age (~2800 Ma). No ~1300 Ma igneous or metamorphic event is known in the area; a major west-northwest-trending dike about 9 km south of the gabbro yields a virtual geomagnetic pole at 122°W, 45°N and seems to be of Abitibi age (~2150 Ma) rather than Mackenzie age (~1250 Ma). A few gabbro samples and some greenstones from the intrusive baked zone have hybrid remanences in which a higher blocking temperature Kenoran-age (~2600 Ma) NRM is superimposed on the gabbro characteristic NRM. However, the Kenoran component may be a younger chemical remanent magnetization (CRM) residing in hematite. The hypothesis that the gabbro characteristic remanence is itself a hybrid of Kenoran and Keweenawan (~1100 Ma) NRM's, which would explain both the high between-sample scatter and the lack of a ~1300 Ma remagnetizing event, is considered but rejected because fewer than 10% of the gabbro samples exhibit multivectorial swings during alternating field or thermal cleaning. Two geomagnetic field reversals are recorded at interior sites, but only one or none is recorded near the margin of the intrusion. The different cooling histories of margin and interior, as well as the bulk of the other evidence, favour magnetization during initial cooling in late Archean time.

Paleomagnetism of the Wintering Lake pluton and the Early Proterozoic tectonic motion of the Superior Boundary Zone, Manitoba

2006 ◽  
Vol 43 (7) ◽  
pp. 1071-1083
Author(s):  
M J Harris ◽  
D TA Symons ◽  
W H Blackburn ◽  
A Turek ◽  
D C Peck
Keyword(s):  
Coarse Grained ◽  
Boundary Zone ◽  
Polar Wander ◽  
Early Proterozoic ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
Paleomagnetic Result ◽  
Tectonic Motion ◽  
Host Rocks ◽  
Superior Craton

This Lithoprobe-funded paleomagnetic study of the Early Proterozoic Wintering Lake granitoid body supports tectonic models that suggest continental accretion of the Trans-Hudson Orogen with the Superior Craton occurred at ~1822 Ma. Thermal demagnetization data for the granitoid specimens suggest that the magnetic remanence carriers are coarse-grained magnetite or titanomagnetite, and saturation isothermal remanence tests suggest that the magnetite is mostly multidomain. Six of seven paleomagnetic contact tests were negative, indicating that the host rocks have been remagnetized and that the granitoid body may have been partially remagnetized near its margins. Acceptable site mean remanence directions for 20 of 21 granitic sites yield a paleopole at 46.8°N, 102.2°W (with semi-axes of the 95% ellipse of confidence about the paleopole of dp = 11° and dm = 11°). The paleopole fits on the extrapolated apparent polar wander path (APWP) for the Superior craton at ~1822 Ma, which is the interpreted emplacement age of the pluton close to the peak of the Trans-Hudson orogeny. This is the first well-constrained paleomagnetic result from the Superior Province that provides direct evidence from concordant paleopoles for the Early Proterozoic accretion of the orogen to the craton. Further, the paleomagnetic results from the pluton's host rocks, along with other recent results from the Superior Boundary Zone, fill in a gap in the APWP for the craton between ~1780 and ~1720 Ma. The Superior path is now shown to form a hairpin as the craton moves from mid to polar paleolatitudes from ~1880 to ~1830 Ma, suffers a stillstand from ~1830 to ~1770 Ma during the peak of the Trans-Hudson orogeny, returns to mid-paleolatitudes from ~1770 to ~1740 Ma, and then moves on to subequatorial paleolatitudes by ~1720 Ma.

Preliminary Proterozoic apparent polar wander paths for the South China Block and their tectonic implications

1998 ◽  
Vol 35 (3) ◽  
pp. 302-320 ◽  
Author(s):  
Huimin Zhang
Keyword(s):  
South China ◽  
North China ◽  
Eastern China ◽  
North China Block ◽  
Polar Wander ◽  
Late Proterozoic ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
Middle Proterozoic

Results of a regional paleomagnetic study of Precambrian rocks in central-east China are summarized and interpreted. The study is a partial outcome of a geoscience transect incorporating three terranes, namely the Yangzi, Jiangnan, and Huaxia blocks. Paleomagnetic poles derived from a range of metamorphic, igneous, and sedimentary rocks define a northeast to southwest swath crossing the present Pacific Ocean and interpreted to embrace Early to Late Proterozoic times. All three terranes define segments of the same swath and correlate with a similar apparent polar wander path previously defined from the North China Block. The results imply that the constituent blocks of eastern China formed a united block during Early to Middle Proterozoic times. Later relatively large fragmentation is confirmed by Late Proterozoic apparent polar wander path records of the North China and South China Blocks.

A regional paleomagnetic study of Archean rocks from the Superior Geotraverse area, northwestern Ontario

1979 ◽  
Vol 16 (10) ◽  
pp. 1906-1919 ◽  
Author(s):  
David J. Dunlop
Keyword(s):  
Reliable Determination ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Northwestern Ontario ◽  
Paleomagnetic Study ◽  
Igneous Activity ◽  
Greenstone Belts ◽  
Mafic Intrusives ◽  
Iron Formations ◽  
East West

Preliminary paleomagnetic data are reported for Archean metavolcanics, felsic and mafic intrusives, gneisses, and iron formations from the Quetico, Shebandowan, and Wabigoon belts in the western Superior Structural Province. Eleven of the 23 formations sampled have been studied in detail using stepwise alternating-field demagnetization and, in some cases, thermal demagnetization. Two characteristic components of magnetization are revealed. One is widespread in occurrence and reasonably well grouped (D = 4.5°, I = + 55.7°, k = 17.9, α95 = 5.4°, N = 40 samples for the Shelley Lake granite for example). It is a regional magnetic overprint due to the Kenoran orogeny, acquired, according to the position of its paleopole (71.7°E, 77.3°N, δp = 5.5°, δm = 8 °for the Shelley Lake granite) on the Laurentian apparent polar wander path and to independent radiometric evidence, about −2600 Ma. The second magnetic component is spotty in occurrence, more prevalent in the Wabigoon belt than elsewhere, and everywhere rather scattered. The only fully reliable determination is D = 66.0°, I = −5.1 °(k = 10.2, α95 = 15°, N = 11 samples) for the Wabigoon gabbro. The corresponding paleopole is either 17.8°E, 13.1°N (δp = 7.5°, δm = 15°) falling at about −2800 Ma on the apparent polar wander path or the antipole of this direction, dating between −1350 and −1250 Ma. The younger date, implying a late ProterQzoic metamorphic event in the region, is more likely than the older age, which would require that the magnetization be primary or a pre-Kenoran overprint. The metamorphism seems to have occurred too early to have been caused by igneous activity ca. 1100 Ma in the nearby Keweenawan basin. About −2600 Ma, the region was in its present orientation, but at a latitude of 20 to 35°N and probably drifting northward. About −1250 Ma, the region was equatorial but rotated 90°, so that presently east–west trending greenstone belts were north–south. It is possible, but un-proven, that a paleoocean existed between the Wabigoon subprovince and the other belts about −1250 Ma, the Wabigoon region having since moved > 500 km westward (present-day direction) to its present location.

scholarly journals Rotation of the Philippine Sea plate inferred from paleomagnetism of oriented cores taken with an ROV-based coring apparatus

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Toshitsugu Yamazaki ◽  
Shun Chiyonobu ◽  
Osamu Ishizuka ◽  
Fumisato Tajima ◽  
Naoki Uto ◽  
...  
Keyword(s):  
Plate Motion ◽  
Philippine Sea Plate ◽  
Late Oligocene ◽  
Clockwise Rotation ◽  
Polar Wander ◽  
Philippine Sea ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Study ◽  
History Of ◽  
The Mean

AbstractReconstructing the history of Philippine Sea (PHS) plate motion is important for better understanding of the tectonics of the surrounding plates. It is generally considered that the PHS plate migrated northward since Eocene, but its rotation has not been constrained well; some reconstructions incorporated a large clockwise rotation but others did not. This is mainly because the difficulty of collecting oriented rocks from the mostly submerged PHS plate hindered establishing an apparent polar wander path. In this study, we conducted a paleomagnetic study of oriented cores taken using an ROV-based coring apparatus from the Hyuga Seamount on the northern part of the Kyushu-Palau Ridge, a remnant arc in the stable interior of the PHS plate. Stepwise thermal and alternating-field demagnetizations were applied to specimens taken successively from two ~ 30 cm long limestone cores of middle to late Oligocene age, and characteristic remanent magnetization directions could be isolated. Declination and inclination of D = 51.5° and I = 39.8°, respectively, were obtained as the mean of the two cores. The easterly-deflected declination means ~ 50° clockwise rotation of the PHS plate since middle to late Oligocene. In addition, ~ 5° latitudinal change of the site is estimated from the mean inclination. The result implies that the Kyushu-Palau Ridge was located to the southwest of the present position in middle to late Oligocene, and that PHS plate rotation as well as the Shikoku and Parece Vela Basin spreading contributed to the eastward migration of the Izu-Ogasawara (Bonin) Arc to the current position.

Wobbles in the Early Cambrian Earth's spin axis? New high-quality paleomagnetic data from NE Brazil

2020 ◽  
Author(s):  
Paul Yves Jean Antonio ◽  
Ricardo Ivan ferreira da Trindade ◽  
Maria Helena B. M. Hollanda ◽  
Bruno Giacomini
Keyword(s):  
Spin Axis ◽  
Magnetic Data ◽  
Equatorial Position ◽  
Polar Wander ◽  
Fine Grained ◽  
True Polar Wander ◽  
Apparent Polar Wander Path ◽  
Paleomagnetic Pole ◽  
Normal Polarity ◽  
Key Pole

<p>The Neoproterozoic-Paleozoic transition (~541 Ma) was a turning point in Earth’s history resulting in great biological changes between the microbial Precambrian life and the Ediacaran biotic revolution with the occupation of the sedimentary substrate, the dawn of biomineralization and the appearance of the earliest multicellular organisms. In parallel, this period is marked by a large plate reorganization leading to the assembly of Gondwana and by major climatic changes (extreme glacial events). Due in part to a poor paleomagnetic database for the different cratons in the Ediacarian-Cambrian times, the global paleogeography at that time still remains controversial. In this study we present a new paleomagnetic pole (Q= 6) for the Monteiro dike swarms in the Borborema Province (NE Brazil). They are fine-grained hornblende dolerite dated by U-Pb on zircon at ~538 Ma. Rock magnetic data indicate that magnetite and pyrrhotite are the main remanence carriers. Positive baked-contact tests support the primary remanence obtained for these dikes (19 sites). A positive reversal test (classified C) was also obtained from the 14 sites with normal polarity and the 5 sites with reversed polarity, indicating that the secular variations was eliminated with our sampling. Our new key pole is not consistent with the classical Apparent Polar Wander Path of the West Gondwana which consists of a long track from a southern polar position at ~590 Ma to an equatorial position at ~520 Ma. The Monteiro paleomagnetic pole suggest instead rapid and small oscillations of the APW, or wobbles, after 560 Ma. These rapid oscillations may be related to inertial readjustments in response to true polar wander (TPW) of the spin axis. TPW events have been suggested from 615 to 590 and then from 575 to 565 Ma in previous works. These TPWs are supposedly caused by changes in the inertia tensor of the Earth due to internal mass redistribution, related to rapid changes in subduction velocity. Possible links between these events and life evolution will also be discussed.</p>

Paleomagnetism of ∼1.09 Ga Lake Shore Traps (Keweenaw Peninsula, Michigan): new results and implications

2013 ◽  
Vol 50 (11) ◽  
pp. 1085-1096 ◽  
Author(s):  
Evgeniy V. Kulakov ◽  
Aleksey V. Smirnov ◽  
Jimmy F. Diehl
Keyword(s):  
Geomagnetic Field ◽  
Serial Correlation ◽  
Lava Flows ◽  
Midcontinent Rift ◽  
Tilt Correction ◽  
Lake Shore ◽  
Paleomagnetic Pole ◽  
Statistical Similarity ◽  
Silver Island ◽  
Keweenaw Peninsula

We report paleomagnetic data from a new section of the ∼1.09 Ga Lake Shore Traps exposed on Silver Island (10 flows) and on the adjacent mainland (two flows) along the northwestern coastline of the Keweenaw Peninsula in Michigan. We also present new data from nine additional lava flows, sampled from the tip of the peninsula previously studied by Diehl and Haig in 1994. Samples from all these lava flows yield well-defined characteristic magnetization directions upon thermal demagnetization. After structural tilt correction, the directions from Silver Island (site-mean declination, D = 276.9°; site-mean inclination, I = 44.4°; 95% radius of confidence for site mean, α95 = 2.6°; number of samples, N = 10) and mainland (D = 298.7°, I = 36.0°, α95 = 10.1°, N = 2) flows are close to the directions from equivalent lava flows from the upper (D = 277.8°, I = 41.0°, α95 = 2.3°, N = 17) and lower (D = 300.0°, I = 34.9°, α95 = 2.3°, N = 10) sections of the middle Lake Shore Traps exposed at the eastern tip of the Peninsula, respectively. Testing the paleomagnetic directions for serial correlation shows that some of the sequential lava flows on Silver Island and from the middle Lake Shore Traps at the tip of the Peninsula record the same vector of the geomagnetic field. Combining these correlated directions yielded new mean directions for Silver Island (D = 277.2°, I = 44.1°, α95 = 3.1°, N = 8), and the upper (D = 277.0°, I = 40.4°, α95 = 3.7°, N = 10) and lower (D = 298.6°, I = 33.3°, α95 = 4.3°, N = 5) middle Lake Shore Traps at the tip of the Peninsula. The statistical similarity of paleomagnetic directions obtained from these two locations with significantly different structural trends supports the conclusions of prior studies that the curvature of the Midcontinent Rift is primary. The new paleomagnetic pole for the Lake Shore Traps is located at 23.1°N, 186.4°E (95% confidence for the paleomagnetic pole, Α95 = 4.0°; N = 31) and merits a nearly perfect six-point classification on the paleomagnetic reliability scale.

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