Paleomagnetism of the Keweenawan Chipman Lake and Seabrook Lake carbonatite complexes, Ontario

1992 ◽  
Vol 29 (6) ◽  
pp. 1215-1223 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Pole Position ◽  
Alteration Zone ◽  
Contact Aureole ◽  
Isothermal Remanent Magnetization ◽  
Abitibi Subprovince ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Host Rocks

The Chipman Lake complex crops out as a series of carbonatite and related alkalic mafic dikes in the Wabigoon Subprovince of the Superior Province, whereas the Seabrook Lake complex crops out as an alkalic syenite – carbonatite stock in the Abitibi Subprovince. Paleomagnetic analysis was done on specimens from 23 and 19 sites located in and around the Chipman Lake and Seabrook Lake complexes, respectively, using detailed alternating-field and thermal step demagnetization and isothermal remanent magnetization tests. Contact tests with adjacent Archean host rocks show that both complexes retain a primary characteristic remanence (ChRM). The Chipman Lake's ChRM is retained in 11 dikes with normal polarity and one dike with reversed polarity and at one site with normal polarity and one site with reversed polarity from the fenite alteration zone. Its ChRM gives a pole position at 186°E, 38°N (dp = 7°, dm = 11°), which corresponds to a Keweenawan age of 1098 ± 10 Ma, suggesting that younger K–Ar amphibole ages do not date emplacement. The ChRM of the host rock, the Chipman Lake diorite stock, gives a pole at 49°E, 51°N (dp = 8°, dm = 13°), showing that it is not part of the Keweenawan complex but may be a 2.45 Ga Matachewan intrusive. The Seabrook Lake complex's ChRM is found at six normal polarity sites from within the complex and at four normal and three reversed polarity sites from within the fenitized Archean granite and Matachewan diabase of the contact aureole. It gives a pole position at 180°E, 46°N (dp = 11°, dm = 17°), which corresponds to a Keweenawan age of 1103 ± 10 Ma, agreeing with K/Ar biotite ages. The paleomagnetic data indicate that no significant motion on the Kapuskasing Structural Zone occurred after emplacement of the complexes excluding minor vertical uplift of less than about 4 km, and that there were multiple polarity transitions of a symmetric Earth's magnetic field during Keweenawan time.

New 42 Ma cratonic North American paleomagnetic pole from the Yukon underscores another Cordilleran paleomagnetism-geology conundrum

2003 ◽  
Vol 40 (10) ◽  
pp. 1321-1334 ◽  
Author(s):  
David TA Symons ◽  
Philippe Erdmer ◽  
Phil JA McCausland
Keyword(s):  
North American ◽  
Magnetic Polarity ◽  
Eastern Coast ◽  
The North ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
North American Craton ◽  
Host Rocks ◽  
Pacific Plate Subduction ◽  
Plate Subduction

Eocene posttectonic plutons of the Beaver River alkalic complex in southeastern Yukon intruded Devonian–Mississippian and Triassic sandstones in the Foothills of the Canadian Cordillera. A paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods. The A component characteristic remanent magnetization (ChRM) resides in magnetite with normal polarity in the 42.6 ± 0.8 Ma Beaver River pluton, reversed polarity in the 42.1 ± 0.7 Ma Larson Creek East pluton, and both polarities in the 41.3 ± 0.4 Ma Larson Creek West pluton, corresponding with magnetic polarity chrons 20n, 19r, and the boundary between chron 19r and 18n, respectively. The ChRMs of the plutons are indistinguishable (2σ) with a mean for the 42.0 ± 0.5 Ma complex of D = 158.8°, I = –73.1° (N = 21 sites, α95 = 3.0°, k = 116.8). A positive paleomagnetic contact test shows the A component to be primary, and the poorly isolated B component suggests the host rocks for Larson Creek West are Early to Middle Devonian. The paleopole for the Beaver River complex at 79.2°N, 145.8°E (N = 21, dp = 4.8°, dm = 5.4°; Q = 7) is concordant with interpolated 42 Ma reference poles for the North American craton. In contrast, paleopoles from the accreted Intermontane and eastern Coast Belt terranes record clockwise rotations of 24° ± 10° (Eocene) and 13° ± 5° (Oligocene–Pliocene), indicating that the allochthonous Intermontane terranes have been progressively driven ~240 ± 120 km eastwards up and over pericratonic and cratonic North American lower crust by Pacific plate subduction since the mid-Eocene.

Age of the Firesand River carbonatite complex from paleomagnetism

1989 ◽  
Vol 26 (11) ◽  
pp. 2401-2405 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Blocking Temperature ◽  
Isothermal Remanent Magnetization ◽  
Carbonatite Complex ◽  
Polar Wander ◽  
Partial Contact ◽  
Apparent Polar Wander Path ◽  
Temperature Spectra ◽  
Middle Proterozoic

The 2.3 km diameter Firesand River complex intrudes Archean volcanics and granites of the Wawa Subprovince in the Superior Province about 8 km east of Wawa, Ontario. It has given differing Middle Proterozoic K–Ar biotite ages of 1018 ± 50 and 1097 Ma. Alternating-field and thermal step demagnetization of specimens from three calcific carbonatite sites, five ferruginous dolomitic carbonatite sites, and one lamprophyre dike site isolated a stable mean direction of 290°, 33 °(α95 = 12°). Isothermal remanent magnetization tests indicate the remanence is held by single-to pseudosingle-domain magnetite and hematite in the carbonatite. The dike remanence is Keweenawan in age, thereby confirming its genetic relationship to the complex, and it gives a positive partial contact test with its host rock, indicating no postintrusive remagnetization. The blocking-temperature spectra indicate that postintrusive uplift has not exceeded about 4 km. The pole position for the complex is 183°E, 27°N (dp = 8°, dm = 13°). This pole lies directly on the well-dated Keweenawan apparent polar wander path, giving an age of 1090 ± 10 Ma, in agreement with the older K–Ar age. It also confirms geologic and aeromagnetic evidence that the complex has not been tectonically tilted since emplacement.

Paleomagnetism of the Maringouin and Shepody formations, New Brunswick: a Namurian magnetic stratigraphy

1990 ◽  
Vol 27 (6) ◽  
pp. 803-810 ◽  
Author(s):  
V. J. DiVenere ◽  
N. D. Opdyke
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
New Brunswick ◽  
Late Paleozoic ◽  
Stratigraphic Sequence ◽  
The North ◽  
Magnetic Stratigraphy ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
The Magnetic Field

Two hundred thirty-five oriented cores were taken in a stratigraphic sequence of 575 m of red sediments from the Namurian Maringouin and Shepody formations. These samples were taken from the south-dipping limb of the Maringouin Anticline on the Maringouin Peninsula in eastern New Brunswick. An additional 59 samples of the Maringouin and Shepody formations were taken from the north-dipping limb for separate fold tests. Progressive thermal demagnetization to temperatures as high as 700 °C permitted the resolution of an intermediate-temperature, syn-folding B component and a high-temperature, pre-folding C component. The C-component mean for the Maringouin Formation yields a north paleopole at 32.4°N, 121.3°E. The Shepody Formation mean yields a paleopole at 35.7°N, 124.3°E. The circles of confidence (α95) for the Maringouin and Shepody formations are 3.8 °and 4.6°, respectively. Plotting sample polarity versus stratigraphie position yields the first coherent magnetic stratigraphy from the late Paleozoic of North America, with five discrete reversed-polarity and five discrete normal-polarity zones. The magnetic field in Namurian times had approximately 50% normal and 50% reversed polarity.

Paleomagnetic Results from the Jurassic Topley Intrusions near Endako, British Columbia

1973 ◽  
Vol 10 (7) ◽  
pp. 1099-1108 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
British Columbia ◽  
Lower Cretaceous ◽  
Remanent Magnetization ◽  
Upper Jurassic ◽  
Pole Position ◽  
Upper Triassic ◽  
Polar Wander ◽  
Quartz Monzonite ◽  
Reversed Polarity ◽  
North American Craton

The Upper Jurassic Topley Intrusions intrude rocks of the tectonically stable Interior Plateau in central British Columbia. A stable primary remanent magnetization of both normal and reversed polarity was isolated after a.f. demagnetization in 19 of 22 sites (109 cores; 208 specimens) representing several of the plutonic units present in this sialic complex of quartz monzonite affinity near Endako, B.C. The unit mean remanence directions support some petrological correlations suggested by Carr, Bright, and White et al., but do not support others. The pole position derived from 13 sites representing 6 plutonic units with a K–Ar radiomelric age of 139 ± 4 m.y. (White et al.) is 128.6 °E, 70.0 °N(δm = 14.4°; δp = 11.4°). This position indicates a smooth polar wander path during the Jurassic between the well defined Upper Triassic and Lower Cretaceous pole positions. It also indicates that the northern Interior Plateau has not been tectonically rotated or translated since emplacement relative to the stable North American craton.

scholarly journals Magnetic stratigraphy of the Villafranchian type-section:(Villafranca d'Asti, Italy)

1999 ◽  
Vol 42 (1) ◽  
Author(s):  
P. Boano ◽  
D. Bormioli ◽  
F. Carraro ◽  
R. Lanza
Keyword(s):  
Remanent Magnetization ◽  
Bedding Plane ◽  
Magnetic Fabric ◽  
Isothermal Remanent Magnetization ◽  
Type Section ◽  
Inclination Shallowing ◽  
Polarity Transition ◽  
Clayey Silt ◽  
Normal Polarity ◽  
Nw Italy

A detailed magnetostratigraphic investigation has been carried out along the section of the Fornace RDB quarry (Villafranca d'Asti, NW Italy), which is the type-section of the Villafranchian and has provided many of the land mammal remains used by Azzaroli (1977) to define the Val Triversa faunal unit (zone MN16a). Poorly consolidated clay and clayey silt are the prevailing lithologies and samples were collected with plastic boxes. Isothermal remanent magnetization measurements showed that haematite is the main ferromagnetic mineral and occurs through the section, whereas iron sulphide is subordinate and only occurs in the lower part. Alternating field demagnetization usually succeeded in isolating a stable component and was used to derive the characteristic remanence by demagnetizing the specimens at 4 to 7 steps in the range 15 to 80 mT. The magnetic fabric was investigated by measuring the anisotropy of the magnetic susceptibility. It was always well defined and characterized by a horizontal foliation matching the bedding plane. The anisotropy of isothermal remanent magnetization was measured on some specimens and yielded fully comparable results. This consistency shows that detrital haematite carries the primary magnetization in these sediments and explains the 20° inclination shallowing of the site mean palaeomagnetic direction. Only one reverse to normal polarity transition has been detected and a direct correlation with the GPTS reference scale of Cande and Kent (1992, 1995) is thus not possible. The age of the Triversa fauna has been much debated in recent literature. Some authors have recently suggested that it is transitional between Ruscinian and Villafranchian, i.e. a little older than previously assumed. According to this hypothesis, the lower part of the RDB section would correlate to the chron C2Ar (upper Gilbert) and the upper part to the chron C2An.3n (lower Gauss), whereas according to the traditional interpretation correlation is to one of the polarity inversions within the middle Gauss (Kaena and Mammoth). An independent age constraint based on magnetostratigraphy will only be possible when other Ruscinian and Villafranchian sections are investigated in the same detail and a correlation between palaeosecular variation is established.

Synopsis of paleomagnetic studies in the Kapuskasing structural zone

1994 ◽  
Vol 31 (7) ◽  
pp. 1206-1217 ◽  
Author(s):  
D. T. A. Symons ◽  
M. T. Lewchuk ◽  
D. J. Dunlop ◽  
V. Costanzo-Alvarez ◽  
H. C. Halls ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Fault Zone ◽  
Limited Area ◽  
The West ◽  
West Side ◽  
Thrust Faulting ◽  
Abitibi Subprovince ◽  
Normal Polarity ◽  
Slip Displacement ◽  
Radiometric Ages

This paper summarizes results from paleomagnetic studies sponsored by Lithoprobe on the Kapuskasing structural zone (KSZ). Data from Archean rocks outside the KSZ indicate that the Wawa Subprovince has not been significantly rotated or translated (< 5°) relative to the Abitibi Subprovince. Results from the granulites and amphibolites indicate that the KSZ underwent several kilometres of uplift at ca. 2.51 Ga and then 10 ± 5° west-northwest tilt with several kilometres of further uplift between 2.04 and 1.88 Ga from thrust faulting on the Ivanhoe Lake fault zone. Localized chemical remagnetization occurred at 1.1 Ga along the west side of the Shawmere anorthosite. Paleomagnetic data from the 2.45 Ga Matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 Ma. Their polarity pattern indicates major north-trending faults with several kilometres of dip-slip displacement. Their remanence confirms that the Superior Province was deformed around the KSZ into an oroclinal flexure with 40° changes in trend between 2.04 and 1.88 Ga. Results from eight 1.1 Ga alkali syenite–carbonatite complexes show that the KSZ and adjacent subprovinces have undergone only minor uplift (< 6 ± 2 km) since emplacement. Also, these data refine the radiometric ages of some complexes, demonstrate that the use of superchrons to correlate Keweenawan units in the Midcontinental Rift is unsound, and show that Keweenawan magnetic field was symmetrical. Many specific conclusions that relate to a given unit or limited area were drawn in the KSZ paleomagnetic studies.

scholarly journals ARCHAEOMAGNETIC STUDIES IN KILNS FROM N. GREECE

2017 ◽  
Vol 43 (4) ◽  
pp. 1888 ◽  
Author(s):  
E. Aidona ◽  
D. Kondopoulou ◽  
M. Alexandrou ◽  
N. Ioannidis
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Archaeological Sites ◽  
Isothermal Remanent Magnetization ◽  
Thermomagnetic Analysis ◽  
Intensity Measurements ◽  
Magnetic Carriers ◽  
Characteristic Component

Archaeomagnetism combines the magnetic properties of baked materials with Archaeology. The archaeomagnetic method can be applied to any kind of permanent - in situ or displaced- burnt structures, such as kilns, ovens, hearths, burnt floors, tiles, bricks and pottery fragments, the latter for intensity measurements only. In this study we present the latest archaeomagnetic results from archaeological sites which are distributed in N. Greece (Polymylos, Sani, Thesssaloniki). The Natural Remanent Magnetization (NRM) and the magnetic susceptibility of the samples have been initially measured. The samples have been subjected to magnetic cleaning (AF and Thermal demagnetizations) and this procedure revealed the characteristic component of the ancient magnetic field. Rock magnetic experiments such as acquisition of the Isothermal Remanent Magnetization (IRM) and thermomagnetic analysis have been performed in pilot samples in order to identify the main magnetic carriers. Finally the secular variation curves for Greece and the SCHA.DIF.3K model were used in order to date these archaeological structures. This dating improved or modified the estimated archaeological ages.

Paleomagnetism of the Pine Point Zn–Pb deposits

1993 ◽  
Vol 30 (5) ◽  
pp. 1028-1036 ◽  
Author(s):  
D. T. A. Symons ◽  
Hairu Pan ◽  
D. F. Sangster ◽  
E. C. Jowett
Keyword(s):  
Late Cretaceous ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Pole Position ◽  
Mississippi Valley ◽  
Western Canada Sedimentary Basin ◽  
Order Of Magnitude ◽  
Mvt Deposits ◽  
Pine Point ◽  
Host Rocks

The Pine Point Zn–Pb deposits are Mississippi Valley-type (MVT) deposits in Middle Devonian dolostone of the Pine Point Formation. The median natural remanent magnetization intensity from 509 specimens from 40 sites is 3.6 × 10−5 A/m. This intensity is an order of magnitude lower than most MVT deposits and is close to the sensitivity of the cryogenic magnetometer, so only the stronger specimens could be analysed paleomagnetically. Isothermal remanent magnetization testing of ores, host rocks, and monomineralic specimens shows that single domain to pseudosingle domain magnetite in sphalerite is the main remanence carrier; magnetite in galena is the next most significant carrier. In contrast, barren dolostone, limestone, and calcite crystals have a much weaker remanence. Using less stringent criteria than is conventional, 17 acceptable site mean remanence directions were determined. Remagnetization circle data indicate that many of the poorly defined sites retain a reversed but nonisolated characteristic remanence. Of the 17 means, 8 form a coherent cluster, the A component, with a mean direction of D = 339°, I = 78° (α95 = 7°, k = 62), giving a pole position of 79°N, 197°E (α95 = 13°). The A pole indicates with > 95%confidence that the MVT ores at Pine Point are Late Cretaceous to Eocene in age, with a mid-Late Cretaceous to Paleocene age (84–58 Ma) being most likely. The dolostone host rocks were remagnetized at the same time. It is concluded that the A component, carried mainly by sphalerite and galena, was formed during the Laramide orogeny (97–58 Ma) when tectonic uplift forced Zn–Pb-rich basinal brines out of the Western Canada sedimentary basin into the Presqu'ile barrier reef on the adjacent foreland shelf.

Paleomagnetism of the Eocene Kamloops Group and the cratonization of Terrane I of the Canadian Cordillera

1989 ◽  
Vol 26 (4) ◽  
pp. 821-828 ◽  
Author(s):  
D. T. A. Symons ◽  
M. R. Wellings
Keyword(s):  
North American ◽  
Remanent Magnetization ◽  
Middle Eocene ◽  
Pole Position ◽  
Canadian Cordillera ◽  
Isothermal Remanent Magnetization ◽  
Clockwise Rotation ◽  
Saturation Isothermal Remanent Magnetization ◽  
The North ◽  
North American Craton

The lower Middle Eocene (49.4 ± 2.4 Ma) Kamloops Group is exposed in the middle of the Quesnellia subterrane of Terrane I. The group consists of the siliciclastic Tranquille Beds and the overlying Dewdrop Flats plateau basalts and andesites. Detailed alternating field (AF) and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site, and saturation isothermal remanent magnetization (SIRM) tests were performed to examine the remanence carriers. The petrology of the gently dipping flows, the presence of antiparallel normal and reverse remanence, the conglomerate test, and the fold test all indicate that a primary remanence has been isolated. It resides in both magnetite and hematite over a broad range of AF coercivities, blocking temperatures, and domain sizes. Its mean direction of 355.0°, 73.4 °(α95 = 6.9°) gives a pole position of 138.4°W, 81.4°N (dp = 11.0°, dm = 12.3°) that is statistically indistinguishable from the 50 Ma reference pole for the North American craton. This indicates that the cratonization of Terrane I was complete by the Middle Eocene after it had undergone ~1300 km of northward translation and ~45 °of clockwise rotation since the mid-Cretaceous.

Defining a paleomagnetic polarity pattern in the Monteregian intrusives

1979 ◽  
Vol 16 (9) ◽  
pp. 1716-1725 ◽  
Author(s):  
J. Foster ◽  
D. T. A. Symons
Keyword(s):  
Stability Index ◽  
Pole Position ◽  
End Points ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Remanence Direction

Oka and nearby small plutons on the western end of the Monteregian Hills were sampled for paleomagnetic study at 43 sites (569 specimens). Every specimen was AF step demagnetized in 4 kA/m increments to 20 or 24 kA/m. Consistent remanence directions were found for 36 sites (452 specimens). Use of a stability index to select only those specimens with the best defined end points does not improve the site statistics. The Oka, Brilund, Carillon, and Ile Cadieux plutons have statistically similar mean remanence direction populations which are different from the Ste. Dorothée sill direction. Except for one Carillon site, all site mean directions are normally polarized, whereas all nine plutons, except for Mt. Johnson, from the middle and eastern end of the Monteregian Hills are reversely polarized. Normally and reversely polarized plutons give statistically similar but antiparallel pole positions, giving a combined pole position of 169.0°W, 72.4°N (δp = 2.8°, δm = 3.7°), which is consistent with the 120 ± 4 Ma radiometric age. The polarity pattern evidence suggests that Oka and adjacent plutons were emplaced rapidly during one normal polarity interval, and that the Monteregian Hills plutons were emplaced progressively from west to east during two normal and two reversed polarity intervals lasting ~ 2 Ma. This leads to some speculations on the plume and rift modes of emplacement.

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