Paleomagnetism of drill cores from Labrador offshore wells

1982 ◽  
Vol 19 (11) ◽  
pp. 2210-2214
Author(s):  
Raymund R. Pätzold ◽  
Ernst R. Deutsch
Keyword(s):  
Thermal Treatment ◽  
Early Cretaceous ◽  
Pole Position ◽  
Magnetic Intensity ◽  
Thermal Demagnetization ◽  
Initial Susceptibility ◽  
Normal Polarity ◽  
Short Core ◽  
Basaltic Material ◽  
Drill Cores

Values of the remanent magnetic intensity and inclination, initial susceptibility, and Koenigsberger ratios were obtained from basaltic material in four short core sections from three wells (Bjarni H81, two sections; Leif M48; Herjolf M92) drilled off Labrador. Published K–Ar dates are latest Jurassic to Early Cretaceous. Alternating-field (AF) demagnetization to 600 Oe (60 mT) and thermal demagnetization to 400 °C yielded stable, comparable remanent inclinations mostly of normal polarity for the Bjarni and Leif samples and revealed a change from reversed to normal polarity in the Bjarni well. Virtual pole position loci calculated from the paleoinclinations after AF and thermal treatment agree with published Early Cretaceous pole positions in the case of one Bjarni core, but the fit is poorer in the case of the second Bjarni core and the Leif core. These are the first paleomagnetic results from offshore Labrador.

Paleomagnetism of the Mesozoic Coast Parallel Dolerite Dikes of West Greenland

1975 ◽  
Vol 12 (7) ◽  
pp. 1244-1248 ◽  
Author(s):  
W. F. Fahrig ◽  
G. Freda
Keyword(s):  
North America ◽  
Pole Position ◽  
West Greenland ◽  
Drill Cores

Paleomagnetic measurements on 61 drill cores from eight sites of the Coast Parallel dikes of west Greenland (Fiskenaesset area) have yielded a pole position at 169°E, 54°N, α95 = 5.9°. When these data are combined with those from the Nunarsuit-Tornarssuk area (Ketelaar 1963) the pole is 168°E, 56°N, α95 = 6°. Reversely magnetized dikes are present in both areas.The Coast Parallel dike pole lies close to the Triassic pole position for North America if corrected for Bullard's fit. The dikes were therefore intruded prior to the Mesozoic separation of Greenland and North America.

Paleomagnetism of the 1180 Ma Grenvillian Umfraville gabbro, Ontario

1978 ◽  
Vol 15 (6) ◽  
pp. 956-962 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
Remanent Magnetization ◽  
Pole Position ◽  
Paleomagnetic Data ◽  
Grenville Province ◽  
Thermal Demagnetization ◽  
Before And After ◽  
Primary Origin

The 1180 ± 20 Ma Umfraville gabbro is a slightly metamorphosed stock in the Grenville Province. It was sampled at 17 sites (183 specimens). After alternating field and thermal demagnetization the gabbro retains the same very stable remanent magnetization of primary origin both before and after screening. The screened AF direction from 10 sites (96 specimens) gives a pole position of 166°E, 11°S (δp = 7°, δm = 10°). This position is ≈ 13° southeast of that originally reported for the gabbro by Hood. This pole position either does not fit or necessitates modifications to the four hypotheses that have been invoked to explain Grenville paleomagnetic data.

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

1976 ◽  
Vol 13 (4) ◽  
pp. 555-562 ◽  
Author(s):  
M. E. Evans ◽  
D. K. Bingham
Keyword(s):  
Northwest Territories ◽  
North American ◽  
Pole Position ◽  
The Other ◽  
Thermal Demagnetization ◽  
Fine Grained ◽  
I 11 ◽  
Two Phases ◽  
Geological Work ◽  
Magnetic Vectors

The Tochatwi Formation comprises some 800 m of fine-grained red to buff sandstone in the upper part of the Great Slave Supergroup. Recent geological work indicates an age of 1700 m.y., but this is not yet known with certainty. Results from 29 sampling sites stratigraphically covering the Tochatwi Formation are presented. Standard paleomagnetic techniques indicate that post-folding remagnetization is common, and this is confirmed by analysis of the magnetic vectors removed as partial thermal demagnetization proceeds. Two phases of remagnetization are recognized, one of which can be attributed to nearby Mackenzie-age intrusions. The other phase is equivalent to a remagnetization observed by other workers in Kahochella Group strata at localities 70 km away. As yet, the source of this remagnetization event cannot be identified. Eight sampling sites have escaped total remagnetization and an earlier, pre-folding remanence has been isolated from these (D = 030, I = −11, k = 14, α95 = 15°). The corresponding pole position (144W, 18S) is remote from those deduced from North American rocks of similar age, and possible explanations of this problem are discussed.

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.

V.—On the Magnetism of the Copper-Manganese-Tin Alloys under varying Thermal Treatment

1912 ◽  
Vol 31 ◽  
pp. 85-99 ◽  
Author(s):  
Alexander D. Ross ◽  
Robert C. Gray
Keyword(s):  
Magnetic Properties ◽  
Thermal Treatment ◽  
Coercive Force ◽  
Solid Solutions ◽  
Critical Temperatures ◽  
Tin Alloys ◽  
Initial Susceptibility ◽  
Copper Manganese ◽  
Different Temperatures

Summary1. Alloys were prepared containing 14, 16, 18, 30, 38, and 48 per cent, of tin, and the remainder copper and manganese in the ratio 7 : 3.2. Tests were carried out at different temperatures on the materials as cast, normalised, annealed, and quenched.3. At 15° C in the normalised condition the six alloys gave I respectively equal to 55, 77, 82, 0·4, 96, and 1, for H = 100.4. When cooled to −190° C the three alloys poor in tin were much more magnetic.5. Annealing produced no decided improvement.6. The susceptibility diminishes with increase of temperature, and the critical temperatures range from 225° to 275−190° C.8. Reannealing tends to restore the initial susceptibility of the quenched material, but has little influence on the coercive force.9. The magnetic properties are probably due to the formation of solid solutions of certain definite concentrations.

scholarly journals Paleomagnetic constraints on the age of the Botucatu Formation in Rio Grande do Sul, southern Brazil

2006 ◽  
Vol 78 (3) ◽  
pp. 591-605 ◽  
Author(s):  
Endale Tamrat ◽  
Marcia Ernesto
Keyword(s):  
Early Cretaceous ◽  
Late Jurassic ◽  
Rio Grande ◽  
Southern Brazil ◽  
Rio Grande Do Sul ◽  
Paleomagnetic Pole ◽  
Oriented Samples ◽  
Normal Polarity ◽  
Reversed Polarity ◽  
Botucatu Formation

Paleomagnetic and rockmagnetic data are reported for the aeolian Botucatu Formation, in the southern Brazilian State of Rio Grande do Sul. Oriented samples were taken from a section located between the cities of Jaguari and Santiago. After thermal and alternating field demagnetization, both normal and reversed characteristic remanent magnetizations were found. These results yielded 13 reversed and 5 normal polarity sites, composing a magnetostratigraphic column displaying a sequence of reversed-normal-reversed polarity events. The paleomagnetic pole calculated for 18 sites is located at 114.7ºE, 78.5ºS (dp=8.1º; dm=1.2º), after restoring the strata to the paleohorizontal. This paleomagnetic pole indicates a Late Jurassic-Early Cretaceous age to the Botucatu Formation in the investigated area, and places the sampling sites at paleolatitudes as low as 21ºS.

Paleomagnetism of the Lac St-Jean anorthosite and related rocks, Grenville Province, Quebec

1983 ◽  
Vol 20 (2) ◽  
pp. 246-258 ◽  
Author(s):  
K. L. Buchan ◽  
W. F. Fahrig ◽  
G. N. Freda ◽  
R. A. Frith
Keyword(s):  
North American ◽  
Regional Metamorphism ◽  
The Other ◽  
Central Portion ◽  
Grenville Province ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Normal Polarity

Alternating field and thermal demagnetization study of the Lac St-Jean anorthosite and related rock units in the central portion of the exposed Grenville Province reveals two components of magnetization, one of reversed and the other of normal polarity. Both components are thought to have been acquired during the last regional metamorphism, which was sufficiently intense in this area (mostly amphibolite grade) to reset any earlier magnetization. Corresponding paleopoles at 193°W, 8°S (dm = 7.3°, dp = 4.6°) and 213°W, 19°S (dm = 10.5°, dp = 8.5°) lie along the 950–900 Ma segment of the recently calibrated Grenville track of the North American apparent polar wander path, a track that has thus far been defined largely by results from rock units of the western Grenville.

The Magnetization Process of Certain Red Beds: Vector Analysis of Chemical and Thermal Results

1974 ◽  
Vol 11 (3) ◽  
pp. 437-471 ◽  
Author(s):  
J. L. Roy ◽  
J. K. Park
Keyword(s):  
Thermal Treatment ◽  
Opposite Polarity ◽  
Vector Analysis ◽  
Magnetization Process ◽  
Red Beds ◽  
Thermal Demagnetization ◽  
Field Evidence ◽  
Reversal Time ◽  
Parallel Direction ◽  
Polarity Field

A vector analysis of chemical leaching and thermal demagnetization results of 179 specimens of the Hopewell Group shows that three magnetizations were acquired in a nearly parallel direction but at different times as indicated by polarity. Field evidence indicates that magnetization occurred within 35 m.y. of deposition. It is suggested that these red beds were magnetized in three stages during a magnetization process which began at the time of deposition; hence producing one detrital (DRM) and two chemical (CRMA and CRMB) remanent magnetizations in that order. The two CRMs can be successively removed chemically to uncover the DRM. The CRMB is demagnetized by thermal treatment at 600–674 °C, but, the DRM and the CRMA cannot be separated thermally. This accounts for apparently aberrant directions obtained after thermal demagnetization at 674 °C, because the resultant vector of the remaining (and sometimes oppositely directed) DRM and CRMA is not directed along the direction of the magnetizing field. However, by vector analysis of the combined chemical and thermal results, the directions of the three magnetizations can be determined and an accurate field direction (174°, + 15°; α95: 3°; pole: 36 °N, 123 °E) is thus obtained. More of the information contained in the rocks can also be retrieved from the within-specimen magnetization observed by cutting specimens at some stage during chemical or thermal treatment. For example, the results indicate the following about field reversals: Several of them occurred at the Pennsylvanian–Mississippian boundary; the intensity of the field may remain constant at the beginning of a reversal; reversals may be rapid, and, in some instances, of short duration, leading to the suggestion that, at reversal time, the field may be subjected to an oscillatory motion before stabilizing in the same or opposite polarity.

Paleomagnetism of the Notre Dame Bay lamprophyre dikes, Newfoundland, and the opening of the North Atlantic Ocean

1979 ◽  
Vol 16 (9) ◽  
pp. 1823-1831 ◽  
Author(s):  
P. L. Lapointe
Keyword(s):  
Thermal Treatment ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Tectonic Setting ◽  
The Other ◽  
The North ◽  
Paleomagnetic Study ◽  
Normal Polarity ◽  
The North Atlantic

Lamprophyre dikes and the Leading Tickles dunite from Notre Dame Bay. Nfld., were sampled for a paleomagnetic study to define their age relationships and the tectonic implications of their emplacements. A single normal polarity direction (328°, +62°) was obtained by alternating field and thermal treatment, from 10 Cretaceous lamprophyre dikes. The paleopole (2I2°E, 67°N) derived from these dikes agrees with the cluster of North American Cretaceous paleopoles. On the other hand. I he Leading Tickles dunite recorded two magnetizations: one (206°, +32°) related to the time of intrusion and interpreted to be Ordovician; the second one (000°, +66°). an overprint, is related to the intrusion of the lamprophyre dikes and interpreted to be Cretaceous. The polarity, paleopole, radiometric age, and tectonic setting of the lamprophyre dikes when compared with the Isachsen dikes. N.W.T., suggest the opening of the North Atlantic Ocean was initiated in the Lower Cretaceous.

Paleomagnetism of the Sutton Lake Proterozoic inlier, Ontario, Canada

1982 ◽  
Vol 19 (6) ◽  
pp. 1330-1332
Author(s):  
E. J. Schwarz ◽  
K. R. Clark ◽  
Y. Fujiwara
Keyword(s):  
Pole Position ◽  
North Pole ◽  
The Other ◽  
Stratigraphic Correlation ◽  
Red Beds ◽  
End Points ◽  
Thermal Demagnetization ◽  
Fine Grained ◽  
Dark Layer ◽  
Volcanic Suite

Thirty-eight cores were collected from eight sites in the Sutton Lake Proterozoic inlier, which is thought to be an extension of the Circum-Ungava Belt. Six sites from a 100 m thick diabase sill yielded essentially single-component magnetization averaging D = 35°, I = −54°, k = 39,α95 = 11°. The diabase dips north at 4° and shows only minor alteration (epidote and chlorite). The other two sites were in a fine-grained dark layer within the sill and in a dike. No end points were observed for these sites upon alternating field and thermal demagnetization. The six diabase sites yielded a north pole at 67°E, 3°S, dm = 15, dp = 11. This pole position is similar to that obtained for the youngest volcanic suite (Flaherty Formation) of the Belcher Islands and to that obtained for red beds of the La Grande 4 outlier, suggesting a time-stratigraphic correlation between these units.

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