Aberrant paleomagnetic directions in the Canadian Cordillera

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dc.contributor.authorMarquis, Guyen_US
dc.date.accessioned2024-08-14T22:37:59Z
dc.date.available2024-08-14T22:37:59Z
dc.date.copyright1988en_US
dc.date.issued1988
dc.degree.departmentDepartment of Physics and Astronomy
dc.degree.levelMaster of Arts M.A.en
dc.description.abstractPaleomagnetism has been applied to two general tectonic problems in the Canadian Cordillera: post-Late Cretaceous latitudinal displacement of allochtonous terranes, and Eocene extension in the Omineca Belt. Aberrant paleomagnetic directions were observed in the Late Cretaceous Carmacks group (70.2 +/- 2.4 Ma), which comprises gently-dipping basaltic and andesitic lava flows overlying volcaniclastics deposits in southern Yukon and northwestern British Columbia. Volcanic sections which overlie Stikinia and Cache Creek terranes were sampled in three regions spread over 300 km. This area lies west of the Tintina-Northern Rocky Mountain Trench fault and east of the Denali-Shakwak fault. The Carmacks group provides some of the first paleomagnetic data from pre-Tertiary volcanic units in the northern Canadian Cordillera. AF and thermal demagnetizations revealed stable components for 18 of the 27 sites collected. Both polarities are observed. The site-mean direction (D = 166.7°, I= -71.4°, 0(9s = 4.8°) is pre-folding and so the magnetization is probably primary (i.e. latest Cretaceous). This gives a paleopole at 106.9°E, 82.5°N, Ags = 7.9°, leading to a northward displacement of 13.4° +/- 8.5° (1500+/-950 km). This is consistent with the shallow paleolatitudes observed for somewhat older units in the Coast Plutonic Complex and is well accommodated by displacement estimates along the Northern Rocky Mountain Trench and associated lineaments, and by terrane motion models in the north Pacific Basin. Aberrant paleomagnetic directions are also observed in Eocene intrusive rocks from the southern Omineca Belt, in southern British Columbia. Since these were fixed in their present positions, the aberrancies observed have to be caused by crustal tilting resulting from brittle normal faulting (domino effect). To the west of the Kettle-Grand Forks metamorphic complex, the Granby Pluton is tilted to the east by 38° +/- 9°. Within the complex, the Coryell Batholith is tilted to the east by 40° +/- 11°. To the east, high-grade metamorphic rocks 10 km west of Castlegar are tilted to the west by 39° +/- 50. These results show that paleomagnetism can be used to determine tilt in plutonic rocks, which usually contain no signature of the paleohorizontal.
dc.format.extent97 pages
dc.identifier.urihttps://hdl.handle.net/1828/18854
dc.rightsAvailable to the World Wide Weben_US
dc.titleAberrant paleomagnetic directions in the Canadian Cordilleraen_US
dc.typeThesisen_US

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