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TitlePaleomagnetism and the kinematic history of mafic and ultramafic rocks in fold mountain belts
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AuthorIrving, E; Yole, R W
SourceThe ancient oceanic lithosphere; by Irving, E; Publications of the Earth Physics Branch vol. 42, no. 3, 1972 p. 87-95, (Open Access)
PublisherDepartment of Energy, Mines and Resources Canada
Mediapaper; on-line; digital
RelatedThis publication is contained in Irving, E; (1972). The ancient oceanic lithosphere, Publications of the Earth Physics Branch vol. 42 no. 3
File formatpdf
ProvinceBritish Columbia
NTS92B; 92C; 92E; 92F; 92K; 92L
AreaVancouver Island
Lat/Long WENS-129.0000 -123.0000 50.0000 48.0000
Subjectstectonics; oceanic lithosphere; ophiolites; paleomagnetism; plate tectonics; Karmutsen Volcanics; Precambrian; Paleozoic
Released1972 01 01
AbstractMafic and ultramafic rocks commonly occur in orogenic belts, and some can be regarded as remnants of oceanic lithosphere trapped in a subduction zone at the edge of oceanic plate. If this is so, then the opposing plate edges must have moved towards one another. The initial (pre-movement) positions of the plate margins can be calculated if there are paleomagnetic results from both margins pertaining to at least two different periods (different field configurations) prior to the movements. Only a few paleomagnetic results relevant to Canadian ultramafic complexes are available. However, the kinematic framework of most Phanerozoic examples could be studied using existing paleomagnetic techniques, and, as an illustration, results from the Pacific Ocean and the Pacific rim of North America are described. These results do not yet meet the full technical requirements, so accurate reconstructions cannot be made, but nevertheless they indicate that since the Triassic the crust of the Pacific Ocean and the western margin of the Cordillera were displaced northwards by several thousand kilometres relative to the main body of North America, and hence that the ultramafic rocks of the Cordillera could be fragments of intervening oceanic lithosphere driven into the continent from the south. Data are insufficient for comparisons relevant to Canadian ultramafic complexes older than late Paleozoic to be made, but a review of the problems allows two conclusions to be made. The first is that the problem of determining the kinematic framework of the Appalachian ophiolites is experimentally accessible and could be readily obtained; such a study could be a test case of the hypothesis of plate tectonics for the Lower Paleozoic. The second conclusion is that in order to determine the kinematic framework of Precambrian occurrences it will almost certainly be necessary to make general use of late orogenic secondary magnetization.