Harbert, W
(1990)
Paleomagnetic data from Alaska: reliability, interpretation and terrane trajectories.
Tectonophysics, 184 (1).
111 - 135.
ISSN 0040-1951
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Abstract
Virtually the entire body of paleomagnetic data collected from southern Alaska depicts a clear decrease in paleolatitude with increasing age, strongly suggesting that southern Alaska represents a displaced terrane. In this paper, paleomagnetic studies from southern Alaska have been classified with respect to a Quality Index that is based on four criteria. These criteria are the presence of both polarities of magnetic remanence, stepwise thermal or alternating field demagnetization of specimens, principal component analysis of demagnetization data, and a successful fold test. Of the 51 studies compiled, only four from southern Alaska and one from western Canada are demonstrated to satisfy all criteria and fall therefore in the category of Group 3, ("highly reliable"). Two studies from southern Alaska satisfy three of the four criteria, lacking both polarities of characteristic remanence, and are judged to be of Group 2 ("reliable"). Two of these paleomagnetic studies constrain the accretion time of the southern Alaska terrane to the relatively stationary region of central Alaska north of the Denali fault. Four paleomagnetic studies from the southern Alaska terrane show a distinct paleolatitude anomaly when compared with their expected paleolatitudes from the North American apparent polar wander path. Using the model of Engebretson et al. (1984), a series of models are presented to best fit these highly reliable and reliable paleomagnetic studies. The model preferred in this article assumes an accretion time with North America of 50 Ma, and documents pre-50 Ma displacement of the southern Alaska terrane on the Kula plate. If the Ghost Rocks paleomagnetic magnetizations (Plumley et al., 1983) are assumed to be of earliest Tertiary age, this model fits all of the low paleolatitudes observed in southern Alaska. Models incorporating coastwise translation of the southern Alaska terrane along the western boundary of the North America plate and a 50 Ma suturing age of this terrane to North America do not satisfy the paleomagnetic constraints. Four of the reliable studies can be modeled assuming strike-slip motion of the southern Alaska terrane along the western boundary of the North America plate if a 40 Ma suturing age is assumed. In this model, however, the paleomagnetic data must be presumed to represent the highest permissible paleolatitude and the Ghost Rocks Formation paleolatitudes are problematically lower than is possible to model with coastwise translation. © 1990.
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