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Plumley, P.W., 1984

A paleomagnetic study of the Prince William Terrane and Nixon Fork Terrane, Alaska

Bibliographic Reference

Plumley, P.W., 1984, A paleomagnetic study of the Prince William Terrane and Nixon Fork Terrane, Alaska: University of California, Santa Cruz, Ph.D. dissertation, 324 p., illust., maps.

Abstract

The mean paleomagnetic inclination of Paleocene volcanics from two regions on Kodiak Island in the Ghost Rocks Formation suggests that the Prince William terrane originated at mid latitudes, about 25 degrees south of its 'expected' Alaskan latitude in Paleocene time. The remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age. The mean declinations of the two regions, however, differ by approximately 120 degrees, suggesting they have rotated with respect to each other, perhaps during emplacement. We suggest that despite the lack of evidence for a major Tertiary suture zone between the Prince William terrane and central Alaska the Prince William and perhaps adjacent terranes may have lain substantially south of their present position in the early Tertiary. Paleomagnetic data from early Ordovician to early Tertiary rocks of the Nixon Fork terrane, central Alaska, provide evidence toward a better understanding of the tectonic evolution of the continental margin of northwestern America. The Nixon Fork terrane, a Paleozoic continental margin assemblage, is bordered on the south by proven allochthonous terranes and to the north by provinces with oceanic affinities far younger in age. Paleomagnetic analysis of the Ordovician limestone sections (Lower Ordovician Novi Mountain and Middle to Upper Ordovician Telsitna Formation) are interpreted as having three components of magnetization. The stable characteristic component is dominantly reversed in polarity and passes the fold test; the intermediate component does not. If the characteristic magnetization is either primary C-DRM (Ordovician in age) or a late stage secondary CRM (mid Paleozoic in age), then little or no poleward displacement with respect to North America is indicated. The mean declination is discordant (54 degrees +/- 10 degrees) in a clockwise sense with respect to the North American mid Paleozoic reference poles. The intermediate component (attributed to a Permo-Triassic event) yields a pole that is similar in co-latitude to that predicted from reference poles for that age. The mean declination is again discordant in a clockwise sense (18 degrees +/- 11 degrees). Analysis of 7 sites from the early Tertiary Nowitna Volcanics that overlap the Nixon Fork and Innoko terranes yield directions that agree with the North American Paleocene reference pole. We tentatively conclude that the Nixon Fork is not a far-traveled terrane.

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