Post-Cretaceous Geotectonic Motion of the Yukon-Tanana Terrane fromPaleomagnetism of the Seymour Creek Stock, Yukon Territory.
McCausland, P J (1), Symons, D T (2), Hart, C J (3)
(1) Univ. Western Ontario, Dept. Earth Sciences, London, Ont N6A 5B7 Canada; (2) Univ. of Windsor, Dept. Earth Sciences, Windsor, Ont N9B 3P4 Canada; (3) Yukon Geology Program, Box 2703 [F-3], Whitehorse, YT Y1A 2C6 Canada
Abstract:
The 4 km$\{2}$ Seymour Creek stock is a Late Cretaceous granodioritic intrusion emplaced into the Jurassic Big Creek and Cretaceous Dawson Range batholiths and older metamorphic host rocks of the Yukon-Tanana Terrane (YTT). Preliminary paleomagnetic results from 14 reversed and 2 normal polarity sites yield a mean characteristic remanent magnetization direction of D=$89\deg$, I=-$83\deg$; $\alpha$$_{95}$=$5.5\deg$, k=46. The corresponding paleopole is at $59\deg$N, $165\deg$W (dp=$10.5\deg$, dm=$10.7\deg$), or close to the Cretaceous stillstand of cratonic North America's apparent polar wander path. Dominantly reversed paleomagnetic results from the $\sim$82 Ma Seymour Creek stock are consistent with primary remanence acquisition during the Earth's 84-79 Ma period of reversed polarity, and they provide a contact test for the dominantly normal polarity results from the $\sim$190 Ma Big Creek Batholith. Both the Seymour Creek and Big Creek paleopoles are slightly near-sided with respect to their reference poles, and both indicate a modest ($\sim$$30\deg$) counter-clockwise rotation of the YTT. These preliminary palaeomagnetic results imply that: 1) the YTT did not participate in the Late Cretaceous northward translation of the terranes underlying the Intermontane Belt; and 2) the YTT rotated counterclockwise, unlike the $\sim$$60\deg$ clockwise rotation inferred for the Intermontane terranes.
