Harris, M J (1), Symons, D (2), Blackburn, W (2); Hart, C (3)
(1) Dept. of Earth Sciences, University of Western Ontario, London, Ont N6A 5B7 Canada; (2) Earth Sciences, University of Windsor, Windsor, Ont N9B 3P4 Canada; (3) Yukon Geology Program, Box 2703, Whitehorse, YT Y1A 2C6 Canada
Abstract:
The $\sim$75 Ma Mount Lorne Stock is located 30 km southeast of Whitehorse in the Stikine Terrane of the northern Canadian Cordillera. The stock was sampled at 20 sites including one mafic dike as a contact test, yielding $\sim$240 specimens for standard paleomagnetic analyses. The characteristic remanent magnetization (ChRM) is carried in magnetite. Site mean ChRM directions were calculated for 18 of the 19 granitoid sites with six sites being normal and directed NNE and steeply down and with the other 12 sites being reversed or antiparallel. The 18 sites give a unit mean ChRM direction of D = $24.2\deg$, I = $75.9\deg$, $\alpha$$_{95}$ = $2.4\deg$ and k = 201. The contact test failed because the dike and stock are similar in age and both have, unfortunately, the same polarity. Geothermobarometric analyses at six sites using the Al-in-hornblende method indicate that the stock has not been tilted, but they do define a north-south trending fault with $\sim$1000m of uplift for the eastern half of the stock. The stock's paleopole is located at $69.1\deg$W, $78.3\deg$N (dp = $4.1\deg$, dm = $4.5\deg$). It indicates 1170 $\pm$ 390 km of northward translation and $57\deg$ $\pm$ $11\deg$ of clockwise rotation for the northern Stikine Terrane from 75 to 50 Ma with respect to the North American craton. These results are in accord with other results from the area, excluding the nearby $\sim$70 Ma Carmacks Group volcanics, and are in accord with other results from southern British Columbia, as well as with plate motion models for the Pacific basin.
