Abstract: The ~177 Ma Teslin Crossing Pluton was studied paleomagnetically to determine the post-Early Jurassic tectonic motions of the northern Stikine Terrane. There are few published tectonic estimates for rock units older than mid-Cretaceous time for the area. The pluton is dominantly monzonite with syenite patches and a more mafic border phase. To the north and south of the pluton are spatially associated sill complexes that are chemically similar and coeval with the pluton. Acceptable geothermometry values from three sites suggest at the 95% confidence level that the pluton has not been tilted since crystallization. This is supported by the circular outcrop pattern of the pluton and the flat-lying host rocks. The pluton was sampled for paleomagnetic analysis at thirteen sites and six sites were sampled in sills from south of the pluton. Fifteen of the nineteen sites give a well-defined mean characteristic remanent magnetic (ChRM) direction for the pluton and sills at a declination = 6°, inclination = 78°, cone of 95% confidence = 9° and precision parameter = 20, corresponding to a paleopole at 110.6°W and 84.3°N (dp = 16°, dm = 17°). It suggests that the northern Stikine Terrane has undergone 21.1° ± 7.4° of net southward translation, or translation away from the reference pole, with respect to the North American craton since Middle Jurassic time. The estimate also suggests a net clockwise rotation of 33° ± 18°. This translation estimate is similar to that for the coeval Fourth of July Batholith that is part of the neighbouring Cache Creek Terrane and indicates that the Stikine and Cache Creek Terranes were proximal to one another at that time. Further, it suggests that these two terranes were offshore of the North American craton, and were carried eastward by the Farallon Plate through the Jurassic.

Authors: Harris, M.J., Symons, D.T.A., Hart, C.J.R., and Blackburn, W.H.

Keywords: igneous petrology, Structural controls

NTS Mapsheet(s): 105E07

Citation: Harris, M.J., Symons, D.T.A., Hart, C.J.R., and Blackburn, W.H., 1999. Jurassic plate motions of the Stikine Terrane, southern Yukon: A paleomagnetic and geothermometric study of the Teslin Crossing Pluton (105E/7). In: Yukon Exploration and Geology 1998, Roots, C.F. and Emond, D.S (eds.), Exploration and Geological Sciences Division, Yukon Region, Indian and Northern Affairs Canada, p. 155-166.

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