Whence Came the Yukon-Tanana Terrane?: Paleomagnetism of the Jurassic Big Creek Batholith, Y.T.
Symons, D T (1), Williams, P R (1), Hart, C J (2)
(1) Earth Science, University of Windsor, Windsor, Ont N9B 3P4 Canada; (2) Yukon Geology Program, Whitehorse, YT Y1A 2C6 Canada
Abstract:
The Yukon-Tanana Terrane (YTT) is a polymetamorphosed pericratonic terrane that underlies much of the Yukon and eastern Alaska inboard of the Coast Mountains. The 190 $\pm$ 5 Ma Big Creek Batholith comprises medium- to very coarse-grained quartz-hornblende syenite to quartz monzonite that intrudes the YTT to the west or outboard of terranes underlying the Intermontane Belt. Using a helicopter 21 sites (245 specimens) were collected from throughout the ~500 km$^{2}$ outcrop area of the batholith and analysed paleomagnetically using alternating field and thermal step demagnetization and isothermal remanence methods. A stable remanence of both normal and reverse polarity was isolated for 19 sites at D = $306\deg$, I = $72\deg$, ($\alpha$$_{95}$ = $4\deg$, k = 82 that gives a pole position at $147\deg$E, $63\deg$N, dp = $6\deg$, dm = $7\deg$. Comparison of this YTT pole to Jurassic poles from terranes underlying the Intermontane Belt suggests that the YTT does not share their Jurassic geotectonic heritage. Jurassic poles from the Quesnel Terrane in the south show northward paleolatitude displacements whereas those from the YTT, Stikine and Cache Creek terranes in the north show southward displacements. However, this YTT result shows a significant counterclockwise rotation whereas the Stikine and Cache Creek poles show significant clockwise rotations.
