Abstract: Early Jurassic plutons in west-central Yukon were emplaced during accretion of the Intermontane terranes onto the western North American margin, and their exhumation is recorded in the sedimentological and geochronological record. Here the aluminum-in-hornblende geothermobarometer is applied to the 200-197 Ma Tatchun batholith and the 188-180 Ma Aishihik batholith, to estimate crystallization depths and exhumation rates. The Tatchun batholith crystallized at 6.4-7.2 kbar (23-26 km), whereas the Aishihik batholith was emplaced at 3.4-4.2 kbar (12-15 km). The Tatchun batholith exhumed at a rate of ~1.2-2.0 mm/a after crystallization, and was likely exposed at surface by the Middle Jurassic. Although subvolcanic equivalents of the Tatchun batholith have been lost to erosion, it could be prospective for deformed copper deposits such as Minto and Carmacks Copper. Hypabyssal and water-saturated phases of the Aishihik batholith suggest that portions of the batholith could be at, or just below, an appropriate crustal level for magmatic-hydrothermal mineralization.

Authors: M.J. Topham, M.M. Allan, J.K. Mortensen, C.J. R. Hart, M. Colpron and P.J. Sack

Citation: Topham, M.J., Allan, M.M, Mortensen, J.K, Hart, C.J.R., Colpron, M. and Sack, P.J., 2016. Crustal depth of emplacement of the Early Jurassic Aishihik and Tatchun batholiths, west-central Yukon. In: Yukon Exploration and Geology 2015, K.E. MacFarlane and M.G. Nordling (eds.), Yukon Geological Survey, p. 233-251.

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