Abstract: Reconnaissance geological mapping in the Coal River map area of southeastern Yukon investigated several small mid-Cretaceous plutons. The intrusions are composed of unfoliated or incipiently foliated, fine to coarse-grained, equigranular and porphyritic, biotite ± hornblende quartz monzodiorite to granodiorite. They are metaluminous to peraluminous and have reduced to oxidized geochemical characteristics. The composition of selected samples is consistent with magma formation from partial melting of infracrustal source rocks.U-Pb ages were obtained for nine plutons from five or six zircon single-grain analyses by the isotope dilution thermal ionization mass spectrometry method with chemical abrasion (CA-TIMS). All interpreted ages are concordant within statistical uncertainty. The plutons range in age from 99.80 ± 0.03 to 97.70 ± 0.03 Ma. Given the primarily unfoliated nature of the plutons, contractional, fabric-forming deformation within the Cordilleran orogeny must therefore have largely ceased at the present level of exposure in the Coal River area by the time of intrusion (ca. 98 Ma).The ages and compositions of the plutons in Coal River map area are consistent with their being part of the Tay River plutonic suite, a northwest-trending belt of coeval and compositionally similar plutons and local volcanic rocks (South Fork volcanic suite) that, when augmented by the addition of the Coal River plutons, extends approximately 465 km with a width of up to 150 km.

Authors: Pigage, L.C., Crowley, J.L., Roots, C.F., and Abbott, J.G.

Citation: Pigage, L.C., Crowley, J.L., Roots, C.F., and Abbott, J.G., 2014. Geochemistry and U-Pb zircon geochronology of mid-Cretaceous tay river suite intrusions in southeast Yukon. In: Yukon Exploration and Geology 2013, K.E. MacFarlane, M.G. Nordling, and P.J. Sack (eds.), Yukon Geological Survey, p. 169-194.

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