This Atlas presents an extensive geoscience data set for the Late Triassic to Jurassic plutons that intrude the Intermontane terranes in Yukon. Plutons of this age are associated with significant porphyry Cu ± Au ± Mo deposits in British Columbia. In Yukon, Cu–Au–Ag deposits at Minto and Carmacks Copper are hosted by an Early Jurassic batholith but are not typical porphyry deposits. This project aims to provide the regional framework for Late Triassic to Jurassic plutons and associated mineral occurrences in southern Yukon. We systematically describe over 34 plutons and present new data for most of these, including 47 U-Pb zircon dates, 44 Ar-Ar dates, 187 whole-rock geochemical analyses, 30 whole-rock Sr and Nd isotope analyses, 27 feldspar Pb isotope analyses, zircon Hf isotope analyses for 22 samples and 26 pressure estimates from aluminum-in-hornblende analyses. Complementing these analytical data are extensive photomicrographs, photographs and maps.

End-on arc collision and onset of the northern Cordilleran orogen is recorded in Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon, and in development of the synorogenic Whitehorse trough (WT). A synthesis of the extensive data set for these plutons supports interpretation of the magmatic and tectonic evolution of the northern Intermontane terranes. Late Triassic juvenile plutons that locally intrude the Yukon-Tanana terrane represent the northern extension of arc magmatism within Stikinia. Early Jurassic plutons that intrude Stikinia and Yukon-Tanana terranes were emplaced during crustal thickening (200–195 Ma) and subsequent exhumation (190–178 Ma). The syn-collisional magmatism migrated to the south and shows increasing crustal contributions with time. This style of magmatism in Yukon contrasts with coeval, juvenile arc magmatism in British Columbia (Hazelton Group), that records southward arc migration in the Early Jurassic. Exhumation and subsidence of the WT in the north were probably linked to the retreating Hazelton arc by a sinistral transform. East of WT, Early Jurassic plutons intruded into Yukon-Tanana record continued arc magmatism in Quesnellia. Middle Jurassic plutons were intruded after final enclosure of the Cache Creek terrane and imbrication of the Intermontane terranes. The post-collisional plutons have juvenile isotopic compositions that, together with stratigraphic evidence of surface uplift, are interpreted to record asthenospheric upwelling and lithospheric delamination. A revised tectonic model proposes that entrapment of the Cache Creek terrane was the result of Hazelton slab rollback and development of a sinistral transform fault system linked to the collision zone to the north.

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for a copy of this paper please contact the Yukon Geological Survey; geology@yukon.ca.

Two distinct but undeformed suites of granitic plutons intrude deformed siliciclastic rocks in western Dorsey Terrane. A calc-alkaline hornblende-bearing gabbro to granodiorite stock has been dated at 181.5 Ma (by the Rb/Sr method). The second suite consists of highly evolved late-orogenic granites of the Thirtymile stock and Hake Batholith, which are approximately 100 Ma. The penetrative fabric of the metasedimentary rocks indicates generally eastward-vergent layer-parallel shear. The deformation of the siliciclastic rocks is thus constrained at older than 181 Ma. The absence of resetting of the Rb-Sr isotopic ratios of the Jurassic pluton indicates that the mid-Cretaceous magmatism was emplaced at a shallow crustal depth. Since the Jurassic pluton has both a 'juvenile' Sr isotopic ratio of 0.7045 and chemistry indicative of a largely mantle-derived source, a subduction-related setting for magma generation is likely. The spatial relationship of craton-derived clastic rocks and these plutons requires that subduction had an eastward polarity.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

The early Tertiary magmatic episode in the northern Canadian Cordillera is linked to the restructuring of the Kula-North American plate system from orthogonal to oblique convergence. Resultant volcanism was widespread, and remnant successions outcrop along the eastern margin of the Coast Plutonic Complex (CPC). The Sifton Range volcanic complex of southwestern Yukon is a member of the Paleogene Sloko-Skukum Group, and comprises a 900-m thick, shallow-dipping, volcanic succession dominated by intermediate to evolved lava and pyroclastic rocks deposited in a northwesterly trending half-graben. Locally, the volcanic sequence is intruded by alkali-feldspar granites of the CPCs Nisling Plutonic Suite dated at 57.5 Ma. Felsite sills radiate from the main intrusive body, and together with numerous basaltic to dacitic dykes traverse the volcanic package. Both the felsic volcanic rocks and epizonal granitoids exhibit anomalous enrichments in large-ion lithophile elements indicating crustal contributions during the late-stage petrogenesis of the complex. In addition, the Sifton Range intrusive rocks exhibit modal mineralogy reflective of lower ambient pressures relative to the compositionally similar Annie Ned granites along the Alaska Highway between Stony Creek and Mendenhall, 20 km south of the complex. The amount of post-Eocene uplift (ca. 30 m/Ma) that exposed the contact between the intrusive and corresponding volcanic rocks is constrained by the presence of a calc-silicate bed at an elevation of 1830 m within the upper volcanic stratigraphy.

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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.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.