Paleozoic platformal and basinal strata of Cassiar Terrane are separated from rocks of Yukon-Tanana Terrane to the west by an unexposed fault in southeast Glenlyon map area. Quartzite, marble, phyllite, and amphibolite are grouped in Cassiar Terrane, and no rocks of Slide Mountain Terrane are recognized. The mid-Cretaceous Glenlyon batholith contains pendants of Cassiar Terrane and is intruded by at least five andesite dykes. West of the fault, the Yukon-Tanana Terrane includes: (1) mafic volcaniclastic rocks with preserved primary textures; (2) coarse-grained quartz-feldspar grit; and (3) metasiltstone and semi-pelitic schist. The grit is intruded by foliated hornblende granodiorite, likely of early Mississippian age. Small outcrops of tectonized serpentinite were tectonically emplaced into Yukon-Tanana Terrane, and a positive magnetic anomaly parallel to the fault suggests an unexposed extension to the southwest. Two mylonite localities and evidence of brittle cataclasis up to 1 km on either side of the presumed buried fault suggest a complex structural history along this terrane boundary.

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

Between the Cretaceous granitic rocks (Hake Batholith on the west; Cassiar Batholith to the east) are three belts of metamorphic rocks, collectively part of Yukon-Tanana terrane. These are remnants of oceanic and continental volcanic arcs, and marginal basin sediments of Early to mid-Paleozoic age. At the head of Borden Creek are thick carbonate and andesitic volcanic rocks correlated with Klinkit Group. The Ram Creek fault and Hidden Lake fault are not exposed but deduced to be steeply dipping brittle structures with northeastward thrust or transpressional offset, based upon more complete exposure to the southeast in 105B/3 map area. The former is likely of Cretaceous age; the latter was active between mid-Permian and Early Jurassic time.

The Southwest McQuesten-northern Carmacks area is primarily underlain by rocks of the Yukon-Tanana terrane which is divided into two distinct belts separated by the Willow Creek fault: 1) a central belt of polydeformed, upper greenschist-amphibolite facies metasedimentary and metaplutonic rocks of Permian and older ages; and 2) a northeastern belt of generally undeformed and unmetamorphosed volcano-plutonic rocks of the Early Mississippian Reid Lakes complex. The southern part of the area is underlain mainly by rocks of Quesnellia and Stikinia, including: 1) Paleozoic retrogressed metamorphic rocks of the Boswell assemblage; 2) Upper Triassic augite-phyric volcanic rocks; and 3) Early Jurassic granitoids of the Aishihik plutonic suite. These rocks are dissected by a series of dextral strike-slip faults, probably related to the Teslin fault system. Post-accretion rocks include: 1) mid-Cretaceous biotite monzogranite plutons; 2) dacite and minor basalt of the Upper Cretaceous Carmacks Group; and 3) Quaternary basalt of the Selkirk volcanics. The southwest McQuesten-northern Carmacks area is under-explored, but shares many geological attributes with nearby, highly prospective districts such as the Dawson Range mineral belt, the recently discovered White Gold area and the producing Minto Mine.

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

The Yukon-Tanana Terrane (YTT) is a terrane of pericratonic affinity which occupies an intermediate position between continental margin rocks of Ancestral North America (Cassiar Terrane, Selwyn Basin) to the east and arc and oceanic terranes accreted in Mesozoic time to the west (Quesnellia, Stikinia and Cache Creek). It consists of polydeformed and metamorphosed Paleozoic metasedimentary and meta-igneous rocks which have isotopic and provenance ties to Archean and Proterozoic cratonic source regions, comparable to those of sedimentary strata from northwestern Canada, but whose paleogeographic evolution with respect to the Laurentian craton is enigmatic. The YTT is host to significant base metal occurrences, including the Wolverine and Kudz Ze Kayah deposits in the Finlayson Lake district, in the part of the terrane which lies northeast of Tintina Fault.

Lower Paleozoic miogeoclinal calcareous rocks of the Cassiar Terrane are intruded by the Early Cretaceous Glenlyon Batholith. Garnet-biotite and garnet-muscovite-biotite-aluminum silicatequartz geothermobarometry on the intrusive wall rocks indicate metamorphism to lower amphibolite facies at temperatures of approximately 700°C and pressures of approximately 3 kbar. Progressive deformation, indicated by porphyroblast-matrix relationships, are interpreted to be a result of minor displacements of the country rock associated with and facilitated by intrusion of the Glenlyon Batholith, followed by static heating. Isolated skarn units exist along contacts between the batholith and its wall rocks. A skarn unit is also present along a nearby north-northeast-trending dextral strike-slip fault that predates and is intruded by the batholith.

Preliminary geological map includes mineral occurrences and isotopic age dates.

This field trip crosses southwestern Yukon and examines the geology of the Intermontane and Insular terranes, and synorogenic sedimentary basins that developed during Mesozoic terrane accretion.