A copy of this thesis is available at the EMR library – QE195.M3 1997. This thesis is available online at https://doi.org/10.7939/R3DJ58N76.

Mafic volcanic and clastic strata of the Middle Triassic Joe Mountain Formation, east of Lake Laberge, Yukon, represent a juvenile volcanic arc sequence. Mafic volcanic rocks of the Upper Triassic Lewes River Group were formed in the spatial and temporal continuity of Joe Mountain volcanism. Carbonate sedimentation took place in shallow oceanic subbasins adjacent to the arc from the Carnian to Rhaetian; these subbasins were separated by physiographic boundaries inherent to the arc, resulting in lateral stratigraphic variations. Polymictic conglomerate and turbiditic sequences of the Lower-Middle Jurassic Laberge Group unconformably overlie Triassic rocks. Two north-northwest strike-slip faults, the Laurier Creek and the Goddard, control the distribution of units. Joe Mountain Formation rocks are characterized by an east-west structural trend, whereas the Upper Triassic and Jurassic sequences are characterized by north-northwest trending tight folds and thrust faults. At least five post-accretion igneous suites intrude or overlie older stratigraphy, including the Late Cretaceous Open Creek volcanic complex.

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.

Granodiorite of the Coast Plutonic Complex intruded metasedimentary rocks in the Dezadeash Range of the northern Coast Belt in the late Mesozoic. Graphitic staurolite-biotite schist, associated with the Kluane Metamorphic Assemblage, underlies the western Dezadeash Range, whereas cordierite-biotite gneiss, previously correlated with the Late Proterozoic - Paleozoic Nisling Assemblage, is exposed in the eastern and southern regions. A terrane boundary was placed in the central Dezadeash Range. Recent petrographic studies reveal a southeastward increase in metamorphic grade. Prograde appearance of cordierite partly obliterated an older schistosity and caused a fabric change near the postulated terrane boundary. Furthermore, typical continental margin rocks, such as marble and quartzite, are not observed. This suggests that all metamorphic rocks in the Dezadeash Range can be correlated with the Kluane Metamorphic Assemblage, whereas Nisling Assemblage rocks occur in the Coast Mountains to the east. Therefore, the terrane boundary is located in the Dezadeash River valley, further southeast than previously thought.

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

A lithologic succession is recognized in tectonites of the eastern Teslin suture zone in south-central Yukon. Metagraywacke and quartzite, marble, mafic metavolcanics, and interbedded metagraywacke and argillite outcrop on both limbs of an upright northwest-trending syncline at Little Salmon Lake. A body of equigranular granodiorite intrudes the basal stratigraphic units. The granodiorite and its host sediments were penetratively deformed during top-to-the-SW shearing and greenschist facies metamorphism. The granodiorite gives a Devono-Mississippian U-Pb zircon age (353 +1.3/-1.4 Ma) which is interpreted as the minimum age of crystallization. This provides a minimum depositional age for these suture zone protoliths. Based on the sedimentary succession and the age constraints, the eastern suture zone protoliths show a clear genetic link to other pericratonic terranes in the northern Cordillera.

The Cache Creek (CCT) and Slide Mountain terranes (SMT), including the Seventymile Terrane in Alaska of the Northern Cordillera consist of oceanic assemblages that have been tectonically emplaced. The CCT has been enclosed by a series of arc terranes, whereas the SMT has been thrust onto pericratonic North America. Detailed studies of ultramafic rocks in CCT, SMT, Livengood Terrane and the Kluane metamorphic assemblage across Yukon, Alaska and British Columbia were conducted at nine site locations. The most common type of ultramafic rock present at these localities is serpentinized harzburgite. The ultramafic rocks from the CCT and SMT have been interpreted as the lower layers from dismembered ophiolite complexes. Samples collected from the CCT are consistently harzburgite, whereas samples from the SMT are both mantle-derived harzburgite and lherzolite. The variety of ultramafic rock present in the SMT suggests they were generated within contrasting geological settings.

The central Pelly Mountains in southeastern Yukon Territory consist of imbricate thrust sheets, which have undergone syn and post-thrusting deformation and metamorphism. The local geology is further complicated by intrusion of Upper Cretaceous batholiths, and by strike-slip faulting related to the Tintina Fault, a major northwest-trending transcurrent fault of uppermost Cretaceous or early Tertiary age. This faulting disrupts the northeast edge of the study area. Upper Devonian and Mississippian strata are present in at least two of the thrust sheets, but the Mississippian volcanic rocks occur in only one of them. The volcanic rocks consist of volcaniclastic material with minor interbedded flows, and were deposited in a submarine environment. Several coeval and cogenetic syenite and trachyte domes and small stocks are the remains of vent areas. Although the volcanic rocks are all highly altered and show evidence of widespread chemical mobility, trace element data indicate that the rocks are meta-luminous trachytes, most closely resembling peralkaline volcanics generated in extensional environments. This suggestion of a predominantly extensional tectonic setting in mid-Mississippian time in the Pelly Mountains is consistent with recent tectonic syntheses for the area. Stratabound and stratiform massive base metal sulphide deposits that occur within the Mississippian volcanic sequence are similar in many respects to the Kuroko-type volcanogenic massive sulphide deposits of Japan. The Pelly Mountains deposits, however, are among the first known occurrences in the world of Kuroko-type mineralization in a rift environment. A copy of this thesis is available at the EMR library – QE195 M67 1979. This thesis is available online at http://hdl.handle.net/2429/22257.

Paleozoic rocks of the Pelly Mountains, central Yukon, preserve greater than 150 m.y. of sedimentation, magmatism and base-metal mineralization. To identify secular trends in regional tectonics and metallogeny, a multi-year project on the stratigraphy of the Pelly Mountains in the Quiet Lake (105F) and Finlayson Lake (105G) map areas was initiated. Field studies during summer 2015 focused on two stratigraphic intervals: (1) mafic volcanic, volcaniclastic and clastic rock successions assigned to the Cambrian-Ordovician Cloutier and Groundhog formations (Kechika group); and (2) felsic volcanic, volcaniclastic and clastic rock successions assigned to the Devonian-Mississippian Black Slate and Felsic Volcanic formations (Seagull group). Cambrian-Ordovician strata were deposited in a marine environment characterized by episodic mafic volcanism and extensional tectonism. Devonian-Mississippian strata record the transition from an extensional turbidite basin to a metalliferous volcanic rift basin, and resemble key rock assemblages of the Selwyn basin (Earn Group) and Yukon-Tanana terrane (Grass Lakes and Wolverine Lake groups).

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