not_specified

Stratigraphic and structural relationships within Stikinia, and overlap assemblages of the Whitehorse trough, are investigated in the Teslin Mountain area, southern Yukon. The Middle Triassic Joe Mountain Formation is dominated by a thick sequence of aphyric basalt produced by subaqueous volcanism. The Upper Triassic Lewes River Group displays complex lateral and vertical lithological and facies changes. It illustrates synvolcanic terrane exhumation, with erosion of the volcanic upland leading to deposition of thick volcaniclastic sequences, in parallel with ongoing clastic and carbonate sedimentation in marginal basins. Unravelling the Lewes River Group stratigraphy is critical in understanding the latest stages of Stikinia arc volcanism and the onset of Whitehorse trough marine sedimentation in the Early-Middle Jurassic. Further mapping and analytical work will focus at characterizing the Joe Mountain Formation and Lewes River Group, to determine how Stikinia evolved prior to final amalgamation of the Intermontane terranes with North America.

Regional bedrock mapping has revised structural and stratigraphic relationships in the northeastern corner of the Glenlyon map area (NTS 105L). Three structural panels, separated by south and southwest dipping thrust faults, subdivide the area. Cambrian (?) to Ordovician metasedimentary and volcanic rocks underlie the southwestern panel and include all exposures southwest of the Duo fault. Ordovician to Silurian (?) siliciclastic and carbonate strata and phyllite units that are intruded by Late Devonian porphyritic rocks underlie the central panel. Silurian (?) to Triassic siliciclastic and carbonate strata in the northern panel occur to the north, and in the footwall of, the Twopete fault. Mid-Cretaceous granitic rocks that crop out near Kalzas Mountain and occur below the surface near Dromedary Mountain intrude the central and northern panels. Northeast-verging folds and thrust faults deform layered rocks in the northeastern Glenlyon area and are offset by north-south oriented, steeply dipping structures with both normal and strike-slip motion. Upper Devonian Earn Group strata host layered sulphide bodies and polymetallic veins that contain lead, zinc and silver. This mineralization occurs in the footwall of the Twopete fault, a regional structure that originally developed as a Late Devonian synsedimentary fault. Ordovician and Silurian (?) quartz-rich clastic rocks are unlike coeval basinal facies rocks mapped elsewhere within the Selwyn basin in Yukon. These rocks represent slope facies deposits that mark a transition from basin to platform that is the northern extension of the McEvoy platform–Selwyn basin boundary.

Detailed mapping of Yukon-Tanana Terrane in Glenlyon map area has identified two Carboniferous volcanic successions, and their subvolcanic intrusions. The early-to mid-Mississippian Little Kalzas succession consists predominantly of calc-alkaline volcanic and volcaniclastic rocks which formed in a continental arc setting. Minor alkali basalt occurs stratigraphically below and above the calc-alkaline rocks.The Little Salmon succession, of mid-Mississippian to early Pennsylvanian age, represents a second cycle of continental arc magmatism. It consists of calc-alkaline andesite and volcaniclastic rocks near Little Salmon Lake, but passes laterally along strike to alkali basalt of within-plate affinity. The occurrence of alkaline magmatism within these continental arc sequences suggests episodic rifting of the arc. The occurrence of Mn-rich exhalite within the rifted arc sequence of the Little Salmon succession suggests that this environment may also have been favourable for production and deposition of metal-rich solutions.

A copy of this thesis is available at the EMR library – QE195.S748 1994.

The Teslin suture zone (TSZ) forms the fundamental boundary between rocks deposited along the ancient margin of North America and allochthonous terranes to the west. Both North American and allochthonous rocks were ductilely deformed and concurrently metamorphosed under upper greenschist to amphibolite facies conditions at temperatures of 450-650°C and pressures greater than or equal to 6 kbars, probably during Late Triassic to mid-Jurassic time. North-northwest-striking foliation dips steeply in the western portion of the TSZ, but flattens to the east in North American autochthonous rocks. The TSZ in the combined eastern Laberge/western Quit Lake map area is divisible into three distinct elongate structural domains parallel to the NNW-trending TSZ. Domains are identified by the distribution of differently oriented stretching lineations, Le1 and Le2, which formed during non-coaxial ductile deformation, and their associated "motion planes." Le1 trends westward and plunges down dip, whereas Le2 trends NNW-SSE and plunges shallowly. Le1 and Le2 are associated with the same mineral assemblages and formed under similar metamorphic conditions. Silicate mineral assemblages record temperatures up to 625°C, and pressures to 8 kbars; carbonate assemblages record temperatures in the range 350-500°C. The difference in temperature suggested by these assemblages may reflect lower temperatures of ductile flow and recrystallization in carbonate rocks. Elongate lensoidal domains of Le1 are separated from each other by narrower NNW-trending zones of Le2, forming a regional-scale anastomosing shear zone. Two western domains of Le1 chiefly comprise allochthonous rocks, or rocks of uncertain affinity; however, the eastern domain comprises North American autochthonous rocks, previously considered to be unaffected by TSZ metamorphism and deformation. Macroscopic and microscopic kinematic indicators consistently record right-lateral or top-to-the-north movement parallel to Le2. Kinematics associated with Le1 are more complex. To the west, kinematic indicators record west-side-down (normal) movement parallel to Le1; elsewhere, both reverse and normal movement are recorded. Field relations suggest Le1 began forming earlier than Le2, followed by a period during which both Le1 and Le2 formed, and ended with movement parallel only to Le2. These geometries and movement histories indicate that rocks of the TSZ and structurall associated autochthonous rocks record a history of right-lateral transpression along this portion of the North American margin during Triassic-Jurassic time. Movement consisted of early tectonic shortening at a high angle to the ancient margin, followed by a period of right-lateral translation approximately parallel to the Mesozoic margin of western North America.

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.

The Richardson anticlinorium is a major tectonic feature marking the eastern limit of the Cordilleran orogen in northern Yukon and Northwest Territories. Limited structural observations on the eastern flank of the Richardson anticlinorium indicate that the strain intensity increases significantly close to major faults that are associated with deformation zones tens to hundreds of metres wide. A predominant dextral sense of motion is documented for several major faults belonging to the Richardson fault array. However, second-order features exhibit highly variable kinematics. In several cases, strike-slip faults cut shallower dipping faults and follow steep bedding planes, suggesting that dextral motion occurred in a previously deformed and tilted sedimentary succession. The amount of displacement along the Richardson fault array is poorly constrained. Further investigation is warranted as potential large displacements may bear significant consequences on palinspastic reconstructions.

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).

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.