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.

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.

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.

The Tummel fault zone, a northwest-trending belt of rocks of uncertain age and/or tectonic affinity, separates Paleozoic miogeoclinal strata of Cassiar Terrane from Yukon-Tanana Terrane metavolcanic and metasedimentary rocks. Northeast of the fault, Cassiar Terrane comprises pelitic and semipelitic rocks with rare amphibolite, which are correlated with the Kechika Group. These are overlain by carbonate correlated with the Askin Group. Southwest of the fault, in Yukon-Tanana Terrane, Devono-Mississippian siliciclastic rocks are overlain by Mississippian arc volcanic rocks. Granodiorite and diorite of the Telegraph Plutonic Suite (348-350 Ma) intrude the siliciclastic rocks. Foliated greenstone, leucogabbro intrusions, serpentinite and chert occur in the Tummel fault zone. The Early Cretaceous Glenlyon Batholith intrudes strata of Cassiar Terrane. Contact metamorphism recognized across the Tummel fault zone is interpreted to have been imposed by the Glenlyon Batholith. If correct, this interpretation requires that post-mid-Cretaceous displacement across the Tummel fault zone has been minimal (~5 km).

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

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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.

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 history of an eclogite sample and a mica schist sample from the western Teslin zone are discussed in view of garnet zoning profiles. The preliminary metamorphic results support the contention (de Keijzer et al., in press), based on earlier regional and structural arguments, of a structural contact (the "basal thrust" of de Keijzer et al., in press) between the Last Peak eclogite (part of the Anvil assemblage) and metasedimentary rocks of North American affinity to the west of it. Consequently, the eclogite is considered "exotic" with respect to the metasedimentary rocks. The proposed position of the Last Peak eclogite, a few hundred metres above the interpreted basal thrust within the zone of ductile thrusting, explains why it has experienced pervasive amphibolitization (hydration) since fault zones commonly act as conduits for fluid. It is unclear how much of the amphibolite-to-greenschist facies Anvil rocks surrounding the eclogite have experienced earlier high-pressure metamorphism.

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