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.

The Teslin suture zone (TSZ) is a Late Triassic to mid-Jurassic subduction complex and forms the fundamental boundary between rocks deposited along the ancient western margin of North America, and allochthonous terranes to the west. The north-northwest-trending TSZ in the Big Salmon Range includes sedimentary and volcanic strata, basalt, peridotite, and granodiorite metamorphosed to middle greenschist to epidote-amphibolite facies and variably mylonitized. Petrochemical study of co-existing phases now being initiated should allow the assignment of P-T limits attending the recrystallization. Geologic mapping and structural analysis along three 10-15 km transects normal to the trend of the TSZ delineates two populations of stretching lineations, Lm1 and Lm2, in north-northwest-trending, steeply-dipping mylonitic foliation. Lm1, best developed in the western portion of the TSZ, plunges moderately to steeply west. Tight to isoclinal fold axes parallel Lm1. Lm2, best developed to the east, plunges gently north-northwest and south-southeast. Open to isoclinal fold axes parallel to Lm2, and fractures are locally present normal to Lm2. Folds initiated during mylonitization as open structures with axes parallel to Lm, and do not record unrelated pre- to post-mylonitic fold events. Crenulation and intersection lineations vary in orientation between schistosity planes in the shear zone. The stretching lineations, Lm1 and Lm2, formed parallel to their bulk movement directions. Kinematic indicators consistently record right-lateral movement parallel to Lm2. Preliminary interpretation of Lm1 kinematics indicate dominantly normal movement parallel to Lm1, or west-side-down.

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The geochronology and geochemistry of Cretaceous intrusions and associated mineralization in southeastern Yukon and southwestern NWT is the focus of a new research project. The objective is to investigate the southeastern extension of well-established plutonic suites currently recognized in central and western Yukon. Here we report five new U-Pb zircon ges from the study area that indicate that at least three distinct ages of intrusions are present. Two bodies (Bennett Creek pluton and an unnamed body west of Tungsten) give ages of ~91 Ma and are correlated with the Tombstone Plutonic Suite. Two phases of the Coal River batholith give ages of ~96 Ma and are considered to be part of the Tay River plutonic suite. Finally, the Mt. Billings Batholith east of Tuchitua Junction gives an age of ~106 Ma, and is correlated with the Anvil plutonic suite. Compositionally, the intrusions range from monzogranite to granodiorite and most contain at least minor amounts of biotite ± hornblende ± magnetite. Also, they are dominantly peraluminous to slightly metaluminous, subalkalic, relatively oxidized, and appear to span I-, S-, and A-type (within-plate) fields on various lithogeochemical discriminant plots. These new data will help constrain genetic and exploration models for a wide variety of Cretaceous intrusion-related gold and base metal mineral deposit types in the study area.

Regional-scale thrust faults in the Klondike District separate major lithologic units that include medium-grade metamorphic rocks of the Upper Permian Klondike Schist and middle to late Paleozoic Finlayson (Nasina) assemblage, as well as relatively low-grade greenstone and ultramafic rocks of the Slide Mountain terrane. These units were emplaced in the Jurassic as a series of kilometre-scale stacked thrust slices that are locally separated by additional ultramafic slices. A distinctive set of post-metamorphic compressional structures related to thrusting, particularly a set of ductile recumbent folds and associated spaced cleavage, is preserved in all thrust slices and is well developed near bounding faults. In carbonaceous units within the Klondike Schist, spatially associated with some thrusts, carbonaceous material is locally concentrated along the thrust-related spaced cleavage. Thrust-related fabrics are overprinted by kink-folding that locally affects the Finlayson assemblage, but is mainly developed in Klondike Schist. Gold-bearing veins appear confined to Klondike Schist and were emplaced in local sites of extension controlled principally by axial surfaces of these kink folds.

The Kluane Ranges, located in southwest Yukon, are underlain by Late Paleozoic to Late Triassic volcanic and sedimentary rocks assigned to Wrangellia. Bedrock mapping completed within the White River area indicates Wrangellian rocks underwent several phases of deformation between Late Triassic and Miocene time. Middle Triassic marine, fine-grained sedimentary rocks are preserved in grabens where they are overlain by basal conglomerates and breccias of the Nikolai formation. The grabens are related to uplift associated with the deposition of Nikolai formation flood basalts and intrusion of ultramafic bodies. Late Jurassic to Early Cretaceous compression resulted in structural stacking of older rocks and northeast- and southwest-verging overturned folds. Latest (?) Cretaceous to Miocene dextral strike-slip along the Denali fault system led to the formation of steeply dipping faults, extensional and compressional basins and refolding of older regional scale folds. Reactivation of Jura-Cretaceous faults also occurred at this time. An enigmatic pre-Middle Triassic deformation event is believed to be preserved locally in rocks of the Hasen Creek Formation.

Now in its second year, the Ancient Pacific Margin National Mapping (NATMAP) project continues to make progress in elucidating the stratigraphic framework of Yukon-Tanana Terrane of northern British Columbia and Yukon. Updated composite stratigraphic sections for the Finlayson Lake district, Glenlyon, Wolf Lake and Jennings River areas, and from previous studies in the Aishihik Lake area and northern Dawson Range, show that Yukon-Tanana Terrane originated as a dynamic mid- to late Paleozoic (pericratonic) arc system. The evolution of this arc system was punctuated by arc-building events, arc rifting and development of back-arc basins, and episodes of contractional deformation between Late Devonian and early Pennsylvanian. Its development terminated in late Pennsylvanian time with the opening of a marginal basin and the subsequent mid-Permian calc-alkaline volcanism, high-pressure metamorphism and regional deformation of the terrane.