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.

In the Ogilvie Mountains, west-central Yukon, the upper Proterozoic to Lower Cambrian Mount Harper Group (informal name) contains strata equivalent to both basal Windermere Supergroup and Lower Cambrian rocks in other areas of the North American Cordillera. Strata of the Mount Harper group are directly time constrained: the basal Windermere equivalents by a ca. 750 Ma U-Pb age from a volcanic complex which both conformably overlies and intertongues with the sedimentary rocks; the disconformably overlying units by the presence of Lower Cambrian trace fossils. The lower Mount Harper Group (LMHG) unconformably overlies a thick succession of dolostones informally named the Fifteenmile Group. A breccia layer is discontinuously preserved on the unconformity surface. This breccia contains silcretes and calcretes that record several episodes of subaerial exposure. Rare interbedded debris flows suggest that the most recent of these episodes was coincident with initial deposition of the LMHG conglomerates. Silcretes and calcretes in this succession suggest that, at the onset of Windermere deposition in this area, a temperate to equatorial, probably semi-arid to arid climate regime prevailed. Elsewhere, basal breccias in Windermere-equivalent strata generally have been interpreted as fault-related, but some contain features compatible with a karstic origin. A synsedimentary normal fault forms the southern margin of an asymmetric, east-trending half- graben basin which contains the lower Mount Harper Group. Basin fill appears to have been derived exclusively from source areas to the south. Proximal facies consist of fault-talus breccia and up to 1100 m of debris-flow conglomerates that were deposited in coalescing alluvial fans. Intermediate and distal facies include mid-to-lower fan conglomerates and sandstones deposited by sheetfloods, distal debris flows and braided channel streamflows. A basin-fill coarsening-upward megasequence in the eastern part of thc study area records a change from lacustrine redbeds to lower alluvial fan sandstones and conglomerates. The LMHG half-graben basin was formed, and sedimentation was controlled, by normal faulting along the southern margin. Synsedimentary faulting and minor back-stepping of the fault controlled development of the internal sequences. Volcanism conformably postdates this sedimentation, but northerly derived coarse clastic rocks of the upper Mount Harper group (UMHG) .

Studies of biogeochemical and evolutionary change in the Neoproterozoic require a detailed understanding of stratigraphic successions and their intrabasinal correlation to integrate those records into regional and global frameworks. The early Neoproterozoic Fifteenmile Group in the Ogilvie Mountains has previously been shown to archive important information on the evolution of the biosphere, including ocean redox and early evolution of eukaryotes. Here, we formally define the Chandindu Formation, a 150 to 420-m-thick siltstone-dominated mixed carbonate-siliciclastic succession of the lower Fifteenmile Group in the Coal Creek and Hart River inliers. We present ten sections of the Chandindu Formation and propose a type section and formalization to promote the development of a consistent stratigraphic framework for Proterozoic successions in northwest Canada.The Chandindu Formation begins with muddy tidal flat facies, which are succeeded by shale-siltstone-sandstone coarsening-upward cycles deposited in a predominantly subtidal environment. However, carbonate occurrences throughout the entire unit suggest localized carbonate buildups, likely nucleated on fault-bound paleohighs where siliciclastic background sedimentation was low. These paleohighs originated from rift-inherited complex basin topography and syn-depositional faulting during deposition of the upper Chandindu Formation.

Mica-quartz schist and olivine serpentinites form the Kluane metamorphic assemblage, a 150-km-long belt that is wedged between the Yukon-Tanana Terrane and the Insular Superterrane in the northern Coast Belt. The olivine serpentinites are serpentinized dunites that occur as lens-shaped bodies, interlayered along strike, with the mica-quartz schist. The larger ultramafic bodies developed a foliation and shear sense that is similarly oriented to those in the adjacent schist, suggesting 'Alpine-type' emplacement. Tectonic juxtaposition of schist and ultramafic rocks occurred during collapse and subduction of a back-arc basin underneath the North American continental margin in the Late Cretaceous. Oxygen isotope analyses point to values similar to known ophiolitic serpentinites. The ultramafic rocks are interpreted to be part of an oceanic crust that formed topographic highs during subduction and were subsequently sheared off and tectonically interleaved with metasedimentary rocks during the accretionary process.

The Paleoproterozoic Wernecke Supergroup is a >13 km-thick metasedimentary succession exposed in the Wernecke, Ogilvie and Richardson mountains of central and northern Yukon. A program of field and laboratory investigations was initiated in 2007 in order to constrain the provenance, age and environment of deposition of the Wernecke Supergroup, as well as to better constrain the age of subsequent Proterozoic deformation (Racklan orogeny). Clastic and carbonate samples were collected from the Wernecke Supergroup for analysis of detrital and metamorphic minerals, as well as whole rocks, using a range of isotopic methods. Preliminary results from U-Pb analysis of detrital zircons from quartz sandstone beds, using ion probe mass spectrometry, are provided in this report. Patterns of the detrital zircon ages are broadly comparable to other Paleo- to Mesoproterozoic basins in Canada, suggesting a common Laurentian source. The maximum age of the Supergroup of 1.61 ± 0.03 Ga is provided by the age of the youngest detrital grain, which is ~0.1 Ga younger than expected.

A copy of this thesis is available at the EMR library – QE195 M321.

The Rackla River area is underlain by normal faulted and gently folded sedimentary strata of the Paleoproterozoic Wernecke Supergroup, Mesoproterozoic Pinguicula Group, Neoproterozoic Hematite Creek Group and Windermere Supergroup, and Paleozoic Bouvette Formation. Gabbro dikes and sills that are likely age equivalent to the ca. 1380 Ma Hart River Sills cut the Wernecke Supergroup rocks. The presence of a mafic volcaniclastic horizon within the Bouvette allows its informal subdivision into a lower and upper member. These volcaniclastic rocks may the distal equivalent to volcanic rocks near the Tiger deposit, located ~20 km to the southwest. Three major angular unconformities are documented in the map area: at the base of the Rapitan Group, the base of the lower Bouvette, and the base of the upper Bouvette Formation.

Mackenzie Mountains supergroup (MMSG) strata in the Wernecke Mountains are described in detail. Three new formations are assigned to the revised and formalized Hematite Creek Group, which forms the base of the MMSG. The Dolores Creek Formation (black mudrocks and microbial dolostone) is the basal unit of the MMSG. The Black Canyon Creek Formation (cyclic peritidal dolostone) and Tarn Lake Formation (desiccation-cracked, shallow-marine siltstone and sandstone) are probably equivalent to the ‘H1 unit’ and Tsezotene Formation in NWT, respectively. The Hematite Creek Group is overlain by the Katherine Group (thick quartz arenite-dominated succession). The highest MMSG strata documented belong to the Basinal assemblage (Little Dal Group). Regional thickness and lithofacies variations in two of the new formations suggest that the basin had considerable paleobathymetric variation that is not consistent with patterns established in NWT. The economic potential of the succession is unknown.

Volcanic rocks in the Dawson map-area occur as isolated lenses within the early Paleozoic Selwyn Basin assemblage and as sets of flows and complexes within Proterozoic carbonate rocks near the edge of the Mackenzie Platform. Mount Harper complex, an example of the latter group, has been studied in greater detail than the others because it is more completely exposed, and contains two mafic to felsic volcanic cycles. Unlike the sedimentary rocks, whose correlation with established units in the Wernecke Mountains and Alaska is now well advanced, understanding of the stratigraphic position and internal relations of the volcanic piles is less definite. This report, based on two field mapping seasons, has two parts. Characteristics of the two volcanic groups and correlative occurrences are discussed in the first part; the second presents interpretations from the stratigraphy of the Mount Harper complex as an illustration of the style of volcanism in the region.

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.