The Upper Triassic to Middle Jurassic Whitehorse Trough is a 500-km-long forearc basin developed on the eastern margin of the Stikine Terrane. Basin fill in the Fish Lake syncline consists of Early to Middle Jurassic strata of the Laberge Group. Re-examined fossil collections record all ammonite zones from the Upper Pliensbachian to lowest Bajocian (except for the recessive or volcanic Aalenian Stage), suggesting that the Laberge Group is a conformable sequence. Biostratigraphic dating of oldest conglomerates indicates that source area uplift occurred first in the north in the Early Pliensbachian, progressing southwards through the Late Pliensbachian. Periodic, basin-wide anoxia was prevalent during the Middle and Late Toarcian, indicated by abundant Bositra, a low-oxygen-tolerant bivalve. The final stage of basin-fill, Early Bajocian chert-pebble conglomerates, provides a maximum age constraint on the amalgamation of the Cache Creek and Stikine terranes.

A copy of this thesis is available at the EMR library – QE681.C43 2000.

The tectonic evolution of the Whitehorse trough in central Yukon is largely preserved by the Early to Middle Jurassic Laberge Group, an ~3000-m thick succession of synorogenic clastic strata that unconformably overlies arc and arc marginal rocks of the Lewes River Group. A two-year project was initiated to test a Sinemurian to Toarcian transgression of basal Laberge Group strata westward across the Whitehorse trough and examine the regional relationships between the timing of Jurassic exhumation, sedimentation, and terrane accretion in the northern Canadian Cordillera. Field studies in 2017 targeted basal Laberge Group strata at seven locations in central Yukon. At each field locality, basal Laberge Group strata are known or inferred to unconformably overlie the Povoas formation and multiple units of the Aksala formation. Pre-Early Jurassic unconformities may indicate variable basin topography due to the complex internal stratigraphy of the Lewes River Group, or that regional exhumation and erosion affected the Whitehorse trough prior to Laberge Group sedimentation.

The Mount M'Clintock map area, northeast of Whitehorse, is dominated by Middle Triassic to Jurassic sedimentary and volcanic strata of Stikinia with small portions of the Cache Creek and Yukon-Tanana Terranes. These assemblages were deformed prior to the mid-Cretaceous intrusion of three plutonic suites and the deposition of two suites of volcanic rocks. Sedimentary rocks previously mapped as undifferentiated Lewes River and Laberge Group strata are separated into their respectve groups and further sub-divided into several members. Lewes River Group rocks form three units that are Carnian and older, Norian, and Upper Norian in age and are represented by siliceous siltstone and calcareous sandstone, conglomerate and limestone respectively. Laberge Group strata are divided according to lithology and dominated by siltstone-sandstone couplets and massive siltstone with lesser conglomerate and volcanogenic sandstone. Volcanic rocks previously mapped as Hutshi Group are divided into the dominantly mafic and submarine, MiddleTriassic Joe Mountain volcanic complex (JMVC) and the dominantly felsic and sub-aerial Mount Byng volcanic complex (BCVC). The volcanic and sedimentary rocks generally increase in age from Middle Triassic to Jurassic from west to east across the map area. Plutons cutting these strata belong to the M'Clintock Lakes (120 Ma), the Whitehorse (115 Ma), and the Mount McIntyre (109 Ma) plutonic suites. The predominantly felsic fragmental rocks of the BCVC are genetically associated with the Byng Creek pluton of the Mount McIntyre plutonic suite. The BCVC is nested into the country rocks and its eastern margin and is preserved as the rim of a tilted caldera. Strata of the Laberge and Lewes River groups are folded throughout. Wavelengths are on the order of approximately 1-2 km, but are much tigter in black siltstone units and adjacent to northwest-trending faults. Faults are ubiquitous throughout the map area and form three sets. North-trending faults are the most common. They are spaced a few kilometres from each other and dictate the physiography and drainage of the region. Northwest-trending faults, in the northeastern corner of the map area control the Teslin River valley and juxtapose Yukon-Tanana rocks with Stikinia. Older faults are dominantly east-trending but are terminated or reactivated by younger faults. Copper (gold-molybdenum-tungsten) skarns and gold-bearing quartz veins are the two mineral deposit types most likely to be discovered in the map area. The source of the placer gold in Sheldon Creek is unknown but may be related to gold veins in the JMVC, BCVC, Sheldon Creek volcanics or the surrounding sedimentary rocks. Hydrothermal activity in the JMVC is characterized by orange weathering alteration, breccias, and carbonate veins. Cache Creek rocks in the southern part of the map area are targets for listwaenite associated gold veins.

The Whitehorse Trough, south-central Yukon, originated as a Mesozoic fore-arc basin separating the allochthonous Stikine Terrane to the west from the North American craton. Late Triassic erosion of a volcanic arc supplied detritus to the basin. Subsequent cessation of volcanism, unroofing and deep erosion of the arc into the Middle Jurassic resulted in a progressive increase in granodioritic sediment. Late Triassic-Jurassic Laberge conglomerate within the Whitehorse Trough are coarse, polymictic and typically massive. Inverse or normal grading, planar stratification and cross-bedding are less common. Conglomerates are debris flow, sheet-flood and bar deposits of braided alluvial fan-deltas. These conglomerates usually overlie and grade basinward into feldspathic graywacke or arkosic sandstone. Crystal tuffs grade laterally into sandstone and occur as interbeds as well. Sandstones commonly display trough cross-bedding or planar stratification. Hummocky cross-stratification rarely occurs in sandstones interbedded with bioturbated silty mudstone. Other facies include graded sandstone-mudstone with Bouma BC(E) sequences; float-stone/micritic limestone and rare calcarenite/rudite. Sandstone-conglomerate facies transitions indicate a vertical progression from shallow marine and shoreface sedimentary strata of Late Triassic age to coarse alluvial fan conglomerates of Jurassic age, reflecting progradation of fan-delta systems with progressive infilling of the basin. The Stikine Terrane accreted to North America in the Late Jurassic with basin shallowing and closure reflected by changes in the sedimentary sequences.

The Whitehorse Trough, a Mesozoic sedimentary basin in south-central Yukon that has potential for gas and oil, consists of the Lewes River Group (Triassic), the Laberge Group (Jurassic), and the Tantalus Formation (Jura-Cretaceous). The Laberge Group in the Carmacks (115I) and Laberge (105E) map areas is subdivided into four informal lithostratigraphic units: the Richthofen, Tanglefoot, Conglomerate and Nordenskiold formations. The Richthofen formation, distinguished by siltstone to very fine sandstone and mudstone couplets, is exposed in the southern part of the Laberge map area where it rests unconformably to conformably on the Lewes River Group and is unconformably and/or conformably overlain by the Tanglefoot formation. The Tanglefoot formation, distinguished by coalbearing, interbedded sandstone and mudstone, is exposed in the northern part of the Laberge map area and the southern part of the Carmacks map area where it rests unconformably on the Lewes River Group, and is overlain by the Tantalus Formation. The Conglomerate (conglomerate) and Nordenskiold (dacite tuff) formations occur as minor units within the Tanglefoot formation. The Richthofen-Tanglefoot formation unconformity and/or conformity is a potential petroleum play in the central Whitehorse Trough, whereas the Lewes River Group-Tanglefoot formation unconformity is a potential petroleum play in the northern Whitehorse Trough.

The paleomagnetic signature of the mid-Cretaceous Mount McIntyre Pluton, west of Whitehorse, was evaluated to develop a better understanding of the motion history of Cordilleran terranes through time. Excluding an anomalous result from the Carmacks Group, all previous tectonic estimates for terranes in the Yukon have been extrapolated from Alaska, British Columbia or the northwestern United States. The Mount McIntyre Pluton (109 Ma) and the adjacent Whitehorse Pluton (112 Ma), are granitic bodies that intrude Triassic and Jurassic sedimentary strata of the Stikine Terrane. Paleomagnetic measurements on samples from 20 granitic sites yielded three clusters of ChRM directions. Each cluster is specific to a geographical area of the Mount McIntyre pluton. The two most northeasterly sites are from a region of mixed igneous rocks between the Mount McIntyre and Whitehorse Plutons and thus are not considered. The other 11 northern sites give a well-defined mean ChRM direction that is steeply down and northeast. Seven sites in the southern part of the pluton gave a well-defined ChRM direction that is directed steeply down and to the northwest. The mean paleopole for the southern sites give an estimate of ~3900 km of northward or poleward translation with no rotation. In contrast, the paleopole for the northern sites in the Mount McIntyre Pluton suggests a poleward translation ~1600 km with ~80° of clockwise rotation. The motion must have occurred between 109 Ma and 45 Ma because earlier studies have shown that Stikine Terrane was fixed with respect to North America by Eocene time. The southern sites of the Mount McIntyre pluton support an estimate of ~2300 km of northward displacement between ~70 Ma and 45 Ma as derived from the ~70 Ma Carmacks Group volcanics. The result from the northern sites is statistically similar to the value determined for the Whitehorse Pluton, as do several other igenous units in southern British Columbia. Geobarometric estimates, made to determine the nature of any post-crystallization tilting of the pluton, were inconclusive. The contrast in tectonic motion estimates for the northern and southern portions of the Mount McIntyre pluton can be accommodated by a large fault between the portions, but a more definitive explanation requires the accumulation of more paleomagnetic sampling, age dating and structural information.

Whitehorse trough is a northwestward-tapering belt of Upper Triassic to Lower Cretaceous volcanic and sedimentary rocks extending ~650 km from the British Columbia–Yukon border, north to the vicinity of Carmacks in south-central Yukon. It consists of three main stratigraphic units (i.e., the Lewes River Group, Laberge Group and Tantalus Formation) representing three sedimentary basins, partially overlapping in space and time. The Laberge Group (Lower-Middle Jurassic), informally subdivided into the Richthofen, Tanglefoot and Nordenskiold formations, was deposited in the Laberge basin, a collapsing fore-arc basin in which the arc was undergoing uplift and erosion. The Richthofen formation consists of conglomerate, massive sandstone, sandstone-mudstone couplets, volcaniclastic rocks and minor limestone interpreted as submarine fan systems. The Tanglefoot formation consists of coal-bearing sandstone, mudstone, conglomerate, volcaniclastic rocks and minor limestone interpreted as delta systems and shallow marine deposits. The Richthofen and Tanglefoot formations are the same age (i.e., Sinemurian to Bajocian), but the Richthofen formation is restricted to the southern half of the basin, whereas the Tanglefoot formation occurs in the northern half. The Nordenskiold formation consists of subaerially erupted, resedimented volcaniclastics deposited mainly during Pliensbachian time. The Richthofen formation is interpreted as a spent source rock and the Nordenskiold formation is not a source rock. The Tanglefoot formation is interpreted as a potential source rock and possibly an effective source rock. It contains petroleum fluid inclusions (mainly 23°- 32° and 40°- 44° API gravity) indicating a minimum trapping temperature of 110-115°C. The Tanglefoot formation is also a potential reservoir rock.

Upper Triassic carbonate, volcanic and clastic rocks deposited in the Whitehorse Trough, a Mesozoic forearc basin, are well-exposed at Hill 4308. The deposition of these rocks occurred in three distinct stages: 1) sedimentation of lime sands and clastics on the flank of a volcanic high, 2) development of reefal carbonates and associated limestones, and 3) renewal of clastic deposition with both erosion and continued growth of patch reefs. The reefal carbonates are similar in structure and composition to reefal carbonates at Lime Peak about 6 km to the south, but the stratigraphic section at Lime Peak differs from that at Hill 4308, the former representing more continuous deposition of carbonate on an underlying clastic foundation. Differences between Hilll 4308 and Lime Peak may reflect local variation in relative sea level and in the distribution and intensity of clastic sedimentation experienced by nearby localities in tectonically active areas.

The McQuesten River region in the northern part of the McQuesten and Mayo map areas (scale 1:250 000) is underlain by Upper Proterozoic to Mississippian rocks that were deposited in an offshelf setting during the formation of the northern Cordilleran continental margin, deformed during the Mesozoic, and intruded by pre and post-kinematic intrusions. The Selwyn Basin phase of evolution of the continental margin is represented by rock units that correlate with units defined in the eastern part of Selwyn Basin. Dark clastic and rare felsic metavolcanic rocks of the Deconian-Mississippian Earn Group unconformably overlie rocks of the Selwyn Basin phase and are overlain conformably by the Mississippian Keno Hill quartzite. Dark, fine-grained metaclastic rocks of unknown age locally overlie Keno Hill quartzite. Four episodes of plutonism can be distinguished in the area, the earliest probably Early Paleozoic in age, another mid-Triassic in age, and two phases of Cretaceous granitic magmatism. Early Paleozoic bodies are typically metre-scale, fine-grained diabasic dikes and sills intruding rocks of the Hyland Group. Mid-Triassic diorite to gabbro occurs in discontinuous pods of various sizes, primarily in the Tombstone Thrust sheet where they intrude Devonian and Mississippian rocks. The most voluminous and widespread granitic rocks are the early Late Cretaceous Tombstone intrusions (92 ± 2 Ma). Typical Tombstone intrusions are weakly porphyritic, medium-grained hornblende-biotite granite to granodiorite, but they range from syenite to granodiorite and are locally peraluminous. The latest episode of granitic magmatism, the 65 ± 3 Ma McQuesten intrustions, is not yet fully delineated but includes five stocks of peroluminous potassium feldspar megocrystic granite. Paleozoic and Mesozoic structures occur in the region. The Sprague Creek Fault, a pre-Late Cambrian normal fault, is inferred from stratigraphic relationships. A possibly Jurassic phase of shortening is represented by west-northwest-trending, south-vergent folds that pre-date Jura-Cretaceous structures. The most pervasive and important phase of deformation is Jura-Cretaceous in age and kinematically complex. The Robert Service and Tombstone thrusts and Tombstone Strain Zone formed between the Late Jurassic and early Late Cretaceous during northward and northwestward displacement of more southerly hanging wall rocks. The McQuesten River region has numerous mineral occurrences, a long history of mining and mineral exploration and good potential for further discoveries.