Southeastern Yukon Research Articles

Boninitic magmatism in a continental margin setting, Yukon- Tanana terrane, southeastern Yukon, Canada

Mid-Paleozoic mafic rocks in the Finlayson Lake region of the Yukon-Tanana terrane, southeastern Yukon, Canada, have the diagnostic geochemical signatures of boninites: high MgO, Cr, Ni, and Co contents, intermediate SiO 2 contents, high Mg#9s (MgO/ (MgO+FeO*), Al 2 O 3 /TiO 2 , and Zr(Hf)/middle rare earth element (REE) ratios; low TiO 2 , REE, and high-field-strength element contents; and U-shaped primitive mantle–normalized trace element patterns. However, unlike most modern and ancient boninitic rocks that are typically associated with intraoceanic realms, those from the Finlayson Lake region are part of a mid-Paleozoic continental margin arc-backarc magmatic system. We propose a model in which the boninitic rocks from the Finlayson Lake region formed as a result of spreading ridge propagation into an arc built on composite basement of oceanic and continental crust. In the oceanic segment, upwelling asthenosphere induced melting of a subducted-slab metasomatized refractory mantle source to form boninitic magmatism. In the continental sector, upwelling asthenospheric mantle, and/or the melts derived thereof, induced crustal melting, which explains the large volume of temporally equivalent felsic volcanic and intrusive rocks.

Why are Arctic ground squirrels more stressed in the boreal forest than in alpine meadows?

Arctic ground squirrels (Spermophilus parryii plesius Richardson) in the southeastern Yukon live in both boreal forest and alpine tundra habitats. We live-trapped young male and female squirrels in both habitat types and subjected them to a standardized hormonal-challenge protocol to assess the responsiveness of their hypothalamic-pituitary-adrenal axis. Alpine squirrels had levels of free cortisol at the baseline (initial) bleed following their removal from traps that were 3 times higher in males and 5 times higher in females compared with boreal forest squirrels. Females, but not males, from the boreal forest were dexamethasone resistant, while neither sex from the alpine habitat was resistant. Free cortisol in alpine squirrels also responded more dramatically after the injection of adrenocorticotropic hormone. Corticosteroid-binding globulin levels were significantly lower in forest than alpine squirrels and these levels were not markedly affected by the challenge protocol. Glucose levels were significantly higher in boreal than alpine squirrels and the pattern differed between the two sites in response to the protocol. Hematocrits were significantly higher in alpine squirrels. Collectively, this evidence suggests that Arctic ground squirrels were more chronically stressed in the boreal forest than in the alpine meadows. The most likely explanation for our results is higher predation risk in the forest compared with alpine meadows, as forage availability and population density were not significantly different between the two habitats.

Carbon and peat accumulation over the past 1200 years in a landscape with discontinuous permafrost, northwestern Canada

Apparent recent carbon and peat accumulation rates over the past 1200 years were measured in five peat landforms in the discontinuous permafrost zone near Fort Simpson, Northwest Territories, Canada. The White River volcanic ash layer was used as a chronostratigraphic horizon to ensure a consistent time span of peat deposition among peat cores and to allow a large core sample size (n = 20 cores in each landform) without the expense of radiocarbon dating. Apparent recent carbon accumulation rates were not significantly different (p>0.05) among rich fen (13.58 ± 1.07 g C m−2yr−1), peat plateau (13.31 ± 2.20 g C m−2yr−1) and collapse fen (13.54 ± 1.50 g C m−2yr−1). Poor fen and ombrotrophic bog accumulation rates were 20.34 ± 2.86 and 21.81 ± 3.25 g C m−2yr−1, respectively, and were not significantly different from each other. Variation within the poor fen and ombrotrophic bog cores is attributed to microtopography, with hollows accumulating carbon at significantly greater rates than hummocks. Vertical peat accumulation rates vary significantly in the poor fen, with hummocks showing a greater annual vertical accumulation rate than hollows. Vertical peat accumulation rates ranged from 0.282 ± 0.052 mm yr−1in the peat plateau to 0.563 ± 0.070 mm yr−1in the ombrotrophic bog. Variations in mean core bulk density were also significant and ranged from 0.071 ± 0.011 g cm−3(collapse fen) to 0.102 ± 0.011 g cm−3(poor fen). A regional survey incorporating measurements from other parts of the southwestern Northwest Territories and the southeastern Yukon show rates similar to those near Fort Simpson. These rates are significantly lower than published rates from other parts of northern Canada, Finland, and the former Soviet Union. Low and variable summer precipitation in the region may contribute to the low carbon accumulation rates through decreased plant production and/or increased aerobic decomposition.

The Slide Mountain Terrane and the structural evolution of the Finlayson Lake Fault Zone, southeastern Yukon

The Finlayson Lake Fault Zone forms a fundamental, but little studied, tectonic boundary between strata of autochthonous North America and the accreted Slide Mountain and Yukon–Tanana terranes in southeastern Yukon. A structural and petrologic study was undertaken to examine the depositional environment of the Slide Mountain Terrane, its tectono-thermal evolution in the fault zone, and its relationship with the Yukon–Tanana Terrane. The Slide Mountain and Yukon–Tanana terranes are divisible into units dominated by metavolcanic and metasedimentary rocks. Field observations and whole-rock geochemistry indicate that Slide Mountain greenstone is ocean-floor basalt deposited in a deep submarine basin with a proximal terrigenous sediment influx. Either a marginal- or ocean-basin setting is supported by the data. Slide Mountain greenstone is thrust northeastward over metasedimentary rocks of Slide Mountain Terrane and southwestward over rocks of the Yukon–Tanana Terrane. Regional metamorphic grade ranges from subgreenschist to greenschist facies. Pressure–temperature estimates for the subgreenschist–greenschist facies transition are 270–310 °C and 2.1–3.6 kbar (1 kbar = 100 MPa), based on assumed geothermal gradients and the reaction isograd Pmp + Chl = Act + Ep + H2O. Metamorphic peak postdates motion along the westernmost reverse fault that juxtaposes the Slide Mountain and Yukon–Tanana terranes. We interpret the Finlayson Lake Fault Zone as a northeasterly directed thrust sequence disrupted by synmetamorphic back thrusts. The back thrusting may be the consequence of shortening in the upper crust, or larger scale processes such as "tectonic wedging" of Yukon–Tanana Terrane under Slide Mountain Terrane.

Observations of thermospheric horizontal neutral winds at Watson Lake, Yukon Territory (Λ = 65°N)

Fabry‐Pérot interferometer observations of the thermospheric O I (6300 Å) emission have been conducted from an airglow observatory at a dark field site in the southeastern Yukon Territory, Canada, for the period November 1991 to April 1993. The experiment, operated in an unattended, remote fashion, has resulted in a substantial data set from which mean neutral winds have been determined. Dependent upon geomagnetic activity, the nocturnal location of the site is either equatorward of the auroral oval or within the oval boundaries. The data set is rich enough to permit hourly binning of neutral winds based upon the Kp geomagnetic disturbance index as well as the season. For cases of low geomagnetic activity, the averaged, vector horizontal neutral wind exhibits the characteristics of a midlatitude site displaying antisunward pressure‐gradient‐driven winds. As the geomagnetic activity rises the late afternoon and evening winds slowly rotate sunward in an anticlockwise direction, initially remaining near 100 m/s in speed but eventually increasing to 300 m/s for Kp > 5. For the higher levels of activity the observed neutral wind flow pattern resembles a higher‐latitude polar cap pattern characterized by ion drag forcing of thermospheric neutral gases. In addition, rotational Coriolis forcing on the dusk side enhances the ion drag forcing, resulting in dusk winds which trace out the clockwise dusk cell plasma flow. On the dawn side the neutral winds also rotate in an anticlockwise direction as the strength of geomagnetic disturbances increase. Since the site is located at a transition latitude between the midlatitude and the polar cap, the data set provides a sensitive test for general circulation models which attempt to parameterize the contribution of magnetospheric processes. A comparison with the vector spherical harmonic (VSH) model indicates several regions of poor correspondence for December solstice conditions but reasonable agreement for the vernal equinox.

Range extensions and rare vascular plants from southeastern Yukon Territory

Range extensions and rare vascular plants from southeastern Yukon Territory

Geology and U–Pb geochronology of the Klondike District, west-central Yukon Territory

Geological mapping and U–Pb geochronology of the Klondike District provide new information on the nature and evolution of the Yukon–Tanana terrane (YTT) in western Yukon. The area is underlain by a sequence of thrust panels of regional extent. A continuously mappable sequence of interlayered metasedimentary and metavolcanic rocks is intruded by a variety of deformed metaplutonic rocks within two of these thrust sheets. Layering in the metasediments and metavolcanics is considered to be at least in part transposed stratigraphy. Small bodies of greenstone and altered ultramafic rocks thought to be part of the Slide Mountain terrane occur discontinuously along the thrust faults.U–Pb age determinations indicate that the uppermost thrust panel (assemblage I), which underlies much of the Klondike District, consists largely of metamorphosed, mid-Permian felsic plutonic, subvolcanic, and tuffaceous rocks. Beneath assemblage I is a second thrust panel (assemblage II), also of large areal extent, of mid-Paleozoic or older metasedimentary and mafic and felsic metavolcanic rocks, intruded by a large body of latest Devonian – Early Mississippian granitic augen orthogneiss. U–Pb analyses of zircon from the orthogneiss reflect both lead loss and a significant inherited zircon component. A third structural unit (assemblage III), which consists mainly of carbonaceous schist and phyllite, crops out in the northern part and along the southwestern edge of the study area, where it underlies both assemblages I and II.The earliest stage of deformation and metamorphism that affected the area (F1) produced the pervasive recrystallization fabric characteristic of all of the metamorphic rocks in assemblages I, II, and III, and occurred between mid-Permian and Late Triassic time. Thrust faulting, presumed to be northerly or northeasterly directed, postdates Late Triassic but predates mid-Cretaceous. The second phase of deformation (F2) was either synchronous with or later than thrust faulting. Monazite ages for the augen orthogneiss indicate that at least local metamorphism and (or) deformation lasted until Early Cretaceous time.Close similarities between composition, U–Pb ages, as well as timing and style of deformation, documented in the Klondike District and observed elsewhere in the YTT in southeastern Yukon and east-central Alaska suggest that much of the YTT either evolved as a single entity or else shared a very similar history.

Blueschist and eclogite in mylonitic allochthons, Ross River and Watson Lake areas, southeastern Yukon

Two new occurrences of eclogite associated with mylonitic rocks are documented. The first, near Ross River, is in a quartz-rich metasedimentary host that includes glaucophane schist. The host forms part of a belt of high-pressure rocks more than 50 km long and several kilometres wide between Ross River and Faro. In the second occurrence, north of Watson Lake, eclogite is associated with mafic and ultramafic rocks occurring in a klippe more than 100 km2 in area that rests on unmetamorphosed Triassic rocks of the North American miogeocline. Geothermobarometry shows that the eclogites were metamorphosed at 10–15 kb (1 kb = 100 MPa), between 470 and 750 °C. These peak conditions are comparable to those for other eclogites in the Yukon and adjacent Alaska. The age of metamorphism and mylonitization is Triassic or older.The high-pressure rocks occur at the leading edge of the most inboard accreted terrane, along its boundary with North American miogeoclinal strata, over a length of several hundred kilometres. Their extensive distribution makes these rocks regionally mappable units. This supports other evidence that both the Yukon–Tanana terrane and mylonite sheets obducted on North American foreland rocks are composed in part of trench and subduction-zone material.

Petrology and tectonic significance of augen gneiss from a belt of Mississippian granitoids in the Yukon-Tanana terrane, east-central Alaska

An approximately east-west-trending belt of porphyritic peraluminous granitoids, metamorphosed and deformed to augen gneiss, is exposed for 400 km across the Yukon-Tanana terrane. This belt consists of compositionally, texturally, and isotopically similar, concordant intrusions of augen gneiss in the Big Delta, Eagle, and Tanacross quadrangles of east-central Alaska, in the Fiftymile batholith of west-central Yukon Territory, and in two batholiths in the offset part of the Yukon-Tanana terrane northeast of the Tintina fault in southeastern Yukon Territory. Chemical analyses of augen gneiss from widely separated localities within the Big Delta intrusion suggest that the various samples are related by crystal fractionation. Comparison of major- and trace-element data from concordant layers of augen-poor gneiss and aplitic gneiss with similar data from adjacent augen gneiss suggests that the layers represent co-magmatic sills of more highly differentiated filter-pressed melt. Similarities between elemental abundances, particularly those of rare-earth elements, in augen gneiss from the large bodies in the Big Delta, Eagle, and Tanacross quadrangles, Alaska, and southeastern Yukon Territory suggest a common origin for these bodies. The peraluminous composition of the gneiss, its high initial 87 Sr/ 86 Sr ratio and high Th concentration indicate that the augen gneiss protolith contains a large component of crustal material. Geochronologic studies of augen gneiss in east-central Alaska and southeastern Yukon Territory indicate a Mississippian intrusive age and an early Proterozoic age for the crustal component. The augen gneiss bodies were intruded late in a middle Paleozoic volcanic-plutonic episode, and they may represent a deeply eroded continental magmatic arc. Regional amphibolite-facies metamorphism and mylonitization may have occurred late during the tectonic episode that resulted in intrusion of the porphyritic granitoid protoliths.

Evolution of the Yukon-Tanana terrane: Evidence from southeastern Yukon Territory

The Yukon-Tanana terrane (YTT) in southeastern Yukon consists predominantly of a mid-Paleozoic volcanic-plutonic (arc?) assemblage built on continental crust. The YTT had experienced strong deformation and metamorphism by Late Triassic time. By mid-Cretaceous the metamorphic complex and Late Triassic clastic rocks derived from it were imbricated with middle and upper Paleozoic “ophiolitic” sheets. The YTT differs markedly from adjacent parts of the North American continental margin in both its depositional and tectonic histories. The composition and tectonic history of the YTT is comparable to that of the Kootenay and Barkerville terranes of southern and central British Columbia from which the YTT may have been displaced.

Volcanogenic massive sulfide deposits associated with highly alkaline rift volcanics in the southeastern Yukon Territory

Volcanogenic massive sulfide deposits associated with highly alkaline rift volcanics in the southeastern Yukon Territory

Geological setting and tectonic significance of Mississippian felsic metavolcanic rocks in the Pelly Mountains, southeastern Yukon Territory

The central Pelly Mountains in southeastern Yukon Territory consist of imbricate thrust sheets, which have undergone syn- and post-thrusting deformation and metamorphism. The local geology is further complicated by the intrusion of Late Cretaceous batholiths, and by strike-slip faulting related to the Tintina Fault, a major northwest-trending transcurrent fault of latest Cretaceous or early Tertiary age. This faulting disrupts the northeast edge of the study area.Upper Devonian and Mississippian strata are present in at least two of the structural packages, but the Mississippian metavolcanic rocks occur only in the lowermost package. Rb–Sr geochronology indicates a mid-Mississippian age for the igneous suite. The volcanic rocks consist of volcaniclastic material with minor interbedded flows, and were deposited in a submarine environment. Several coeval and cogenetic syenite and trachyte domes and small stocks are the remains of vent areas. Although the volcanic rocks are all highly altered and show evidence of widespread chemical mobility, trace element data indicate that the rocks are metaluminous trachytes, most closely resembling peralkaline volcanics generated in extensional environments. This suggestion of a predominantly extensional tectonic setting in mid-Mississippian time in the Pelly Mountains is consistent with recent tectonic syntheses for the area.

Interesting vascular plants from southeastern Yukon Territory

Interesting vascular plants from southeastern Yukon Territory

A unique stratigraphic record of late Tertiary–Quaternary events in southeastern Yukon

A succession of fluvial sediments with minor coal, basaltic lava, five tills, and fossiliferous intertill sediments exposed along the Liard River where it crosses the Liard Plain provides a remarkably continuous record of geologic–climatic events in this region. The coal bearing sediments and lava were previously described and interpreted as Tertiary–Quaternary in age. The Quaternary sediments record four major intervals of glaciation and three nonglacial intervals not previously recognized in this region.

Botany of Southeastern Yukon Adjacent to the Canol Road.A. E. Porsild

Previous articleNext article No AccessNew Biological BooksBotany of Southeastern Yukon Adjacent to the Canol Road. A. E. Porsild F. B. FosbergF. B. Fosberg Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 27, Number 4Dec., 1952 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/399151 PDF download Crossref reports no articles citing this article.

LATE QUATERNARY GEOLOGY AND FROST PHENOMENA ALONG ALASKA HIGHWAY, NORTHERN BRITISH COLUMBIA AND SOUTHEASTERN YUKON

Research Article| September 01, 1952 LATE QUATERNARY GEOLOGY AND FROST PHENOMENA ALONG ALASKA HIGHWAY, NORTHERN BRITISH COLUMBIA AND SOUTHEASTERN YUKON CHARLES S DENNY CHARLES S DENNY U. S. GEOLOGICAL SURVEY, WASHINGTON, D. C. Search for other works by this author on: GSW Google Scholar GSA Bulletin (1952) 63 (9): 883–922. https://doi.org/10.1130/0016-7606(1952)63[883:LQGAFP]2.0.CO;2 Article history received: 02 Feb 1951 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation CHARLES S DENNY; LATE QUATERNARY GEOLOGY AND FROST PHENOMENA ALONG ALASKA HIGHWAY, NORTHERN BRITISH COLUMBIA AND SOUTHEASTERN YUKON. GSA Bulletin 1952;; 63 (9): 883–922. doi: https://doi.org/10.1130/0016-7606(1952)63[883:LQGAFP]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Reconnaissance field work along the Alaska Highway in northern British Columbia and southeastern Yukon furnishes preliminary data on the later Quaternary history of the region, and on the processes and results of intensive frost action. Extensive erosion surfaces were developed prior to glaciation, such as the Alberta Plateau of northeastern British Columbia and the Yukon Plateau in southern Yukon.In the region from Dawson Creek to Fort Nelson, British Columbia, the drift is dominantly a slightly weathered bouldery clay till of Wisconsin age, deposited by ice that came from the east. In the northern Rocky Mountains, the last eastward advance of the Wisconsin glaciers to the mountain front preceded the maximum westward advance of the ice sheets. In the foothills belt west of the Highway, the tills of these two advances are separated by lake deposits. Much of the drift is probably pre-Altamont in age and was subjected to vigorous frost action during the Altamont substage. The climate ameliorated perhaps with the advent of the post-glacial optimum and possibly coincident with the development of prairies. A recent change from prairie to forest perhaps indicates a slight cooling in recent time. In the northern Rocky Mountains, four substages of Wisconsin glaciation are recognized tentatively on the basis of morainal deposits and outwash terraces. The upper Liard basin is characterized by extensive pitted outwash plains, probably of late Wisconsin age. From Teslin Lake to Whitehorse, the Highway is bordered by extensive terraces of gravel and sand deposited in ice-marginal streams and lakes.Intensive frost action has modified pre-existing land forms and has produced a wide variety of features, such as talus, blockfields, stone rings, stone stripes, and terraces. Long smooth slopes, chiefly due to mass movements such as solifluction, are characteristic of the landscapes. These slopes and ancient soil structures extend down into forested areas and probably developed prior to the advent of forests, doubtless prior to the post-glacial optimum. Phenomena resulting from intensive frost action at the present time are restricted largely to areas above timber line. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A 4000-Mile Flight Through North-Western Canada

The aerial flight of some 4000 miles which commenced at Prince Rupert, B.C., and took me through northern British Columbia, south-eastern Yukon and the Mackenzie River district and ended at Edmonton, Alberta, was undertaken during the month of August, 1935, for the purpose of inspecting the work of several geological parties working in these northern regions.