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1
Plint, Heather E., and Terence M. Gordon. "The Slide Mountain Terrane and the structural evolution of the Finlayson Lake Fault Zone, southeastern Yukon." Canadian Journal of Earth Sciences 34, no. 2 (February 1, 1997): 105–26. http://dx.doi.org/10.1139/e17-009.
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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.
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Gehrels, George E. "Detrital zircon geochronology of the Taku terrane, southeast Alaska." Canadian Journal of Earth Sciences 39, no. 6 (June 1, 2002): 921–31. http://dx.doi.org/10.1139/e02-002.
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UPb geochronologic studies have been conducted on 60 detrital zircon grains from Permian(?) and Triassic metasandstones of the Taku terrane in central southeast Alaska. The resulting ages are mainly in the range 349387 Ma, with five additional grains that yield probable ages ranging from ~906 to ~2643 Ma. These ages are similar to the ages of detrital zircons in Carboniferous and older rocks of the YukonTanana terrane, which lies directly east of the Taku terrane. In contrast, these ages are different from the ages of detrital zircon grains in the Alexander terrane to the west. The data are accordingly consistent with models in which the Taku terrane is a western component of the Stikine and YukonTanana terranes, and that this crustal fragment is separated by a fundamental tectonic boundary from rocks of the Alexander and Wrangellia terranes to the west.
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Hansen, Vicki L. "Yukon-Tanana terrane: A partial acquittal." Geology 18, no. 4 (1990): 365. http://dx.doi.org/10.1130/0091-7613(1990)018<0365:yttapa>2.3.co;2.
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Creaser, Robert A., Larry M. Heaman, and Philippe Erdmer. "Timing of high-pressure metamorphism in the Yukon – Tanana terrane, Canadian Cordillera: constraints from U – Pb zircon dating of eclogite from the Teslin tectonic zone." Canadian Journal of Earth Sciences 34, no. 5 (May 1, 1997): 709–15. http://dx.doi.org/10.1139/e17-057.
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Zircon from eclogite near Last Peak in the Teslin tectonic zone yielded a U–Pb isotopic age of 269 + 2 Ma (2σ), the first precise age for such a rock in the Yukon –Tanana terrane of the Canadian Cordillera. Both the morphology and geochemistry of the eclogitic zircons indicate a metamorphic origin, and the U – Pb age therefore constrains the timing of peak high-pressure metamorphism in this rock. The U – Pb age demonstrates for the first time that an Early Permian high-pressure metamorphic event occurred in rocks now making up the Teslin tectonic zone, and possibly elsewhere in the Yukon – Tanana terrane. This U – Pb age provides a new geochronologic "pin" in the evolution of the Yukon – Tanana terrane prior to its Mesozoic accretion to the North American continental margin and, combined with recent 40Ar/39Ar muscovite data, indicates that high-pressure metamorphism at this time was a relatively short-lived event.
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Devine, Fionnuala, Donald C. Murphy, and Sharon D. Carr. "Yukon–Tanana terrane in the southern Campbell Range, Finlayson Lake belt, southeastern Yukon: the geological setting of retrogressed eclogite of the Klatsa metamorphic complex." Canadian Journal of Earth Sciences 44, no. 3 (March 1, 2007): 317–36. http://dx.doi.org/10.1139/e06-110.
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Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.
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Selby, David, Robert A. Creaser, and Bruce E. Nesbitt. "Major and trace element compositions and Sr-Nd-Pb systematics of crystalline rocks from the Dawson Range, Yukon, Canada." Canadian Journal of Earth Sciences 36, no. 9 (September 1, 1999): 1463–81. http://dx.doi.org/10.1139/e99-058.
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Geochemical (major, trace, and rare earth elements) and isotopic (Nd, Sr, and Pb) data of the Devono-Mississippian Wolverine Creek Metamorphic Suite, mid-Cretaceous Dawson Range batholith, mid-Cretaceous Casino Plutonic Suite, and Late Cretaceous plutons provide new information on the origin and evolution of the rocks from the Dawson Range in west-central Yukon, northern Canadian Cordillera. Isotopic and other geochemical data for the Wolverine Creek Metamorphic Suite metasedimentary rocks indicate that the detrital components were derived from two distinct provenances: (1) the North America craton, which contributed evolved felsic, upper crustal material; and (2) a calc-alkaline arc, which shed juvenile mafic-intermediate material. The geochemical affinity of the metaigneous rocks indicates that the Yukon-Tanana terrane represented a continental arc during Devonian-Mississippian times, with magmas derived from geochemically primitive sources and partial melting of the Yukon-Tanana terrane supracrustal rocks. The Dawson Range batholith likely represents crustally derived magmas from the Yukon-Tanana terrane during the mid-Cretaceous, with the contemporaneous Casino Plutonic Suite representing a late-stage fractionate of these magmas. The Late Cretaceous porphyry Cu mineralization is genetically related to plutons derived from mantle-source magmas related to active subduction.
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Golding, M. L., J. K. Mortensen, F. Ferri, J. P. Zonneveld, and M. J. Orchard. "Determining the provenance of Triassic sedimentary rocks in northeastern British Columbia and western Alberta using detrital zircon geochronology, with implications for regional tectonics." Canadian Journal of Earth Sciences 53, no. 2 (February 2016): 140–55. http://dx.doi.org/10.1139/cjes-2015-0082.
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Triassic rocks of the Western Canada Sedimentary Basin (WCSB) have previously been interpreted as being deposited on the passive margin of North America. Recent detrital zircon provenance studies on equivalent Triassic rocks in the Yukon have suggested that these rocks were in part derived from the pericratonic Yukon–Tanana terrane and were deposited in a foreland basin related to the Late Permian Klondike orogeny. Detrital zircons within a number of samples collected from Triassic sediments of the WCSB throughout northeastern British Columbia and western Alberta suggest that the bulk of the sediment was derived from recycled sediments of the miogeocline along western North America, with a smaller but significant proportion coming from the Innuitian orogenic wedge in the Arctic and from local plutonic and volcanic rocks. There is also evidence of sediment being derived from the Yukon–Tanana terrane, supporting the model of terrane accretion occurring prior to the Triassic. The age distribution of detrital zircons from the WCSB in British Columbia is similar to those of the Selwyn and Earn sub-basins in the Yukon and is in agreement with previous observations that sediment deposited along the margin of North America during the Triassic was derived from similar source areas. Together these findings support the model of deposition within a foreland basin, similar to the one inferred in the Yukon. Only a small proportion of zircon derived from the Yukon–Tanana terrane is present within Triassic strata in northeastern British Columbia, which may be due to post-Triassic erosion of the rocks containing these zircons.
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Erdmer, P., and H. Baadsgaard. "2.2 Ga age of zircons in three occurrences of Upper Proterozoic clastic rocks of the northern Cassiar terrane, Yukon and British Columbia." Canadian Journal of Earth Sciences 24, no. 9 (September 1, 1987): 1919–24. http://dx.doi.org/10.1139/e87-182.
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Analyses of detrital zircons from three occurrences of Upper Proterozoic clastic rocks of the northern Cassiar terrane in Yukon and northern British Columbia yield a U–Pb age of 2224 ± 22 Ma. The zircons apparently belong to a single population similar in age to zircons in stratigraphically equivalent rocks of the southern Cassiar terrane and to zircons in rocks in the Yukon–Tanana terrane of Alaska. A source terrane or area of the required age and extent has not yet been identified.
9
Mortensen, J. K., and G. A. Jilson. "Evolution of the Yukon-Tanana terrane: Evidence from southeastern Yukon Territory." Geology 13, no. 11 (1985): 806. http://dx.doi.org/10.1130/0091-7613(1985)13<806:eotyte>2.0.co;2.
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Nelson, JoAnne L. "The Sylvester Allochthon: upper Paleozoic marginal-basin and island-arc terranes in northern British Columbia." Canadian Journal of Earth Sciences 30, no. 3 (March 1, 1993): 631–43. http://dx.doi.org/10.1139/e93-048.
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The Sylvester Allochthon is a composite klippe of upper Paleozoic ophiolitic, island-arc, and pericratonic assemblages, which rests directly on the Cassiar terrane, a displaced sliver of Ancestral North America. Each tectonic assemblage occurs at a distinct and consistent structural level within the allochthon. They are assigned, respectively, to the Slide Mountain, Harper Ranch, and Yukon–Tanana terranes. The Sylvester Allochthon provides a view of the structural relationships between these terranes prior to Early Cretaceous – early Tertiary strike-slip dismemberment, as well as possible sedimentological links to late Paleozoic North America. Slide Mountain Terrane assemblages, designated divisions I and II, form the lowest structural panels. Chert – quartz sandstones are interbedded with Lower Mississippian deep-water sediments in division I and ocean-floor basalts and deep-water sediments in division II. They are similar in age and character to sandstones in the autochthonous Earn Group. Division II assemblages represent atypical oceanic crust and upper mantle assemblages. Continuous basalt–sedimentary sequences, well dated by conodont faunas, span Early Mississippian to mid-Permian time. Feeders for the basalts are sills rather than sheeted dyke swarms, suggesting very slow spreading and high(?) sedimentation rates in a marginal-basin setting. These supracrustal sequences are thrust-imbricated with ultramafite–gabbro panels. Division II is in part overlain by a Triassic siliciclastic and limy sedimentary sequence, which resembles the basal Takla Group, Slocan Group, and autochthonous Triassic units. Division III occupies the highest structural levels in the allochthon. With one exception, thrust sheets within it consist of Pennsylvanian to Upper Permian mixed calc-alkaline volcanic and plutonic rocks, chert, tuff, and limestone, assigned to the Harper Ranch Terrane. One panel, assigned to the Yukon–Tanana Terrane, consists of an Early Mississippian quartz diorite pluton with Precambrian inheritance that intrudes older volcanogenic sediments, pyroclastics, limestone, and siliciclastic sediments. Preferred pre-Mesozoic restoration of these terrane elements shows a Harper Ranch arc, built partly on pericratonic Yukon–Tanana and partly on primitive oceanic basement (division III), which is separated from North America by the Slide Mountain marginal basin (divisions I and II).
11
Simard, Renée-Luce, Jaroslav Dostal, and Charlie F. Roots. "Development of late Paleozoic volcanic arcs in the Canadian Cordillera: an example from the Klinkit Group, northern British Columbia and southern Yukon." Canadian Journal of Earth Sciences 40, no. 7 (July 1, 2003): 907–24. http://dx.doi.org/10.1139/e03-025.
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The late Paleozoic volcanic rocks of the northern Canadian Cordillera lying between Ancestral North America to the east and the accreted terranes of the Omineca belt to the west record early arc and rift magmatism along the paleo-Pacific margin of the North American craton. The Mississippian to Permian volcano-sedimentary Klinkit Group extends discontinuously over 250 km in northern British Columbia and southern Yukon. The two stratotype areas are as follows: (1) in the Englishman Range, southern Yukon, the English Creek Limestone is conformably overlain by the volcano-sedimentary Mount McCleary Formation (Lower Clastic Member, Alkali-Basalt Member and Volcaniclastic Member), and (2) in the Stikine Ranges, northern British Columbia, the Screw Creek Limestone is conformably overlain by the volcano-sedimentary Butsih Formation (Volcaniclastic Member and Upper Clastic Member). The calc-alkali nature of the basaltic volcaniclastic members of the Klinkit Group indicates a volcanic-arc setting ((La/Yb)N = 2.774.73), with little involvement of the crust in their genesis (εNd = +6.7 to +7.4). Alkali basalts in the Mount McCleary Formation ((La/Yb)N = 12.517.8) suggest periodic intra-arc rifting events. Broadly coeval and compositionally similar volcano-sedimentary assemblages occur in the basement of the Mesozoic Quesnel arc, north-central British Columbia, and in the pericratonic YukonTanana composite terrane, central Yukon, suggesting that they all represent pieces of a single long-lived, late Paleozoic arc system that was dismembered prior to its accretion onto Ancestral North America. Therefore, YukonTanana terrane is possibly the equivalent to the basement of Quesnel terrane, and the northern Quesnel terrane has a pericratonic affinity.
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Symons, D. TA, M. J. Harris, P. JA McCausland, W. H. Blackburn, and C. JR Hart. "MesozoicCenozoic paleomagnetism of the Intermontane and YukonTanana terranes, Canadian Cordillera." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1163–85. http://dx.doi.org/10.1139/e04-086.
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Lithoprobe Slave Northern Cordillera Lithospheric Evolution (SNORCLE) transect support enabled 24 paleomagnetic collections (536 sites, 6547 specimens) to be made in the northern Cordillera. Paleopoles from 16 studies are integrated with other published paleopoles to present a tectonic synthesis for the Intermontane Belt (IMB) and YukonTanana (YT) terranes since 215 Ma. It shows that the YT terrane has been parautochthonous with the North American craton at least since the Early Jurassic. Since 54 Ma the IMB terranes have rotated steadily clockwise at 0.29° ± 0.11°/Ma on top of the YT terrane and craton or by 16° ± 6° clockwise. Between 102 ± 14 and 54 Ma, the IMB terranes rotated another 35° ± 14° clockwise, probably during Paleocene collision with the craton, and were translated 8.3° ± 7.0° (2σ) (915 ± 775 km) northward, probably during the Late Cretaceous on the Kula plate. The 915 km estimate is much less than most paleomagnetic estimates for "Baja BC" but agrees with the geological evidence. These post-Jurassic estimates are used to reconstruct the position of the Late Triassic Jurassic cratonic apparent polar wander path for the IMB. The resulting IMB path is found to be concordant with the Cache Creek and Quesnellia terrane poles, indicating that these terranes were together and close to the craton in the Early Jurassic. These results place the IMB terranes close to the Pacific coastline of the northern USA and southern Canada but rotated 35° ± 14° counterclockwise, in the Jurassic and Early Cretaceous.
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Calvert, Andrew J., Nathan Hayward, Rajesh Vayavur, and Maurice Colpron. "Seismic and gravity constraints on the crustal architecture of the Intermontane terranes, central Yukon." Canadian Journal of Earth Sciences 54, no. 7 (July 2017): 798–811. http://dx.doi.org/10.1139/cjes-2016-0189.
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In 2004, two seismic reflection lines were shot across the Mesozoic Whitehorse trough and adjacent terranes. Three-dimensional first-arrival tomographic inversion is used to constrain lithology to 800–1200 m depth, and surface structures are extrapolated into the middle crust using the coincident reflection data. In the Yukon–Tanana terrane, the metasedimentary Snowcap assemblage is characterized by velocities of 4.5–5.5 km/s, while in Quesnellia, velocities of 5.0–6.0 km/s occur at 500 m depth, and probably represent igneous rocks of the Tatchun batholith. Across the Whitehorse trough, velocities >4.0 km/s correspond to clastic rocks of the Jurassic Laberge and Triassic Lewes River groups; velocities <4.0 km/s probably present the clastic Jurassic to Cretaceous Tantalus Formation. Several near-surface units with velocities of 2.0–3.0 km/s are identified; some correlate well with volcanic rocks of the Upper Cretaceous Carmacks Group, but others could be attributable to alluvial deposits or faulting. The Big Salmon fault is interpreted to dip southwest, implying that rocks of the Yukon–Tanana terrane extend beneath Quesnellia. Stikinia and Quesnellia underlie up to 5–8 km of Triassic to Early Cretaceous sedimentary strata, and appear to be a single allochthon within an 18–20 km deep synform above the Yukon–Tanana terrane, which we name the Northern Intermontane synform. In general, reflection geometries in the upper crust are complex, but are consistent with large-scale imbricate structures that have been dissected into numerous blocks by displacement along moderately to steeply dipping strike-slip faults, which may be part of a crustal-scale flower structure extending to the base of the crust.
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Johnston, S. T., D. Canil, and L. H. Heaman. "Permian exhumation of the Buffalo Pitts orogenic peridotite massif, northern Cordillera, Yukon." Canadian Journal of Earth Sciences 44, no. 3 (March 1, 2007): 275–86. http://dx.doi.org/10.1139/e06-078.
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We report the results of a geochemical and UPb zircon geochronological study aimed at constraining the timing and tectonic setting of the exhumation of an orogenic peridotitic mantle massif in central Yukon within northern Canadian Cordillera. The Buffalo Pitts orogenic massif is inferred to have been exhumed into continental metasedimentary rocks within the pericratonic YukonTanana terrane. Structurally admixed with the peridotite were boudins of metaleucogabbro and metatroctolite. A metamorphic aureole, defined by migmatite with abundant leucosome, characterizes the metasedi mentary wall rocks to the massif. Whole-rock chemical analyses indicate significant light rare-earth element enrichment of the leucogabbro and the metatroctolite, characteristics commonly ascribed to within-plate or rift settings. Crystallization of the leucogabbro occurred at 261.5 ± 2.3 Ma. The metatroctolite yields a similar crystallization age. These ages are coeval with metamorphism of the wall rocks to the orogenic massif, as indicated by leucosome crystallization at 262.3 ± 0.43 Ma. These geochemical and geochronological data are consistent with the orogenic massif having been exhumed within a continental rift at about 262 Ma, giving rise to metamorphism of the upper crustal rocks into which the massif was exhumed, and coeval with rift-related magmatism. Regional considerations suggest that rifting occurred within the back arc of a northeast-facing magmatic arc, represented by the Klondike schist. Coeval eclogite and blueschist along the northeast margin of the YukonTanana terrane may mark the paleo-trench, along which a southwest-dipping slab is assumed to have subducted beneath YukonTanana terrane.
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Petrie, Meredith Blair, Jane A. Gilotti, William C. McClelland, Cees Van Staal, and Sierra J. Isard. "Geologic Setting of Eclogite-facies Assemblages in the St. Cyr Klippe, Yukon–Tanana Terrane, Yukon, Canada." Geoscience Canada 42, no. 3 (July 29, 2015): 327. http://dx.doi.org/10.12789/geocanj.2015.42.073.
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The St. Cyr area near Quiet Lake hosts well preserved to variably retrogressed eclogite found as sub-metre to hundreds of metre-long lenses within quartzofeldspathic schist in south-central Yukon, Canada. The St. Cyr klippe consists of structurally imbricated, polydeformed and polymetamorphosed units of continental arc crust and ultramafic–mafic rocks. Eclogite-bearing quartzofeldspathic schist forms thrust slices in a 30 km long by 6 km wide, northwest-striking outcrop belt. The schist unit comprises metasedimentary and felsic intrusive rocks that are intercalated on the metre to tens of metres scale. Ultramafic rocks, serpentinite and associated greenschist-facies metagabbro form imbricated tectonic slices within the eclogite-bearing quartzofeldspathic unit, which led to a previously held hypothesis that eclogite was exhumed within a tectonic mélange. The presence of phengite and Permian zircon crystallized under eclogite-facies metamorphic conditions in the quartzofeldspathic host rocks indicate that the eclogite was metamorphosed in situ together with the schist as a coherent unit that was part of the continental arc crust of the Yukon–Tanana terrane, rather than a mélange associated with the subduction of oceanic crust of the Slide Mountain terrane. Petrological, geochemical, geochronological and structural similarities link St. Cyr eclogite to other high-pressure localities within Yukon, indicating the high-pressure assemblages form a larger lithotectonic unit within the Yukon–Tanana terrane.RÉSUMÉLa région de St-Cyr renferme des éclogites bien conservées à légèrement rétrogradées qui se présentent sous forme de lentilles allant de la fraction de mètre à quelques centaines de mètres de longueur, au sein d’un schiste quartzofeldspathique du centre-sud du Yukon au Canada. La klippe de St-Cyr est structurellement constituée d’unités imbriquées, polydéformées et polymétamorphisées de croûte d’arc continental et de roches ultramafiques à mafiques. Les schistes quartzofeldspathiques à lentilles d’éclogites forment des écailles de chevauchement d’une bande de 30 km de longueur par 6 km de largeur de direction nord-ouest. Les schistes sont constitués de roches métasédimentaires et de roches intrusives felsiques intercalées à des intervalles qui vont du mètre à quelques dizaines de mètres. Les roches ultramafiques, serpentinites et métagabbros au facies à schiste vert forment des écailles tectoniques imbriquées au sein de l’unité quartzofeldspathique à lentilles d’éclogite, d’où une précédente hypothèse voulant que les éclogites soient un produit d’exhumation à partir d’un mélange tectonique. La présence de phengite et de zircon permien cristallisé sous conditions métamorphiques du faciès à éclogite au sein de la roche hôte quartzofeldspathique indiquent que l’éclogite a été métamorphisée en place, avec le schiste comme unité cohérente du terrane de croûte d’arc continental de Yukon–Tanana, plutôt qu’un mélange associé à une subduction de croûte océanique du terrane de Slide Mountain. Des similarités pétrologiques, géochimiques, géochronologiques et structurales lient les éclogites de St-Cyr à d’autres lieux de hautes pressions au Yukon, ce qui indique que les assemblages de hautes pressions forment une unité lithotectonique plus grande au sein du terrane de Yukon–Tanana.
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Mortensen, J. K. "Pre-Mid-Mesozoic tectonic evolution of the Yukon-Tanana Terrane, Yukon and Alaska." Tectonics 11, no. 4 (August 1992): 836–53. http://dx.doi.org/10.1029/91tc01169.
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Piercey, Stephen J., Donald C. Murphy, James K. Mortensen, and Suzanne Paradis. "Boninitic magmatism in a continental margin setting, Yukon- Tanana terrane, southeastern Yukon, Canada." Geology 29, no. 8 (2001): 731. http://dx.doi.org/10.1130/0091-7613(2001)029<0731:bmiacm>2.0.co;2.
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Gehrels, George E. "Geology of the Chatham Sound region, southeast Alaska and coastal British Columbia." Canadian Journal of Earth Sciences 38, no. 11 (November 1, 2001): 1579–99. http://dx.doi.org/10.1139/e01-040.
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The Coast Mountains orogen is thought to have formed as a result of accretion of the Alexander and Wrangellia terranes against the western margin of the Stikine and YukonTanana terranes, but the nature and age of accretion remain controversial. The Chatham Sound area, which is located along the west flank of the Coast Mountains near the Alaska British Columbia border, displays a wide variety of relations that bear on the nature and age of the boundary between inboard and outboard terranes. Geologic and UPb geochronologic studies in this area reveal a coherent but deformed and metamorphosed sequence of rocks belonging to the YukonTanana terrane, including pre-mid-Paleozoic marble, schist, and quartzite, mid-Paleozoic orthogneiss and metavolcanic rocks, and upper Paleozoic metaconglomerate and metavolcanic rocks. These rocks are overlain by Middle Jurassic volcanic rocks (Moffat volcanics) and Upper Jurassic Lower Cretaceous strata of the Gravina basin, both of which also overlie Triassic and older rocks of the Alexander terrane. This overlap relationship demonstrates that the Alexander and Wrangellia terranes were initially accreted to the margin of inboard terranes during or prior to mid-Jurassic time. Accretion was apparently followed by Late Jurassic Early Cretaceous extensiontranstension to form the Gravina basin, left-slip along the inboard margin of AlexanderWrangellia, mid-Cretaceous collapse of the Gravina basin and final structural accretion of the outboard terranes, and early Tertiary dip-slip motion on the Coast shear zone.
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Samson, Scott D., P. Jonathan Patchett, William C. McClelland, and George E. Gehrels. "Nd and Sr isotopic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaskan and Canadian Cordillera." Canadian Journal of Earth Sciences 28, no. 6 (June 1, 1991): 939–46. http://dx.doi.org/10.1139/e91-085.
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Nd and Sr isotopic ratios are reported from 15 samples of plutons of the northern Coast Mountains batholith (CMB), between. the Alexander–Wrangellia terrane and the Stikine terrane of southeastern Alaska. Samples of plutons that are part of the Late Cretaceous – Eocene CMB suite have a range in initial εNd of −3.0 to −0.2 and 87Sr/86Sr of 0.70494–0.70607. There is no correlation of isotopic ratio with age, lithology, or geographic location of these plutons. Two plutons that are probably older than the bulk of the CMB plutons have present-day εNd values of −6.8 and −2.6.The Late Cretaceous – Eocene plutons have Nd depleted-mantle model ages (tDM) of 620–1070 Ma. These data indicate that the northern CMB must contain a significant component of old, evolved continental crust. The presence of an old crustal component is further demonstrated by inherited zircons of average Early Proterozoic age contained in some plutons. The mid to Late Proterozoic tDM ages of the CMB plutons are therefore a result of a mixture of Early Proterozoic crustal material with. younger, juvenile crust. The most likely source of this old crustal component is the Yukon–Tanana terrane, a fragment composed of ancient crustal material that occurs within and directly to the west of the northern CMB. The juvenile component is probably a combination of material derived from the mantle and from anatexis of the surrounding juvenile terranes. Crustal anatexis may have occurred as a result of the intrusion of mafic melts related to subduction along the outboard margin of the Alexander–Wrangellia terrane, by crustal thickening due to the underthrusting of the Alexander–Wrangellia terrane beneath the Yukon–Tanana and Stikine terranes, or by a combination of both processes.
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Giesler, Dominique, George Gehrels, Mark Pecha, Chelsi White, Intan Yokelson, and William C. McClelland. "U–Pb and Hf isotopic analyses of detrital zircons from the Taku terrane, southeast Alaska." Canadian Journal of Earth Sciences 53, no. 10 (October 2016): 979–92. http://dx.doi.org/10.1139/cjes-2015-0240.
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The Taku terrane consists of metamorphosed Carboniferous through Triassic marine clastic strata, volcanic rocks, and limestone that occur along the western margin of the Coast Mountains in southeastern Alaska. These rocks are juxtaposed along mid-Cretaceous thrust faults over Jura-Cretaceous basinal strata of the Gravina belt to the west and beneath Proterozoic through Carboniferous metamorphic rocks of the Yukon–Tanana terrane to the east. This paper presents U–Pb ages and Hf isotope analyses of detrital zircons from the Taku terrane, and compares these values with information from the adjacent Wrangellia, Alexander, and northern and southern portions of the Yukon–Tanana terrane (YTTn and YTTs). These comparisons suggest that (i) Carboniferous strata of the Taku terrane were shed mainly from mid-Paleozoic igneous rocks of YTTs, (ii) Permian strata of the Taku terrane were shed from mid-Paleozoic igneous rocks and intraformational Lower Permian volcanic rocks of YTTs as well as Upper Permian volcanic rocks exposed in YTTn, and (iii) Triassic sandstones were shed from mid-Paleozoic igneous rocks of YTTs, whereas conglomerates were shed mainly from mid-Paleozoic arc rocks in YTTn. Hf isotope analyses of Paleozoic zircons record increasing continental input during Silurian–Devonian and Permian phases of magmatism. Similarities in isotopic characteristics, combined with stratigraphic and geochemical information presented by previous workers, suggest that strata of the Taku terrane accumulated on (and partly as lateral equivalents of) rocks of YTTs, and that the combined assemblages formed outboard or along strike of YTTn.
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Beranek, Luke P., James K. Mortensen, Michael J. Orchard, and Thomas Ullrich. "Provenance of North American Triassic strata from west-central and southeastern Yukon: correlations with coeval strata in the Western Canada Sedimentary Basin and Canadian Arctic Islands." Canadian Journal of Earth Sciences 47, no. 1 (January 2010): 53–73. http://dx.doi.org/10.1139/e09-065.
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New detrital mineral age and whole-rock geochemical data provide the first constraints on the composition and source of North American Triassic strata in the northern Canadian Cordillera. Conodont-bearing Triassic strata collected from five locations across west-central to southeastern Yukon contain trace-element ratios ((La/Yb)N = ∼8; Eu/Eu* = ∼0.66), εNd(248 Ma) values (–9 to –10), and detrital zircon ages (400–680, 980–1200, 1500–1650, 1800–2000 Ma) that correspond with those of coeval rocks in the Canadian Arctic Islands and the Western Canada Sedimentary Basin of British Columbia and Alberta. The majority of detrital zircons were cannibalized from Ellesmerian clastic wedge and western Laurentian margin strata and recycled into Triassic rocks. Conspicuous early Paleozoic and Neoproterozoic detrital zircons may have been ultimately derived from allochthonous rocks of Caledonian–Baltican affinity in northern North America, such as the Pearya and Arctic Alaska – Chukotka terranes. One Early Triassic unit in eastern Yukon contains ca. 360 Ma detrital muscovite, and samples from several localities include single-grain occurrences of Mississippian detrital zircon. Mississippian detrital mineral ages likely record a partial source from mid-Paleozoic rocks of the allochthonous Slide Mountain and Yukon–Tanana terranes following their Late Permian – Early Triassic emplacement onto the Cordilleran margin. More substantial evidence of terrane-derived sediment deposited along the North American margin may be further identified within Triassic strata that are exposed to the west (outboard) of our sample sites, immediately adjacent to the Slide Mountain and Yukon–Tanana terranes.
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Hansen, Vicki L. "A model for terrane accretion: Yukon-Tanana and Slide Mountain Terranes, northwest North America." Tectonics 7, no. 6 (December 1988): 1167–77. http://dx.doi.org/10.1029/tc007i006p01167.
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Nelson, JoAnne, and George Gehrels. "Detrital zircon geochronology and provenance of the southeastern Yukon–Tanana terrane." Canadian Journal of Earth Sciences 44, no. 3 (March 1, 2007): 297–316. http://dx.doi.org/10.1139/e06-105.
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Two samples of late Paleozoic grit and Late Mississippian quartzite–chert conglomerate collected from southeastern Yukon–Tanana terrane (YTT) — a composite thrust sheet resting structurally above North American parautochthonous strata and intervening imbricate sheets of the late Paleozoic oceanic Slide Mountain terrane — yielded, respectively, 89 and 74 concordant or nearly concordant (<20% discordant) U–Pb ages on single detrital zircons. They provide constraints on the provenance of this allochthonous pericratonic terrane. Zircons in the grit range from 1770 to 2854 Ma, with a well-defined Early Proterozoic peak between 1800 and 2100 Ma. Precambrian zircons in the conglomerate also show a dominant peak between 1800 and 2100 Ma and smaller peaks between 2200 and 3200 Ma, with a few older grains, and younger grains with ages of 998, 1219, 1255, 1256, and 1417 Ma. The conglomerate also yielded three Devonian grains, with ages of 366 ± 23, 373 ± 12, and 379 ± 23 Ma. Their ages are approximately coeval with the oldest felsic to intermediate arc- and rift-related magmatism in the YTT. The age spectra from southeastern YTT units compare closely with those from Mississippian and older pericratonic units in the Coast Mountains, confirming correlations previously made on lithologic grounds. They also strongly resemble detrital zircon populations from craton-derived Paleozoic units of the northern North American autochthon. This robust U–Pb data set lends support to the idea that YTT once formed part of the outer, active margin of the North American continent, prior to Mississippian rifting and marginal ocean basin development.
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Gehrels, George E., William C. McClelland, Scott D. Samson, and P. Jonathan Patchett. "U–Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska." Canadian Journal of Earth Sciences 28, no. 8 (August 1, 1991): 1285–300. http://dx.doi.org/10.1139/e91-114.
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Metamorphic rocks within and west of the northern Coast Mountains in southeastern Alaska consist of an Upper Proterozoic(?) to upper Paleozoic continental margin assemblage that we interpret to belong to the Yukon-Tanana terrane. U–Pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of ~495 Ma, ~750 Ma, 1.05–1.40 Ga, 1.75–2.00 Ga, ~2.3 Ga, 2.5–2.7 Ga, and ~3.0 Ga. Multigrain fractions from two samples yield upper intercepts between 2.0 and 2.3 Ga, but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of < 2.0 and > 2.3 Ga grains. Zircons in these rocks generally overlap in age with (i) detrital zircons in metasedimentary rocks of the Yukon–Tanana terrane in eastern Alaska and Yukon, (ii) detrital zircons in strata of the Cordilleran miogeocline, and (iii) plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata. In addition, the pre-1.7 Ga grains overlap in age with dated crystalline rocks of the western Canadian Shield. These similarities raise the possibility that metaclastic rocks in the northern Coast Mountains accumulated in proximity to western North America. The younger zircon populations were likely shed from mid-Proterozoic to early Paleozoic igneous rocks that now occur locally (but may have been widespread) along the Cordilleran margin. Recognition of a continental margin assemblage of possible North American affinity in the Coast Mountains raises the possibility that some arc-type and oceanic terranes inboard of the Coast Mountains may be large klippen that have been thrust over the North American margin.
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Nelson, JoAnne, and Richard Friedman. "Superimposed Quesnel (late PaleozoicJurassic) and YukonTanana (DevonianMississippian) arc assemblages, Cassiar Mountains, northern British Columbia: field, UPb, and igneous petrochemical evidence." Canadian Journal of Earth Sciences 41, no. 10 (October 1, 2004): 1201–35. http://dx.doi.org/10.1139/e04-028.
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Allochthons in the Cassiar Mountains of northern British Columbia contain assemblages belonging to two distinct Canadian Cordilleran terranes, YukonTanana (YTT) and Quesnellia. These assemblages, of pre-Late Devonian, DevonianMississippian, PennsylvanianPermian, and Early Jurassic age, occur in intrusive and depositional, as well as structural, contact with each other. The allochthons are gently dipping thrust panels, interrupted by the mid-Cretaceous Cassiar Batholith. A key element for correlation across the batholith is the Mississippian and older pericratonic Dorsey Complex. New DevonianMississippian UPb ages for deformed plutons within it document an igneous suite like those in type YukonTanana exposures farther north. Other characteristics of the Dorsey Complex that ally it with YTT are orthoquartzites and grits, and amphibolite bodies with transitional mid-ocean ridge basalt (MORB) to ocean-island basalt (OIB) petrochemical signatures. Unconformities, deformed clasts in the late Paleozoic sequences, and a shared mid-Permian intrusive suite show that later arcs onlapped the mid-Paleozoic and older YTT assemblage. The Early Jurassic intrusive suite cuts all major contacts and fabrics except the terrane-bounding fault between the Slide Mountain and combined YTTQuesnel terranes. It represents a northern continuation of a plutonic belt that extends the length of the Mesozoic Quesnel magmatic arc. These relationships carry important implications for Cordilleran terrane history and the tectonic evolution of the North American margin. At least some of the major terranes were not unrelated entities prior to their accretion to the continent, but a system of superimposed and interconnected arcs that developed over a protracted time interval, with complex and evolving paleogeographic configurations much like the modern western Pacific province.
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Colpron, Maurice, Kaesy Gladwin, Stephen T. Johnston, James K. Mortensen, and George E. Gehrels. "Geology and juxtaposition history of the Yukon-Tanana, Slide Mountain, and Cassiar terranes in the Glenlyon area of central Yukon." Canadian Journal of Earth Sciences 42, no. 8 (August 1, 2005): 1431–48. http://dx.doi.org/10.1139/e05-046.
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In central Yukon, the pericratonic YukonTanana terrane (YT) is juxtaposed with the Cassiar terrane (CT, parautochthonous North America) along the Tummel fault zone (TFZ), a 34 km wide, northwest-trending belt comprising imbricate fault slices of Slide Mountain terrane (SM, greenstone, chert, serpentinite) and synorogenic clastic rocks. Northeast of the TFZ, the CT comprises Paleozoic metapelitic rocks, marble, and amphibolite of continental margin affinity. To the southwest, the YT consists of a pre-Late Devonian metasedimentary complex overlain and intruded by Mississippian clastic, volcanic, and plutonic successions of continental arc affinity. In the TFZ, Middle to Late Permian ocean-floor basalt of the SM shows evidence of crustal contamination, suggesting deposition at the edge of a marginal ocean basin. Deformation features in the TFZ include early ductile fabrics overprinted by younger brittle structures. Triassic synorogenic clastic rocks in the TFZ, and at the base of a klippen above the YT, suggest that terrane imbrication began shortly after the Early Triassic. 40Ar/39Ar mica ages from the region suggest cooling of the YT, SM, and part of CT below 300 °C by Early Jurassic time. Pervasive brittle structures in the Ragged Lake klippe, which roots into the TFZ, indicate brittle thrusting of the SM over the CT in post-Triassic time. Early Cretaceous plutons intrude the CT (Glenlyon Batholith) and the TFZ (leucogabbro) and impose a contact aureole that extends westward into the YT. Steep brittle structures that deformed the TFZ also affect, in part, the Glenlyon Batholith but do not significantly offset its contact aureole. Consequently, little displacement can have occurred along the TFZ after Early Cretaceous time.
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Rubin, Charles M., and Jason B. Saleeby. "Tectonic framework of the upper Paleozoic and lower Mesozoic Alava sequence: a revised view of the polygenetic Taku terrane in southern southeast Alaska." Canadian Journal of Earth Sciences 28, no. 6 (June 1, 1991): 881–93. http://dx.doi.org/10.1139/e91-080.
Full textAbstract:
Fragments of upper Paleozoic and lower Mesozoic metavolcanic and metasedimentary sequences of the Taku terrane are exposed discontinuously along a narrow belt in southeast Alaska and form a distinct lithostratigraphic package in the Ketchikan area called the Alava sequence. Crinoidal and argillaceous marble, carbonaceous phyllite, argillite, mafic flows, pillow breccia, pyroclastic tuff, and quartzite characterize the sequence. These strata are unconformably overlain by Upper Jurassic to Lower Cretaceous fine- to coarse-grained epiclastic rocks of the Gravina sequence. The upper Paleozoic part of the Alava sequence may be correlative with the Yukon–Tanana terrane, whereas the Middle and Upper Triassic portion of the Alava sequence may represent a metamorphic vestige of the Stikine terrane. Both parts are now exposed on the western flank of the Coast Plutonic Complex, in contrast with their correlatives to the east. These relations suggest that the Stikine and Alexander terranes were juxtaposed prior to deposition of the Gravina sequence. The western boundary between rocks of North American affinity and allochthonous ensimatic crustal fragments of the Alexander and Wrangellian terranes lies west of the Coast Plutonic Complex.
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Stevens, R. A., P. Erdmer, R. A. Creaser, and S. L. Grant. "Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon–Tanana terrane of south-central Yukon." Canadian Journal of Earth Sciences 33, no. 1 (January 1, 1996): 103–16. http://dx.doi.org/10.1139/e96-011.
Full textAbstract:
Metamorphosed and ductilely deformed sedimentary, plutonic, and volcanic rocks of the Nisutlin and Anvil assemblages make up the Yukon–Tanana terrane in the Teslin tectonic zone study area. The Nisutlin assemblage consists of siliceous schist–quartzite and graphitic phyllite that share a primary depositional contact, and Early Mississippian tonalite to quartz diorite that intrudes the siliceous schist–quartzite and possibly the graphitic phyllite. The Anvil assemblage includes metagabbro and mafic schist–greenstone that share an intrusive contact relationship. Tonalite to quartz diorite of the Nisutlin assemblage is characterized by minor zircon inheritance with an average Proterozoic age, εNd(350 Ma) values of −2.5 to −6.2, and Nd model ages of 1.50–1.79 Ga. These data suggest that the magmatic bodies have inherited a component of continentally derived material. Primary contact relationships and age data indicate that the Nisutlin assemblage had formed by Mississippian time, and regional correlations show that this assemblage makes up a large part of the Yukon–Tanana terrane of southern Yukon. Assembly of the Nisutlin assemblage by Mississippian time indicates that it did not form as a late Paleozoic and early Mesozoic subduction melange, and it suggests that its tectonic fabrics did not result from the progressive growth of a Permo-Triassic subduction complex. We suggest that the Nisutlin assemblage was part of a crustal block that lay outboard of North America in Mississippian time, and that it lay in the hanging-wall plate of a Permo-Triassic subduction zone as a relatively coherent assemblage, rather than forming within the zone as a subduction complex.
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Piercey, Stephen J., James K. Mortensen, Donald C. Murphy, Suzanne Paradis, and Robert A. Creaser. "Geochemistry and tectonic significance of alkalic mafic magmatism in the Yukon-Tanana terrane, Finlayson Lake region, Yukon." Canadian Journal of Earth Sciences 39, no. 12 (December 1, 2002): 1729–44. http://dx.doi.org/10.1139/e02-090.
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This paper provides an integrated field and geochemical study of weakly alkalic, ~360 Ma mafic rocks from the YukonTanana terrane in the Finlayson Lake region, southeastern Yukon. These mafic rocks occur as dykes and sills that crosscut older felsic metavolcanic rocks and metasedimentary rocks (Kudz Ze Kayah unit) or as flows interlayered with carbonaceous metasedimentary rocks. The mafic rocks have signatures similar to those of ocean-island basalts, moderate TiO2 and P2O5 contents, elevated high field strength element and light rare earth element contents, and εNd350 = +1.1. A subset of the dykes (group 4b) has similar geochemical characteristics but with higher Th/Nb and lower Nb/U ratios, higher Zr and light rare earth element contents, and εNd350 = 2.8. The geochemical and isotopic attributes of these rocks are consistent with formation from either lithospheric or asthenospheric sources during decompression melting of the mantle, with some rocks exhibiting evidence for crustal contamination (group 4b). The alkalic basalts are interpreted to represent ~360 Ma ensialic back-arc rifting and basin generation. It is envisioned that east-dipping subduction, represented by slightly older magmatic suites (Fire Lake unit), was disrupted by subduction hinge roll-back, westward migration of arc magmatism, and the onset of back-arc extension. Decompression melting of the mantle associated with back-arc generation resulted in mantle melting and the formation of the alkalic basalts. The spatial association of this mafic magmatism with crustally derived felsic volcanic rocks and contained volcanogenic massive sulphide mineralization suggests that the associated deposits (Kudz Ze Kayah, GP4F) formed within an ensialic back-arc environment.
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Mathez, E. A., A. G. Duba, C. L. Peach, A. Léger, T. J. Shankland, and G. Plafker. "Electrical conductivity and carbon in metamorphic rocks of the Yukon-Tanana Terrane, Alaska." Journal of Geophysical Research: Solid Earth 100, B6 (June 10, 1995): 10187–96. http://dx.doi.org/10.1029/95jb00615.
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ALEINIKOFF, JOHN N., CYNTHIA DUSEL-BACON, and HELEN L. FOSTER. "Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska." Geological Society of America Bulletin 97, no. 5 (1986): 626. http://dx.doi.org/10.1130/0016-7606(1986)97<626:goagar>2.0.co;2.
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McClelland, William C., Lawrence M. Anovitz, and George E. Gehrels. "Thermobarometric constraints on the structural evolution of the Coast Mountains batholith, central southeastern Alaska." Canadian Journal of Earth Sciences 28, no. 6 (June 1, 1991): 912–28. http://dx.doi.org/10.1139/e91-083.
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Thermobarometric data from amphibolite-facies metamorphic rocks west of the Coast Mountains batholith provide important constraints on the structural evolution of the mid-Cretaceous Sumdum–Fanshaw fault system and Late Cretaceous – Paleocene Le Conte Bay shear zone in central southeastern Alaska. Ductile structures that make up the Sumdum–Fanshaw fault system record the east-directed underthrusting of the Alexander terrane and Gravina belt beneath the Ruth assemblage (Yukon–Tanana terrane) and Taku terrane. These structures are truncated to the east by the Le Conte Bay shear zone. Temperature and pressure estimates calculated from the garnet–biotite geothermometer and garnet–rutile–ilmenite–plagioclase–quartz geobarometer suggest juxtaposition of the Gravina belt and Yukon–Tanana terrane at relatively deep levels (>7 kbar) during mid-Cretaceous time. Rocks west of the Le Conte Bay shear zone yield thermobarometric estimates of 465–890 ± 50 °C and 7.1–11.8 ± 1 kbar (1 kbar = 100 MPa). Late Cretaceous and Paleocene metamorphism associated with the Le Conte Bay shear zone reflects synkinematic emplacement of tonalitic intrusions along the western margin of the Coast Mountains batholith. Thermobarometric results from samples adjacent to the tonalite bodies record uplift and retrogression and suggest tonalite emplacement at 7.5–7.7 ± 1 kbar. An eastward increase in thermobarometric estimates observed in Thomas and Le Conte bays is inferred to record uplift and east-side-up tilting of rocks west of and within the Le Conte Bay shear zone during Late Cretaceous and Paleocene time. Rocks within the Le Conte Bay shear zone were apparently rapidly (1.5–2 mm/a) uplifted to shallow crustal levels prior to mid-Eocene time. Thermobarometric results for the Petersburg region are similar to those previously reported along the western flank of the northern Coast Mountains batholith.
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Gehrels, G. E., and P. A. Kapp. "Detrital zircon geochronology and regional correlation of metasedimentary rocks in the Coast Mountains, southeastern Alaska." Canadian Journal of Earth Sciences 35, no. 3 (March 1, 1998): 269–79. http://dx.doi.org/10.1139/e97-114.
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U-Pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the Coast Mountains in southeastern Alaska. These rocks belong to the Port Houghton assemblage, which consists of upper Paleozoic pelitic and psammitic schist, metaconglomerate, metabasalt, and marble. The Port Houghton assemblage rests unconformably(?) on metamorphosed and deformed mid-Paleozoic arc-type volcanics (Endicott Arm assemblage), which gradationally overlie upper Proterozoic(?) - lower Paleozoic continental margin strata (Tracy Arm assemblage). Three main clusters of ages are present: 330-365 Ma (19 grains), 1710-2000 Ma (27 grains), and 2450-2680 Ma (6 grains). Additional grains are approximately 2334, 2364, and 3324 Ma. Comparison of these ages with detrital zircon ages in other Cordilleran assemblages supports previous interpretations that metasedimentary rocks in the Coast Mountains (i) form a southwestern continuation of the Yukon-Tanana terrane of eastern Alaska and Yukon, (ii) are not correlative with strata of the Alexander terrane, and (iii) contain detritus that was probably shed from cratonal rocks in the Canadian Shield to the east. Several scenarios exist to explain the occurrence of these continental margin rocks west (outboard) of arc-type and ocean-floor assemblages such as the Stikine, Cache Creek, Quesnel, and Slide Mountain terranes.
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McClelland, William C., George E. Gehrels, Scott D. Samson, and P. Jonathan Patchett. "Protolith Relations of the Gravina Belt and Yukon-Tanana Terrane in Central Southeastern Alaska." Journal of Geology 100, no. 1 (January 1992): 107–23. http://dx.doi.org/10.1086/629574.
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Hansen, Vicki L., Matthew T. Heizler, and T. Mark Harrison. "Mesozoic thermal evolution of the Yukon-Tanana Composite Terrane: New evidence from40Ar/39Ar data." Tectonics 10, no. 1 (February 1991): 51–76. http://dx.doi.org/10.1029/90tc01930.
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de Keijzer, Martin, Paul F. Williams, and Richard L. Brown. "Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America." Canadian Journal of Earth Sciences 36, no. 3 (March 25, 1999): 479–94. http://dx.doi.org/10.1139/e98-096.
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The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.
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Erdmer, Philippe. "Eclogitic rocks in the St. Cyr klippe, Yukon, and their tectonic significance." Canadian Journal of Earth Sciences 29, no. 6 (June 1, 1992): 1296–304. http://dx.doi.org/10.1139/e92-103.
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Until recently, the Nisutlin allochthonous assemblage, a part of the Yukon–Tanana composite terrane interpreted as trench mélange from a late Paleozoic – Mesozoic arc system, was the only tectonic assemblage known to include subducted material in the northern Cordillera. The discovery of eclogitic rocks in two parts of a klippe of the Anvil allochthonous assemblage, which comprises mafic ophiolitic rocks, above the Cassiar terrane west of the Tintina fault confirms other evidence that subducted oceanic crust was also returned to the surface. The eclogitic rocks have been largely retrograded by postsubduction metamorphism. Their existence is interpreted as additional evidence of the link between nappes above the Cassiar terrane and their inferred root, the Teslin suture zone. The Nisutlin and Anvil allochthonous assemblages can now be interpreted, not simply as crustally metamorphosed assemblages with minor, structurally interleaved high-pressure components, but as deeply metamorphosed and intensely strained slices of continental and oceanic crust switched from subducting slab to overriding plate and returned to the surface during collision of the arc with the North American margin.
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Kapp, Paul A., and George E. Gehrels. "Detrital zircon constraints on the tectonic evolution of the Gravina belt, southeastern Alaska." Canadian Journal of Earth Sciences 35, no. 3 (March 1, 1998): 253–68. http://dx.doi.org/10.1139/e97-110.
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Upper Jurassic - Lower Cretaceous marine clastic strata and mafic to intermediate volcanic rocks of the Gravina belt are part of a complex suture zone separating the Alexander and Wrangellia terranes on the west from the Yukon-Tanana and Stikine terranes to the east. U-Pb ages have been determined on 118 single detrital zircon grains from Gravina strata in an effort to determine the tectonic setting of the Gravina belt and the paleoposition of outboard terranes prior to their Late Cretaceous juxtaposition against inboard terranes. Samples from five stratigraphic units yield ages of 105-120 (n = 5), 140-165 (n = 56), 310-380 (n = 17), 400-450 (n = 19), 520-560 (n = 5), 920-1310 (n = 5), and 1755-1955 Ma (n = 5). The 105-120 and 140-165 Ma grains were shed primarily from arc-related plutons that lie outboard of the Gravina belt. The lack of 120-140 Ma ages coincides with a lull in magmatism in the outboard arc and in the western United States, which suggests that Gravina strata accumulated during major changes in plate motion along the Cordilleran margin. The 400-560 Ma zircons were derived from rocks of the Alexander terrane which also lie to the west. In contrast, the 310-380 and >900 Ma grains were apparently shed from inboard regions. Likely sources include the Yukon-Tanana and Stikine terranes in the northern Cordillera and assemblages in the northern California region which contain igneous rocks and detrital zircons of the appropriate ages. Our data accordingly support models in which the Gravina basin formed in narrow rift or transtensional basins, whereas the outboard Alexander and Wrangellia terranes were located along the California - Oregon - Washington - British Columbia - Alaska margin. Our data are less supportive of models in which the Gravina strata and underlying Alexander and Wrangellia terranes were separated from western North America by a large ocean basin, or were located along the coast of Mexico.
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Lange, Ian M., Warren J. Nokleberg, Steven R. Newkirk, John N. Aleinikoff, Stanley E. Church, and H. Roy Krouse. "Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana Terrane, eastern Alaska Range, Alaska." Economic Geology 88, no. 2 (April 1, 1993): 344–76. http://dx.doi.org/10.2113/gsecongeo.88.2.344.
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Brown, E. H., G. E. Gehrels, and V. A. Valencia. "Chilliwack composite terrane in northwest Washington: Neoproterozoic–Silurian passive margin basement, Ordovician–Silurian arc inception." Canadian Journal of Earth Sciences 47, no. 10 (October 2010): 1347–66. http://dx.doi.org/10.1139/e10-047.
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The Chilliwack composite terrane in northwest Washington is part of an assemblage of mid-Paleozoic arc terranes extending from California to Alaska. Some terranes bear evidence of exotic origin, whereas others apparently formed proximal to western Laurentia, posing a complex problem in unraveling the Paleozoic accretionary history of the Cordillera. In our proposed broader definition, the Chilliwack composite terrane includes the volcanic and sedimentary East Sound and Chilliwack groups, and the plutonic and metamorphic Turtleback and Yellow Aster complexes. New zircon ages indicate that the plutonic and volcanic rocks are mutually related as parts of the same arc complex and that its inception was as old as Late Ordovician to Silurian, older than most other parts of the mid-Paleozoic terrane assemblage. Basement to the arc complex is a passive margin assemblage of metamorphosed quartzose sandstone and calc-silicate rock of the Yellow Aster Complex, bracketed in age by ca. 1000 Ma detrital zircons and 418 Ma intrusive rocks. This association of paragneiss basement and overlying and (or) intruding arc resembles that of older parts of the extensive Yukon–Tanana terrane in the northern Cordillera. Detrital zircon ages support a western Laurentian pericratonic origin for the paragneiss basement and the overlying arc. However, an early to mid-Paleozoic connection of this assemblage to the exotic outboard Alexander terrane is also indicated, based on (1) Mesoproterozoic and early Paleozoic detrital zircons in Devonian sedimentary rocks of the arc, and also in certain other pericratonic Devonian terranes and strata of the miogeocline; (2) Late Ordovician – Silurian igneous ages; and (3) an earliest Devonian or older metamorphic age of the basement paragneiss.
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Knight, E., D. A. Schneider, and J. Ryan. "Thermochronology of the Yukon-Tanana Terrane, West-Central Yukon: Evidence for Jurassic Extension and Exhumation in the Northern Canadian Cordillera." Journal of Geology 121, no. 4 (July 2013): 371–400. http://dx.doi.org/10.1086/670721.
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Creaser, Brian, and George Spence. "Crustal structure across the northern Cordillera, Yukon Territory, from seismic wide-angle studies: Omineca Belt to Intermontane Belt." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1187–203. http://dx.doi.org/10.1139/e04-093.
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A seismic refraction wide-angle reflection experiment shot in 1997 in the southern Yukon Territory crosses the Omineca Belt, which includes the strike-slip Tintina Fault, and terminates within the Intermontane Belt of the northern Canadian Cordillera. Lithospheric structure is interpreted from two-dimensional forward and inverse modelling of traveltimes, combined with forward-amplitude modelling, and from 2.5-dimensional modelling of gravity data. Beneath the Cassiar terrane and the North America miogeocline, average velocities in the upper 20 km of crust are < 6.1 km/s. In the west beneath the accreted Cache Creek, Slide Mountain, and YukonTanana terranes, average velocities increase to ∼6.3 km/s. In the upper crust, the velocity model beneath these terranes thus correlates with more mafic accreted material and not with a subsurface extension of the Cassiar terrane. The Tintina Fault is a crustal-scale structure across which significant structural differences occur. A mid-crustal reflector terminates to the east of the Tintina Fault. The crust immediately west of the fault is thicker (∼37 km) than the crust to the east (∼34 km); the thick crust may suggest movement along the fault from a region of thicker crust to the south. Lower crustal velocities range from 6.4 to 6.7 km/s, with the lowest velocities located 2550 km west of the Tintina Fault, coincident with the location of the thickest crust. A reflector at 28 km depth may correspond to the top of Proterozoic cratonic basement in the lowermost crust. Upper mantle velocities just below the Moho range from 7.8 to 7.9 km/s, consistent with the high heat flow in the region.
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Piercey, Stephen J., James K. Mortensen, and Robert A. Creaser. "Neodymium isotope geochemistry of felsic volcanic and intrusive rocks from the YukonTanana Terrane in the Finlayson Lake Region, Yukon, Canada." Canadian Journal of Earth Sciences 40, no. 1 (January 1, 2003): 77–97. http://dx.doi.org/10.1139/e02-094.
Full textAbstract:
DevonianMississippian felsic rocks from the Finlayson Lake region have variable geochemical and Nd isotopic characteristics that provide insights into the tectonic and metallogenic evolution of the YukonTanana terrane (YTT), and the northern Cordillera. Late Devonian (~365360 Ma) calc-alkaline and tholeiitic arc felsic rocks in the mafic-dominated Fire Lake unit yield εNd350 = 4.8 and +0.1, respectively, and have 1.491.94 Ga depleted mantle model ages (TDM). DevonianMississippian (~360356 Ma) felsic volcanic (Kudz Ze Kayah unit, Wolverine succession) and intrusive rocks (Grass Lakes suite) associated with volcanogenic massive sulphide (VMS) deposits have εNd350 = 7.8 to 9.5 with TDM = 1.592.25 Ga. A granitoid sample from the Early Mississippian (~350345 Ma) Simpson Range plutonic suite has εNd350 = 12.9 and TDM = 2.01 Ga, similar to previously reported values for this suite. The VMS-associated Grass Lakes suite of granitoids has higher high field strength element (HFSE) and rare-earth element (REE) contents, and higher Zr/Sc, Zr/TiO2, Nb/La, and Zr/La values relative to the Simpson Range plutonic suite; these geochemical features are similar to coeval VMS-associated felsic volcanic rocks in the Kudz Ze Kayah unit. The identification of similar HFSEREE-enriched felsic volcanic and subvolcanic intrusive rocks may aid in delineating prospective regions for VMS mineralization in the YTT and other continental-margin arc to back-arc environments. The geochemical and Nd isotopic data for these YTT felsic rocks suggest that they reflect episodic mid-Paleozoic arc (Fire Lake unit; Simpson Range plutonic suite) and back-arc magmatism (Kudz Ze Kudz unit; Wolverine succession) built upon a transitional basement with variable, but significant, influence from evolved (Proterozoic) crustal materials.
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BERMAN, R. G., J. J. RYAN, S. P. GORDEY, and M. VILLENEUVE. "Permian to Cretaceous polymetamorphic evolution of the Stewart River region, Yukon-Tanana terrane, Yukon, Canada:P-Tevolution linked within situSHRIMP monazite geochronology." Journal of Metamorphic Geology 25, no. 7 (September 2007): 803–27. http://dx.doi.org/10.1111/j.1525-1314.2007.00729.x.
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Erdmer, Philippe. "Blueschist and eclogite in mylonitic allochthons, Ross River and Watson Lake areas, southeastern Yukon." Canadian Journal of Earth Sciences 24, no. 7 (July 1, 1987): 1439–49. http://dx.doi.org/10.1139/e87-136.
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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.
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Simard, Renée-Luce, Jaroslav Dostal, and Maurice Colpron. "Rifting of a Mississippian continental arc system: Little Salmon formation, Yukon–Tanana terrane, northern Canadian Cordillera." Canadian Journal of Earth Sciences 44, no. 9 (September 1, 2007): 1267–89. http://dx.doi.org/10.1139/e07-022.
Full textAbstract:
The Yukon–Tanana terrane in the northern Canadian Cordillera records the development of a series of mid- to late Paleozoic arc systems, punctuated by intra-arc deformation, uplift, and episodic rifting coeval with back-arc extension, built upon a metasedimentary basement of northwestern Laurentian affinity. In central Yukon, the Little Kalzas formation records the development of one of these Mississippian continental arcs, whereas the Little Salmon formation records the development of an intra-arc rift basin within a continental arc. The Little Salmon formation lower succession comprises mainly volcaniclastic rocks derived from erosion of Early Mississippian and older units, including rocks of the Little Kalzas continental arc. Above a medial limestone member, the upper succession of the Little Salmon formation includes alkali basalt, breccia, and crystal and ash tuffs in the north and predominantly epiclastic rocks interbedded with crystal and ash tuffs in the south. The alkali basalts have the geochemical characteristics of ocean-island basalts and their positive ε Nd 340 (+7.3) and low 87Sr/86Sr values (0.705) suggest a primitive magma source with little or no involvement of continental crust. The transition between the northern and southern facies of the upper succession of the Little Salmon formation coincides with a northeast-trending synvolcanic fault inferred to have controlled alkali basalt eruptions and deposition of Mn-bearing exhalite in the north and basin plain sedimentation in the south. The environment of deposition of the Little Salmon formation resembles that of the modern Sumisu rift in the Izu–Bonin–Mariana arc system or the early stages of development of the Japan island-arc system.
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Morris, George A., and Robert A. Creaser. "Correlation of mid-Cretaceous granites with source terranes in the northern Canadian CordilleraLithoprobe Publication 1475." Canadian Journal of Earth Sciences 45, no. 3 (March 2008): 389–403. http://dx.doi.org/10.1139/e08-002.
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This study presents a broad geochemical and isotopic synthesis of mid-Cretaceous granites in the southern Yukon as well as a comparative data set for granites sourced from, and hosted by, accreted terranes in the west through to ancient cratonic rocks in the east. We present data from a traverse perpendicular to the strike of the northern Canadian Cordillera allowing comparison with the growing body of such data derived from the host terranes. Trace elements, specifically the “subduction signature,” allow the discrimination of oceanic verses continental crustal sources. Comparison of isotopic ratios of Sr and, particularly, Nd with published data further refine the correlation of granites with their source terranes. Granites are initially divided based upon their host morphogeological belts, however, our study indicates that the source terranes transcend these traditional boundaries. For Intermontane Belt hosted granites three distinct sources can be identified: an isotopically primitive (Sri, 0.7050; ϵNdT, 2.3 to –1.2), subduction-related source probably associated with the mid-Cretaceous continental margin; an isotopically primitive (Sri, 0.7032 to 0.7035; ϵNdT, 4.2 to 1.4), non-subduction-related source identified as the host Cache Creek terrane; and an isotopically slightly more evolved (Sri, 0.7094 to 0.7101; ϵNdT, 4.5 to –7.3), subduction-related source identified as the host Stikine terrane. Immediately east of the Teslin Tectonic Zone (TTZ), pericratonic Omineca granites (Sri, 0.7032 to 0.7076; ϵNdT, 2.0 to –5.4) do not correlate with their host terranes, but instead show marked similarities with granites immediately to the west of the TTZ suggesting that the same, or similar crustal sources extend further east in the subsurface than previously thought. In the eastern pericratonic Omineca Belt, there is a substantial jump to more evolved isotopic values (Sri, 0.7172 to 0.7354; ϵNdT, –16.6 to –21.7) for granites that extend to the most easterly exposed plutons of the cratonic Omineca Belt. These more isotopically evolved granites correlate with isotopic values for the pericratonic Yukon–Tanana and Cassiar terranes, as well as cratonic North America.
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Monger, Jim W. H. "Logan Medallist 1. Seeking the Suture: The Coast-Cascade Conundrum." Geoscience Canada 41, no. 4 (December 3, 2014): 379. http://dx.doi.org/10.12789/geocanj.2014.41.058.
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The boundary between rocks assigned to the Intermontane superterrane in the interior of the Canadian Cordillera and those of the Insular superterrane in the westernmost Cordillera of British Columbia and southeastern Alaska lies within/along the Coast Mountains, in which is exposed the core of an orogen that emerged as a discrete tectonic entity between 105 and 45 million years ago. Evidence from the Coast Mountains and flanking areas indicates that parts of the Intermontane superterrane (in Stikinia and Yukon-Tanana terranes) were near those of the Insular superterrane (Wrangellia and Alexander terranes) by the Early Jurassic (~180 Ma). This timing, as well as paleobiogeographic and paleomagnetic considerations, appears to discount a recent hypothesis that proposes westward-dipping subduction beneath an intra-oceanic arc on Insular superterrane resulted in arc-continent collision and inaugurated Cordilleran orogenesis in the Late Jurassic (~146 Ma). The hypothesis also relates the subducted ocean that had separated the superterranes to a massive, faster-than-average-velocity seismic anomaly in the lower mantle below the eastern seaboard of North America. To create such an anomaly, subduction of the floor of a large ocean was needed. The only surface record of such an ocean in the interior of the Canadian Cordillera is the Cache Creek terrane, which lies within the Intermontane superterrane but is no younger than Middle Jurassic (~174 Ma). This terrane, together with the probably related Bridge River terrane in the southeastern Coast Mountains, which is as young as latest Middle Jurassic (164 Ma) and possibly as young as earliest Cretaceous (≥ 130 Ma), appear to be the only candidates in Canada for the possible surface record of the seismic anomaly. SOMMAIRELa limite entre les roches assignées au Superterrane d’intermont de l’intérieur des Cordillères canadiennes et celles du Superterrane insulaire dans la portion la plus à l’ouest de la Cordillère de Colombie-Britannique et du sud-est de l’Alaska se trouvent dans et au long de la Chaîne côtière, au sein de laquelle affleure le noyau d’un orogène qui est apparu comme entité tectonique distincte entre 105 et 45 millions d’années. Des indices de la Chaîne côtière et des régions environnantes montrent que des portions du Superterrane d’intermont (dans les terranes de Stikinia et de Yukon-Tanana) se trouvaient alors près de celles du Superterrane insulaire (terranes de Wrangellia et d’Alexander) au début du Jurassique (~180 Ma). Cette chronologie, ajoutée à certains facteurs paléobiogéographiques et paléomagnétiques semblent discréditer une hypothèse récente voulant qu’une subduction à pendage ouest sous un arc intra-océanique sur le Superterrane insulaire résultait d’une collision entre un arc et le continent, initiant ainsi l’orogénèse de la Cordillère à la fin du Jurassique (~146 Ma). Cette hypothèse relie aussi l’océan subduit qui séparait les superterranes à une anomalie de vitesse sismique plus rapide que la normale dans le manteau inférieur sous le littoral maritime oriental de l’Amérique du Nord. Pour créer une telle anomalie, la subduction du plancher d’un grand océan était nécessaire. La seule indication de surface de l’existence d’un tel océan à l’intérieur de la Cordillère canadienne est le terrane de Cache Creek qui, bien qu’il se trouve dans le Superterrane d’intermont, est plus ancien que le Jurassique moyen (~174 Ma). Ce terrane, avec son équivalent probable de Bridge River dans le sud-est de la Chaîne côtière, qui est aussi jeune que la fin du Jurassique (164 Ma) et peut-être aussi jeune que le début du Crétacé (≥ 130 Ma), semblent être les seuls candidats au Canada offrant des vestiges en surface de cette anomalie sismique.
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Symons, D. T. A., and P. J. A. McCausland. "Paleomagnetism of the Fort Knox Stock, Alaska, and rotation of the Yukon–Tanana terrane after 92.5 Ma." Tectonophysics 419, no. 1-4 (June 2006): 13–26. http://dx.doi.org/10.1016/j.tecto.2006.04.001.
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Pavlis, Terry L., Virginia B. Sisson, Helen L. Foster, Warren J. Nokleberg, and George Plafker. "Mid-Cretaceous extensional tectonics of the Yukon-Tanana Terrane, Trans-Alaska Crustal Transect (TACT), east-central Alaska." Tectonics 12, no. 1 (February 1993): 103–22. http://dx.doi.org/10.1029/92tc00860.
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