Late Triassic to Jurassic Magmatic and Tectonic Evolution of the Intermontane Terranes in Yukon, Northern Canadian Cordillera: Transition From Arc to Syn-Collisional Magmatism and Post-Collisional Lithospheric Delamination

End-on arc collision and onset of the northern Cordilleran orogen is recorded in Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon, and in development of the synorogenic Whitehorse trough (WT). A synthesis of the extensive data set for these plutons supports interpretation of the magmatic and tectonic evolution of the northern Intermontane terranes. Late Triassic juvenile plutons that locally intrude the Yukon-Tanana terrane represent the northern extension of arc magmatism within Stikinia. Early Jurassic plutons that intrude Stikinia and Yukon-Tanana terranes were emplaced during crustal thickening (200–195 Ma) and subsequent exhumation (190–178 Ma). The syn-collisional magmatism migrated to the south and shows increasing crustal contributions with time. This style of magmatism in Yukon contrasts with coeval, juvenile arc magmatism in British Columbia (Hazelton Group), that records southward arc migration in the Early Jurassic. Exhumation and subsidence of the WT in the north were probably linked to the retreating Hazelton arc by a sinistral transform. East of WT, Early Jurassic plutons intruded into Yukon-Tanana record continued arc magmatism in Quesnellia. Middle Jurassic plutons were intruded after final enclosure of the Cache Creek terrane and imbrication of the Intermontane terranes. The post-collisional plutons have juvenile isotopic compositions that, together with stratigraphic evidence of surface uplift, are interpreted to record asthenospheric upwelling and lithospheric delamination. A revised tectonic model proposes that entrapment of the Cache Creek terrane was the result of Hazelton slab rollback and development of a sinistral transform fault system linked to the collision zone to the north

Early Ordovician Seamounts Preserved in the Canadian Cordillera: Implications for the Rift History of Western Laurentia

The breakup of the supercontinent Rodinia and development of the western Laurentian rifted margin are in part recorded by Neoproterozoic to mid-Paleozoic igneous and sedimentary rock successions in the Canadian Cordillera. New bedrock mapping and volcanic facies analysis of Early Ordovician mafic rocks assigned to the Menzie Creek Formation in central Yukon allow reconstruction of the depositional environment during the volcanic eruptions, whole-rock geochemical data constrain the melting depth and crust-mantle source regions of the igneous rocks within the study area, and zircon U-Pb age studies provide determination of the precise timing of submarine eruptions. Menzie Creek Formation volcanic rocks are interlayered with continental slope strata and show lithofacies consistent with those of modern seamount systems. Representative seamount facies contain several kilometers of hyaloclastite breccia and pillow basalt with rare sedimentary rocks. Menzie Creek Formation seamounts form a linear array parallel to the Twopete fault, an ancient extensional or strike-slip fault that localized magmatism along the nascent western Laurentian margin. Zircon grains from two volcanic successions yielded high-precision chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) dates of ca. 484 Ma (Tremadocian), which are interpreted as the age of eruption. Menzie Creek Formation rocks are alkali basalt and have oceanic-island basalt–like geochemical compositions. The whole-rock trace element and Nd-Hf isotope compositions are consistent with the partial melting of subcontinental lithospheric mantle at ~75–100 km depth. Post-rift, Early Ordovician seamounts in central Yukon record punctuated eruptive activity along a rift-related fault, the separation of a continental fragment from western Laurentia, or the oblique post-breakup kinematics from the counterclockwise rotation of Laurentia that facilitated local extension in the passive margin

A Viable Hypomorphic Allele of the Essential IMP3 Gene Reveals Novel Protein Functions in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the essential IMP3 gene encodes a component of the SSU processome, a large ribonucleoprotein complex required for processing of small ribosomal subunit RNA precursors. Mutation of the IMP3 termination codon to a sense codon resulted in a viable mutant allele producing a C-terminal elongated form of the Imp3 protein. A strain expressing the mutant allele displayed ribosome biogenesis defects equivalent to IMP3 depletion. This hypomorphic allele represented a unique opportunity to investigate and better understand the Imp3p functions. We demonstrated that the +1 frameshifting was increased in the mutant strain. Further characterizations revealed involvement of the Imp3 protein in DNA repair and telomere length control, pointing to a functional relationship between both pathways and ribosome biogenesis

Provenance and paleotectonic setting of North American Triassic strata in Yukon : the sedimentary record of pericratonic terrane accretion in the northern Canadian Cordillera

Detrital mineral geochronology, trace element and Nd isotope geochemistry, and field studies provide constraints for the source and paleotectonic setting of Late Devonian to Late Triassic North American strata in the northern Cordillera. Late Devonian-Early Mississippian clastic wedge deposits in northern Yukon and Northwest Territories record the influx of northerly derived sediment from the Innuitian orogenic belt. Isotopic data suggest that Innuitian clastic material was consistently recycled into post-Late Devonian Cordilleran margin strata. Early to Late Triassic sedimentation in Yukon was related to Late Permian-Early Triassic collision of the pericratonic Yukon-Tanana terrane (YTT) with western North America. Permo-Triassic closure of a marginal back-arc basin, whose remnants comprise the Slide Mountain terrane (SMT), juxtaposed YTT against the ancestral North American margin. The age and nature of this collision is analogous to that of the Sonoman orogeny in the southwestern United States and argues for accretionary tectonism along much of the Cordilleran margin during final construction of the Pangean supercontinent. Three stages of basin evolution following Late Permian-Early Triassic tectonism are now recognized in the northern Cordillera: (1) Early(?) to Middle Triassic SMT-YTT overlap assemblage- Early(?) to Middle Triassic coarse sandstone and conglomerate underlain by SMT in southeastern Yukon have detrital mineral ages which suggest that these strata represent westerly derived, first-cycle deposits shed from YTT following collision. (2) Early(?) to Middle Triassic peripheral foreland basin - Ladinian (Middle Triassic) strata in southeastern Yukon contain detrital mineral ages which document the first known occurrences of sediment derived from allochthonous terranes to the west deposited on North America. These data call for pre-Ladinian peripheral foreland basin development along the former Cordilleran margin. This depocentre is now largely buried under younger Mesozoic allochthons; however, Early(?) to Middle Triassic rocks that comprise the YTT-SMT overlap may represent correlatives to these Ladinian strata. (3) Middle to Late Triassic overlap assemblage – Tectonic quiescence in Middle to Late Triassic time led to development of an overlap assemblage linking the YTT, SMT, and ancestral North American margin. These units comprise a geodynamic linkage between outboard pericratonic terranes and the North American plate.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

The Great Preglacial “Bell River” of North America: Detrital Zircon Evidence for Oligocene–Miocene Fluvial Connections Between the Colorado Plateau and Labrador Sea

The idea of a great pre-glacial river that drained much of North America into the Arctic waters of modern Canada was first suggested in 1895 by Robert A. Bell. In the 1970s, petroleum exploration in Hudson Strait and the Labrador Sea located the massive, submerged delta of what is now known as the Bell River. Reconstructions suggest that three main branches of the Bell River joined up near modern Hudson Bay. The eastern branch largely drained the Canadian Shield, but the central and western branches had headwaters in the Cordilleran orogenic belt and its foreland in the present-day U.S. and northwestern Canada, respectively.We present new detrital zircon U–Pb data from Lower Oligocene and Lower Miocene sand from an exploration well in the Saglek delta of the northern Labrador Sea. In conjunction with other detrital zircon results from the Labrador Sea (and elsewhere) these data record the configuration and history of this continental-scale drainage basin in more detail. Mesozoic and younger detrital zircon grains (< 250 Ma) are subordinate to Precambrian age groupings, but Cenozoic populations become more abundant during the Oligocene, suggesting that the basin had expanded into areas now occupied by the Colorado Plateau and the Basin-and-Range Province. Proterozoic and Phanerozoic detrital zircon grain populations in Saglek delta sediments are similar to those of the Pliocene Colorado River. The results support an earlier idea that initial incision of the Grand Canyon and denudation of the Colorado Plateau were associated with a north-flowing paleo-river that fed into the Bell River basin. This contribution continued until the Pliocene capture of this ancestral river by the Gulf of California basin, after which the excavation of the modern Grand Canyon was completed. The Bell River drainage basin was later blocked by the expansion of Pleistocene ice sheets.L'idée d'un grand fleuve préglaciaire qui drainait une grande partie de l'Amérique du Nord vers les eaux arctiques du Canada moderne a été suggérée pour la première fois en 1895 par Robert A. Bell. Dans les années 1970, l'exploration pétrolière dans le détroit d'Hudson et la mer du Labrador a localisé l'immense delta submergé de ce qui est maintenant connu sous le nom de rivière Bell. Les reconstructions suggèrent que trois bras principaux de la rivière Bell se rejoignent près de la baie d'Hudson moderne. Le bras oriental drainait en grande partie le Bouclier canadien, tandis que le bras central et le bras occidental avaient des sources dans la ceinture orogénique de la Cordillère et son avant-pays dans les États-Unis et le nord-ouest du Canada actuels, respectivement.Nous présentons de nouvelles données U–Pb sur zircons détritiques issus de sable de l'Oligocène inférieur et du Miocène inférieur provenant d'un puits d'exploration dans le delta de Saglek, dans le nord de la mer du Labrador. En conjonction avec d'autres résultats de zircons détritiques de la mer du Labrador (et d'ailleurs), ces données enregistrent la configuration et l'histoire de ce bassin versant à l'échelle continentale avec plus de détail. Les grains de zircons détritiques mésozoïques et plus jeunes (< 250 Ma) sont subordonnés aux groupes d'âge précambriens, mais les populations cénozoïques deviennent plus abondantes au cours de l'Oligocène, ce qui suggère que le bassin s'est étendu dans des zones maintenant occupées par le plateau du Colorado et la province de Basin-and Range. Les populations de grains de zircons détritiques du Protérozoïque et du Phanérozoïque dans les sédiments du delta de Saglek sont similaires à celles du fleuve Colorado du Pliocène. Les résultats corroborent une idée antérieure selon laquelle l'incision initiale du Grand Canyon et la dénudation du plateau du Colorado étaient associées à une paléo-rivière coulant vers le nord qui alimentait le bassin de la rivière Bell. Cette contribution s'est poursuivie jusqu'à la capture de cette rivière ancestrale par le bassin du golfe de Californie au Pliocène, après quoi l'excavation du Grand Canyon moderne a été achevée. Le bassin versant de la rivière Bell a ensuite été bloqué par l'expansion des calottes glaciaires du Pléistocène

The Great Preglacial “Bell River” of North America: Detrital Zircon Evidence for Oligocene–Miocene Fluvial Connections Between the Colorado Plateau and Labrador Sea

The idea of a great pre-glacial river that drained much of North America into the Arctic waters of modern Canada was first suggested in 1895 by Robert A. Bell. In the 1970s, petroleum exploration in Hudson Strait and the Labrador Sea located the massive, submerged delta of what is now known as the Bell River. Reconstructions suggest that three main branches of the Bell River joined up near modern Hudson Bay. The eastern branch largely drained the Canadian Shield, but the central and western branches had headwaters in the Cordilleran orogenic belt and its foreland in the present-day U.S. and northwestern Canada, respectively.   We present new detrital zircon U–Pb data from Lower Oligocene and Lower Miocene sand from an exploration well in the Saglek delta of the northern Labrador Sea. In conjunction with other detrital zircon results from the Labrador Sea (and elsewhere) these data record the configuration and history of this continental-scale drainage basin in more detail. Mesozoic and younger detrital zircon grains (&lt; 250 Ma) are subordinate to Precambrian age groupings, but Cenozoic populations become more abundant during the Oligocene, suggesting that the basin had expanded into areas now occupied by the Colorado Plateau and the Basin-and-Range Province. Proterozoic and Phanerozoic detrital zircon grain populations in Saglek delta sediments are similar to those of the Pliocene Colorado River. The results support an earlier idea that initial incision of the Grand Canyon and denudation of the Colorado Plateau were associated with a north-flowing paleo-river that fed into the Bell River basin. This contribution continued until the Pliocene capture of this ancestral river by the Gulf of California basin, after which the excavation of the modern Grand Canyon was completed. The Bell River drainage basin was later blocked by the expansion of Pleistocene ice sheets.L'idée d'un grand fleuve préglaciaire qui drainait une grande partie de l'Amérique du Nord vers les eaux arctiques du Canada moderne a été suggérée pour la première fois en 1895 par Robert A. Bell. Dans les années 1970, l'exploration pétrolière dans le détroit d'Hudson et la mer du Labrador a localisé l'immense delta submergé de ce qui est maintenant connu sous le nom de rivière Bell. Les reconstructions suggèrent que trois bras principaux de la rivière Bell se rejoignent près de la baie d'Hudson moderne. Le bras oriental drainait en grande partie le Bouclier canadien, tandis que le bras central et le bras occidental avaient des sources dans la ceinture orogénique de la Cordillère et son avant-pays dans les États-Unis et le nord-ouest du Canada actuels, respectivement.  Nous présentons de nouvelles données U–Pb sur zircons détritiques issus de sable de l'Oligocène inférieur et du Miocène inférieur provenant d'un puits d'exploration dans le delta de Saglek, dans le nord de la mer du Labrador. En conjonction avec d'autres résultats de zircons détritiques de la mer du Labrador (et d'ailleurs), ces données enregistrent la configuration et l'histoire de ce bassin versant à l'échelle continentale avec plus de détail. Les grains de zircons détritiques mésozoïques et plus jeunes (&lt; 250 Ma) sont subordonnés aux groupes d'âge précambriens, mais les populations cénozoïques deviennent plus abondantes au cours de l'Oligocène, ce qui suggère que le bassin s'est étendu dans des zones maintenant occupées par le plateau du Colorado et la province de Basin-and Range. Les populations de grains de zircons détritiques du Protérozoïque et du Phanérozoïque dans les sédiments du delta de Saglek sont similaires à celles du fleuve Colorado du Pliocène. Les résultats corroborent une idée antérieure selon laquelle l'incision initiale du Grand Canyon et la dénudation du plateau du Colorado étaient associées à une paléo-rivière coulant vers le nord qui alimentait le bassin de la rivière Bell. Cette contribution s'est poursuivie jusqu'à la capture de cette rivière ancestrale par le bassin du golfe de Californie au Pliocène, après quoi l'excavation du Grand Canyon moderne a été achevée. Le bassin versant de la rivière Bell a ensuite été bloqué par l'expansion des calottes glaciaires du Pléistocène

Reliability and longitudinal change of detrital-zircon age spectra in the Snake River system, Idaho and Wyoming: An example of reproducing the bumpy barcode

Detrital-zircon age-spectra effectively define provenance in Holocene and Neogene fluvial sands from the Snake River system of the northern Rockies, U.S.A. SHRIMP U-Pb dates have been measured for forty-six samples (about 2700 zircon grains) of fluvial and aeolian sediment. The detrital-zircon age distributions are repeatable and demonstrate predictable longitudinal variation. By lumping multiple samples to attain populations of several hundred grains, we recognize distinctive, provenance-defining zircon-age distributions or "barcodes," for fluvial sedimentary systems of several scales, within the upper and middle Snake River system. Our detrital-zircon studies effectively define the geochronology of the northern Rocky Mountains. The composite detrital-zircon grain distribution of the middle Snake River consists of major populations of Neogene, Eocene, and Cretaceous magmatic grains plus intermediate and small grain populations of multiply recycled Grenville (∼950 to 1300 Ma) grains and Yavapai-Mazatzal province grains (∼1600 to 1800 Ma) recycled through the upper Belt Supergroup and Cretaceous sandstones. A wide range of older Paleoproterozoic and Archean grains are also present. The best-case scenario for using detrital-zircon populations to isolate provenance is when there is a point-source pluton with known age, that is only found in one location or drainage. We find three such zircon age-populations in fluvial sediments downstream from the point-source plutons: Ordovician in the southern Beaverhead Mountains, Jurassic in northern Nevada, and Oligocene in the Albion Mountains core complex of southern Idaho. Large detrital-zircon age-populations derived from regionally well-defined, magmatic or recycled sedimentary, sources also serve to delimit the provenance of Neogene fluvial systems. In the Snake River system, defining populations include those derived from Cretaceous Atlanta lobe of the Idaho batholith (80 to 100 Ma), Eocene Challis Volcanic Group and associated plutons (∼45 to 52 Ma), and Neogene rhyolitic Yellowstone-Snake River Plain volcanics (∼0 to 17 Ma). For first-order drainage basins containing these zircon-rich source terranes, or containing a point-source pluton, a 60-grain random sample is sufficient to define the dominant provenance. The most difficult age-distributions to analyze are those that contain multiple small zircon age-populations and no defining large populations. Examples of these include streams draining the Proterozoic and Paleozoic Cordilleran miogeocline in eastern Idaho and Pleistocene loess on the Snake River Plain. For such systems, large sample bases of hundreds of grains, plus the use of statistical methods, may be necessary to distinguish detrital-zircon age-spectra

Miocene to Holocene landscape evolution of the western Snake River Plain region, Idaho: Using the SHRIMP detrital zircon provenance record to track eastward migration of the Yellowstone hotspot

We report new U-Pb detrital zircon sensitive high-resolution ion microprobe (SHRIMP) age data (702 grains) from 13 samples collected from Miocene to Holocene sedimentary deposits in the western Snake River Plain region. These samples effectively show that modern stream sediments of the Snake River system reliably and repeatedly record the detrital zircon age populations that are present as sources in their drainage basins across the Cordilleran thrust belt and Basin and Range Province. We use this framework and the provenance of Neogene sedimentary rocks in the region to test the effect of the migrating Yellowstone hotspot on regional drainage patterns in southern Idaho since the middle Miocene. Our results indicate that Neogene paleodrainages were first directed radially away from the tumescent Yellowstone highland, then subsequently reversed their flow toward the subsiding Snake River Plain basin. This occurred in east-progressing time-constrained intervals starting at 16 Ma. In northern Nevada, the drainage divide is represented by a northeast-trending, southeast-migrating crest of high topography. Specifically, middle to late Miocene (16-10 Ma) sedimentary deposits of the western Snake River Plain and Oregon-Idaho graben contain early to middle Eocene (52-42 Ma) detrital zircon populations sourced in Challis magmatic rocks north of the Snake River Plain. Middle Jurassic (160 Ma) and middle to late Eocene (42-35 Ma) detrital zircons, sourced from rocks in northern Nevada, are not present. Late Eocene detrital zircons from Nevada are present in two younger than 7 Ma sedimentary units of the Idaho Group along the Oregon-Idaho border. This indicates that by the late Miocene, southeastward headward erosion of the paleo-Owyhee River into the Owyhee Plateau had captured drainage from north-central Nevada and directed it northwestward toward the subsiding western Snake River Plain. The modern Owyhee Plateau is still a topographic high, in contrast to the modern Snake River Plain, suggesting that lowering of the regional Snake River Plain base level, rather than crustal subsidence, drove stream capture. By the late Pliocene (3 Ma), Middle Jurassic detrital zircons are recorded in the Glenns Ferry Formation and Tuana Gravel of the central Snake River Plain, suggesting that surface subsidence reversed the flow direction of paleo-Salmon Falls Creek from southward into Nevada to northward toward Idaho. Miocene strata of the western Snake River Plain lack recycled Proterozoic detrital zircons that are ubiquitous in sedimentary rocks of the central and southeast Idaho thrust belts. Such detrital zircons appear on the central and western Snake River Plain in early Pliocene to Holocene (4-0 Ma) deposits. This records capture of drainage from the eastern Snake River Plain. The Yellowstone hotspot controlled the east-migrating continental divide, in the wake of which formed the western-draining, and progressively eastward-collecting, Snake River system

Silurian flysch successions of Ellesmere Island, Arctic Canada, and their significance to northern Caledonian palaeogeography and tectonics

<p>Detrital zircon provenance studies of Silurian flysch units that underlie the Hazen and Clements Markham fold belts of Ellesmere Island, Arctic Canada, were conducted to evaluate models for northern Caledonian palaeogeography and tectonics. Llandovery flysch was deposited along an active plate margin and yields detrital zircons that require northern derivation from the adjacent Pearya terrane. If Pearya originated near Svalbard and NE Greenland, it was transported by strike-slip faults to Ellesmere Island by the Early Silurian. Wenlock to Ludlow turbidites yield Palaeozoic–Archaean detrital zircons with dominant age-groupings <em>c</em>. 650, 970, 1150, 1450 and 1650 Ma. These turbidite systems did not fill a flexural foreland basin in front of the East Greenland Caledonides, but rather an east–west-trending trough that was probably related to sinistral strike-slip faulting along the northern Laurentian margin. The data support provenance connections with the Svalbard Caledonides, especially Baltican-affinity rocks of SW Spitsbergen that were proximal to NE Greenland during the Baltica–Laurentia collision. Pridoli flysch has sources that include Pearya, the East Greenland Caledonides and the Canadian Shield. Devonian–Carboniferous molasse in Arctic Canada has analogous detrital zircon signatures, which implies recycling of Silurian flysch during mid-Palaeozoic (Ellesmerian) collisional tectonism or that some collisional blocks were of similar Baltican–Laurentian crustal affinities. </p