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The Fire Bay Formation of Trettin (1998), Clements Markham belt, Ellesmere Island, Canada, includes volcanic rocks described as Silurian in age based on Llandovery graptolites in adjacent clastic rocks. New field observations suggest the Llandovery fossils are from packages of the Silurian Danish River and/or Lands Lokk formations that are fault-bounded rather than stratigraphically tied to Ordovician sections that contain a 470.0 [+ or -] 0.2 Ma lithic tuf, volcaniclastic units with maximum depositional ages (MDAs) of 466 [+ or -] 2 and 462 [+ or -] 2 Ma based on detrital zircon, volcanic clasts with ages of 498 [+ or -] 6, 478 [+ or -] 4, and 477 [+ or -] 8 Ma, and Ordovician conodonts and graptolites of Darriwilian and Sandbian age, respectively. Since the Fire Bay Formation of Trettin (1998) lacks a type section and is fault-bounded with ambiguous age relationships, Ordovician volcanic units and fault-bounded clastic rocks correlated with the Hazen Formation are both included in the Fire Bay assemblage following the original interpretations of Trettin and Nowlan (1990). The Fire Bay assemblage records juvenile Ordovician arc magmatism proximal to the Pearya terrane. The adjacent Lands Lokk Formation yields bimodal age peaks at 440-430 and 465 Ma, MDA of 424 [+ or -] 3 Ma, and [epsilon][Hf.sub.(t)] values of -5 to +10. The signature matches Ordovician Pearya units and Silurian circum-Arctic arc sources but there is no evidence for Silurian arc magmatism between the Pearya terrane and Laurentian margin, compatible with Pearya accretion during oblique Ordovician arc collision and Silurian sinistral translation along the northern Laurentian margin. Key words: U/Pb dating, Pearya terrane accretion, Ordovician arcs, biostratigraphy, detrital zircon, Ellesmere Island La Formation de Fire Bay deTrettin (1998), de la ceinture de Clements Markham de l'île d'Ellesmere (Canada), comprend des roches volcaniques décrites comme étant d'âge silurien à la lumière de graptolites llandovériens dans des roches clastiques attenantes. De nouvelles observations de terrain portent à croire que les fossiles llandovériens proviennent de paquets des formations siluriennes de Danish River ou de Lands Lokk qui sont bordés par des failles plutôt que d'être reliés stratigraphiquement à des séquences ordoviciennes qui contiennent un tuf lithique de 470,0 [+ ou -] 0,2 Ma, des unités volcanoclastiques d'âge de dépôt maximum (ADM) de 466 [+ ou -] 2 Ma et 462 [+ ou -] 2 Ma à la lumière de zircons détritiques, des clastes volcaniques ayant produit des âges de 498 [+ ou -] 6 Ma, 478 [+ ou -] 4 Ma et 477 [+ ou -] 8 Ma et des conodontes et graptolites ordoviciens d'âge darriwillien et sandbien, respectivement. Comme la Formation de Fire Bay de Trettin (1998) n'a pas de coupe type et est bordée par des failles dont les relations d'âge sont ambiguës, des unités volcaniques ordoviciennes et des roches clastiques bordées par des failles corrélées à la Formation de Hazen sont incluses dans l'assemblage de Fire Bay, suivant les interprétations initiales de Trettin et Nowlan (1990). L'assemblage de Fire Bay témoigne d'un magmatisme d'arc ordovicien proximal par rapport au terrane de Pearya. La Formation de Lands Lokk attenante donne des pics d'âges bimodaux à 440-430 Ma et 465 Ma, un ADM de 424 [+ ou -] 3 Ma et des valeurs de [epsilon][Hf.sub.(t)] de -5 à +10. Cette signature concorde avec des unités ordoviciennes de Pearya et des sources d'arc circumarctique siluriennes, mais il n'y a aucun indice de magmatisme d'arc silurien entre le terrane de Pearya et la marge laurentienne, ce qui est compatible avec l'accrétion de Pearya durant la collision oblique d'un arc ordovicien et une translation senestre silurienne le long de la marge septentrionale de la Laurentie. [Traduit par la Rédaction] Mots-clés : datation U/Pb, accrétion du terrane de Pearya, arcs ordoviciens, biostratigarphie, zircon détritique, île d'Ellesmere, Introduction The Pearya terrane on the northern margin of Laurentia plays a critical role in tectonic models for the Paleozoic evolution of the circum-Arctic region that advocates for large-scale transfer [...]

Enigmatic successions of deep-water strata referred to as the Nesmith beds and Grant Land Formation comprise the exposed base of the Franklinian passive margin sequence in northern Ellesmere Island, Nunavut. To test stratigraphic correlations with Ediacaran to Cambrian shallow-water strata of the Franklinian platform that are inferred by regional basin models, >500 detrital zircons from the Nesmith beds and Grant Land Formation were analyzed for sediment provenance analysis using laser ablation (LA-ICP-MS) and ion-microprobe (SIMS) methods. Samples of the Nesmith beds and Grant Land Formation are characterized by 1000-1300,1600-2000, and 2500-2800 Ma detrital zircon age distributions and indicate provenance from rock assemblages of the Laurentian craton. In combination with regional stratigraphic constraints, these data support an Ediacaran to Cambrian paleodrainage model that features the Nesmith beds and Grant Land Formation as the offshore marine parts of a north- to northeast-directed depositional network. Proposed stratigraphic correlations between the Nesmith beds and Ediacaran platformal units of northern Greenland are consistent with the new detrital zircon results. Cambrian stratigraphic correlations within northern Ellesmere Island are permissive, but require further investigation because the Grant Land Formation provenance signatures agree with a third-order sedimentary system that has been homogenized by longshore current or gravity-flow processes, whereas coeval shallow-water strata yield a restricted range of detrital zircon ages and imply sources from local drainage areas or underlying rock units. The detrital zircon signatures of the Franklinian passive margin resemble those for the Cordilleran and Appalachian passive margins of Laurentia, which demonstrates the widespread recycling of North American rock assemblages after late Neoproterozoic continental rifting and breakup of supercontinent Rodinia. Des suites non conventionnelles de strates d'eau profonde, connues sous le nom de lits Nesmith et Formation de Grant Land, comprennent la base affleurant de la sequence de bordure passive franklinienne dans le nord de l'lle d'Ellesmere, au Nunavut. Dans le but de verifier les correlations stratigraphiques avec des strates ediacariennes et cambriennes d'eau peu profonde de la plateforme franklinienne, inferees par une modelisation des bassins regionaux, plus de 500 zircons detritiques des lits Nesmith et de la Formation de Grant Land ont ete analyses pour la provenance des sediments; les methodes utilisees comprennent l'ablation laser-spectrometrie de masse a source a plasma inductif (LA-ICP-MS) et les microanalyses ioniques (SIMS). Des echantillons des lits Nesmith et de la Formation de Grant Land sont caracterises par des distributions d'age de zircons detritiques de 1000-1300,1600-2000 et 2500-2800 Ma; ils proviendraient d'assemblages de roches du craton laurentien. Combinees aux contraintes stratigraphiques regionales, ces donnees supportent un modele de paleodrainage, de l'Ediacarien au Cambrien, lequel montre les lits Nesmith et la Formation de Grand comme etant les parties marines au large d'un reseau de deposition, de direction nord a nord-est. Les correlations proposees entre les lits Nesmith et les unites ediacariennes de plateforme du nord du Groenland concordent avec les nouveaux resultats sur les zircons detritiques. Les correlations stratigraphiques cambriennes a l'interieur de l'lle d'Ellesmere sont facultatives, mais elles demandent plus d'etudes puisque les signatures de provenance de la Formation de Grant Land concordent avec un systeme sedimentaire de troisieme ordre qui a ete homogeneise par les courants littoraux ou les processus d'ecoulement gravitaire, alors que les strates contemporaines d'eau peu profonde ont donne une plage restreinte d'ages des zircons detritiques, impliquant une provenance de drainage local ou d'unites rocheuses sous-jacentes. Les signatures des zircons detritiques de la bordure passive franklinienne ressemblent a celles des bordures passives de la Cordillere et des Appalaches de la Laurentie, ce qui demontre le recyclage etendu des assemblages de roches de l'Amerique du Nord, apres la distension continentale au Neoproterozoique et le fractionnement du supercontinent Rodina. [Traduit par la Redaction], Introduction The Franklinian basin of the Canadian Arctic Islands and northern Greenland comprises an integral part of the Franklinian passive margin sequence that was deposited along the northern edge of [...]

Detrital zircon provenance investigations of mid-Paleozoic sandstone from the western Ellesmerian clastic wedge and Cordilleran miogeocline in northern Yukon and Northwest Territories, northwestern Canada, provide critical new data on the source of foreland basin sedimentation attributed to terrane accretion and plate convergence along the ancestral Arctic margin of North America. Late Devonian and early Mississippian clastic wedge strata yield 'exotic' ca. 360-390, 430-460, 530-680, and 1500-1600 Ma detrital zircon populations that are consistent with source rocks that originated near the Caledonian and Timanian orogenic belts. Specifically, the Pearya and Arctic Alaska-Chukotka terranes, the landmass of Crockerland, and Caledonian rocks in eastern Greenland are the inferred sources for exotic detrital zircons in clastic wedge strata. Progressive recycling of Ellesmerian foreland basin sediments into the continental margin environment along northwestern Laurentia is indicated by the presence of ca. 360-430 Ma and 1500-1600 Ma detritai zircons in post-tectonic, middle to late Mississippian miogeoclinal strata in Yukon. Provenance data from these Mississippian samples record a dramatic shift in the source of the Cordilleran miogeocline, since Caledonian and Baltican (Timanide) detritai zircon signatures are not recognized in preLate Devonian sedimentary rocks in western Canada. Devonian strata of the Alexander terrane and Yreka subterrane (eastern Klamath terrane) have Caledonian and Baltican detrital zircon age signatures similar to Ellesmerian clastic wedge sandstones, implying that several Cordilleran terranes originated in the paleo-Arctic realm. Speculative correlations suggest that the Arctic Alaska--Chukotka terrane was located to the west of Crockerland and the Canadian Arctic Islands in pre-Cretaceous time, prior to opening of the Amerasian basin. Rifting models for the western Arctic Ocean featuring counterclockwise rotation of the Arctic Alaska--Chukotka terrane away from the Canadian Arctic Islands may need reevaluation. doi:10.1130/B30120.1

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).sub.N] = ~8; Eu/Eu* = ~0.66), ζ[Nd.sub.(248Ma)] 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-Baltic an 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--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. De nouvelles donnees sur Page des mineraux detritiques et la geochimie de la roche entiere fournissent le premier cadre pour la composition et la source des strates du Trias d'Amerique du Nord dans la Cordillere canadienne septentrionale. Des strates du Trias contenant des conodontes out ete recueillies a cinq endroits du centre-ouest au sud-est du Yukon; elles contiennent des rapports d'elements traces [((La/Yb).sub.N] = ~8; Eu/Eu* = ~0,66), des valeurs de ζ[Nd.sub.(248 Ma)] de -9 a -10, et des ages de zircons detritiques (400-680, 980-1200, 1500-1650, 1800-2000 Ma) qui correspondent a ceux de roches de meme age dans les ties de l'Arctique canadien et du bassin sedimentaire de l'Ouest canadien en Colombie-Britannique et en Alberta. La plupart des zircons detritiques ont ete cannibalises de strates du coin de sediments clastiques ellesmeriens et de strates de la bordure laurentienne puis recycles dans des roches du Trias. Des zircons detritiques proeminents du PaleozoVque precoce et du NeoproteiozoVque pourraient a la limite provenir de roches allochtones d'affinite caledonienne-balte dans le nord de l'Amerique du Nord, telles que les terranes de Pearya et d'Alaska-Chukotka dans l'Arctique. line unite du Trias precoce dans Test du Yukon conlient de la muscovite detrilique dalanl d'environ 360 Ma et des echantillons de plusieurs localites comprennent des occurrences de grains uniques de zircon detritiques dalant du Mississippien. Les ages des mineraux detritiques datanl du Mississippien enregistrent probablement une source partielle de roches du PaleozoVque moyen des terranes allochtones de Slide Mountain et de Yukon-Tanana a la suite de leur mise en place au Permien tardif - Trias precoce dans la bordure de la Cordillere. Des evidences plus substantielles de sediments derives de terranes et deposes le long de la bordure nord-americaine peuvent etre miens identifies dans les strates du Trias qui affleurent a I'ouest (a l'exterieur) de nos sites d'echantillonnage, immediatement adjacentes aux terranes de Slide Mountain et de Yukon-Tanana. [Traduit par la Redaction], Introduction Triassic strata of the eastern Canadian Cordillera and adjacent autochthon are recognized as a variable sequence of c;ontinental margin rocks exposed from the Canadian Arctic Islands south to the [...]

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. Keywords: Snake River Plain, Yellowstone hotspot, Neogene, SHRIMP detrital zircon, Idaho, Nevada.

The juxtaposition of the composite Pearya terrane and the northern Laurentian margin at Ellesmere Island, Nunavut, Canada, has significant ramifications for the Paleozoic tectonic history of the circum-Arctic region. Published tectonic models rely upon interpretation of the subduction-related Kulutingwak Formation as an indicator of Ordovician and/or Silurian accretion (Trettin, 1998). New igneous and detrital zircon U-Pb and Lu-Hf isotopic data from 16 samples collected in the Yelverton Inlet–Kulutingwak Fiord region of northern Ellesmere Island suggest that the Kulutingwak Formation of Trettin (1998) contains structural blocks derived from both the Pearya terrane and Silurian strata associated with the ancestral Laurentian margin. Data from this study demonstrate a complex provenance history for rocks within the Petersen Bay, Kulutingwak Fiord, and Emma Fiord fault zones, with age probability peaks of ca. 470 Ma, 650 Ma, and 960–980 Ma that suggest affinity with the Pearya terrane, and age probability peaks of ca. 1800 Ma and 2700 Ma that indicate connections to the Laurentian margin. The combination of these signatures in Kulutingwak Formation rocks suggests that the Pearya terrane was proximal to the northern Laurentian margin by Late Ordovician time. Silurian and younger strike-slip displacement on the major fault zones resulted in the incorporation of blocks derived from the Pearya terrane basement and Silurian clastic rocks into the Kulutingwak Formation. Silurian displacement along these strike-slip faults, which are integral components of the Canadian Arctic transform system, is recorded by syndepositional deformation structures in the Danish River Formation and prevented the transition from soft to hard collision of the Pearya terrane. The two-stage model for the Pearya terrane—accretion followed by significant translation—provides a process for developing complex steep terrane boundaries with contentious displacement histories that are common in accretionary orogens [ABSTRACT FROM AUTHOR]

Pennsylvanian rocks of the northern U.S. Rocky Mountains are mature quartzose sandstones. This paper uses detrital zircon geochronology on seven samples from the Wood River Formation, Tensleep Sandstone, and Weber Sandstone to determine if these sandstones have a common provenance, representing eastern Laurentian and Appalachian sand reworked within shallow-marine and eolian environments from the Wyoming craton westward to the Pioneer thrust plate of south-central Idaho. Our work suggests that this continental sand blanket was mixed with local sources on the south in the Yavapai-Mazatzal provinces of the Ancestral Rocky Mountains and in samples from the western Cordilleran thrust belt in south-central Idaho. In total, these Pennsylvanian sandstones contain a broad spectrum of detrital zircon U-Pb ages including, from old to young: A) minor Archean-age (3300-2550 Ma) populations; B) Paleoproterozoic (2000-1600 Ma), Mesoproterozoic (1470-1350 Ma), and major "Grenvillian" (1250-950 Ma) populations; and C) Cryogenian- to Ediacaran-age (665-565 Ma) and minor Paleozoic (495-410 Ma) populations. We interpret these detrital zircon ages to represent provenance mainly from the Appalachian mountain belt of eastern North America; however, central Appalachian versus northern Appalachian derivation is not clearly distinguished. The Weber Sandstone from the north flank of the Uinta Mountains in northeast Utah contains a strong 1700-1640 Ma age population derived from the Yavapai-Mazatzal provinces in the adjacent Ancestral Rocky Mountains. The shallow-marine Hailey Member of the Wood River Formation in south-central Idaho yields a population of >1800 Ma detrital zircons reworked from the uplifted Mississippian Copper Basin Formation. Both the Hailey and Wilson Creek Members of the Wood River Formation contain unique 640-490 Ma grains that may represent provenance from the Big Creek-Beaverhead plutonic belt of east-central Idaho and/or eastern Klamath terrane in the Klamath Mountains of northwest California and southwest Oregon. These new data support published models for Pennsylvanian-Permian transport of siliciclastic sediment with sources mainly from the North American craton, north of the Ancestral Rocky Mountains, into continental margin basins. [ABSTRACT FROM AUTHOR]