Lemieux et al 2011 devonian d zr peel
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Detrital Zircon geochronology of the devonian clastic wedge of northern Canada.

Detrital Zircon geochronology of the devonian clastic wedge of northern Canada.

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  • 1. 515 Detrital zircon geochronology and provenance of Devono-Mississippian strata in the northern Canadian Cordilleran miogeocline1,2 Yvon Lemieux, Thomas Hadlari, and Antonio Simonetti Abstract: U–Pb ages have been determined on detrital zircons from the Upper Devonian Imperial Formation and Upper Devonian – Lower Carboniferous Tuttle Formation of the northern Canadian Cordilleran miogeocline using laser ablation – multicollector – inductively coupled plasma – mass spectrometry. The results provide insights into mid-Paleozoic sediment dispersal in, and paleogeography of, the northern Canadian Cordillera. The Imperial Formation yielded a wide range of de- trital zircon dates; one sample yielded dominant peaks at 1130, 1660, and 1860 Ma, with smaller mid-Paleozoic (*430 Ma), Neoproterozoic, and Archean populations. The easternmost Imperial Formation sample yielded predominantly late Neoproterozoic – Cambrian zircons between 500 and 700 Ma, with lesser Mesoproterozoic and older populations. The age spectra suggest that the samples were largely derived from an extensive region of northwestern Laurentia, including the Canadian Shield, igneous and sedimentary provinces of Canada’s Arctic Islands, and possibly the northern Yukon. The pres- ence of late Neoproterozoic – Cambrian zircon, absent from the Laurentian magmatic record, indicate that a number of grains were likely derived from an exotic source region, possibly including Baltica, Siberia, or Arctic Alaska – Chukotka. In contrast, zircon grains from the Tuttle Formation show a well-defined middle Paleoproterozoic population with dominant relative probability peaks between 1850 and 1950 Ma. Additional populations in the Tuttle Formation are mid-Paleozoic (*430 Ma), Mesoproterozoic (1000–1600 Ma), and earlier Paleoproterozoic and Archean ages (>2000 Ma). These data lend support to the hypothesis that the influx of sediments of northerly derivation that supplied the northern miogeocline in Late Devonian time underwent an abrupt shift to a source of predominantly Laurentian affinity by the Mississippian. ´ ´ ˆ ´´ ´ ´ ´ ` Resume : Des ages U–Pb ont ete determines par spectrometrie de masse a plasma inductif avec multicollecteur apres abla-` ´ ´ ´ tion au laser sur des zircons detritiques provenant de la Formation Imperial (Devonien superieur) et de la Formation Tuttle ´ ` ´ ´ ` ´ (Devonien – Carbonifere inferieur) du miogeoclinal de la Cordillere canadienne septentrionale. Les resultats fournissent des ´ ´ ¨ ´ ´ ` apercus de la dispersion des sediments au Paleozoıque moyen et de la paleogeographie de la Cordillere canadienne septen- ¸ ´ ´ ´ trionale. La Formation Imperial a donne une grande plage de dates sur des zircons detritiques; un echantillon a donne des´ ` ´ ¨ pics dominants a 1130, 1660 et 1860 Ma ainsi que des populations moindres datant du Paleozoıque moyen (*430 Ma), du ´ ´ ¨ ´ ´ ` ´ Neoproterozoıque et de l’Archeen. L’echantillon le plus a l’est de la Formation Imperial a donne des zircons datant surtout ´ ´ ¨ ´ du Neoproterozoıque tardif – Cambrien, soit entre 500 et 700 Ma, avec des populations moindres datant du Mesoprotero- ´ ¨ ˆ ` ´ ´ zoıque et plus anciennes. Les plages d’ages suggerent que les echantillons proviennent surtout d’une region extensive dans le nord-ouest de la Laurentie, incluant le Bouclier canadien, les provinces ignees et sedimentaires des ˆles de l’Arctique ca- ´ ´ ı ´ ´ ´ ¨ nadien et possiblement du nord du Yukon. La presence de zircons datant du Neoproterozoıque tardif – Cambrien, lesquels ´ sont absents des donnees magmatiques laurentiennes, indique qu’un certain nombre de grains proviennent sans doute d’une ´ ´ region source exotique, possiblement de Baltica, de la Siberie ou du terrane Arctic Alaska – Chukotka. Cependant, les zir- ´ ´ ´ ¨ cons provenant de la Formation Tuttle montrent une population bien definie du Paleoproterozoıque moyen avec des pics de ´ ´ ¨ probabilite relative entre 1850 et 1950 Ma. D’autres populations dans la Formation Tuttle datent du Paleozoıque moyen ´ ´ ¨ ´ ´ ¨ ´ ´ (*430 Ma), du Mesoproterozoıque (1000–1600 Ma) ainsi que du Paleoproterozoıque inferieur et de l’Archeen (>2000 Ma). ´ ` ´ ´ Ces donnees supportent l’hypothese que l’influx de sediments provenant du Nord qui a fourni le miogeoclinal septentrional ´ ´ au Devonien tardif a subi un changement abrupt vers une source d’affinite surtout laurentienne vers le Mississippien. ´ [Traduit par la Redaction] Received 23 November 2009. Accepted 26 May 2010. Published on the NRC Research Press Web site at cjes.nrc.ca on 9 February 2011. Paper handled by Associate Editor W.J. Davis. Y. Lemieux and T. Hadlari.3,4 Northwest Territories Geoscience Office, Box 1500, 4601-B, 52 Avenue, Yellowknife, NT X1A 2R3, Canada. A. Simonetti.5 Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, Canada. 1This article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh. 2Northwest Territories Geoscience Office Contribution 0047. Geological Survey of Canada Contribution 20100432. 3Corresponding author (e-mail: thomas.hadlari@nrcan-rncan.gc.ca). 4Present address: Geological Survey of Canada, 3303, 33rd St. NW, Calgary, AB T2L 2A7, Canada. 5Present address: 156 Fitzpatrick Hall, University of Notre Dame, Notre Dame, IN 46556.Can. J. Earth Sci. 48: 515–541 (2011) doi:10.1139/E10-056 Published by NRC Research Press
  • 2. 516 Can. J. Earth Sci. Vol. 48, 2011Introduction folded miogeoclinal strata are exposed at the mountain front. The area preserves a relatively complete Cambrian to Dev- Despite an increasing number of U–Pb geochronology and onian, rift to post-rift passive-margin succession that liesNd isotopic studies that provided new perspectives on re- with a pronounced unconformity on a thick succession ofgional patterns of sediment dispersal in northwestern Canada Proterozoic sedimentary rock (Fig. 3; Aitken et al. 1982). Aand adjacent Arctic region in Paleozoic time (e.g., McNicoll wedge of Cretaceous siliciclastic strata, interpreted to haveet al. 1995; Garzione et al. 1997; Gehrels et al. 1999; Patch- been deposited in a foreland basin setting, overlies the Pale-ett et al. 1999; Miller et al. 2006), the tectonic setting and ozoic succession.paleogeography during deposition of the Devono-Mississip- In Cambrian to Middle Devonian time, the northern Cana-pian succession in the northern Canadian Cordilleran mio- dian Cordilleran miogeocline was a continental margingeocline is not well understood. marked by deposition of extensive carbonate platform and Prior to the late Devonian, the northern Cordilleran mar- minor associated siliciclastic rocks (Mackenzie Platform;gin was dominated by an extensive shallow-water carbonate Fritz et al. 1991), and, to the west, deeper water siliciclasticplatform thickening markedly westward toward a fine- and minor carbonate succession (Fig. 3; Pugh 1983). Detritalgrained basinal succession (e.g., Fritz et al. 1991). The plat- zircon ages from Cambrian sandstone in east-central Alaskaform was flanked to the east by the Laurentian Precambrian suggest provenance largely from regions of the CanadianShield, which provided most of the sediment for the clastic Shield (Gehrels et al. 1999).deposits (Gordey et al. 1991). By the late Devonian, an in- In the late Devonian, passive-margin sedimentation wasflux of fine siliciclastic sediment blanketed the northern interrupted by a major change in tectono-sedimentologicalshelf and platform, marking a profound change in depositio- elements with uplift of clastic sourcelands north and west ofnal regime and tectonic setting along the Cordilleran margin the platform and influx of thick wedges of coarse and fine(Morrow and Geldsetzer 1988). In northern Yukon and clastic sediments (Pugh 1983; Gordey et al. 1991). TheNorthwest Territories, the Middle Devonian to Early Car- Upper Devonian Imperial Formation (Bassett 1961), mark-boniferous Imperial Assemblage, including the Hare Indian, ing the transition from carbonate to sand-grade siliciclasticCanol, Imperial, Tuttle, and Ford Lake formations, was in- deposition in the northern miogeocline (e.g., Gordey et al.terpreted by Gordey et al. (1991) to have been derived from 1991), includes a thick sequence of marine shale, siltstone,an uplifted region in northern Yukon. On the basis of Nd and very fine- to fine-grained sandstone that overlies blackisotopic constraints, Garzione et al. (1997) and Patchett et siliceous shale of the Canol Formation. Within the studyal. (1999) argued that the Imperial Assemblage was likelyderived from Ordovician to Early Carboniferous orogenic area, the Imperial Formation has been interpreted as Fras-systems in Greenland and the Canadian Arctic, as proposed nian–Famennian shelf sandstones and basinal turbidites withby Embry and Klovan (1976). More recently, detailed sedi- an eastward or northeastward sediment source inferred frommentology of the Upper Devonian Imperial Formation and outcrop studies (Braman and Hills 1992), and as a west- toTuttle Formation (Hadlari et al. 2009) indicated derivation southwestward-prograding submarine slope and fan complexfrom a northeastern and eastern source region. (Hadlari et al. 2009). To the north and west, the Imperial Formation is composed of turbidites interpreted to have Paleozoic sediment dispersal in the northern Cordillera been derived largely from northern source regions (Gordeycan be better constrained with detrital zircon geochronology et al. 1991; Braman and Hills 1992). Seventeen single zircondata. Few U–Pb detrital zircon studies have been carried out dates from the Imperial Formation in northwestern Yukonin strata of the miogeocline in the northern Canadian Cordil- (C. Garzione, G. Ross, J. Patchett, and G. Gehrels unpub-lera (e.g., Beranek et al. 2010). In this paper, we present lished data, discussed in Gehrels et al. 1999) indicated anew U–Pb detrital zircon dates obtained using laser ablation dominance of >1.8 Ga detritus, consistent with derivation– multicollector – inductively coupled plasma – mass spec- from Canadian Shield sources, with a subordinate populationtrometry (LA–MC–ICP–MS) from the Upper Devonian Im- of mid-Paleozoic (400–450 Ma) grains. Single zircon grainsperial Formation and Upper Devonian – LowerCarboniferous Tuttle Formation exposed in the northern from a Late Devonian sandstone-bearing unit in east-centralMackenzie Mountains (Figs. 1, 2). The purpose of the study Alaska yielded chiefly 430 Ma, Paleoproterozoic (>1.8 Ga),is to constrain the provenance of sandstones within these and Archean grains, consistent with an influx of detritus, intwo units to better understand regional patterns of mid-Pale- part, from Laurentian source regions (Gehrels et al. 1999).ozoic sediment dispersal in the northern Cordillera and to Similar results have been reported from Devonian to Car-draw conclusions regarding paleogeography of northern boniferous sandstones of northeastern Yukon Territory (Be-Laurentia. As our data indicate, the zircons from the Impe- ranek et al. 2010).rial and Tuttle formations were likely derived from an ex- East of Arctic Red River (see Fig. 2 for location), Impe-tensive region of northern Laurentia, including the rial Formation is unconformably overlain by wedge of Cre-northwestern Canadian Shield, provinces of Canada’s Arctic taceous clastic sediments deposited in a foreland basinIslands, and Greenland. setting (Aitken et al. 1982); west of Arctic Red River, how- ever, the Imperial Formation is conformably overlain by the Upper Devonian – Lower Carboniferous Tuttle Formation, aGeological setting thick succession of alternating conglomerate, coarse- to fine- The study area lies along the northern margin of the grained sandstone, siltstone, and shale. The contact with theMackenzie Mountains and encompasses the southern Peel Imperial Formation is interpreted as a facies boundary and,Plateau and Plain (Peel Region) of the northern Interior therefore, is diachronous (Pugh 1983). Hills and BramanPlains (Figs. 2); it occupies a region where imbricated and (1978) and Braman and Hills (1992) interpreted the Tuttle Published by NRC Research Press
  • 3. Lemieux et al. 517Fig. 1. Tectonic assemblage map of Yukon Territory, Northwest Territories and Nunavut showing location of study area and Fig. 2. Geol-ogy after Wheeler et al. (1996), paleocurrent data from Embry and Klovan (1976) and Hadlari et al. (2009).Formation as a southward-advancing turbidite succession. In The sub-Cretaceous unconformity marks a hiatus in thecontrast, Pugh (1983) viewed the unit as a deltaic depositio- sedimentary record as Late Carboniferous to Jurassic stratanal system and interpreted the shale-out to the west as indi- are absent from the northern Interior Plains. The end of con-cating southwest-prograding deposition despite a progressive tinental margin sedimentation and beginning of widespreadsouthward decrease in grain size and trend to better sorting. compressional deformation in the northern Cordillera inBy the mid-Mississippian, marine clastic and carbonate dep- Mesozoic time (e.g., Berman et al. 2007) influenced the de-osition with sediment derivation from the craton to the east velopment of foreland basins adjacent to the mountain frontwas re-established (Gordey et al. 1991). (Dixon 1999). Clastic sedimentation in the northern Interior Published by NRC Research Press
  • 4. Fig. 2. Simplified geological map (modified after Hadlari et al. 2009) of southern Peel Plateau and Peel Plain, and the northern Mackenzie Mountains showing seismic line traces and 518 clinoform progradation directions, turbidite paleocurrents, and locations of the detrital zircon samples. Geology after Wheeler et al. (1996).Published by NRC Research Press Can. J. Earth Sci. Vol. 48, 2011
  • 5. Lemieux et al. 519Fig. 3. Schematic stratigraphic section for the southern Peel Plateau and Peel Plain and northern Mackenzie Mountains. Modified afterMorrow et al. (2006). Published by NRC Research Press
  • 6. 520 Can. J. Earth Sci. Vol. 48, 2011Plains in the Late Cretaceous was controlled largely by, and large enough (i.e., > 40 mm across, see as follows) for laserderived from, the active Cordillera to the south and west ablation analyses. In contrast, the much finer grained Impe-(Dixon 1999). rial samples yielded a smaller fraction of zircons that were sufficiently large for analysis. Selected grains were, asU–Pb geochronology much as possible, free of fractures, inclusions, and altera- tion. U–Pb geochronology of zircons was conducted bySample description and analytical procedures LA–MC–ICP–MS at the Radiogenic Isotope Facility at the This study presents U–Pb geochronological results for University of Alberta, Edmonton, Alberta, using analyticalfour samples from the Devono-Mississippian clastic succes- procedures described by Simonetti et al. (2005). The analy-sion in the Peel Region, two from the Imperial Formation ses involved ablation of zircons using a 40 mm diameter la-(samples 07TH33B and 07WZ020A), and two from the Tut- ser spot size for 30 s. A ‘‘standard-sample-standard’’ methodtle Formation (samples 07WZ019A and 06YHL046B); their was used to correct instrumental drift during a single lasergeographic locations are shown in Fig. 2 and given in ablation session and involved analysis of an internal stand-Table 1. ard after every 12 unknown grains; this protocol was devel- Sample 07TH33B was collected at the type section of Im- oped for provenance studies focusing on the dating of aperial Formation (Fig. 2). Located near the eastern erosional large number of detrital zircon grains (Simonetti et al.edge of Imperial Formation, the type section preserves the 2005) The collector configuration allows for the simultane-oldest strata of Imperial Formation, which were deposited ous measurement of ion signals ranging in mass from 238Uas a shallow shelf-like accumulation of sediment that pro- to 203Tl. Periodically, a 30 s blank measurement was per-graded southwestward into a generally westward-deepening formed, which included correction for the 204Hg contribu-basin (Hadlari et al. 2009). The sampled interval consists of tion; ion-counter bias was also determined using a mixedfine-grained cross-stratified sandstone from the locally de- solution of Pb and Tl. Common Pb correction was appliedveloped shallow-marine facies. using an initial Pb composition taken from Stacey and West of Imperial River, the Imperial Formation is inter- Kramers (1975).preted as a succession of submarine fan and slope sand-stones and shales exceeding 500 m in thickness that, based Results of U–Pb analysisupon paleocurrent and seismic data, are interpreted to have The results are presented in Table 1 (with uncertainties atbeen deposited by a system that prograded in a west-south- the 2s level) and shown in relative age–probability diagramswest direction (Hadlari et al. 2009). Tuttle Formation is gen- (from Ludwig 2003) in Fig. 5. The diagrams present the sumerally Famennian to Tournasian in age (Allen et al. 2009), of all ages from a sample as a normal distribution based onoverlies the Imperial Formation, is partly defined by me- the age and uncertainty of each analysis, the areas underdium sand and coarser grain sizes, and represents a rejuve- each curve are equal. Interpretations for <1000 Ma grainsnation of sand-grade siliciclastic input to the basin from the are based on 206Pb/238U ages, which yield more precise re-northeast (Hadlari et al. 2009). Based upon the depositional sults given the low concentration of 207Pb in younger zir-system, the three remaining samples are significantly cons. For grains >1000 Ma, analyses are based on 207Pb/younger than 07TH33B because they are located over 206Pb ages. To reduce the effect of discordance, possibly re-100 km west of Imperial River. Considering their mutual sulting from isotopic disturbance and (or) inheritance, analy-proximity, we have placed the three western samples in or- ses that are >5% discordant or >5% reverse discordantder by the stratigraphic level that was sampled within the (italics in Table 1) have been excluded from further consid-combined Imperial–Tuttle formation section. Sample eration.07WZ020A, a massive fine-grained sandstone, was collected A total of 67 zircons were analyzed from samplea few metres above the Canol–Imperial contact along a trib- 07TH33B (Imperial Formation), of which 54 were consid-utary of the Snake River near the western edge of the study ered (Fig. 5; Table 1). A significant number of zirconsarea. From the middle part of the section, sample yielded age clusters between 380 and 711 Ma (n = 26),06YHL046B was collected from a *150 m high bluff of with peaks evident at 390, 555, and 670 Ma. Twenty-fiveconspicuously hard and massive, medium- to coarse-grained, zircons yielded Proterozoic dates, with the most dominantquartz-rich sandstone sharply overlying shale and siltstone peaks at 1100, 1350, 1670, and 1950 Ma; only one zirconwest of Cranswick River (Fig. 4). Although the bluff was falls in the interval 2100–2500 Ma. Three Archean zirconsmapped as Imperial Formation by Norris (1982), the grain were documented (i.e., 2625, 2796, and 2820 Ma).size is clearly atypical of Imperial Formation, and is inter- Ninety-one zircons extracted from the westernmost sam-preted here as part of Tuttle Formation. Sample 07WZ019A ple of the Imperial Formation (07WZ020A) were analyzed,is conglomerate of Tuttle Formation from the top of the Im- of which 61 are within 5% of the concordia. This sampleperial–Tuttle section at Flyaway Creek; the section exposes has a dominant zircon age population (n = 46) betweena thin interval, *50 m thick, of sandstone and conglomerate *1000 and 2100 Ma, with major peaks at 1130, 1660, andoverlying *600 m in thickness of Imperial Formation (Ha- 1860 Ma, and subordinate age groups at 1300–1550, 1730–dlari et al. 2009). The entire sample of quartz clast conglom- 1800, 1900–2100 Ma. The sample also includes (i) fourerate with sandstone matrix was crushed for analysis. lower Paleozoic zircons at 424, 432, 438, and 505 Ma; (ii) Each sample yielded euhedral to anhedral, colourless to four Neoproterozoic grains at 570, 597, 645, and 855 Ma;pink or yellow, generally well-rounded zircons consistent and (iii) seven Archean zircons between 2614 and 2806 Ma.with a detrital origin. Samples from the Tuttle Formation There is a gap between 2100 and 2600 Ma.were sufficiently coarse grained to yield abundant zircons Ninety-one zircon were analyzed from sample Published by NRC Research Press
  • 7. Lemieux et al. 521Fig. 4. (a) Field photograph showing the contact between the Imperial Formation and overlying Tuttle Formation in the Cranswick Riverarea. The bluff (in the middle ground) was mapped as Imperial Formation by Norris (1982). View to northeast; field of view in middleground is *4 km. (b) Close-up of approximate contact (dashed line) between the Imperial and Tuttle formations. Geologist for scale. SeeFig. 2 for location of photographs.06YHL046B (Tuttle Formation); 18 zircon have not been 1512 Ma (n = 2), and 1597–1731 Ma (n = 5). One grainconsidered further. A 440 Ma Silurian-age peak is evident, yielded a Neoproterozoic date (940 Ma).represented by seven grains between 428 and 444 Ma. The A total of 112 zircons were analyzed from samplesample yielded 45 grains between *1800 and 2800 Ma, 07WZ019A (Tuttle Formation), of which 99 were consid-with dominant age peaks at 1860 and 2780 Ma, and subordi- ered. A 1937 Ma Paleoproterozoic age peak is evident innate age groups between *2000 and 2700 Ma. Twenty zir- the zircon population, with 50 grains falling in the intervalcons fall in the intervals 1038–1366 Ma (n = 13), 1494– 1792–2000 Ma; a subordinate age cluster occurs at 430 Ma, Published by NRC Research Press
  • 8. 522 Table 1. U–Pb data of detrital zircons. Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) Sample 07TH33B (UTM ZONE 9N, N7221831, E553690) 1 217352 Infinite 0.4578 0.012 0.0607 0.002 0.96 380 15 383 10 368 25 –3.1 2 266037 29559.7 0.4382 0.008 0.0585 0.001 0.92 366 13 369 7 370 32 0.8 3 97534 Infinite 0.4601 0.006 0.0600 0.001 0.93 376 12 384 5 393 27 4.3 4 141527 Infinite 0.4855 0.010 0.0629 0.001 0.91 393 14 402 8 409 34 3.8 5 105463 Infinite 0.4873 0.009 0.0629 0.001 0.90 393 13 403 7 409 34 3.8 6 116583 Infinite 0.4960 0.012 0.0644 0.001 0.95 402 15 409 10 413 27 2.6 7 87935 Infinite 0.4998 0.014 0.0649 0.002 0.91 405 15 412 11 416 37 2.6 8 57814 Infinite 0.5677 0.013 0.0724 0.002 0.94 451 16 457 10 422 29 -6.8 9 57549 Infinite 0.5629 0.011 0.0716 0.001 0.93 446 15 453 9 425 29 –4.8 10 191304 Infinite 0.5751 0.009 0.0734 0.001 0.95 457 15 461 7 451 23 –1.2 11 204407 Infinite 0.4615 0.013 0.0582 0.002 0.95 365 15 385 11 476 29 23.4 12 325769 Infinite 0.6521 0.015 0.0809 0.002 0.95 501 19 510 12 518 26 3.3 13 61741 Infinite 0.7202 0.019 0.0883 0.002 0.96 545 22 551 15 521 26 –4.6 14 193746 Infinite 0.7096 0.016 0.0863 0.002 0.94 533 20 544 12 556 29 4.0 15 109660 Infinite 0.7400 0.016 0.0897 0.002 0.96 554 20 562 12 559 24 1.0 16 202468 Infinite 0.7514 0.022 0.0907 0.003 0.97 560 24 569 17 564 24 0.8 17 340492 Infinite 0.7230 0.014 0.0878 0.002 0.93 542 19 552 11 567 28 4.3 18 141712 4571.37 0.6721 0.039 0.0810 0.004 0.92 502 30 522 30 575 57 12.7 19 134699 33674.67 0.7638 0.021 0.0917 0.002 0.94 565 22 576 16 584 29 3.3 20 296319 Infinite 0.7744 0.014 0.0931 0.002 0.95 574 20 582 10 593 24 3.2 21 229189 Infinite 0.7777 0.017 0.0931 0.002 0.95 574 21 584 13 596 25 3.6 22 278753 25341.2 0.6959 0.020 0.0830 0.002 0.93 514 20 536 15 605 32 15.0 23 417489 Infinite 0.7199 0.016 0.0863 0.002 0.96 534 20 551 12 606 23 11.9 24 365918 Infinite 0.9035 0.017 0.1043 0.002 0.94 640 22 654 12 670 25 4.5 25 203291 Infinite 0.8012 0.020 0.0918 0.002 0.93 566 21 598 15 670 30 15.5 26 100302 Infinite 0.9362 0.022 0.1071 0.002 0.94 656 24 671 16 675 29 2.8 27 273595 Infinite 0.9270 0.025 0.1091 0.003 0.96 667 27 666 18 677 23 1.4 28 188263 Infinite 0.9401 0.020 0.1078 0.002 0.95 660 24 673 14 679 25 2.8 29 227461 10831.45 0.9981 0.052 0.1146 0.005 0.91 699 39 703 37 684 54 –2.2 Can. J. Earth Sci. Vol. 48, 2011 30 278435 Infinite 0.9515 0.017 0.1096 0.002 0.96 670 23 679 12 698 22 4.0Published by NRC Research Press 31 312369 Infinite 0.8629 0.033 0.0991 0.004 0.97 609 30 632 24 702 24 13.2 32 165271 Infinite 0.9856 0.026 0.1107 0.003 0.96 677 27 696 18 707 24 4.3 33 217427 Infinite 1.0312 0.015 0.1166 0.001 0.91 711 23 720 11 717 29 0.9 34 227825 28478.1 0.9579 0.023 0.1031 0.002 0.94 633 24 682 16 819 28 22.8 35 71442 Infinite 1.6142 0.031 0.1607 0.003 0.93 961 33 976 19 953 27 –0.8 36 102579 Infinite 1.9582 0.060 0.1866 0.006 0.97 1103 47 1101 34 1059 21 –4.2 37 725341 Infinite 1.4684 0.041 0.1403 0.004 0.93 846 33 917 26 1084 31 21.9 38 259436 Infinite 1.9815 0.037 0.1867 0.003 0.95 1103 39 1109 21 1095 22 –0.8 39 198957 Infinite 1.9575 0.051 0.1833 0.005 0.96 1085 43 1101 28 1097 21 1.1
  • 9. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 40 802664 21693.62 1.9697 0.045 0.1865 0.004 0.93 1102 40 1105 25 1106 28 0.3 41 224638 1936.534 1.8174 0.064 0.1809 0.006 0.92 1072 47 1052 37 1118 36 4.1 42 1011788 2007.516 2.4696 0.224 0.2155 0.019 0.98 1258 119 1263 114 1272 33 1.1 43 243064 Infinite 2.1622 0.178 0.1784 0.014 0.97 1058 91 1169 96 1330 38 20.4 44 607082 530.203 2.5457 0.133 0.2178 0.010 0.91 1270 71 1285 67 1333 49 4.7 45 522574 Infinite 2.6736 0.083 0.2244 0.007 0.97 1305 56 1321 41 1341 20 2.6 46 1073922 Infinite 2.6708 0.062 0.2241 0.005 0.96 1304 49 1320 31 1345 20 3.1 47 114935 Infinite 2.8172 0.049 0.2294 0.004 0.93 1332 45 1360 24 1374 25 3.1 48 385586 16764.6 2.7961 0.049 0.2198 0.003 0.91 1281 42 1355 24 1452 27 11.8 49 1398896 Infinite 3.3621 0.044 0.2658 0.003 0.95 1519 50 1496 20 1487 19 –2.1 50 1668858 Infinite 2.6855 0.035 0.1994 0.002 0.93 1172 38 1324 17 1555 22 24.6 51 505990 Infinite 4.3155 0.105 0.3056 0.007 0.97 1719 66 1696 41 1659 19 –3.6 52 1627787 Infinite 3.9893 0.076 0.2831 0.005 0.96 1607 57 1632 31 1670 19 3.8 53 630839 Infinite 4.2327 0.086 0.2952 0.006 0.96 1668 60 1680 34 1688 19 1.2 54 488924 Infinite 4.6379 0.339 0.3078 0.021 0.94 1730 129 1756 128 1727 51 –0.2 55 840928 Infinite 4.6572 0.069 0.3100 0.005 0.95 1741 58 1760 26 1779 19 2.1 56 200124 939.5515 5.5286 0.415 0.3341 0.025 0.97 1858 148 1905 143 1893 33 1.8 57 481859 Infinite 5.7437 0.120 0.3505 0.007 0.96 1937 71 1938 40 1929 19 –0.4 58 673729 2029.306 5.7164 0.107 0.3497 0.006 0.95 1933 68 1934 36 1935 20 0.1 59 933238 Infinite 5.6258 0.080 0.3369 0.005 0.95 1872 62 1920 27 1968 18 4.9 60 966251 Infinite 6.2317 0.095 0.3725 0.006 0.95 2041 69 2009 31 1976 18 –3.3 61 1716228 17693.07 6.2476 0.108 0.3704 0.006 0.94 2031 69 2011 35 2011 22 –1.0 62 883413 Infinite 5.9951 0.114 0.3495 0.007 0.96 1932 68 1975 37 2021 18 4.4 63 322605 1097.296 7.6982 0.196 0.3990 0.010 0.95 2164 83 2196 56 2206 22 1.9 64 1093494 Infinite 11.6411 0.170 0.4771 0.007 0.95 2515 84 2576 38 2625 17 4.2 65 1548221 30964.42 14.8244 0.277 0.5507 0.010 0.96 2828 100 2804 52 2796 17 –1.1 66 390767 Infinite 15.4936 0.348 0.5625 0.013 0.96 2877 108 2846 64 2820 17 –2.0 67 3034842 35704 10.4927 0.353 0.3826 0.013 0.97 2089 94 2479 83 2832 17 26.2 Sample 07WZ020A (UTM Zone 9N, N7277599, E308503) 1 126733 Infinite 0.5336 0.015 0.0693 0.002 0.96 432 18 434 12 420 25 –2.8 2 340726 Infinite 0.5227 0.008 0.0679 0.001 0.95 424 14 427 6 441 23 3.9Published by NRC Research Press 3 259160 Infinite 0.5501 0.011 0.0703 0.001 0.96 438 16 445 9 454 24 3.6 4 297800 Infinite 0.4928 0.007 0.0623 0.001 0.94 390 13 407 6 483 24 19.3 5 699418 Infinite 0.4709 0.012 0.0584 0.001 0.94 366 14 392 10 516 30 29.1 6 357235 238.9533 0.6515 0.083 0.0815 0.010 0.97 505 64 509 65 525 70 3.8 7 371429 Infinite 0.5386 0.013 0.0664 0.002 0.94 414 16 437 10 529 28 21.7 8 256729 Infinite 0.7658 0.016 0.0925 0.002 0.96 570 21 577 12 582 24 1.9 9 109026 Infinite 0.8092 0.018 0.0970 0.002 0.94 597 22 602 13 587 28 –1.6 10 433467 Infinite 0.6441 0.012 0.0775 0.001 0.96 481 17 505 9 595 23 19.2 11 181581 Infinite 0.9039 0.011 0.1052 0.001 0.95 645 21 654 8 656 23 1.7 523
  • 10. 524 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 12 1016871 3697.711 1.3405 0.048 0.1418 0.005 0.96 855 39 863 31 887 26 3.6 13 158487 Infinite 1.6375 0.030 0.1613 0.003 0.95 964 34 985 18 996 22 3.2 14 753417 39653.5 1.7187 0.044 0.1676 0.004 0.96 999 39 1016 26 1044 23 4.3 15 972131 Infinite 1.8740 0.032 0.1789 0.003 0.96 1061 37 1072 18 1091 20 2.7 16 555233 Infinite 1.8900 0.064 0.1790 0.006 0.96 1061 47 1078 36 1097 25 3.3 17 1298874 4071.706 1.8714 0.132 0.1781 0.012 0.94 1056 76 1071 75 1101 53 4.1 18 202173 Infinite 2.0020 0.037 0.1871 0.003 0.94 1106 38 1116 21 1115 24 0.8 19 334811 Infinite 2.0319 0.042 0.1902 0.004 0.96 1122 41 1126 23 1115 21 –0.6 20 85633 Infinite 2.0206 0.036 0.1856 0.003 0.93 1097 37 1122 20 1130 25 2.9 21 433460 Infinite 2.0282 0.043 0.1890 0.004 0.96 1116 41 1125 24 1134 21 1.6 22 135092 Infinite 2.0534 0.056 0.1873 0.005 0.95 1107 44 1133 31 1154 25 4.1 23 393360 19668 2.1728 0.042 0.1995 0.003 0.92 1173 40 1172 23 1161 28 –1.0 24 158101 Infinite 2.2812 0.022 0.2067 0.001 0.93 1211 37 1206 11 1166 24 –3.9 25 457060 Infinite 1.6001 0.087 0.1451 0.008 0.97 874 54 970 53 1168 27 25.2 26 1110968 Infinite 1.6735 0.014 0.1527 0.001 0.94 916 28 999 8 1185 21 22.7 27 1177595 Infinite 2.1699 0.054 0.1985 0.005 0.97 1167 45 1171 29 1185 20 1.5 28 260928 Infinite 2.2472 0.063 0.2032 0.006 0.96 1192 49 1196 33 1186 22 –0.5 29 1078929 Infinite 2.3740 0.104 0.2117 0.009 0.97 1238 64 1235 54 1228 27 –0.8 30 166663 Infinite 2.3208 0.038 0.2022 0.003 0.95 1187 40 1219 20 1237 22 4.0 31 241826 Infinite 2.3165 0.064 0.2031 0.006 0.97 1192 48 1217 34 1243 21 4.1 32 393935 Infinite 2.2663 0.169 0.1945 0.013 0.92 1146 86 1202 90 1279 62 10.4 33 376764 1638.1 2.3487 0.076 0.1995 0.006 0.94 1173 50 1227 40 1304 30 10.0 34 395046 Infinite 2.5778 0.049 0.2173 0.004 0.94 1268 44 1294 25 1330 24 4.7 35 127330 Infinite 2.8597 0.065 0.2341 0.005 0.94 1356 50 1371 31 1366 24 0.8 36 236473 Infinite 2.5301 0.068 0.2065 0.005 0.96 1210 48 1281 34 1383 23 12.5 37 230817 Infinite 3.0753 0.044 0.2455 0.003 0.94 1415 47 1427 21 1402 21 –0.9 38 344399 Infinite 2.9715 0.050 0.2393 0.004 0.94 1383 47 1400 24 1411 22 2.0 39 441807 14726.89 3.2392 0.066 0.2544 0.004 0.91 1461 50 1467 30 1465 29 0.3 40 147977 Infinite 3.2981 0.066 0.2546 0.004 0.91 1462 50 1481 30 1474 28 0.8 41 669286 Infinite 3.3311 0.059 0.2585 0.005 0.95 1482 51 1488 26 1505 20 1.5 42 1296589 Infinite 3.4601 0.056 0.2636 0.004 0.96 1508 51 1518 24 1533 19 1.6 Can. J. Earth Sci. Vol. 48, 2011 43 491753 1576.13 3.0343 0.278 0.2285 0.019 0.92 1327 118 1416 130 1548 73 14.3Published by NRC Research Press 44 131575 Infinite 4.1502 0.081 0.2915 0.006 0.95 1649 59 1664 32 1649 20 0.0 45 228486 337.4977 4.3403 0.233 0.3062 0.015 0.94 1722 101 1701 91 1653 38 –4.2 46 321559 Infinite 3.9912 0.130 0.2809 0.009 0.97 1596 71 1632 53 1660 19 3.9 47 1031062 Infinite 4.0686 0.081 0.2883 0.006 0.96 1633 59 1648 33 1664 19 1.9 48 528558 Infinite 4.3359 0.084 0.3050 0.006 0.96 1716 61 1700 33 1669 19 –2.8 49 590211 Infinite 3.0786 0.314 0.2133 0.022 0.99 1246 132 1427 146 1684 30 26.0 50 600365 Infinite 4.3516 0.116 0.3040 0.008 0.97 1711 69 1703 45 1701 19 –0.6 51 593925 Infinite 3.8213 0.069 0.2633 0.005 0.96 1507 53 1597 29 1710 19 11.9
  • 11. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 52 728551 3223.678 4.3360 0.792 0.2943 0.053 0.99 1663 306 1700 310 1747 41 4.8 53 386808 16817.72 4.6421 0.095 0.3115 0.006 0.93 1748 62 1757 36 1748 24 0.0 54 624037 Infinite 4.6055 0.058 0.3077 0.004 0.95 1729 56 1750 22 1766 19 2.1 55 2324654 36899.3 4.0873 0.067 0.2723 0.004 0.95 1553 53 1652 27 1793 20 13.4 56 775421 2959.62 4.6605 0.150 0.3029 0.010 0.97 1706 75 1760 57 1825 20 6.5 57 456978 Infinite 4.2560 0.077 0.2740 0.005 0.96 1561 55 1685 31 1832 18 14.8 58 1267941 4103.37 3.6877 0.111 0.2384 0.007 0.95 1378 57 1569 47 1841 23 25.2 59 640904 Infinite 5.2003 0.111 0.3332 0.007 0.96 1854 68 1853 39 1848 18 –0.3 60 842510 Infinite 5.0816 0.084 0.3242 0.005 0.96 1810 62 1833 30 1854 18 2.4 61 449007 Infinite 5.2542 0.072 0.3332 0.005 0.95 1854 61 1861 26 1860 18 0.3 62 178341 Infinite 5.5673 0.102 0.3465 0.006 0.96 1918 67 1911 35 1870 19 –2.6 63 462742 Infinite 5.1635 0.121 0.3234 0.007 0.93 1807 66 1847 43 1875 26 3.7 64 2906290 10416.8 3.8769 0.187 0.2447 0.012 0.98 1411 80 1609 78 1892 18 25.4 65 878581 2670.46 4.1829 0.112 0.2585 0.006 0.93 1482 57 1671 45 1913 27 22.5 66 1133511 4048.255 5.6088 0.427 0.3423 0.023 0.90 1898 141 1917 146 1919 64 1.1 67 954093 Infinite 5.7962 0.078 0.3545 0.005 0.95 1956 64 1946 26 1931 18 –1.3 68 125954 Infinite 5.7371 0.118 0.3456 0.007 0.95 1914 68 1937 40 1934 21 1.0 69 276151 Infinite 5.8263 0.112 0.3524 0.007 0.96 1946 69 1950 37 1937 19 –0.5 70 661599 2584.37 4.8255 0.262 0.2931 0.014 0.91 1657 95 1789 97 1964 46 15.6 71 641871 Infinite 4.9901 0.230 0.2908 0.013 0.98 1646 90 1818 84 2005 19 17.9 72 628332 Infinite 6.2959 0.131 0.3659 0.008 0.96 2010 73 2018 42 2022 18 0.6 73 1454081 Infinite 5.8633 0.124 0.3421 0.007 0.96 1897 69 1956 41 2026 19 6.4 74 569035 Infinite 6.8134 0.148 0.3905 0.008 0.96 2125 79 2087 45 2041 18 –4.1 75 540218 13505.46 6.4420 0.141 0.3624 0.007 0.93 1994 72 2038 45 2072 24 3.8 76 2375359 Infinite 5.9257 0.104 0.3289 0.006 0.96 1833 64 1965 35 2117 18 13.4 77 763478 21813.7 7.6396 0.276 0.3721 0.013 0.97 2039 95 2190 79 2330 19 12.5 78 261215 4213.14 7.7344 0.778 0.3480 0.034 0.97 1925 197 2201 221 2442 42 21.2 79 1196610 10978.1 8.7709 0.263 0.3711 0.011 0.95 2035 85 2314 69 2576 21 21.0 80 1757086 Infinite 10.8700 0.261 0.4452 0.011 0.97 2374 91 2512 60 2607 17 9.0 81 593333 7510.545 12.4287 0.219 0.5121 0.007 0.90 2666 88 2637 46 2614 25 –2.0 82 662851 12747.13 12.1365 0.259 0.5015 0.010 0.95 2620 95 2615 56 2616 20 –0.2 83 416360 Infinite 12.9122 0.260 0.5159 0.010 0.96 2682 97 2673 54 2657 17 –0.9Published by NRC Research Press 84 252375 Infinite 13.1744 0.276 0.5171 0.011 0.96 2687 98 2692 56 2676 17 –0.4 85 208645 Infinite 11.6138 0.424 0.4548 0.016 0.97 2416 114 2574 94 2678 18 9.8 86 1148347 Infinite 7.6352 0.513 0.3010 0.020 0.99 1696 124 2189 147 2685 20 36.8 87 1089764 6263.011 13.2524 0.216 0.5143 0.008 0.96 2675 91 2698 44 2720 17 1.7 88 808986 3595.492 13.2011 0.297 0.5020 0.011 0.96 2622 98 2694 61 2743 18 4.4 89 2297798 10687.43 14.0788 0.229 0.5194 0.008 0.95 2697 92 2755 45 2806 17 3.9 90 2196173 Infinite 11.3921 0.208 0.4155 0.008 0.96 2240 78 2556 47 2827 17 20.7 91 2605994 Infinite 14.3094 0.171 0.5033 0.006 0.94 2628 84 2770 33 2886 18 8.9 525
  • 12. 526 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) Sample 06YHL046B (UTM Zone 9N, N7272396, E343816) 1 306103 21864.5 0.4471 0.011 0.0586 0.001 0.90 367 13 375 9 412 38 10.8 2 143296 Infinite 0.5353 0.013 0.0686 0.002 0.96 428 16 435 11 439 25 2.6 3 267931 Infinite 0.5415 0.008 0.0698 0.001 0.95 435 15 439 7 449 24 3.1 4 269063 Infinite 0.5246 0.009 0.0667 0.001 0.95 416 14 428 7 450 23 7.5 5 305544 25462.04 0.5388 0.011 0.0690 0.001 0.91 430 15 438 9 452 33 4.8 6 191005 Infinite 0.5527 0.010 0.0706 0.001 0.95 440 15 447 8 452 24 2.8 7 117843 Infinite 0.5512 0.010 0.0696 0.001 0.94 434 15 446 8 453 27 4.3 8 87963 Infinite 0.5519 0.008 0.0697 0.001 0.94 435 14 446 6 457 24 4.9 9 273721 Infinite 0.5580 0.010 0.0712 0.001 0.94 444 15 450 8 461 27 3.8 10 244012 Infinite 0.5268 0.010 0.0673 0.001 0.96 420 15 430 8 464 23 9.4 11 157050 6828.25 0.5478 0.008 0.0693 0.001 0.94 432 14 444 7 476 25 9.3 12 250449 Infinite 0.5569 0.012 0.0701 0.001 0.96 437 16 450 9 488 23 10.5 13 90322 Infinite 0.5830 0.009 0.0726 0.001 0.94 452 15 466 8 488 26 7.4 14 75488 Infinite 0.5878 0.009 0.0735 0.001 0.93 457 15 469 7 489 27 6.5 15 258727 Infinite 0.5517 0.014 0.0694 0.002 0.94 433 17 446 11 489 29 11.6 16 540430 24565 0.4523 0.009 0.0569 0.001 0.91 357 12 379 8 505 33 29.3 17 667919 Infinite 0.5657 0.017 0.0701 0.002 0.97 437 19 455 14 514 23 15.0 18 61977 Infinite 0.5407 0.008 0.0656 0.001 0.91 410 13 439 6 553 30 25.9 19 667782 897.556 1.2921 0.107 0.1382 0.011 0.97 835 72 842 70 946 40 11.7 20 554178 Infinite 1.5739 0.027 0.1571 0.003 0.96 940 32 960 16 987 21 4.7 21 1153240 31168.66 1.7696 0.026 0.1748 0.002 0.93 1038 34 1034 15 1045 24 0.7 22 53008 Infinite 1.9203 0.040 0.1822 0.004 0.95 1079 39 1088 23 1067 24 –1.2 23 827576 Infinite 1.9780 0.036 0.1875 0.003 0.96 1108 39 1108 20 1106 20 –0.2 24 48901 Infinite 2.1117 0.041 0.1952 0.004 0.94 1149 40 1153 23 1106 25 –3.9 25 276073 21236.4 1.8961 0.045 0.1767 0.004 0.93 1049 39 1080 26 1121 28 6.4 26 493272 Infinite 2.0163 0.038 0.1879 0.003 0.96 1110 39 1121 21 1138 21 2.4 27 385501 Infinite 2.1941 0.027 0.2006 0.002 0.95 1179 38 1179 15 1168 20 –0.9 28 391950 23055.89 2.1692 0.031 0.1970 0.002 0.92 1159 37 1171 17 1178 26 1.6 29 862341 16908.65 2.1118 0.040 0.1932 0.003 0.90 1139 38 1153 22 1181 30 3.6 Can. J. Earth Sci. Vol. 48, 2011 30 329913 Infinite 2.2349 0.035 0.2006 0.003 0.95 1179 40 1192 19 1198 21 1.6Published by NRC Research Press 31 1542492 23022.28 2.2253 0.039 0.2020 0.003 0.93 1186 40 1189 21 1215 26 2.4 32 963785 19669.07 2.3924 0.042 0.2128 0.003 0.92 1244 41 1240 22 1243 27 –0.1 33 183429 Infinite 2.5816 0.025 0.2189 0.002 0.93 1276 40 1295 13 1302 22 2.0 34 805537 44752.06 2.6900 0.056 0.2234 0.005 0.96 1300 47 1326 28 1366 21 4.9 35 387711 Infinite 2.9232 0.053 0.2292 0.004 0.95 1330 46 1388 25 1468 20 9.4 36 184140 Infinite 3.3213 0.085 0.2559 0.006 0.93 1469 56 1486 38 1494 27 1.7 37 582297 Infinite 3.4728 0.046 0.2661 0.003 0.95 1521 50 1521 20 1512 20 –0.6 38 283821 Infinite 3.1801 0.065 0.2393 0.005 0.95 1383 50 1452 30 1525 21 9.3 39 98480 Infinite 3.8013 0.085 0.2746 0.006 0.95 1564 58 1593 35 1597 22 2.0
  • 13. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 40 534604 Infinite 4.1880 0.070 0.2967 0.005 0.96 1675 57 1672 28 1650 19 –1.5 41 774143 3351.27 4.0421 0.059 0.2841 0.004 0.95 1612 54 1643 24 1679 19 4.0 42 271748 Infinite 4.2425 0.065 0.2948 0.004 0.95 1665 56 1682 26 1683 19 1.1 43 1049121 2149.839 4.4244 0.111 0.3093 0.008 0.96 1737 68 1717 43 1731 20 –0.4 44 1083148 16924.2 5.2375 0.104 0.3449 0.006 0.93 1910 67 1859 37 1807 24 -5.7 45 345860 Infinite 5.1241 0.078 0.3283 0.005 0.95 1830 61 1840 28 1837 19 0.4 46 87174 Infinite 5.0542 0.081 0.3175 0.005 0.94 1777 60 1828 29 1844 21 3.6 47 908076 Infinite 4.8886 0.093 0.3145 0.006 0.96 1763 62 1800 34 1848 19 4.6 48 160593 Infinite 5.1285 0.074 0.3232 0.005 0.95 1806 60 1841 27 1850 19 2.4 49 158205 Infinite 5.2452 0.144 0.3314 0.009 0.96 1845 74 1860 51 1855 21 0.5 50 217662 Infinite 5.1917 0.104 0.3269 0.006 0.96 1823 65 1851 37 1855 19 1.7 51 286154 Infinite 5.1969 0.118 0.3299 0.007 0.96 1838 69 1852 42 1858 19 1.1 52 908503 Infinite 5.1060 0.101 0.3245 0.006 0.96 1812 65 1837 36 1881 18 3.7 53 380632 Infinite 5.2275 0.092 0.3266 0.006 0.96 1822 63 1857 33 1882 18 3.2 54 547020 30390.02 5.4287 0.102 0.3397 0.006 0.95 1885 66 1889 36 1884 20 0.0 55 418269 Infinite 5.1815 0.097 0.3247 0.006 0.96 1813 64 1850 35 1886 19 3.9 56 547155 Infinite 5.3779 0.100 0.3358 0.006 0.96 1867 66 1881 35 1887 18 1.1 57 383706 Infinite 5.2456 0.106 0.3247 0.006 0.93 1813 64 1860 37 1899 24 4.5 58 823007 39190.81 5.5397 0.101 0.3455 0.006 0.95 1913 67 1907 35 1905 19 –0.4 59 227125 Infinite 5.7988 0.144 0.3527 0.009 0.97 1948 76 1946 48 1927 18 –1.1 60 415084 29648.85 5.5268 0.086 0.3346 0.005 0.95 1860 62 1905 30 1937 20 3.9 61 863196 Infinite 5.4964 0.070 0.3343 0.004 0.95 1859 61 1900 24 1943 18 4.3 62 568320 33430.6 5.6318 0.112 0.3386 0.006 0.95 1880 67 1921 38 1945 21 3.3 63 301989 Infinite 5.9578 0.228 0.3544 0.013 0.94 1956 91 1970 75 1981 30 1.3 64 1654832 7576.821 5.9299 0.170 0.3536 0.010 0.97 1952 81 1966 56 1989 18 1.9 65 134120 Infinite 6.3813 0.096 0.3660 0.005 0.95 2011 67 2030 30 2014 20 0.2 66 453298 11928.89 6.4458 0.162 0.3719 0.009 0.93 2038 77 2039 51 2028 26 –0.5 67 213612 Infinite 6.2961 0.073 0.3578 0.004 0.95 1972 63 2018 23 2042 18 3.4 68 340590 Infinite 6.9231 0.087 0.3816 0.005 0.95 2084 68 2102 27 2103 18 0.9 69 169094 Infinite 7.2633 0.110 0.3982 0.006 0.95 2161 72 2144 32 2108 18 –2.5 70 254999 1432.578 7.0782 0.224 0.3826 0.011 0.92 2088 86 2121 67 2132 31 2.1 71 288084 10288.7 7.7350 0.149 0.4007 0.006 0.91 2172 74 2201 42 2218 25 2.1Published by NRC Research Press 72 243308 Infinite 8.2218 0.117 0.4142 0.005 0.92 2234 72 2256 32 2259 22 1.1 73 713263 3114.684 7.9414 0.163 0.4009 0.007 0.91 2173 75 2224 46 2274 26 4.4 74 297895 Infinite 9.1338 0.172 0.4395 0.008 0.96 2349 83 2351 44 2334 18 –0.6 75 627237 36896.29 8.9794 0.166 0.4289 0.008 0.95 2301 81 2336 43 2369 18 2.9 76 588155 Infinite 9.5616 0.116 0.4463 0.005 0.95 2379 77 2393 29 2396 17 0.7 77 744871 Infinite 9.5427 0.175 0.4456 0.008 0.96 2376 83 2392 44 2404 17 1.2 78 688756 Infinite 10.3881 0.132 0.4568 0.006 0.95 2426 79 2470 31 2500 17 3.0 79 315734 Infinite 11.5054 0.202 0.4803 0.008 0.96 2529 88 2565 45 2578 17 1.9 527
  • 14. 528 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 80 1051667 11308.25 11.6350 0.191 0.4878 0.007 0.93 2561 85 2575 42 2597 21 1.4 81 364050 18202.49 12.1285 0.247 0.4954 0.010 0.95 2594 93 2614 53 2625 19 1.2 82 669068 Infinite 12.8725 0.298 0.5058 0.012 0.96 2639 100 2670 62 2692 17 2.0 83 266386 15669.75 13.5506 0.232 0.5139 0.008 0.95 2673 91 2719 47 2732 0 2.1 84 1157294 23618.24 13.5933 0.215 0.5159 0.008 0.95 2682 90 2722 43 2763 17 2.9 85 726324 Infinite 5.7927 0.047 0.3488 0.003 0.95 1929 60 1945 16 2763 17 30.2 86 224223 Infinite 14.1944 0.243 0.5260 0.009 0.95 2725 94 2763 47 2766 17 1.5 87 1081708 Infinite 13.7710 0.280 0.5164 0.010 0.96 2684 97 2734 56 2772 16 3.2 88 291226 32358.45 15.2514 0.227 0.5606 0.008 0.95 2869 96 2831 42 2791 17 –2.8 89 784822 Infinite 14.0101 0.221 0.5179 0.008 0.95 2690 91 2750 43 2796 17 3.8 90 221940 11681.04 14.6259 0.276 0.5342 0.009 0.94 2759 96 2791 53 2804 20 1.6 91 661730 16967.4 13.2108 0.382 0.4874 0.014 0.96 2559 106 2695 78 2814 18 9.1 Sample 07WZ019A (UTM Zone 9N, N7264442, E359044) 1 236069 Infinite 0.5339 0.012 0.0686 0.001 0.93 427 16 434 10 411 31 –4.1 2 158894 Infinite 0.5413 0.007 0.0691 0.001 0.94 431 14 439 6 449 25 4.2 3 169361 24194.49 0.5446 0.013 0.0699 0.001 0.91 436 16 441 10 450 35 3.2 4 219902 Infinite 0.5603 0.012 0.0711 0.002 0.96 443 16 452 10 483 23 8.2 5 138225 Infinite 0.5987 0.010 0.0752 0.001 0.94 468 16 476 8 499 25 6.2 6 43200 Infinite 0.8074 0.017 0.0953 0.002 0.90 587 20 601 13 587 35 0.0 7 762022 Infinite 0.8569 0.015 0.1016 0.002 0.96 624 22 628 11 649 22 3.9 8 488809 Infinite 1.9039 0.040 0.1810 0.004 0.94 1072 39 1082 23 1076 25 0.4 9 361175 Infinite 2.1540 0.040 0.1969 0.004 0.96 1159 41 1166 21 1148 21 –1.0 10 1622331 Infinite 1.9717 0.036 0.1832 0.003 0.96 1084 38 1106 20 1155 20 6.1 11 1164812 Infinite 2.0176 0.025 0.1867 0.002 0.95 1103 36 1121 14 1157 20 4.7 12 189339 Infinite 2.1414 0.053 0.1949 0.005 0.96 1148 45 1162 29 1161 21 1.1 13 534112 Infinite 2.1332 0.052 0.1954 0.005 0.96 1151 44 1160 28 1176 20 2.1 14 1087331 Infinite 2.1283 0.024 0.1927 0.002 0.95 1136 36 1158 13 1199 20 5.2 15 579976 Infinite 2.2720 0.035 0.2043 0.003 0.95 1198 40 1204 18 1206 20 0.6 16 238926 Infinite 2.5542 0.058 0.2188 0.005 0.96 1276 48 1288 29 1283 21 0.6 17 731780 27102.97 2.8115 0.059 0.2357 0.005 0.94 1364 49 1359 28 1353 23 –0.9 Can. J. Earth Sci. Vol. 48, 2011 18 197573 Infinite 2.9058 0.072 0.2386 0.006 0.96 1380 53 1383 34 1371 20 –0.6Published by NRC Research Press 19 319831 Infinite 2.9654 0.057 0.2380 0.004 0.96 1376 49 1399 27 1421 20 3.1 20 1763546 37522.25 3.1919 0.044 0.2504 0.003 0.94 1441 47 1455 20 1458 21 1.2 21 1165661 Infinite 3.1639 0.049 0.2447 0.004 0.95 1411 48 1448 22 1500 20 5.9 22 326466 Infinite 4.0963 0.070 0.2877 0.005 0.95 1630 56 1654 28 1657 19 1.6 23 269106 Infinite 4.3279 0.078 0.3014 0.005 0.96 1698 59 1699 31 1667 19 –1.9 24 1083663 4496.527 4.3773 0.093 0.3020 0.006 0.96 1701 62 1708 36 1728 20 1.5 25 1087129 4496 4.3773 0.093 0.3020 0.006 0.96 1701 62 1708 36 1728 20 1.5 26 1867953 8633 4.4188 0.083 0.3006 0.006 0.96 1694 60 1716 32 1752 19 3.3 27 552668 21256.46 4.5575 0.070 0.3063 0.004 0.93 1722 57 1742 27 1753 22 1.8
  • 15. Lemieux et al. Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 28 138866 12624.2 5.1890 0.136 0.3370 0.008 0.92 1872 71 1851 48 1782 28 -5.1 29 154462 Infinite 4.9268 0.117 0.3188 0.007 0.96 1784 68 1807 43 1792 20 0.4 30 317874 Infinite 5.0859 0.097 0.3259 0.006 0.96 1818 64 1834 35 1820 19 0.1 31 434288 Infinite 4.8797 0.074 0.3147 0.005 0.95 1764 59 1799 27 1821 18 3.2 32 549866 Infinite 5.1098 0.108 0.3280 0.007 0.96 1829 67 1838 39 1837 18 0.4 33 1074683 Infinite 4.9281 0.088 0.3189 0.006 0.96 1784 62 1807 32 1842 18 3.1 34 532559 Infinite 5.1321 0.079 0.3268 0.005 0.95 1823 61 1841 28 1851 18 1.5 35 486350 Infinite 5.3359 0.133 0.3378 0.008 0.97 1876 73 1875 47 1867 18 –0.5 36 800934 Infinite 5.2065 0.096 0.3297 0.006 0.96 1837 65 1854 34 1868 19 1.7 37 521522 Infinite 5.3560 0.100 0.3374 0.006 0.96 1874 66 1878 35 1870 18 –0.2 38 559878 Infinite 5.2597 0.104 0.3319 0.007 0.96 1847 66 1862 37 1877 18 1.6 39 504199 Infinite 5.5461 0.111 0.3455 0.007 0.96 1913 69 1908 38 1878 18 –1.9 40 1003017 Infinite 5.5034 0.116 0.3425 0.007 0.96 1898 70 1901 40 1890 18 –0.5 41 895742 Infinite 5.3744 0.122 0.3341 0.008 0.96 1858 70 1881 43 1892 18 1.8 42 500929 25046.47 5.5076 0.122 0.3395 0.007 0.95 1884 70 1902 42 1899 21 0.7 43 750593 27799.75 5.5746 0.089 0.3432 0.005 0.95 1902 64 1912 31 1906 20 0.2 44 1060337 4331 5.7025 0.128 0.3561 0.008 0.96 1964 73 1932 43 1909 19 –2.9 45 699671 46644.7 5.6450 0.111 0.3442 0.007 0.96 1907 68 1923 38 1914 19 0.4 46 117007 Infinite 5.6858 0.135 0.3462 0.008 0.96 1917 73 1929 46 1915 20 –0.1 47 1110942 Infinite 5.3918 0.093 0.3325 0.006 0.96 1850 64 1884 32 1915 18 3.4 48 536381 Infinite 5.7471 0.110 0.3527 0.007 0.96 1947 69 1938 37 1918 18 –1.5 49 1763494 Infinite 5.3154 0.053 0.3283 0.003 0.95 1830 58 1871 19 1920 18 4.7 50 601071 Infinite 5.8051 0.144 0.3536 0.009 0.97 1952 76 1947 48 1921 18 –1.6 51 391738 Infinite 5.8067 0.092 0.3547 0.006 0.95 1957 66 1947 31 1923 18 –1.8 52 661043 Infinite 5.5558 0.069 0.3388 0.004 0.95 1881 61 1909 24 1929 18 2.5 53 582311 44793.16 5.4333 0.115 0.3315 0.007 0.96 1845 68 1890 40 1929 19 4.3 54 989480 Infinite 5.5502 0.089 0.3395 0.005 0.96 1884 64 1908 31 1931 18 2.4 55 409767 Infinite 5.6852 0.132 0.3470 0.008 0.96 1920 73 1929 45 1932 18 0.6 56 579405 38627 5.4663 0.076 0.3325 0.004 0.95 1851 61 1895 26 1932 19 4.2 57 585154 24381.42 5.5893 0.096 0.3405 0.006 0.94 1889 65 1914 33 1933 20 2.2 58 845458 Infinite 5.5816 0.095 0.3410 0.006 0.96 1891 65 1913 32 1933 18 2.2 59 488616 Infinite 5.8468 0.097 0.3528 0.005 0.94 1948 66 1953 32 1937 21 –0.6Published by NRC Research Press 60 561851 Infinite 5.7123 0.118 0.3498 0.007 0.96 1934 70 1933 40 1940 19 0.4 61 738167 Infinite 5.8019 0.085 0.3523 0.005 0.95 1945 65 1947 28 1941 18 –0.2 62 956282 Infinite 5.5300 0.090 0.3365 0.005 0.96 1870 64 1905 31 1941 18 3.7 63 624261 11350.2 5.6911 0.231 0.3523 0.014 0.95 1945 96 1930 78 1942 27 –0.2 64 949801 39575.05 5.7439 0.106 0.3505 0.006 0.95 1937 68 1938 36 1948 19 0.5 65 1509648 Infinite 5.7635 0.073 0.3527 0.004 0.95 1947 63 1941 25 1950 19 0.1 66 402045 Infinite 5.8819 0.075 0.3524 0.004 0.94 1946 63 1959 25 1954 19 0.4 67 388872 Infinite 5.7827 0.118 0.3468 0.007 0.96 1919 69 1944 40 1955 18 1.8 529
  • 16. 530 Table 1 (continued). Isotopic ratios Apparent ages (Ma) 206Pb 206 Pb 207 Pb 206 Pb Err. 206 Pbà ± 207 Pbà 207 Pbà Disc. Grain # (cps) 204 Pb 235 U ± (2s) 238 U ± (2s) corr. 238 U (2s) 235 U ± (2s) 206 Pbà ± (2s) (%) 68 361914 Infinite 5.9507 0.134 0.3582 0.008 0.96 1974 74 1969 44 1955 18 –0.9 69 1328626 Infinite 5.6982 0.092 0.3463 0.006 0.96 1917 65 1931 31 1958 18 2.1 70 1454322 19135.82 5.6395 0.091 0.3416 0.005 0.94 1894 63 1922 31 1959 22 3.3 71 352352 Infinite 5.7087 0.145 0.3428 0.009 0.97 1900 75 1933 49 1961 18 3.1 72 1837660 48359.47 5.7008 0.073 0.3451 0.004 0.95 1911 62 1931 25 1963 19 2.6 73 1593995 31879.9 5.9513 0.060 0.3608 0.003 0.94 1986 62 1969 20 1968 19 –0.9 74 817904 Infinite 5.9524 0.096 0.3570 0.006 0.96 1968 67 1969 32 1974 18 0.3 75 1598760 Infinite 5.8846 0.081 0.3537 0.005 0.95 1952 64 1959 27 1981 18 1.4 76 705124 Infinite 5.9911 0.077 0.3527 0.004 0.95 1948 63 1975 25 1994 18 2.3 77 1067547 4490 5.9714 0.224 0.3550 0.013 0.98 1959 94 1972 74 1994 19 1.8 78 521489 37249.21 6.0960 0.081 0.3583 0.004 0.93 1974 63 1990 26 2000 22 1.3 79 776775 Infinite 5.8919 0.131 0.3449 0.008 0.96 1910 71 1960 44 2010 18 5.0 80 382391 Infinite 5.9778 0.115 0.3406 0.006 0.96 1889 67 1973 38 2040 19 7.4 81 313544 Infinite 6.6290 0.104 0.3734 0.006 0.95 2046 69 2063 32 2051 19 0.3 82 302188 9443.374 6.7424 0.189 0.3745 0.009 0.92 2051 80 2078 58 2078 28 1.3 83 313566 Infinite 6.6748 0.140 0.3716 0.008 0.95 2037 74 2069 43 2081 20 2.1 84 260927 Infinite 6.9272 0.194 0.3814 0.010 0.94 2083 83 2102 59 2088 24 0.2 85 586554 13640.79 6.7869 0.093 0.3762 0.004 0.92 2059 66 2084 29 2120 23 2.9 86 517437 Infinite 6.9086 0.146 0.3766 0.008 0.96 2060 75 2100 44 2128 19 3.2 87 211504 Infinite 7.5536 0.170 0.3997 0.009 0.96 2168 81 2179 49 2151 18 –0.8 88 402300 12190.9 7.2474 0.177 0.3852 0.009 0.94 2100 79 2142 52 2167 24 3.1 89 1942357 Infinite 6.6772 0.128 0.3543 0.006 0.94 1955 68 2070 40 2184 22 10.5 90 1052854 Infinite 7.5010 0.180 0.3922 0.009 0.97 2133 82 2173 52 2212 18 3.6 91 199856 33309.27 8.0738 0.164 0.4063 0.008 0.96 2198 79 2239 45 2250 19 2.3 92 404980 25311.27 8.0241 0.169 0.4049 0.008 0.95 2192 80 2234 47 2254 19 2.8 93 344700 Infinite 7.7519 0.144 0.3896 0.007 0.95 2121 74 2203 41 2257 19 6.0 94 237583 47516.52 8.4847 0.215 0.4131 0.010 0.95 2229 86 2284 58 2303 21 3.2 95 215540 Infinite 8.5484 0.167 0.4214 0.008 0.94 2267 80 2291 45 2307 21 1.8 96 412688 8971.482 8.7221 0.186 0.4267 0.008 0.91 2291 80 2309 49 2318 26 1.2 97 1935088 8562.34 7.9150 0.171 0.3893 0.008 0.96 2120 78 2221 48 2332 19 9.1 98 560728 Infinite 9.0870 0.199 0.4414 0.010 0.96 2357 87 2347 51 2335 18 –0.9 Can. J. Earth Sci. Vol. 48, 2011 99 477989 Infinite 8.7823 0.150 0.4224 0.007 0.95 2271 78 2316 40 2347 18 3.2Published by NRC Research Press 100 624181 Infinite 8.9060 0.168 0.4243 0.008 0.96 2280 81 2328 44 2360 18 3.4 101 380158 47519.8 8.6830 0.208 0.4094 0.010 0.96 2212 85 2305 55 2370 18 6.6 102 694627 Infinite 9.2172 0.211 0.4382 0.010 0.96 2343 88 2360 54 2379 18 1.5 103 1168349 16004.78 9.1020 0.210 0.4309 0.010 0.95 2310 86 2348 54 2385 20 3.1 104 432616 Infinite 9.2924 0.167 0.4286 0.008 0.95 2299 80 2367 43 2411 18 4.6 105 385544 Infinite 9.9495 0.315 0.4585 0.014 0.96 2433 104 2430 77 2417 21 –0.7 106 2043110 Infinite 9.6659 0.170 0.4431 0.008 0.96 2364 82 2403 42 2444 17 3.2 107 1072864 Infinite 9.7237 0.200 0.4452 0.009 0.96 2374 86 2409 50 2448 17 3.0
  • 17. Lemieux et al. 531 represented by three grains between 427 and 436 Ma. Note: cps, counts per second; Err. corr., error correction; Disc., discordance; UTM, Universal Transverse Mercator. Analyses that are >5% discordant or >5% reverse discordant (in italics in table) have Disc. Eleven zircons fall in the interval 1076–1458 Ma, whereas (%) 5.1 4.6 2.7 2.9 0.6 22 grains form an age group between 2051 and 2448 Ma. The sample yielded four Archean zircons at 2685, 2714, 2761, and 2770 Ma. ± (2s) 22 20 18 17 17 Discussion: paleogeographic implication of results The detrital zircons in the Imperial and Tuttle formations Pbà Pbà 2600 2685 2714 2761 2770 were likely derived from one or more source regions charac- 207 206 terized by sedimentary and (or) igneous provinces compris- ing largely (i) Paleoproterozoic and Archean (i.e., > 1.6 Ga) ± (2s) zircons, (ii) Mesoproterozoic zircons with abundant ‘‘Gren- ville-aged’’ grains in the 1.0–1.3 Ga interval, and (iii) late 40 56 36 51 49 Precambrian and early Paleozoic zircons in the 400–500 and 500–700 Ma intervals (Fig. 5). Samples from the Impe- rial Formation show a similar detrital zircon age spectrum; the westernmost sample (07WZ020A; Fig. 2), however, is Pbà 2548 2639 2688 2729 2770 U 235 207 marked by a greater proportion of Mesoproterozoic (and older) grains, whereas the eastern sample 07TH33B (Fig. 2) Apparent ages (Ma) contains predominantly late Neoproterozoic (and younger) (2s) zircons. Here, we cannot rule out the possibility that a minor 81 93 86 95 95 ± fraction of a total population was missed because of the rel- atively low number of grains (n £ 61) dated in these samples (e.g., Vermeesch 2004). In contrast, the Tuttle Formation Pbà 2466 2561 2641 2681 2752 U samples display a more restricted relative probability age 238 206 distribution, marked by a strong peak of middle Paleoproter- ozoic ages, with lesser peaks representing Mesoproterozoic, earlier Paleoproterozoic, and Archean ages. From two sam- corr. 0.92 0.95 0.95 0.96 0.96 Err. ples, our Tuttle Formation results are similar to detrital zir- con from five samples of Tuttle Formation collected from the Richardson Mountains that have prominent ages of ca. ± (2s) 360–390, 1000–1300, and 1800–2000 Ma, with minor 0.006 0.010 0.007 0.010 0.009 amounts of 430–680 Ma (Beranek et al. in press). The spectrum of Paleoproterozoic and Archean zircon ages in the Imperial Formation is marked by dates in the in- 0.4661 0.4879 0.5063 0.5158 0.5324 tervals 1.8–2.1 and 2.6–2.8 Ga, and a virtual absence of Pb U grains between 2.1 and 2.6 Ga. The age spectrum of the 238 206 Tuttle Formation, on the other hand, is defined by an overall predominance of 1.8–2.0 Ga (and older) zircons. These ages ± (2s) match well those in basement provinces of the northwestern 0.177 0.263 0.177 0.255 0.252 Canadian Shield (Fig. 6), in particular, the 1845 Ma Ga Fort Simpson Arc, 1.84–1.95 Ga Wopmay Orogen, 1.92–2.1 Ga Taltson Arc, and >2.5 Ga Slave and Rae provinces (Fig. 6; 11.2917 12.4471 13.1177 13.7007 14.3063 e.g., Hoffman 1988; Villeneuve et al. 1991, 1993; Bostock Pb and van Breemen 1994; Gehrels and Ross 1998). As demon- U 235 207 strated by the 1.8–2.0 Ga detrital zircon in Mesoproterozoic Isotopic ratios strata from the East Greenland Caledonides (Watt et al. been excluded from further consideration. 2000), the Greenland portion of Laurentia is also a potential 13412.13 1828.363 10132.2 Infinite Infinite source for Paleoproterozoic grains within Imperial and Tut- Pb Pb tle formations. Ca. 1.74–1.79 Ga igneous rocks in the west- 206 204 ern Churchill Province are a potential source for provenance of the 1.75–1.80 Ga zircons (Hoffman 1988; van Breemen etTable 1 (concluded ). al. 2005), as are ca. 1.74–1.78 Ga igneous rocks in northern 455949 496249 427837 829406 156779 206Pb (cps) Greenland (e.g., Nutman et al. 2008). Grains from Imperial Formation between 2.0 and 2.5 Ga are of interest, as they are common in Paleozoic miogeocli- Grain # nal strata in the northern Cordillera and the clastic wedge of the Arctic Islands, but largely absent in the southern Cordil- 108 109 110 111 112 lera (e.g., Gehrels et al. 1995; McNicoll et al. 1995; Gehrels Published by NRC Research Press
  • 18. 532 Can. J. Earth Sci. Vol. 48, 2011Fig. 5. U–Pb age spectra of single detrital zircon grains for the Imperial and Tuttle formations, northern Mackenzie Mountains. Samples arearranged from oldest at the base to youngest at the top. The grouping between 500 and 700 Ma (grey shading) stands out as it is absentfrom the Laurentian magmatic record. Plot includes all analyses with <5% discordance.and Ross 1998; Nelson and Gehrels 2007). They could have is likely that much of the Proterozoic strata remained unex-been sourced from the 2.0–2.4 Ga accreted Hottah, Buffalo posed throughout the Late Devonian and Early Carbonifer-Head, and Chinchaga terranes within the Wopmay orogen, ous. Thus, the Paleoproterozoic and Archean zircons in ourthe ca. 2.35 Ga Arrowsmith orogen of the Rae domain samples probably originated from many different provinces(Berman et al. 2005), or recycling of Paleoproterozoic strata of the adjacent northwestern Canadian Shield and likelyof the western Churchill Province, in which abundant 1.9– went through multiple sedimentary cycles prior to their dep-2.4 Ga zircons have been documented (Davis et al. 2005). osition in the Peel Region.They could also have been recycled from Neoproterozoic The origin of the Mesoproterozoic zircon in our samplesstrata deposited along the northwestern margin (present-day is unclear. On geochronological and geochemical grounds,coordinates) of Laurentia that yielded abundant Paleoproter- Rainbird et al. (1992, 1997) interpreted the 1.0–1.6 Ga zir-ozoic and Archean zircons (Fig. 7; Rainbird et al. 1992, con within Neoproterozoic quartzarenites of the Shaler and1997). Given the presence of thick early and middle Paleo- Mackenzie Mountains supergroups in northwestern Canadazoic strata preserved in the Interior Plains and Arctic Plat- to have been sourced from the Grenville orogen and trans-form (e.g., Fritz et al. 1991; Trettin et al. 1991), however, it ported over 3000 km across the Laurentian craton in exten- Published by NRC Research Press
  • 19. Fig. 6. Basement domains of northern Laurentia, northern Cordilleran miogeocline and outboard terranes, Pearya terrane, and Innuitian orogen. Locations of samples from other studies discussed in text are indicated. Question marks indicate areas of uncertain basement affinity. North America modified after Gehrels et al. (1999), Gehrels and Ross (1998), Ross and Villeneuve (2003), and Nelson and Gehrels (2007). Greenland modified after Kirkland et al. (2009) and St. Onge et al. (2009). Lemieux et al.Published by NRC Research Press 533
  • 20. 534 Can. J. Earth Sci. Vol. 48, 2011Fig. 7. Probability–density diagrams illustrating U–Pb age spectra of single detrital zircon grains for Proterozoic strata of the CanadianArctic Islands and northern Mackenzie Mountains and Interior Plains. The compilation includes data from the Neoproterozoic Shaler Groupand Mackenzie Mountains reported in Rainbird et al. (1992, 1996, 1997) and Villeneuve et al. (1998). Data from the Imperial and Tuttleformations are from this study.sive Neoproterozoic river systems. An alternative possibility bard (Pettersson et al. 2009) are consistent with thisis that these grains were derived from more ‘‘proximal’’ hypothesis. Given the presence, however, of Grenville-agedsources, as growing evidence suggests that 1.0–1.3 Ga crust detrital zircons in Neoproterozoic and Paleozoic sedimentarywas present along and outboard of the Canadian Cordilleran rocks from Greenland and throughout Laurentia, includingmargin (e.g., Gehrels and Ross 1998; Ross et al. 2005; Le- the Cordillera, Canadian Shield, and Arctic Islands, whichmieux et al. 2007; Nelson and Gehrels 2007). Alternatively, may have been recycled in any number of configurations,McNicoll et al. (1995) documented a number of Mesoproter- these grains provide limited diagnostic provenance informa-ozoic zircon grains (mostly between 1.04 and 1.20 Ga) from tion.sandstones of the Middle and Upper Devonian clastic wedge An exposed late Neoproterozoic – Cambrian source is in-in the Arctic Islands, as well as many Paleoproterozoic and dicated by the presence, in the Imperial Formation, of 500–Archean zircons (Fig. 8). McNicoll et al. (1995) postulated 700 Ma detrital zircons (grey shading in Fig. 5). This agethat metamorphic and metasedimentary rocks of the East range stands out as it is virtually absent from the mid-Paleo-Greenland Caledonian orogen provided the best potential zoic miogeoclinal record of the North American Cordillera,source of Mesoproterozoic detrital zircon. This hypothesis including in terranes of the mid- to late Paleozoic peri-Lau-was later supported by Patchett et al. (1999) who singled rentian realm (Fig. 8; e.g., Gehrels et al. 1995; Gehrels andout the Caledonian orogenic belt as the only plausible ulti- Ross 1998; Nelson and Gehrels 2007). Gehrels and Dickin-mate sediment source for marginal Cambrian to Devonian son (1995) dated 500–525 Ma zircons in Triassic miogeocli-strata present in the Franklinian mobile belt of Arctic Can- nal strata in Nevada and tied their provenance to nearbyada, based on their Nd isotopic signature and known paleo- plutons in the western United States. There is no known lo-current directions. Patchett and colleagues further inferred cal source for zircons of this age in the region of our studythat following subsequent uplift and erosion of the active area. One possibility is that these grains were derived fromFranklinian belt in Middle and Late Devonian time, as pro- ca. 575 and 570 Ma synrift volcanic rocks that are preservedposed by Embry and Klovan (1976), recycled sediments within Neoproterozoic Windermere Supergroup strata fromlargely propagated southwestward from the orogenic system, the southeastern Canadian Cordillera (Colpron et al. 2002).reaching the northwestern margin of North America and giv- This hypothesis is unlikely because mafic and alkaline vol-ing rise to the thick Upper Devonian Imperial Assemblage. canic rocks are unlikely to yield voluminous zircon, and itThe occurrence of relatively abundant Grenvillian detrital would have required northeasterly and (or) easterly sedimentzircon ages within the Cambrian Portfjeld Formation of transport across the basin, in a general direction opposite tonorthern Greenland (Kirkland et al. 2009), the Scottish Cale- known paleocurrent data within the Imperial Formationdonides (Cawood et al. 2007), and lesser amounts in Sval- (Gordey et al. 1991; Braman and Hills 1992; Hadlari et al. Published by NRC Research Press
  • 21. Lemieux et al. 535Fig. 8. Probability–density diagrams illustrating U–Pb age spectra of single detrital zircon grains for selected Devonian miogeoclinal strataalong the North American Cordilleran margin. Also included are data from strata of the Devonian clastic wedge of Arctic Canada (McNi-coll et al. 1995). Data for east-central Alaska reported in Gehrels et al. (1999); data for northern British Columbia reported in Gehrels andRoss (1998) and Ross et al. (1993); data for Nevada reported in Gehrels and Dickinson (1995); data for Sonora reported in Gehrels andStewart (1998). The grey shading highlights a range of ages that is absent from the Laurentian magmatic record.2009). Another alternative is that these grains were derived buried on the continental shelves of the Arctic Ocean, layfrom the 503 Ma igneous rocks of Pearya Terrane, northern outboard of the Arctic North American margin in mid-Pale-Ellesmere Island (Trettin et al. 1987), however, very limited ozoic time, and may have been an important source of sedi-geochronological data from Pearya have not recognized ment for the Sverdrup Basin from the Carboniferous to the520–700 Ma magmatism; a detrital zircon study of rocks Jurassic (Embry 1992). Miller et al. (2006) speculated thatfrom Pearya that predate accretion to Laurentia would test the landmass consisted of igneous and (or) sedimentarythis option. source regions comprising predominantly 500–600 Ma zir- In a detrital zircon study of Triassic sandstone from the con, with subordinate Ordovician and late Precambrian pop-circum-Arctic region, Miller et al. (2006) reported domi- ulations. In contrast, grains from the Ivishak Formation werenantly 500 to 700 Ma zircon populations in sandstone from interpreted to have been derived from late Precambrian plu-the Pat Bay and Ivishak formations, northern Axel Heiberg tons dated in basement rocks of Arctic Alaska (e.g., AmatoIsland and northeastern Alaska, respectively (Fig. 9). On the et al. 2009), which were also interpreted to have contributedbasis of facies change (Embry 1991) and the dominance of abundant 540–700 Ma detrital zircon to Paleozoic siliciclas-Meso- and Paleoproterozoic detrital zircons within the sam- tic strata of Seward Peninsula (Amato et al. 2009), part ofple, the Pat Bay Formation was inferred by Miller et al. the Arctic Alaska – Chukotka terrane. During Paleozoic(2006) to have been shed from a proposed landmass termed time, Arctic Alaska – Chukotka had affinities with Siberia‘‘Crockerland’’ and situated to the north of the present-day (Patrick and McClelland 1995), as demonstrated by 420–sampling site (see Embry 1992); it is unknown whether 490, 520–720, and 900–2000 Ma detrital zircon within Dev-Crockerland was a distinct landmass or part of a larger cra- onian to Mississippian strata from Wrangel Island, part ofton (Siberia?). This proposed landmass, which may lie the eastern Siberian Shelf (Miller et al. 2010). Largely based Published by NRC Research Press
  • 22. 536 Can. J. Earth Sci. Vol. 48, 2011Fig. 9. Probability–density diagrams illustrating U–Pb age spectra of single detrital zircon grains for Triassic strata of the Canadian ArcticIslands and northern Arctic Alaska terrane. The compilation includes data from the Pat Bay and Ivishak formations reported in Miller et al.(2006) and Villeneuve et al. (1998). The grey shading highlights a range of ages that is absent from the Laurentian magmatic record. Datafor the Imperial and Tuttle formations are also shown (this study).on the occurrence of dominant 540–700 Ma zircon in Paleo- southwestern Siberia (e.g., Gladkochub et al. 2006; Amatozoic strata, Arctic Alaska – Chukotka terrane is interpreted et al. 2009; Pease and Scott 2009), Arctic Alaska – Chu-to be exotic to Laurentia in early Paleozoic (Amato et al. kotka (e.g., Patrick and McClelland 1995; Johansson et al.2009), and it possibly accreted to northern Laurentia by the 2004), and Avalonia (Murphy et al. 2004). Whether sedi-Devonian (Lane 2007; Colpron and Nelson 2009). From the ment from these cratons could reach Laurentia in early andperspective of Imperial Formation, the presence of 500– (or) mid-Paleozoic time is very poorly understood (Miller et700 Ma zircons in circum-Arctic Triassic strata not only al. 2006; Lane 2007). Recent early- to mid-Paleozoic globalsuggest an Arctic provenance for these grains within the Im- plate reconstructions (e.g., Scotese 2001; Lawver et al.perial Formation, but that this source was available to north- 2002; Golonka et al. 2003) have positioned Baltica and Si-ern Laurentia as early as the Devonian. berian cratons in relative proximity to each other, outboard The occurrence of 500–700 Ma zircons, a significant of the northern (present-day coordinates) Laurentian margin.component of the detrital zircon population in the Imperial It appears that Baltica and Laurentia shared a complex his-Formation, provides important insights into patterns of sedi- tory of Neoproterozoic and Paleozoic major orogenic andment dispersal in the northern Cordillera in Late Devonian break-up events (Torsvik et al. 1996) and formed part oftime. Because zircon of these ages are virtually absent from the same continent following the Siluro-Devonian Caledo-the Laurentian magmatic record (e.g., Amato et al. 2009), nian event (e.g., Golonka et al. 2003) and, therefore, mayincluding basement of the east Greenland Caledonides (e.g., have been in position to supply sediment to Laurentia byWatt et al. 2000), it seems clear that a number of zircon in Devonian time (Fig. 10). The detrital zircon within Imperialthe Peel Region were derived from an ‘‘exotic’’ source re- and Tuttle formations, however, do not reflect the 980–gion. Zircons of these ages have been documented in mag- 710 Ma accretionary tectonic events of northern Balticamatic provinces on other continents, such as the eastern (e.g., Pease et al. 2008) nor the 980–910 and 830–710 Mamargin of Baltica (e.g., Willner et al. 2003), northern and igneous activity associated with the Valhalla orogeny of Published by NRC Research Press
  • 23. Lemieux et al. 537Fig. 10. Middle to Late Devonian paleogeography showing Laurentia, Baltica, and Siberia after Lawver et al. (2002) and Golonka et al.(2003).Scotland, East Greenland, Svalbard, and Norway (Cawood dence for progressive docking of an allochthonous landmasset al. 2010). We cannot rule out a Baltican source, which to northwestern Laurentia from Silurian through Early Car-would have been on the eastern, or opposite, margin of the boniferous time, and speculated the terrane to include partCaledonides, but we might also expect 980–720 Ma detrital of the Siberia craton (possibly including Arctic Alaska –zircon if it were a dominant source. On the present eastern Chukotka). If part of Siberia (as, or including, Crockerland)margin of Laurentia, at right angles to all known paleocur- was the ultimate source for the late Neoproterozoic andrent directions (Embry and Klovan 1976; Hadlari et al. Cambrian zircons in the Imperial Formation, it had to be ex-2009), Avalonian rocks of Cambrian age contain a high pro- posed and provide sediments to the northern mainland priorportion of ca. 580–680 Ma detrital zircon (Murphy et al. to the Carboniferous. The absence of 500–700 Ma zircons in2004). By Early–Middle Devonian time, Avalonia collided Devonian strata, albeit from a restricted data set, of the Arc-with southern Baltica and Laurentia during the Acadian or- tic Islands and Cordilleran miogeocline (see earlier in theogeny (e.g., van Staal et al. 1998); however, Acadian fore- text), including the overlying Upper Devonian – Lower Car-land basin sandstones from New England contain boniferous Tuttle Formation (this study) is of interest andpredominantly 420–460 and 1000–1260 Ma detrital zircon, may suggest the source to have supplied a very restricted re-attributed to recycling of the preexisting continental margin gion of the northern mainland over a limited period of time.rather than a large influx of Avalonian sediment (McLennan Our data, therefore, document a significant shift in prove-et al. 2001). Siberia has a Precambrian history similar to nance from a source with ‘‘Siberian’’ affinity to one with aLaurentia (e.g., Rainbird et al. 1998), including ca. 2100– predominantly Laurentian signature, in part supporting the1800 Ma assembly of Archean cratons but ending with a ca. interpretation of Gordey et al. (1991), who suggested that750–700 Ma rift-to-drift transition away from Rodinia (e.g., by the mid-Mississippian, sedimentary rock of westerly andPisarevsky et al. 2008). northerly derivation had given way to clastic input from the In a synthesis of the mid-Paleozoic tectonic evolution of Laurentian craton.northwestern North America, Lane (2007) documented evi- The Devonian, Silurian, and late Ordovician grains popu- Published by NRC Research Press
  • 24. 538 Can. J. Earth Sci. Vol. 48, 2011lating the Imperial and Tuttle formations were likely derived Laurentia in Late Devonian time to a source of Laurentianfrom igneous rocks along the Canada – Alaska Arctic mar- affinity by Mississippian time.gin (e.g., Gehrels and Ross 1998). The Devonian and LateOrdovician grains could have been derived from (i) 354– Acknowledgements406 Ma syntectonic granite to monzodiorite of the northern This work was funded by the Northern Oil and Gas Sci-Yukon (Gordey et al. 1991; Lane 1997); (ii) Middle and ence Research Initiative 2005–2009 of Indian and NorthernUpper Devonian plutons of the northern Axel Heiberg and Affairs Canada (INAC) through the ‘‘Regional GeoscienceEllesmere islands (Trettin et al. 1987, 1992); and (iii) 454 Ma Studies and Petroleum Potential of the Peel Plateau andvolcanics of the northern Ellesmere Islands (Trettin et al. Plain, NWT and Yukon’’ Project and the INAC Strategic In-1987). As suggested by their occurrence in Imperial and vestments in Northern Economic Development ProgramTuttle formations, as well as in Middle and Upper Devon- (SINED). The Radiogenic Isotope Facility (RIF) at the Uni-ian strata of the Arctic Islands, northwest Yukon, and east- versity of Alberta is supported by a Natural Sciences andcentral Alaska (e.g., McNicoll et al. 1995; Gehrels et al. Engineering Research Council of Canada (NSERC) Major1999), ca. 430 Ma grains likely blanketed much of north- Facility Access grant. Staff at the RIF is thanked for theirwestern Laurentia as a result of orogenic magmatism along collaboration. Robert H. Rainbird reviewed an early versionthe margin of Arctic Alaska and the Canadian Arctic of the manuscript and offered constructive comments. We(Gordey et al. 1991; Gehrels and Ross 1998; Gehrels et gratefully acknowledge the Associate Editor W.J. Davis andal. 1999; Lane 2007). Coupled with the presence of 500– very helpful reviews by J.M Amato and V. Pease.700 Ma detrital zircons inferred to have been derived froma source exotic to Laurentia, the lower Paleozoic detrital Referenceszircons may even record magmatism of the arc(s), conti- Aitken, J.D., Cook, D.G., and Yorath, C.J. 1982. Upper Rampartsnental or otherwise, that collided with the northern Lauren- River (106G) and Sans Sault Rapids (106H) map areas, Districttian margin. of Mackenzie. Geological Survey of Canada, Memoir 388, 48 p. In summary, detrital zircons in the Imperial and Tuttle Allen, T.L., Fraser, T.A., and Utting, J. 2009. Upper Devonian toformations were likely derived from an extensive region of Carboniferous strata II — Tuttle Formation Play. In Regionalnorthwestern Lauentia, including the northwestern Canadian Geoscience Studies and Petroleum Potential, Peel Plateau andShield, igneous and sedimentary provinces of Canada’s Arc- Plain: Project Vol. Edited by L.J. Pyle and A.L. Jones. North-tic Islands, and possibly the northern Yukon. Given the high west Territories Geoscience Office and Yukon Geological Sur-resistance of zircons, we must allow for multiple stages of vey of Canada, NWT Open File 2009-02, pp. 365–409.recycling from older sedimentary successions. Ultimate Amato, J.M., Toro, J., Miller, E.L., Gehrels, G.E., Farmer, G.L.,sources for some zircons documented here possibly include Gottlieb, E.S., and Till, A.B. 2009. Late Proterozoic – Paleozoic(i) the East Greenland Caledonides; (ii) part of the Siberian evolution of the Arctic Alaska – Chukotka terrane base on U–Pb igneous and detrital zircon ages: Implications for Neoproterozoiccraton, which may include Arctic Alaska – Chukotka that paleogeographic reconstructions. Geological Society of Americalay outboard of Laurentia in early Paleozoic time; (iii) Bal- Bulletin, 121(9–10): 1219–1235. doi:10.1130/B26510.1.tica; and (iv) Precambrian provinces of Laurentia, in partic- Bassett, H.G. 1961. Devonian stratigraphy, central Mackenzieular basement rocks of northern Greenland, the Trans- River region, Northwest Territories, Canada. In Proceedings ofHudson Orogen, the western Churchill Province of central the 1st International Symposium on Arctic Geology, Vol. 1. Edi-Laurentia, and the Grenville Province of eastern Laurentia. ted by G.O. Raasch. University of Toronto Press, Toronto, Ont., pp. 481–498.Conclusions Beranek, L.P., Mortensen, J.K., Lane, L., Allen, T., Fraser, T., Ha- dlari, T., and Zantvoort, W.G. 2010. Detrital zircon geochronol- This study presents detrital zircon analyses from the ogy of the western Ellesmerian clastic wedge, northwesternUpper Devonian Imperial Formation and Upper Devonian – Canada: insights on Arctic tectonics and evolution of the north-Lower Carboniferous Tuttle Formation, exposed in the ern Cordilleran miogeocline. Geological Society of Americanorthern Mackenzie Mountains of the southern Peel Region. Bulletin, 122: 1899–1911.The Imperial Formation records records a wide spectrum of Berman, R.G., Sanborn-Barrie, M., Stern, R.A., and Carson, C.J.U–Pb ages from late Precambrian and early Paleozoic, 2005. Tectonometamorphism at ca. 2.35 and 1.85 Ga in the RaeMeso- and Paleoproterozoic, and Archean source rocks. domain, western Churchill Province, Nunavut, Canada: insightsThis age spectrum favors derivation predominantly from from structural, metamorphic and in situ geochronological ana-northern Laurentia. The presence of late Precambrian and lysis of the southwestern Committee Bay Belt. Canadian Miner- alogist, 43: 409–442. doi:10.2113/gscanmin.43.1.409.early Paleozoic zircons, absent from the Laurentian mag- Berman, R.G., Ryan, J.J., Gordey, S.P., and Villeneuve, M. 2007.matic record, suggest provenance from an exotic source re- Permian to Cretaceous polymetamorphic evolution of the Stew-gion to the north. Possible sources include Baltica, Arctic art River region, Yukon–Tanana terrane, Yukon, Canada: P–TAlaska – Chukotka, and Siberia. evolution linked with in situ SHRIMP monazite geochronology. In contrast, the detrital age spectrum of Tuttle Formation Journal of Metamorphic Geology, 25(7): 803–827. doi:10.1111/j.samples displays a more restricted age distribution consis- 1525-1314.2007.00729.x.tent with derivation ultimately from sources with Laurentian Bostock, H.H., and van Breemen, O. 1994. Ages of detrital andaffinity. These data, therefore, indicate that sediment prove- metamorphic zircons and monazites from pre-Taltson magmaticnance underwent an abrupt shift from an influx of northerly zone basin at the western margin of the Rae Province. Canadianderived sediments including zircon ages apparently exotic to Journal of Earth Sciences, 31: 1353–1364. Published by NRC Research Press
  • 25. Lemieux et al. 539Braman, D.R., and Hills, L.V. 1992. Upper Devonian and Lower of Sonora, Mexico. Journal of Geophysical Research, 103(B2): Carboniferous Miospores, Western District of Mackenzie and 2471–2487. doi:10.1029/97JB03251. Yukon Territory, Canada. Palaeontographica Canadiana 8, pp. Gehrels, G.E., Dickinson, W.R., Ross, G.M., Stewart, J.H., and Ho- 1–97. well, D.G. 1995. Detrital zircon reference for Cambrian to Trias-Cawood, P.A., Nemchin, A.A., Strachan, R., Prave, T., and Krab- sic miogeoclinal strata of western North America. Geology, bendam, M. 2007. Sedimentary basin and detrital zircon record 23(9): 831–834. doi:10.1130/0091-7613(1995) along East Laurentia and Baltica during assembly and breakup 023<0831:DZRFCT>2.3.CO;2. of Rodinia. Journal of the Geological Society, 164(2): 257–275. Gehrels, G.E., Johnsson, M.J., and Howell, D.G. 1999. 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