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Yukon, Canada: Implications Regarding a Linkage Between the Wrangellia Composite Terrane and the Western Margin of Laurasia

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Yukon, Canada: Implications Regarding a Linkage Between the Wrangellia Composite Terrane and the Western Margin of Laurasia Canadian Journal of Earth Sciences Provenance analysis of the Dezadeash Formation (Jura- Cretaceous), Yukon, Canada: Implications regarding a linkage between the Wrangellia composite terrane and the western margin of Laurasia Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2017-0244.R2 Manuscript Type: Article Date Submitted by the 05-Sep-2018 Author: Complete List of Authors: Lowey, Grant;Draft Pilot Mountain Keyword: Provenance, geochemistry, petrography, Dezadeash, Wrangellia Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 89 Canadian Journal of Earth Sciences 1 1 2 3 4 5 6 7 8 9 10 Provenance analysis of the Dezadeash Formation (Jura-Cretaceous), Yukon, Canada: 11 Implications regarding a linkage between the Wrangellia composite terrane 12 and the western margin of Laurasia 13 14 15 16 17 Draft 18 19 20 Grant W. Lowey 21 22 23 24 P.O. Box 21254 25 Whitehorse, Yukon, Canada, Y1A 6R2 26 (E-mail: [email protected]) 27 28 29 30 Keywords Provenance, geochemistry, petrography, Dezadeash, Wrangellia, turbidite 31 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 89 2 32 Abstract: The Mesozoic convergence of the allochthonous Wrangellia composite terrane 33 (WCT) with the western margin of Laurasia coincided with the construction of the Chitina 34 magmatic arc on the WCT, and the dispersal of volcanic flows and sediment gravity flows 35 into an adjacent flysch basin. The basin, preserved as the Gravina-Nutzotin belt, includes 36 the Dezadeash Formation in southwest Yukon, the Nutzotin Mountains sequence in 37 southern Alaska, and the Gravina belt in southeastern Alaska. The Dezadeash Formation is 38 a submarine fan system comprising stacked channel-lobe transition and lobe deposits 39 interposed with overbank deposits. Conglomerate pebble-counts, sandstone point-counts, 40 detrital zircon ages, and major element, trace element, rare earth element, and Sm-Nd 41 isotopic geochemistry of sandstone, mudstone, and hemipelagite beds suggests that the 42 deposits consist mainly of first-cycle Draftvolcanogenic detritus shed from the undissected 43 Chitina arc, in addition to material eroded from the WCT. The arc was constructed of 44 undifferentiated magma sourced from the depleted mantel, as well as older crustal material 45 attributed to the WCT proxying for continental crust. The compositional provenance 46 results, together with published paleocurrent data for the Dezadeash Formation and 47 compositional and directional provenance indicators from the Nutzotin Mountains sequence 48 and Gravina belt, does not require a sediment source from Laurasia. The provenance record 49 is compatible with deposition of the Gravina-Nutzotin belt in a convergent plate margin 50 setting. 51 52 Introduction 53 The Dezadeash Formation is part of the Gravina-Nutzotin belt (Berg et al., 1972), 54 an assemblage of Late Jurassic to Early Cretaceous volcanolithic turbidites up to 3000 m 55 thick with locally important interbedded conglomerate and volcanic rocks, that extends https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 89 Canadian Journal of Earth Sciences 3 56 from southeastern Alaska, through southwestern Yukon, and into southern Alaska. It is 57 subdivided from south to north, into the Gravina belt, Dezadeash Formation, and Nutzotin 58 Mountains sequence (Fig.1). These assemblages are interpreted as submarine fan deposits 59 and submarine volcanic flows that unconformably overly the eastern margin of the 60 allochthonous Wrangellia composite terrane (WCT, ~Insular superterrane, Monger, 2014), 61 a microcontinent assembled in the paleo-Pacific Ocean (Beranek et al., 2014). The 62 Dezadeash Formation and Nutzotin Mountains sequence are interpreted as the same 63 stratigraphic unit that was dismembered and displaced ~370 km by the Denali fault system 64 (Eisbacher, 1976; Lowey, 1998); their geographic continuity with the Gravina belt is 65 uncertain, but all three assemblages were likely deposited in the same overall tectonic 66 setting (Berg et al., 1972). However, Draftthe tectonic setting is controversial due to 67 uncertainties regarding the timing and location of collision of the WCT with Laurasia 68 (McCelland et al., 1992; Monger et al., 1994), the number of volcanic arcs present and their 69 polarity (Nokleberg and Richter, 2007; Gehrels et al., 2009), and whether the margin of 70 Laurasia contributed sediment to the Gravina-Nutzotin belt (Berg et al., 1972; Nokleberg et 71 al., 1985; Kapp and Gehrels, 1998; McClelland and Mattinson, 2000). 72 A compositional provenance link between the Gravina-Nutzotin belt and Laurasia 73 was proposed by Kapp and Gehrels (1998) who concluded that 380-310 and >900 Ma 74 detrital zircons from the Gravina belt were sourced from the continental margin of Laurasia 75 (i.e., Yukon-Tanana and Stikine terranes, Fig. 1). However, Hults et al. (2013) argued that 76 zircons of this age were derived from the WCT, and Yokelson et al. (2015) proposed that 77 detrital zircons from the 'western' Gravina belt were also sourced from the west (i.e., the 78 WCT). A compositional provenance link between the Gravina-Nutzotin belt and Laurasia 79 was also proposed by Berg et al. (1972) and Richter (1976) who suggested that clasts of https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 89 4 80 white vein quartz and metamorphic rocks from the Nutzotin Mountains sequence were 81 derived from Laurasia (i.e., Yukon-Tanana terrane). These observations though, were based 82 on regional mapping over 40 years ago and additional mapping (e.g., Dodds and Campbell, 83 1992), together with sedimentological studies incorporating paleocurrent measurements 84 (e.g., Eisbacher, 1976; Kozinski, 1985; Lowey, 1980, 1998; Cohen, 1992; Manuszak, 85 2000), have cast doubt on a Laurasian source for the clasts. Furthermore, Manuszak et al. 86 (2007) concluded that their study was unable to establish a direct unequivocal provenance 87 link between the Nutzotin Mountains sequence and Laurasia. 88 The Dezadeash Formation is presently located further east than the Nutzotin 89 Mountains sequence, implying that it may have been closer to Laurasia and therefore more 90 likely to contain a record of sedimentDraft derived from the continental margin. On account of 91 the potential limitations of provenance analysis, such as non-unique sediment sources, 92 internal variability within a single source area, incomplete characterization of potential 93 sources, sediment recycling, climatic and erosion effects, grain attrition during transport, 94 hydraulic sorting, and post-depositional alteration (Rollinson, 1993; McLennan et al., 2003; 95 Nie et al., 2012), this paper presents the results of an integrated provenance analysis of the 96 Dezadeash Formation, including pebble-counts of conglomerate beds, radiometric and 97 fossil dating of conglomerate clasts, grain point-counts of thin sections of sandstones, U-Pb 98 dating of detrital zircons from sandstones, and whole-rock geochemisty of sandstone, 99 mudstone, and hemipelagite beds, including major elements, trace elements, rare earth 100 elements, and Sm-Nd isotopes. Paleocurrent data from the Gravina-Nutzotin belt are also 101 reviewed. The primary aim is to characterize the lithological and geochemical composition 102 of the Dezadeash Formation, thereby facilitating comparisons with other Jura-Cretaceous 103 flysch basins exposed along the western margin of North America. Secondary aims are to https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 89 Canadian Journal of Earth Sciences 5 104 use the new compositional dataset to constrain the provenance and tectonic setting of the 105 Dezadeash Formation. 106 107 Geologic Setting 108 The WCT (Fig. 1) is a composite block of three amalgamated tectonostratigraphic 109 terranes referred to as the Alexander, Wrangellia, and Peninsular terranes (Plafker and 110 Berg, 1994). The Alexander terrane includes a basement of Neoproterozoic to early 111 Paleozoic island arc-related volcanic and sedimentary rocks (Nokleberg et al., 1994; 112 Beranek et al., 2012), and also late Paleozoic island arc-related volcanic and sedimentary 113 rocks. The Wrangellia terrane consists mainly of late Paleozoic to early Mesozoic island 114 arc-related volcanic and sedimentary rocks. The Peninsular terrane consists of an 115 assemblage of Mesozoic arc-related volcanic rocks (Nokleberg et al., 1994). The three 116 terranes represent successively higherDraft structural and stratigraphic successions from 117 southeast to northwest (Nokleberg et al., 1994). The Alexander and Wrangellia terranes 118 were contiguous during late Paleozoic time, based on Pennsylvanian-age plutons that 119 intrude both terranes (Gardner et al., 1988). The Peninsular terrane is interpreted to have 120 collided in Late Jurassic time with either the western margin of Laurasia (the Yukon 121 composite terrane), or the combined Alexander-Wrangellia terrane (Clift et al., 2005; 122 Beranek et al., 2014). The WCT, interpreted as part of an obliquely converging oceanic 123 plateau (Greene et al., 2010), was emplaced against the margin of Laurasia during Middle 124 Jurassic to mid-Cretaceous time (Monger et al., 1982; McClelland et al., 1992; Nokleberg 125 et al., 1994). 126 The Yukon composite terrane (YTC, ~Intermontane superterrane, Monger, 2014) 127 (Fig. 1) refers to the polymetamorphosed and polydeformed Yukon-Tanana,
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