Dual provenance signatures of the Triassic northern Laurentian margin from detrital-zircon U-Pb and Hf-isotope analysis of Triassic–Jurassic strata in the Sverdrup Basin Derrick Midwinter1, Thomas Hadlari2, W.J. Davis3, Keith Dewing2, and R.W.C. Arnott1 1DEPARTMENT OF EARTH AND ENVIRONMENTAL SCIENCES, UNIVERSITY OF OTTAWA, 120 UNIVERSITY, OTTAWA, ONTARIO, K1N 6N5, CANADA 2GEOLOGICAL SURVEY OF CANADA, 3303-33RD STREET NW, CALGARY, ALBERTA, T2L 2A7, CANADA 3GEOLOGICAL SURVEY OF CANADA, 601 BOOTH STREET, OTTAWA, ONTARIO, K1S 2V1, CANADA ABSTRACT The tectonic setting of northern Laurentia prior to the opening of the Arctic Ocean is the subject of numerous tectonic models. By better understanding the provenance of detrital zircon in the Canadian Arctic prior to rifting, both the prerift tectonic setting and timing of rifting can be better elucidated. In the Sverdrup Basin, two distinct provenance assemblages are identified from new detrital-zircon U-Pb data from Lower Triassic to Lower Jurassic strata in combination with previously published detrital-zircon data. The first assemblage comprises an age spectrum identical to that of the Devonian clastic wedge in the Canadian Arctic and is termed the recycled source. In contrast, the second assemblage is dominated by a broad spectrum of near syndepositional Permian–Triassic ages derived from north of the basin and is termed the active margin source. Triassic strata of Yukon and Arctic Alaska exhibit a similar dual provenance signature, whereas in northeastern Russia, Chukotka contains only the active margin source. Complementary hafnium isotopic data on Permian–Triassic zircon have eHf values that are consistent with the common evolved crustal signature of the Devonian clastic wedge detrital-zircon grains and Neoproterozoic– Paleozoic basement rocks in the Arctic Alaska–Chukotka microcontinent. Furthermore, newly identified volcanic ash beds throughout the Triassic section from the northern part of the Sverdrup Basin, along with abundant Permian–Triassic detrital zircon, suggest a protracted his- tory of magmatism to the north of the basin. We interpret that these zircons were sourced from a magmatically active region to the north of the Sverdrup Basin, and in the context of a rotational model for opening of Amerasia Basin, this was probably part of a convergent margin fringing northern Laurentia from the northern Cordillera along the outboard edge of Arctic Alaska and Chukotka terranes. In Early Jurassic strata, Permian–Triassic zircons decrease substantially, implying the diminution of the active margin as a sediment source as initial rifting isolated the Permian–Triassic source from the Sverdrup Basin. LITHOSPHERE; v. 8; no. 6; p. 668–683; GSA Data Repository Item 2016151 | Published online 20 May 2016 doi:10.1130/L517.1 INTRODUCTION in Triassic–Jurassic strata in the Sverdrup Basin Carboniferous to the Paleogene (Embry and and compared their age spectra to those from Beauchamp, 2008). The basin is underlain by an Siliciclastic sedimentary successions can other Triassic strata in the circum-Arctic. Those up to 10-km-thick sedimentary pile of Devonian provide an important record of the tectonic set- previous detrital-zircon studies (Miller et al., clastic wedge strata that were deformed during ting and tectonic evolution of a basin through 2006; Omma et al., 2011) in the Sverdrup Basin the Late Devonian–Early Carboniferous Elles- stratigraphic and detrital-zircon patterns. Pre- lacked data from the Late Triassic–Early Juras- merian orogeny (Embry, 1991). Strata equiva- vious efforts to interpret the tectonic evolu- sic Heiberg Formation. This paper provides new lent to the Devonian clastic wedge are widely tion of the Sverdrup Basin have been made detrital-zircon data from this interval, which distributed, including the northern Cordillera (e.g., Balkwill, 1978; Embry and Beauchamp, serves to constrain the provenance of the Sver- of North America, Arctic Alaska, and north- 2008), but important gaps in knowledge remain. drup Basin during the Triassic–Jurassic. Also, ern Russia (Amato et al., 2009; Beranek et al., Incipient rifting of the proto–Amerasia Basin in U-Pb detrital-zircon ages are augmented with 2010a; Drachev, 2011; Lemieux et al., 2011). the Jurassic–Cretaceous (Embry, 1990, 1991; eHf isotopic data for Permian–Triassic zircon The Ellesmerian orogeny was succeeded by Houseknecht and Bird, 2011) was followed by grains. These data provide important insight into initial rifting of the Sverdrup Basin that began opening of the Amerasian ocean basin, which the nature of the source terrane and magmatism in the Early Carboniferous and ended in the separates Arctic Canada, Alaska, and northeast- (cf. Vervoort and Patchett, 1996). Permian (Embry and Beauchamp, 2008). Cur- ern Russia (e.g., Grantz et al., 1979) (Fig. 1). rent models suggest that following the Permian, Previous detrital-zircon studies in the Sver- GEOLOGIC SETTING the Sverdrup Basin was tectonically quiescent drup Basin (Miller et al., 2006; Omma et al., and underwent thermal subsidence until rifting 2011) have identified a detrital-zircon signa- Sverdrup Basin recommenced in the Jurassic (e.g., Embry and ture in Triassic–Jurassic strata that resembles Beauchamp, 2008). that of the underlying Devonian clastic wedge The Sverdrup Basin is located in the Cana- The Triassic stratigraphy of the Sverdrup (e.g., Anfinson et al., 2012a). Those studies also dian Arctic Archipelago (Fig. 2) and records Basin (Fig. 3) is controlled by repetitive trans- identified several different zircon assemblages near continuous sedimentation from the gressive-regressive events (e.g., Embry, 1988; 668 © 2016 Geological Society of Americawww.gsapubs.org | For permission | toVolume copy, contact8 | Number [email protected] 6 | LITHOSPHERE Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/8/6/668/3051096/668.pdf by guest on 26 September 2021 Tectonic evolution of the Triassic northern Laurentian margin | RESEARCH equivalent to the Heiberg Group that comprises five formations in the western part of the basin (Fig. 3; Embry, 1983b). The formations of the Pacific Heiberg Group consist of the sandstone-rich Ocean deltaic Skybattle Formation overlain uncon- formably by marine mudstone of the Grosve- nor Island Formation with the Triassic–Jurassic boundary occurring in its upper part (Embry and Suneby, 1994). These strata then coarsen upward into sandstone-rich strata of the deltaic Maclean Strait Formation with the upper part containing W the base-Sinemurian boundary. Farther upward, AACM these strata are overlain by marine shale of the Arctic NSI Lougheed Island Formation capped by the sand- Ocean e stone-dominant King Christian Formation. During the Triassic there were two princi- pal sources of sediment into the basin deter- Lomonosov Ridg mined by the general facies distributions shown in Figure 4 (Embry, 2009). Sediment transport was directed into the basin from the southern and eastern margins, indicating a southern and eastern sediment source area. U-Pb zircon data (Miller et al., 2006; Anfinson et al., 2012a) and Sm-Nd isotopic data (Patchett et al., 2004) are consistent with recycling from the Devonian Atlantic clastic wedge and older north Laurentian strata Ocean (e.g., Hadlari et al., 2012, 2014). The facies indi- cate that another Triassic sediment source was derived from north of the basin (Embry, 2009), which is consistent with sandstone samples with detrital-zircon age spectra that are different from those on the south side of the basin (Miller et Figure 1. Circum-Arctic orogens, terranes, and locations modified from Colpron and Nelson (2011) al., 2006; Omma et al., 2011). and Pease et al. (2014). AA—Arctic Alaska; AACM—Arctic Alaska–Chukotka microplate; CH—Chu- In the Jurassic–Cretaceous, a narrow paleo- kotka; NSI—New Siberian Islands; NZ—Novaya Zemlya; PE—Pearya; SAS—South Anyui suture zone; high, the Sverdrup Rim (Fig. 2), separated the SV—Svalbard; WI—Wrangel Island; YTT—Yukon Tanana terrane. Black circles represent approximate Sverdrup Basin from the rift grabens of the detrital-zircon sample locations from AA (Miller et al., 2006; Gottlieb et al., 2014); CH (Miller et al., proto–Amerasia Basin (Meneley et al., 1975; 2006; Tuchkova et al., 2011; Amato et al., 2015); WI (Miller et al., 2010); and YTT (Beranek et al., 2010b; Beranek and Mortensen, 2011). The outlines of the SAS and AACM are from Drachev (2011). Red Embry, 1993). The northern source region was circles represent approximate location of eNd or eHf values from AA (Amato et al., 2009); Arctic fully separated from northern Laurentia by the Canada (Anfinson et al., 2012b; Morris, 2013); New Siberian Islands (Akinin et al., 2015); and Siberia opening of the Amerasia Basin in the Cretaceous (Malitch et al., 2010). (Embry, 2009). Paleogeographic Restoration Embry and Beauchamp, 2008). Early Triassic regression (Embry, 1991). Earliest Carnian trans- units of the Sverdrup Basin comprise the Blind gression deposited the Hoyle Bay Formation The tectonic interpretation of the Arctic Fiord Formation, which consists of shale and above the Roche Point Formation. Prograda- region prior to the opening of the Amerasia siltstone representing mid-outer shelf, slope, tion of sandstone-rich, shallow marine deposits Basin is complex and is the subject of much and deeper basin-floor deposits, and the Bjorne (Pat Bay Formation) extended across the basin debate (e.g., Grantz et al., 1979; Embry, 1990; Formation, which consists mostly of sandstone during