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Paleomagnetic Evidence for a Large Rotation of the Yukon Block Relative to Laurentia: Implications for a Low-Latitude Sturtian Glaciation and the Breakup of Rodinia

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Paleomagnetic Evidence for a Large Rotation of the Yukon Block Relative to Laurentia: Implications for a Low-Latitude Sturtian Glaciation and the Breakup of Rodinia Paleomagnetic evidence for a large Yukon block rotation relative to Laurentia Paleomagnetic evidence for a large rotation of the Yukon block relative to Laurentia: Implications for a low-latitude Sturtian glaciation and the breakup of Rodinia Athena E. Eyster1,†, Roger R. Fu2, Justin V. Strauss3, Benjamin P. Weiss2, Charlie F. Roots4,§, Galen P. Halverson5, David A.D. Evans6, and Francis A. Macdonald1 1Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, USA 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Building 54-724, Cambridge, Massachusetts 02139, USA 3Department of Earth Sciences, Dartmouth College, HB6105 Fairchild Hall, Hanover, New Hampshire 03755, USA 4Natural Resources Canada, c/o Box 2703, K-102, Whitehorse, Yukon Y1A 2C6, Canada 5Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montréal, Québec H3A0E8, Canada 6Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA ABSTRACT in Mesoproterozoic and Paleoproterozoic Alternatively, Turner and Long (2008) argued strata, and realigns the orientation of the ca. for NE-SW extension on the western margin of Understanding the tectonic history of the 1260 Ma Bear River dikes with the Mack- Laurentia based on the interpretation of multi- supercontinent Rodinia is crucial for testing enzie dike swarm of northern Canada. This ple NE-SW–oriented structures in the Macken- proposed links among Neoproterozoic tec- reconstruction also facilitates future studies zie Mountains as transfer faults. In addition to tonics, supercontinent cycles, climate, and that relate Neoproterozoic sedimentary and these older structures, which can be interpreted biogeochemistry. The Neoproterozoic Mount structural patterns to the fragmentation of as recording early Neoproterozoic rifting, late Harper volcanics of the Ogilvie Mountains, Rodinia. Finally, this low-latitude pole sup- Neoproterozoic rifting (Windermere Supergroup Yukon, Canada, interfinger with Sturtian- ports the snowball Earth interpretation of and Sequence C of Young et al., 1979) is thought age (ca. 717–660 Ma) glacial deposits that the ca. 717 Ma Sturtian glacial deposits. to have occurred during two separate intervals: were deposited in narrow, fault-bounded ca. 780–660 Ma (Jefferson and Parrish, 1989; basins related to the breakup of Rodinia. INTRODUCTION Mustard, 1991) and ca. 580–560 Ma in the Here, we present new paleomagnetic data southern Cordillera (Colpron et al., 2002; Lund, from the Mount Harper volcanics and iso- The protracted breakup of the superconti- 2008; Lund et al., 2010; Yonkee et al., 2014). late four paleomagnetic directions: a low- nent Rodinia has long been associated with There are numerous candidates for the conti- temperature direction recording the present Neo protero zoic environmental and biological nents that rifted away from Laurentia’s northern geomagnetic field, a mid-temperature direc- change (Kirschvink, 1992; Hoffman and Schrag, and western margins, including Antarctica, Aus- tion consistent with a Cretaceous overprint, 2002; Goddéris et al., 2003). However, the age, tralia, South China, North China, Siberia, and and two high-temperature directions, one of geometry, configuration, and kinematics of Ro- West Africa (Sears and Price, 1978; Moores, which is carried by hematite and likely rep- dinia’s fragmentation remain poorly constrained. 1991; Hoffman, 1991; Dalziel, 1997; Sears and resents a chemical overprint, and the other Because Neoproterozoic-Cambrian strata on the Price, 2003; Pisarevsky et al., 2003; Li et al., of which is carried by magnetite and likely margins of Laurentia are interpreted as pas- 2008; Evans, 2009; Fu et al., 2015; Ernst et al., is a primary direction. This primary pole sive margin sequences (Hoffman, 1991), many 2016). Irrespective of the identity of its former passes the fold and conglomerate tests and paleo geo graphic reconstructions place it at the conjugate partners in Rodinia, Yukon records includes a reversal but is 50° away from the core of Rodinia (e.g., Li et al., 2008). Due to the Neoproterozoic tectonic evolution of both coeval 721–712 Ma Laurentian Franklin this central location, studies of Laurentian basins the northern and western margins of Laurentia large igneous province pole. This difference can assist in understanding the breakup of Ro- (e.g., Thorkelson et al., 2005; Macdonald et al., can be reconciled using a 50° counterclock- dinia (e.g., Ross, 1991; Macdonald et al., 2012; 2012; Strauss et al., 2015), and it is a keystone wise rotation of the Yukon block relative to Strauss et al., 2015). Several discrete extensional for future attempts to elucidate the extensional Laurentia. The prerotation reconstruction of events on the western margin of Laurentia have history in this part of Rodinia. the Yukon block relative to Laurentia aligns been attributed to the rifting of Rodinia, im- Recent geochronological data from Neo- Neoproterozoic fault orientations and facies plying a prolonged and complex breakup his- protero zoic sedimentary successions in Yukon belts between the Wernecke and Mackenzie tory. Early Neoproterozoic (ca. 1.2–0.78 Ga enable more accurate constraints on basin- Mountains, rectifies paleoflow measurements Sequence B of Young et al., 1979) sedimentary forming events in Laurentia during the early successions were interpreted as recording basin- fragmentation of Rodinia. In the Coal Creek †aeyster@ fas .harvard .edu forming events consistent with a NNW-facing inlier of west-central Yukon (Figs. 1 and 2), early §Deceased. margin in present coordinates (Aitken, 1981). Neoproterozoic synsedimentary faulting and GSA Bulletin; Month/Month 2016; v. 128; no. X/X; p. 1–21; doi: 10.1130/B31425.1; 8 figures; 1 table; Data Repository item 2016255.; published online XX Month 2016. For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 1XX, no. XX/XX 1 © 2016 Geological Society of America Eyster et al. 67°N Paleozoic, or Neoproterozoic age. In addition, Richardson fault Yukon NW Park et al. (1992) acknowledged that their re- ka sults were inconclusive due to limited sampling, T Alas Yukon and that additional sampling and examination were needed to validate or refute them. Here, 66°N Knorr Faul we present new paleomagnetic results from the Yukon ar Tatonduk ra Mount Harper volcanics that resolve these un- inlier block y certainties, allowing us to infer the geometry of t Mackenzie Mtn Ogilvie Mtns 65°N Neoproterozoic synsedimentary structures rela- W tive to the Laurentian craton and relative motions Coal Creek e r n inlier e c Snake River Faul Hart River k e s during the breakup of Rodinia, and additionally, inlier Wernecke M 141°W t n to explore the paleomagnetic constraints on the inlier s TintinaTintina faul DDawson thrust 64°N ca. 717 Ma Yukon glacial deposits that may re- awson thru t Dawson cord the initiation of snowball Earth glaciation fault t st 1 on Laurentia. 138°W 0100 136°W 134°W 132°W Selwyn Basi GEOLOGICAL SETTING km Paleozoic to Tertiary cover strata 63°N The Yukon block (Jeletsky, 1962) is a crustal 130°W n fragment separated from contiguous Laurentia Richardson trough 2 to the east by the Richardson trough and the Cryogenian–Ediacaran Windermere Supergroup (Sequence C) Richardson fault array (Fig. 1). The Richardson 128°W Tonian-Cryogenian Mackenzie Mountains Supergroup & trough represents a Cambrian–Devonian deep- Pinguicula and Fifteenmile Groups (Sequence B) water basin formed above a failed rift arm be- Mesoproterozoic Wernecke Supergroup (Sequence A) tween the Yukon block and Mackenzie Platform area detailed in Fig. 2A additional areas noted in text: (Gabrielse, 1967; Pugh, 1983; Norris, 1985; Franklin Large Igneous Province 1. Nite Creek Cecile et al., 1997; Morrow, 1999; Rohr et al., regions of positive aeromagnetic anomalies 2. Thundercloud Range 2011). The Richardson fault array is a regional- scale fault system with a history of reactivation approximate boundary between Yukon block and Laurentia that has controlled sedimentation and deforma- Figure 1. Map of northwest Canada with Proterozoic inliers. Note Richardson trough (after tion in the area since its inception in the Protero- Morrow, 1999) and Richardson fault array separate the Tatonduk, Coal Creek, Hart River, zoic (Eisbacher, 1981, 1983; Norris, 1985, 1997; and Wernecke inliers from the Mackenzie Mountains. The cross-hatched areas indicate Aitken and McMechan, 1992; Aitken, 1993; aeromagnetic highs following Aspler et al. (2003) and Pilkington and Saltus (2009). The Abbott, 1996, 1997; Crawford et al., 2010; Rohr solid green line depicts approximate boundary between the Yukon block and Laurentia. et al., 2011). Proterozoic strata in the Yukon Inset depicts the extent of the Franklin large igneous province (red; Buchan and Ernst, block consist of three major successions (Young 2004, 2013; Buchan et al., 2010). NWT—Northwest Territories. et al., 1979) exposed in four inliers: the Taton- duk, Coal Creek, Hart River, and Wernecke inliers (Fig. 1). The oldest rocks consist of Se- subsidence have been linked to extension on et al., 2000; Denyszyn et al., 2009a, 2009b). quence A, a polydeformed succession of mixed the northern margin of Laurentia (Mac donald Taken at face value, these data connect exten- carbonate and siliciclastic strata of the late Paleo- et al., 2012). In contrast, the later Neoprotero - sion or transtension recorded in
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