Provenance of the Incipient Passive Margin of NW Laurentia (Neoproterozoic): Detrital Zircon from Continental Slope and Basin Floor Deposits of the Windermere Supergroup, Southern Canadian Cordillera

Abstract

The origin of the passive margin forming the paleo-Pacific western edge of the ancestral North American continent (Laurentia) constrains the breakup of Rodinia and sets the stage for the Phanerozoic evolution of Laurentia. The Windermere Supergroup in the southern Canadian Cordillera records rift-to-drift sedimentation in the form of a prograding continental margin deposited between ~730 and 570 Ma. New U-Pb detrital zircon analysis from samples of the post-rift deposits shows that the ultimate source area was the shield of NW Laurentia and the near uniformity of age spectra are consistent with a stable continental drainage system. No western sediment source area was detected. Detrital zircon from postrift continental slope deposits are a proxy for ca. 676-656 Ma igneous activity in the Windermere basin, likely related to continental breakup, and set a maximum depositional age for slope deposits on the eastern side of the basin at 652±9 Ma. These results are consistent with previous interpretations. The St. Mary-Moyie fault zone near the Canada-U.S. border was most likely a major transform boundary separating a rifted continental margin to the north from intracratonic rift basins to the south, resolving north-south variations along western Laurentia in the late Neoproterozoic at approximately 650-600 Ma. For Rodinia reconstructions, the conjugate margin to the southern Canadian Cordillera would have a record of rifting between ~730 and 650 Ma followed by passive margin sedimentation.

Supplemental Material: Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

“…720 Ma) described for the type section of the Windermere Supergroup in southern British Columbia by Ross (1991). This difference suggests that the St. Mary-Moyie fault forms a fundamental tectonic boundary/transition along the rift margin (Lund, 2008;Hadlari et al, 2021) (Brennan et al, 2020b;this work) and southeastern Idaho/northern Utah (Keeley et al, 2013;Balgord et al, 2013;Yonkee et al, 2014;Link et al, 2017). Dashed probability plot lines and transparent gray εHf t data are from prior work in southeastern Idaho (ID) and northern Utah (UT; Yonkee et al, 2014).…”

“…Rather, the Addy Quartzite, which overlies the Three Sisters Formation in northeastern Washington, is likely correlative to the Hamill Group and Camelback Mountain Quartzite, or Sauk I sequence (Lindsey and Gaylord, 1992). Difficulties in correlating these units from northeastern Washington to southern British Columbia could also reflect heterogeneities in Ediacaran-Cambrian rifting/ passive-margin processes along the St. Mary-Moyie fault zone (e.g., Hadlari et al, 2021).…”

“…Despite the progress made, fundamental Cordilleran margin-scale processes such as the number of rifting events and the timing of continental breakup (cf. Colpron et al, 2002;Yonkee et al, 2014;Brennan et al, 2021a;Hadlari et al, 2021) still lack consensus and have contributed to disagreements on Rodinia reconstructions and breakup processes. For example, noteworthy global paleogeographic reconstructions (e.g., Li et al, 2008;Merdith et al, 2021) favor initiation of a breakup event along western Laurentia as early as ca.…”

“…In contrast, workers on the type section of the Neoproterozoic Windermere Supergoup in southern British Columbia generally favor an older, ca. 730-700 Ma (Evenchick et al, 1984;Hadlari et al, 2021) main rift event (e.g., Ross, 1991), with perhaps an additional younger ca. 600-570 Ma rifting event (Colpron et al, 2002;Eyster et al, 2018).…”

Organic matter deposition and preservation in ancient deep‐sea levée sediments: Implications for Neoproterozoic trends in carbon burial

“…The Windermere Supergroup (WSG) consists of an unconformity‐bounded Neoproterozoic succession of mostly metasedimentary rocks associated with the breakup of the Rodinia Supercontinent and subsequent development of a passive continental margin along the western margin of Laurentia (ancestral North America; Stewart, 1972; Ross et al ., 1995; Hadlari et al ., 2021). In outcrop the WSG stretches more than 4000 km from north‐western Mexico through the western United States and Canada to the Yukon–Alaska border (Ross & Arnott, 2007; Fig.…”