U-Pb zircon age constraint for late Neoproterozoic rifting and initiation of the lower Paleozoic passive margin of western Laurentia

Abstract

A concordant U–Pb zircon age of 569.6 ± 5.3 Ma from synrift volcanic rocks of the Hamill Group, southeastern Canadian Cordillera, provides the first direct U–Pb geochronologic constraint on timing of latest Neoproterozoic rifting along western Laurentia. This age confirms a previous estimate of 575 ± 25 Ma for timing of continental breakup, as derived from the analysis of tectonic subsidence in lower Paleozoic miogeoclinal strata of the North American Cordillera. It also corresponds to the timing of passive margin deposition in the "underlying" Windermere Supergroup of the northern Cordillera, as determined by chemostratigraphic correlations. These timing relationships imply a different breakup history for the northern, as compared to the southern, Cordillera. We propose a model that attempts to explain this paradox of Cordilleran geology. The earlier Neoproterozoic (Windermere-age) rifting event probably records breakup of a continental mass from northern Laurentia followed by development of a passive margin. Accordingly, the Windermere Supergroup of the southern Canadian Cordillera was deposited in an intracontinental rift. The second Neoproterozoic rifting (Hamill–Gog) is interpreted to indicate continental breakup and establishment of a passive margin along western Laurentia.

Proterozoic Evolution of the North Atlantic–Arctic Caledonides: Insights from Detrital Zircon Analysis of Metasedimentary Rocks from the Pearya Terrane, Canadian High Arctic

“…Rifting along the western and northern Laurentian margins, initiated in the Cryogenian, resulted in a complex history of basin development along those margins (e.g., Macdonald et al 2012). The timing of the final rift-drift transition along these margins is poorly defined but may have occurred as early as 685 Ma along the western margin and 620 Ma along the northern margin (Colpron et al 2002;Dewing et al 2004;Bradley 2008). Similarly, separation of Amazonia and Laurentia likely initiated in the Cryogenian (e.g., Escayola et al 2011).…”

Detrital zircon geochronology of the Grenville/Llano foreland and basal Sauk Sequence in west Texas, USA

“…In southeast California, the lower boundary of the Sauk Sequence is either at the base of the lower member of the Wood Canyon Formation (Fedo and Cooper, 2001) or the base of the Stirling Quartzite (Hogan et al, 2011) and corresponds in age to the latest Ediacaran (see Colpron et al, 2002;Macdonald et al, 2013), post-dating the fi nal rift event at ca. 580-560 Ma.…”

U–Th–Pb geochronology of meta-carbonatites and meta-alkaline rocks in the southern Canadian Cordillera: A geodynamic perspective

“…This pulse (~800-485 Ma) relates to the controversy over whether one Early Paleozoic rift-drift event, or two separate rift-drift events in the Neoproterozoic and Early Paleozoic affected the western margin of Laurentia (Colpron et al, 2002;Lund et al, 2010;Pyle and Barnes, 2003;Timmons et al, 2001). Our findings, in conjunction with existing sedimentological and geochronological constrains (e.g., Colpron et al, 2002;Goodfellow et al, 1995;Lester et al, 2001;Lund et al, 2010;Pigage and Mortensen, 2004), supplement models depicting the evolution of the western Laurentian margin that indicate a prolonged and diachronous process with multiple extensional episodes characterized by igneous activity and the formation of depositional basins during Neoproterozoic to early Palaeozoic times (Colpron et al, 2002;Harlan et al, 2003;Li et al, 2008;Lund et al, 2010;Pyle and Barnes, 2003;Timmons et al, 2001;Whitmeyer and Karlstrom, 2007).…”

“…These igneous ages postdate syn-rift volcanism of the nearby Hamill Group at~570 Ma (Colpron et al, 2002) and the inferred protolith emplacement age of an amphibolite at~541 Ma (Parrish, 1995;Fig. 6).…”