Detrital zircons from Cambrian rocks of western Laurentia define two episodes of Rodinian rift-related magmatism

Many aspects of the disassembly of Neoproterozoic supercontinent Rodinia remain poorly constrained. Current models for the breakup along western Laurentia (present coordinates) do not fully reconcile stratigraphic observations regarding the timing and mechanisms of continental rifting. Latest Neoproterozoic to Cambrian stratigraphic units exposed along the North American Cordillera from southwestern Canada to the southwestern United States contain Neoproterozoic and Cambrian zircons interpreted to be sourced from rift-related igneous rocks generated during the fragmentation of Rodinia. Two discrete magmatic episodes distinguished by a ca. 50 Myr period of apparent magmatic quiescence are identified using the detrital record:(1) Tonian and Cryogenian to earliest Ediacaran magmatism (mantle plume events followed by rifting); and (2) latest Ediacaran to late Cambrian magmatism. The detrital zircon record of the first episode supports a 660-650 Ma rift-to-drift transition followed by passive margin sedimentation of the upper Windermere Supergroup. After a period of apparent magmatic quiescence from 630-580 Ma, detrital zircon dates of 580-520 Ma from central-western Laurentia provide evidence for renewed rift magmatism preceding the initiation of the lower Paleozoic passive margin. These new U-Pb dates are used to present a refined model of Rodinia disassembly with improved timing constraints suggesting that its final breakup and the Sauk I transgression occurred ca. 520 Ma, in accordance with recent revisions to the timing of the Sauk transgressions in southwestern Laurentia.