Proterozoic mafic magmatic rocks exposed along the western side of North America, or western Laurentia, from Kimberley, British Columbia, through to northwestern Wyoming have been previously divided into two large igneous provinces: the ca. 1460 Ma Moyie-Purcell and the ca. 780 Ma Gunbarrel large igneous provinces. New geochemical analysis from this study demonstrates that there are additional intraplate mafic magmatic rocks present. Distinguishable by variable normalized rare earth element patterns combined with differing slopes on a binary Ti versus V plot, there are 17 identifiable geochemical signatures in the 307 whole-rock and trace-element analyses from this study. Only seven of these signatures can be linked to the ca. 1460 Ma Moyie-Purcell large igneous province, and one signature to the 780 Ma Gunbarrel large igneous province. This study has identified two groups of intrusions with distinct geochemical signatures previously linked with the ca. 1460 Ma Moyie-Purcell large igneous province but now recognized to be separate events, a single unique geochemical signature with a U-Pb age correlative with the Moyie-Purcell large igneous province and seven other heretofore unidentified signatures interpreted to belong to additional undated events.

ABSTRACT Neoproterozoic to Cambrian isolation of Laurentia during the breakup of Rodinia was associated with multiple large igneous provinces, protracted multiphase rifting, and variable subsidence histories along different margin segments. In this contribution, we develop a paleogeographic model for the Neoproterozoic tectonic evolution of Laurentia based on available stratigraphic, paleomagnetic, petrologic, geochronologic, and thermochronologic data. Early Tonian strata are confined to intracontinental basins in northern Laurentia. Breakup of Rodinia around Laurentia began in earnest with emplacement of the ca. 778 Ma Gunbarrel large igneous province, interpreted to have accompanied separation of the North China block along the Yukon promontory, and onset of localized, intracratonic extension southward along the western margin. Eruption of the ca. 760–740 Ma Mount Rogers volcanic complex along the Southern Appalachian segment of the eastern margin may record extension associated with separation of the Kalahari or South American terranes. At about the same time, the Australia-Mawson blocks began separating from the Sonoran segment of the southern margin and Mojave promontory. Emplacement of the ca. 720 Ma Franklin large igneous province along the northern margin was likely associated with separation of Siberia and was followed by widespread bimodal volcanism and extension along the western margin spanning ca. 720–670 Ma, leading to partial separation of continental fragments, possibly including Tasmania, Zealandia, and Tarim. Emplacement of the ca. 615 Ma Central Iapetus magmatic province along the eastern margin marked rifting that led to separation of Baltica and Amazonia, and partial separation of the Arequipa-Pampia-Antofalla fragments. During the late Ediacaran to Cambrian, the western, northern, eastern, and southern margins all experienced a second episode of local extension and mafic magmatism, including emplacement of the ca. 585 Ma Grenville dikes and ca. 540–532 Ma Wichita large igneous province, leading to final separation of continental fragments and Cambrian rift-drift transitions on each margin. Cryogenian rifting on the western and northern margins and segments of the eastern margin was contemporaneous with low-latitude glaciation. Sturtian and Marinoan glacial deposits and their distinctive ca. 660 Ma and 635 Ma cap carbonates provide important event horizons that are correlated around the western and northern margins. Evidence for Ediacaran glaciation is absent on Laurentia, with the exception of glacial deposits in Scotland, and putative glacial deposits in Virginia, which both formed on the poleward edge of Laurentia. Patterns of exhumation and deposition on the craton display spatial variability, likely controlled by the impingement of mantle plumes associated with mantle upwelling and extensional basin formation during the piecemeal breakup of Rodinia. Glaciation and eustasy were secondary drivers for the distribution of erosion and Neoproterozoic sedimentation on North America.