Nature and timing of Franklin igneous events, Canada: Implications for a Late Proterozoic mantle plume and the break-up of Laurentia

Abstract

UPb baddeleyite/zircon ages have been determined for gabbro sills and diabase dykes emplaced during Franklin igneous events in northern Canada. Results for seven widely separated sills from Victoria Island, Coronation Gulf and Bathurst Inlet, and for a single diabase dyke from southeastern Baffin Island, indicate that most of the Franklin igneous activity was synchronous and occurred at 723 + 4/-2 Ma. A UPb baddeleyite/ zircon age of 718 ± 2 Ma for one of the Victoria Island sills suggests that the magmatism continued for at least 5 m.y. after the initial outburst. The short-duration and large volume of the intrusive tholeiitic magmatism and its association with the Natkusiak flood basalts suggest a link with a mantle plume-generated hotspot. The onset of magmatism may have coincided with the arrival of the plume at the base of the lithosphere. Stratigraphic relationships on Victoria Island indicate that differential uplift occurred just prior to the initial outbreak of igneous activity, which is interpreted as a response to doming above the upwelling plume. The exposed record provides no indication of significant pre-volcanic extension and rifting, although some NE-SW extension occurred after the initial eruptive phase. The 779 Ma mafic magmatism in the Mackenzie Mountains, the 723 Ma Franklin events and the 615 Ma Long Range dykes in Labrador are three precisely dated mafic events in North America that may be contemporaneous with various phases of Late Proterozoic break-up of Laurentia. These ages establish key chronological constraints for global correlation of Late Proterozoic epicontinental basins and for Precambrian plate reconstructions. © 1992.