REASSESSING THE MAIN IAPETAN SUTURE IN WESTERN NEWFOUNDLAND: NEW GEOCHRONOLOGICAL CONSTRAINTS ON THE TECTONIC HISTORY OF DASHWOODS AND CORNER BROOK

In western Newfoundland, it has been proposed that Dashwoods is a rifted Laurentian basement block with late-Ediacaran to Cambrian rift-related metasediments, where the main Iapetan suture is east of Dashwoods. This faulted boundary between Dashwoods and the leading edge of the Gander Terrane of Gondwanan affinity is referred to as the Red Indian Line (RIL). However, a recently identified Gondwanan terrane in New England, referred to as the Moretown Terrane, is located inboard of the Gander Terrane and occupies an equivalent structural position to Dashwoods along orogenic strike. This has raised the question of whether Dashwoods, whose basement is unexposed and whose metasediments have not been dated, is equivalent to the Moretown Terrane. This would require that the RIL be located along Dashwoods' western faulted boundary with the Corner Brook Basement Block (CBLB). However, it has been proposed that the CBLB, while Laurentian, is itself far-travelled, displaced dextrally along the Laurentian margin from Labrador to explain an apparent lack of Grenville (1250 - 950 Ma) and Taconic (480 - 450 Ma) magmatism or deformation. Here we present new magmatic and metamorphic geochronological constraints from zircon and titanite on the CBLB and the Humber Margin, demonstrating that the CBLB is not far-travelled. We further characterize potential sources by refining the age and zircon geochemistry of 615 - 600 Ma intrusions on the Humber Margin and on the CBLB to distinguish such populations from 615 - 600 Ma arc magmatism on the Gondwanan terranes. We use this data to re-evaluate 650 - 550 Ma detrital zircon from the Moretown Terrane. Finally, we present new detrital zircon data from the Laurentian Humber Margin, the CBLB, and from three disparate regions of Dashwoods. The interpretation of metamorphic and discordant detrital zircon from Dashwoods present some challenges to tectonic interpretation. Yet, we provide clear evidence for differences in metasedimentary packages on Dashwoods and document examples of Taconic successor basins, post-dating collision between Dashwoods and the Laurentian margin. We then use these data to reevaluate the position of the main Iapetan suture in Newfoundland.