INCEPTION AND PASSIVE MARGIN REACTIVATION OF AULACOGENS ON THE EDIACARAN TO ORDOVICIAN LAURENTIAN IAPETAN MARGIN

Aulacogens of the Laurentian Iapetan margin preserve a cryptic record of Ediacaran to Cambrian rifting and Cambrian to Middle Ordovician passive margin deformation. To elucidate their history and understand how their evolution reflects the tectonic evolution of the Laurentian margin, a review of the tectonostratigraphic evolution of the Laurentian margin and peri-Laurentian realm from New York to Newfoundland coupled with a review of the magmatic and stratal evolution the Ottawa and Saguenay grabens is undertaken. During 620-570 Ma rifting, the Ottawa and Saguenay grabens formed parts of a branching rift system. Mantle plume activity is implied by correlation to CIMP and regional dyke orientations pointing to a plume head near the St. Lawrence Promontory. During rifting leading to the opening of the Taconic Seaway, 554 Ma alkaline flood basalt flows and deltaic progradation occurred at the mouth of the Ottawa Graben, recording rifting and mantle upwelling linked to edge-driven mantle convection beneath thinned Laurentian crust. Following breakup, a link between aulacogens and collinear fracture zones frames subsequent reactivation. During the 510-500 Ma post-rift Hawke Bay event, the Missisquoi fracture zone was reactivated along with the collinear Ottawa Graben and Franklin Basin, taking up regional extensional stress through oblique strike-slip deformation. Paibian (497-495 Ma) reactivation the Ottawa and Saguenay grabens is enigmatic, however the approaching Moretown terrane outboard of the New York Promontory may have played a role in reactivating peri-Laurentian fracture zones and aulacogens. Tremadocian (485-482 Ma) aulacogen reactivation is linked to the onset of segmented forearc spreading in the Taconic Seaway outboard of the Quebec Embayment, which resulted in strike-slip reactivation along the Missisquoi and Saguenay-Montmorency fracture zones. Floian reactivation of the Ottawa Graben (477-475 Ma) was driven by flexural stress from the onset of loading on the most distal parts of the margin. Aulacogens of the Laurentian Iapetan margin provide unique insight into the tectonic evolution and structural inheritance of the Laurentian Iapetan margin, revealing links to mantle plumes, mantle convection and exploitation of inherited margin structures during the advance of subduction zones.