TECTONIC HISTORY OF THE ANNIEOPSQUOTCH ACCRETIONARY TRACT

The Annieopsquotch Accretionary Tract (AAT) is a sinistral-oblique, southeast-directed thrust stack of distinct volcanic slices. The Red Indian Line bounds the AAT to the east and structurally separates it from the underthrusted, peri-Gondwanan Upper Cambrian to Lower Ordovician volcanic and sedimentary rocks of the Victoria Lake Supergroup. To the west, the Lloyds River fault and Hungry Mountain thrust system separate the AAT from tonalite and granodiorite plutons of the Notre Dame arc, which dominate the peri-Laurentian Dashwoods block. The plutons yielded ages between 488 and 456 Ma with an apparent gap in arc magmatism between 480 and 470 Ma. The oldest members of the AAT are represented by c. 480 Ma supra-subduction zone ophiolite complexes (e.g. King George IV, Annieopsquotch, Star Lake), which have been interpreted to represent an infant arc setting formed during subduction initiation. The Dashwoods block has been thrust over these ophiolites by c. 468 Ma. The latter in turn have been underthrust by c. 473 Ma ensialic arc related volcanic rocks correlated with the Buchans Group, and the coeval (?) ophiolitic rocks (gabbro, sheeted dikes, basalt and trondjhemite) of the Skidder complex. The next lower slice in the thrust stack is represented by the c. 462 Ma extensional-arc rocks of the Harbour Round and Sutherlands Pond assemblages. Felsic volcanic rocks of the Buchans, Harbour Round and Sutherlands Pond all display typical peri-Laurentian zircon inheritance patterns. The age progression in arc volcanism and structural relationships suggest that at least part of the AAT formed outboard (east) of the active Laurentian margin (Dashwoods block), probably above a west-dipping intra-oceanic subduction zone. The ensialic arc component of the Buchans and Harbour Round groups either represents a narrow peri-Laurentian sliver outboard of the Dashwoods block or it is a sliver of the Dashwoods suprastructure translated into its present structural position largely during substantial arc-parallel, sinistral strike-slip.