Brunswick subduction complex in the Canadian Appalachians: Record of the Late Ordovician to Late Silurian collision between Laurentia and the Gander margin of Avalon

Abstract

The Brunswick subduction complex in the New Brunswick part of the Canadian Appalachians records the Late Ordovician to Late Silurian collision between Laurentia and the Gander margin of Avalon. The Brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the Quebec reentrant of the Laurentian margin. This part of the margin experienced less underthrusting and exhumation and overprinting by orogen‐parallel faulting than the adjacent promontories where collision started earlier. The early, southeast to east vergent thrust‐related structures represent a progressive D 1 deformation that formed in response to northwestward subduction of the previously extended Gander margin and subsequent tectonic unroofing of the subduction complex. The original, shallow northwestward dipping envelope to S 1 was deformed in the Late Silurian by D 2 upright folds and associated shear zones into a steep belt during terminal collision. The D 2 structures probably formed in response to sinistral transpression. Together, D 1 and D 2 indicate that convergence was oblique and sinistral. Most rocks incorporated in the subduction complex formed in the Tetagouche back arc basin that evolved from rifting of an Arenig magmatic arc built on the Gander margin into a wide marginal basin. Subduction was initiated in the Late Ordovician (≈455 Ma) in the back arc basin following collision of the Middle Ordovician Popelogan arc with Laurentia in the Caradoc, shortly after its opening in the late Arenig (≈473 Ma). The closure history of the Iapetus Ocean involved more than one subduction zone and arc‐continent collision and rivals the southwestern Pacific Ocean in its complexities.