FOLDED THRUST PANELS, MÉLANGES, AND OBLIQUE CLEAVAGE-FOLD RELATIONSHIPS FORMED DURING THE SALINIC AND ACADIAN OROGENIC CYCLES IN ACCRETED OCEANIC ROCKS OF THE FOURNIER SUPERGROUP AND ASSOCIATED SYNOROGENIC SILURIAN COVER ROCKS IN NORTHERN NEW BRUNSWICK, CANADA

Oceanic rocks of the Fournier Supergroup in the Elmtree Inlier were assembled in four thrust panels that were incorporated into the Brunswick subduction complex during Late Ordovician to Telychian (Salinic A) closure of the Ordovician Tetagouche backarc basin. Salinic A tectonism produced mélanges, broken formation and isoclinal folding (F₁). An older syn-oceanic deformation zone characterised by amphibolite tectonites in the ophiolitic Black Point gabbro of panel 1 is interpreted as a fossil oceanic detachment zone, which exhumed serpentinised peridotites and gabbro, preserved as map-scale lenses in the Belledune River mélange, onto the seafloor. Accretion of isolated backarc segments led to local emergence of part of the subduction complex during the Telychian (Salinic A unconformity). Stepping-back and roll back of the subduction zone in turn led to a marine transgression until the Homerian to Ludfordian Salinic B collision of composite Laurentia with the Gander margin, which resulted in folding (F_2a), wide-scale uplift and deposition of terrestrial rocks (Salinic B unconformity), and inversion of the Fredericton Trough foredeep. Salinic B tectonism was followed by slab breakoff, steepening and possibly a dip reversal of the remaining slab during the Ludlow to Pridoli. This led to renewed marine sedimentation, which was terminated by east-northeast trending F_2b folds (Salinic C) at c. 419-418 Ma. F_2a/b folds typically lack an axial planar cleavage. During the Acadian orogenic cycle in the Emsian, F_2a/b folds were locally refolded by F₃ folds and cut by the regional Acadian cleavage (S₃) at various angles, producing oblique-cleavage fold relationships.