Salinic thrust panels, mélanges, and folds with superimposed Acadian oblique cleavage-fold relationships in accreted Ordovician oceanic rocks of the Fournier Supergroup and Silurian synorogenic cover rocks in northern New Brunswick, Canada

Abstract Structural and stratigraphic evidence for the protracted late Katian to Pridoli Salinic closure of the Tetagouche backarc basin in Ordovician and Silurian rocks of the Elmtree Inlier in Northern New Brunswick is presented. Katian to Telychian tectonism (Salinic A) produced mélanges, broken formation, and isoclinal folding (F1) during assembly of the oceanic backarc rocks of the Fournier Supergroup into four thrust panels. A narrow zone of amphibolite tectonites in the ophiolitic Black Point gabbro of panel 1 is interpreted as a fossil oceanic detachment zone that exhumed serpentinized peridotites and gabbro, preserved as large lenses in the Belledune River mélange, onto the seafloor. Piecemeal accretion of backarc segments led to progressive emergence of parts of the subduction complex between the Rhuddanian and the Telychian (Salinic A unconformity). Rollback of the subduction zone subsequently led to a marine transgression until the Homerian to Ludfordian Salinic B collision of composite Laurentia with the Gander margin, which resulted in folding (F2a), thrusting, wide-scale uplift and deposition of terrestrial rocks (Salinic B unconformity), and inversion of the Fredericton Trough foredeep. Subsequent slab breakoff, steepening, and possibly a dip reversal of the remaining slab during the Ludlow to Pridoli led to renewed marine sedimentation, which was terminated by ENE-trending F2b folds (Salinic C) during the Pridoli to earliest Lochkovian. F2a/b folds typically lack an axial planar cleavage and were locally refolded by Acadian F3 folds in the Emsian and cut by the regional NE-striking Acadian cleavage (S3) at various angles, producing oblique-cleavage fold relationships.