TRANSPRESSION AND EXTENSIONAL COLLAPSE - STEEP BELTS AND FLAT BELTS IN THE APPALACHIAN CENTRAL MOBILE BELT, NORTHERN NEW-BRUNSWICK, CANADA

Models of the Appalachian-Caledonian Orogen infer oblique collision an d an enigmatic reversal from sinistral (Silurian) to dextral (Devonian ) transpression. The Miramichi Highlands in Canada are relevant to suc h models because (1) they are a subductional thrust complex in which t he inferred reversal coincided with recumbent folding, and (2) its kin ematic indicators include rotated thrust structures and conjugate sets of coeval structures. Both are easily mistaken as evidence for sinist ral and dextral transpression. The thrust complex is part of the Appal achian Central Mobile Belt and is partitioned into steep belts and fla t belts according to the attitude of the schistosity. We argue that th e steep belts are coeval with Late Silurian plutonism and low-pressure metamorphism, representing transpressional zones (D2) in which the ex tension lineation of D1 thrusting was tilted twice: first from gentle to steep, then back to a gentle plunge. The transpression was synchron ous with exhumation as well as sedimentation. Flat belts represent a l ater flattening (D3) that probably resulted from extensional collapse and preceded Early Devonian dextral transpression (D4) along the Centr al Mobile Belt. Our model for the flat belts differs principally from models proposed for equivalent flat belts in Newfoundland.