Transpression and extensional collapse: Steep belts and flat belts in the Appalachian Central Mobile Belt, northern New Brunswick, Canada

摘要

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