Frontal vs. basal accretion and contrasting particle paths in metamorphic thrust belts

Fold-and-thrust belts at the Appalachian and Grenvillian orogenic fronts developed in similar continental-margin tectonic settings but show marked contrasts in the relative timing of thrust stacking and metamorphism. In the Corner Brook Lake thrust belt of the Appalachian orogen in Newfoundland, thrust stacking took place at shallow-crustal levels and was followed by the development of a foliation under increasing metamorphic conditions. The peak of metamorphism postdated thrusting and overprinted the foliation. In the Grenvillian Gagnon thrust belt in western Labrador, development of a foliation and the stacking of the thrust sheets occurred at near-peak metamorphic conditions at upper- to middle-crustal levels. These contrasting deformational and metamorphic histories reflect different modes of accretion (frontal, basal) in metamorphic thrust wedges. -from Authors