Timing and Development of the Orthotectonic Zone in the Appalachian Orogen of Northwest Newfoundland

Abstract

Examination of part of the Fleur de Lys Supergroup, within the orthotectonic zone of north-west Newfoundland, reveals that regional deformation and metamorphism may not have commenced prior to the Early Ordovician and was not completed until the Devonian. The onset of deformation could have been as young as Llanvirnian.Fleur de Lys metasediments are correlated to the west with moderately deformed and undeformed rocks of the western platform. To the east, they are shown to be in part the lateral age equivalent of ophiolitic rocks. The ophiolites may be fragments of an older foundation to the mafic volcanic and volcanoclastic Baie Verte Group.Polyphase-deformed and regionally metamorphosed terrains (orthotectonic zones) such as the Fleur de Lys, do not form 'instantaneously', but evidently result from a critical sequential and progressive development history, covering a recognizable time span, and probably display characteristics of paratectonic zones at an intermediate stage. Sequential or simultaneous opening and closing of marginal basins is suggested as a mechanism, not only to explain the formation of such zones, but also the regional timing variation that apparently exists within the Appalachian-Caledonian orogen. Such processes are known to have occurred consistently since the Early Tertiary, and can presently be observed along the Western Pacific margin.