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

Siluro-Devonian tectonostratigraphic relationships in the Portage Brook area, northern New Brunswick: implications for timing of deformational events in the Bathurst Mining Camp

“…The recognition that the con glomerates containing polydeformed pebbles can be corre lated with the middle Wenlockian to upper Ludlovian Simpsons Field Formation of the Chaleurs Group implies that D2 de formation occurred in the Early Silurian, prior to deposi tion of this unit. This apparent truncation of the "steep belt" was also noted by de Roo and van Staal (1994). The mafic intrusions are considered to have a similar age or be older because: (1) rocks of hybrid composition and textural evidence suggest magma-mixing (Whalen, 1993); (2) felsic dikes cut mafic rock but no mafic dikes have been observed cutting felsic rock (Whalen, 1993); and (3) the emplacement of mafic in trusions in the Portage Brook and Goodwin Lake areas ap pears to have been controlled by a structure that has been sealed by the peraluminous granite (Fig.…”

“…de Roo and van Staal (1994) proposed the following sequence of events: Late Ordovician subduction, associated with closure of the back arc basin (D i); Late Silurian sinistral transpression resulting from oblique continental collision (D2); Early Devonian extensional collapse (D3); and Middle Devonian dextral transpression (D4). However the relationships described above cast doubt about the timing of the D2 and D3 events.…”

“…Recent work, however, has shown that the early defor mation in the Tetagouche Group is unrelated to the Taconian Orogeny but rather occurred in the Late Ordovician to Early Silurian during closure of a back-arc basin located near the Gondwanan margin (van Staal, 1994), and may form part of the Salinic orogenic belt exposed from western Europe to southern New England (Stewart et al, 1995).…”

“…Recently de Roo and van Staal (1994) recognized at least four tec tonic events (D i to D4) and divided the Bathurst Mining Camp into steep belts dominated by D ) and D2 structures and flat belts characterized by a pervasive flat lying cleav age (S3, described as S2 by Hemstaedt, 1971).…”

“…1), records Late Ordovician to Late Si lurian closure of a back-arc basin and collision between Laurentia and the Gander margin of Gondwana (van Staal, 1994). However, the timing of the deformational events (Di to D4) in the Camp and the relationship of these events to the sedi mentary and tectonic evolution of the Chaleurs Bay Synclinorium are not clearly understood.…”