ATTEMPTED SUBDUCTION OF THE GONDWANAN CONTINENTAL MARGIN BENEATH LAURENTIA: NEW IMAGES FROM REPROCESSED LITHOPROBE SEISMIC REFLECTION DATA ACROSS THE NEWFOUNDLAND APPALACHIANS
In the east, reflections project from the Avalon Zone beneath the Hermitage Bay fault and the eastern Gander zone to the middle and lower crust, where they merge with prominent reflectivity that is interpreted to delineate a sedimentary prism that was foreshortened during Silurian orogenesis. Rocks exposed in the Gander Zone likely represent the upper-crustal portion of the prism, which extends at least 200 km across strike in central Newfoundland.
In western Newfoundland, the wedge of prominent reflectivity tapers and merges with west-dipping reflections that extend from the lower crust into the upper mantle where they disappear near 16 s (~ 50-55 km depth). These layers are interpreted as a relict subduction zone that accommodated juxtaposition of Laurentia with Gondwana.
Several major faults related to Silurian orogenesis can be projected from the surface to the prominent reflections in the middle crust. West- and east dipping faults outline crustal-scale thrust sheets and wedging structures, respectively. Both types of faults appear to feed into the subduction zone via subhorizontal detachments in the lower crust and near the Moho. Thus, in Newfoundland Silurian convergence between Laurentia and Gondwana was accommodated partly by foreshortening of the Gondwanan margin above a west-facing subduction zone.