An improved velocity model for the crust and upper mantle along the central mobile belt of the Newfoundland Appalachian orogen and its offshore extension

New modelling of wide-angle reflection-refraction data of the Canadian Lith oprobe East profile 91-1 along the central mobile belt of the Newfoundland Appalachian orogen reveals new features of the upper mantle, and establishe s links in the crust and upper mantle between existing land and marine wide -angle data sets by combining onshore-offshore recordings. The revised mode l provides detailed velocity structure in the 30-34 km thick crust and the top 30 km of upper mantle. The lower crust is characterized by a velocity o f 6.6-6.8 km/s onshore, increasing by 0.2 km/s to the northeast offshore be neath the sedimentary basins. This seaward increase in velocity may be caus ed by intrusion of about 4 km of basic rocks into the lower crust during th e extension that formed the overlying Carboniferous basins. The Moho is fou nd at 34 km depth onshore, rising to 30 km offshore to the northeast with a local minimum of 27 km. The data confirm the absence of deep crustal roots under the central mobile: belt of Newfoundland. Our long-range (up to 450 km offset) wide-angle data define a bulk velocity of 8.1-8.3 km/s within th e upper similar to 20 lan of mantle. The data also contain strong reflectiv e phases that can be correlated with two prominent mantle reflectors. The u pper reflector is found at similar to 50 km depth under central Newfoundlan d, rising abruptly towards the northeast where it reaches a minimum depth o f 36 km. This reflector is associated with a thin layer (1-2 km) unlikely t o coincide with a discontinuity with a large cross-boundary change in veloc ity The lower reflector at 55-65 km depths is much stronger, and may have s imilar origins to reflections observed below the Appalachians in the Canadi an Maritimes which are associated with a velocity increase to 8.5 km/s. Our data are insufficient for discriminating among various interpretations for the origins of these mantle reflectors.