ABSTRACT

Two deep seismic reflection profiles, which record both sedimentary stratigraphy and the deep structure of the underlying crystalline crust and upper mantle (maximum two-way time of 24 s), were obtained across the continental shelf, slope and rise offshore Nova Scotia. This continental margin was initially formed by rifting between Africa and North America in Triassic-Early Jurassic time. The objective of this study is to delineate both the deep structure associated with the formation of the sediment-filled Scotian Basin and the transition from continental to oceanic crust. One profile, which crosses the central Nova Scotian shelf through the Emerald and Naskapi sub-basins and the Scotian Basin, shows that these half-graben basins are at least 4 s (two-way travel time) deep. Unlike the basins on the Grand Banks, the basin-bounding listric normal faults bordering these basins dip landward, and we speculate that this change in fault polarity may be due to a difference in the fabric of the underlying basement. These faults appear to flatten at depths of about 5 to 6 s. Reflection Moho is clearly delineated on this line, as is the base of a reflective zone in the lower crust. There are spectacular "faults" within the upper mantle and lower crust, the origin of which is uncertain. The crystalline crust thins toward the ocean basin, and is obscured by salt structures below the lower continental slope. Seaward of the salt lies presumed oceanic crust, which displays peculiar internal layering and faulting. How far offshore these unusual characteristics persist is unknown, as they extend to the seaward end of our profile. However, similar changes in the reflection character of oceanic crust have been attributed to changes in the amount of melt production at ancient mid-ocean ridges.

A second profile crosses the margin through the Orpheus graben, and the Abenaki and Sable sub-basins. Preliminary results are included in this presentation.

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