A multichannel seismic-reflection survey of the Newfoundland basin southeast of the Grand Banks was conducted to investigate the rift-drift history of the basin and to examine the nature and location of the continent-ocean boundary. The data suggest that the continent-ocean boundary is marked by the "J" magnetic anomaly (M1-M0), which separates crust having a relatively smooth magnetic field to the west from higher amplitude anomalies to the east. Basement at the boundary is characterized by a set of large volcanic ridges that were constructed simultaneously with the adjacent Southeast Newfoundland Ridge and the J-Anomaly Ridge. The ridges appear to have formed from magma derived from a mantle plume then located beneath the Southeast Newfoundland Ridge.

The Newfoundland basin west of the interpreted continent-ocean boundary exhibits two distinct structural provinces in basement. A large (60 400 km) rift basin, the Salar basin, occurs beneath the continental slope and upper rise and is filled with evaporites that are probably Late Triassic to Early Jurassic in age. Seaward of the Salar basin, a zone of complexly faulted basement blocks with intervening, probably synrift, sedimentary and volcanic fill extends to the J anomaly. Both the blocks and fill are capped by a high-amplitude, relatively flat seismic unconformity. The unconformity pinches out at the J anomaly and appears to correlate with the "U," or Avalon, breakup unconformity on the adjacent Grand Banks.

Late Triassic rifting formed the Salar basin and caused an unknown amount of extension in adjacent continental crust to the east. A second phase of Late Jurassic through Early Cretaceous rifting reactivated parts of the western margin of the Salar basin and probably caused substantial extension and thinning of continental crust to the east. The rifting culminated in broad uplift or doming of this extended crust, erosion of the breakup unconformity, and Barremian-Aptian emplacement of volcanic ridges marking the continent-ocean boundary at the J anomaly. All crustal elements (extended continental crust, J-Anomaly ridges, oldest oceanic crust) appear to have experienced unusually rapid subsidence, much faster than age/depth relationships of normal oceanic crust, following continental br akup.

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