The most obvious evidence for inversion is seen in Triassic-Early Jurassic strata along the E-trending Minas fault zone. Here a series of syndepositional extensional troughs bounded by normal and left-lateral strike-slip faults have been transformed into NE- and SW-trending antiforms and synforms bounded by high-angle and reverse faults. Strata next to these faults dip at 45-90 degrees away from them, have thrust and oblique duplexes, and are occassionally overturned. The overall SW-trending synclinal shape of the main Fundy basin is also consistent with inversion of the main boundary fault system. The timing of the inversion is post-earliest Jurassic, because earliest Jurassic strata are influenced by NW-SE extension and cut by the compressional structures.

Identical structures that we ascribe to inversion have been described in Moroccan Early Mesozoic basins adjacent to the E-trending South Atlas fault zone. Thickness patterns indicate to us that the inversion was of late Early Jurassic to Late Jurassic age--compatible with the age of inversion in the Fundy basin. Other half graben of eastern North America show inversion, indicating NW-SE compression over a longitudinal distance of > 1000 km, with the most eastward basins (e.g., Richmond and Fundy basins) being most strongly affected.

The pattern and timing of inversion seen in the eastern North American and Moroccan half graben suggests an origin from a very strong initial phase of sea-floor spreading in the Middle Jurassic, followed by a decrease through time in the magnitude of NW-SE compression. Such a history seems to characterize many rifted margins, and very strong initial pulse of ridge push at the onset of sea-floor spreading may be a general part of the rifting process.

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