Martha Oliver Withjack¹, Malin I. Somby²

(1) Department of Geological Sciences, Rutgers University, Piscataway, NJ
(2) Exxon Mobil, London, United Kingdom

ABSTRACT: A Tale of Two Margins: A Comparison of the Passive Margins of the Southeastern United States and Norway

The continental margins of the southeastern United States and Norway are classic passive margins. Comparisons of available geological and geophysical information suggest that these margins had very different tectonic histories during rifting but similar tectonic histories during the transition from rifting to drifting.

The duration of rifting and the geometry of the rift-related structures differed on these margins. On the US margin, rifting lasted about 30 Ma (from Late Triassic until breakup during the earliest Jurassic). On the Norwegian margin, rifting lasted much longer, about 100 Ma (from Late Jurassic until continental breakup during the early Tertiary). This prolonged period of extension profoundly thinned the continental crust, especially during the Early Cretaceous. In the southeastern United States, the dominant rift-related structures were basement-involved normal faults. Extensional geometries were more complex on the Norwegian margin because its prerift sedimentary section was thick and included Triassic salt. In response, basement-involved normal faults, detached normal faults, and broad extensional forced folds developed during rifting.

The intensity of igneous activity and the regional strain state were similar on these margins during the transition from rifting to drifting. On both margins, a massive volcanic wedge developed at the ocean-continent boundary (i.e., both margins are volcanic). Abundant sills and dikes intruded the continental crust, and many of the dikes trended perpendicular to the margin. Finally, margin-perpendicular shortening created inversion structures on both margins. Shortening continued on both passive margins during drifting, creating large-scale crustal domes on the Norwegian margin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado