Abstract

Early Jurassic tholeiitic lavas that flowed across Mesozoic basins of northeastern North America were comagmatic, as shown by their geochemistry, petrography, paleomagnetism, radiometric ages, and stratigraphy. The basin basalts are correlated with diabase dikes that intersect the basins but also extend far outside them. If the dikes represent feeders to fissure vents, a vast flood-basalt province must have extended across the rifted terranes of eastern North America in Early Jurassic time. The initial member of the basalt flood was the most uniform and widespread among present basin remnants of the basalts, but subsequent flows may have covered some areas farther from the basins. Other, younger Jurassic flood basalts have been described along submarine sections of the continental shelf and shelf break, and beneath Cretaceous coastal plain sediments in the southeastern United States. Across the inland Mesozoic rift terranes, the initial fissure eruptions produced a temporary basaltic plain perhaps 1600 km long and 200 to 400 km wide, or roughly 500000 km2, rivaling other great continental flood-basalt provinces.

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