Mesozoic igneous activity in the Suwannee terrane, southeastern USA: Petrogenesis and Gondwanan affinities

Drillhole sampling of the rocks beneath the post-upper Jurassic sedimentary cover of the Southeastern Coastal Plain of the United States has revealed that tholeiitic and alkaline basalts and diabases, in addition to high-K rhyolites and granites, are present in the exotic Suwannee terrane. The most reliable published ages for basaltic rocks range from 183+/-5 to 199+/-8 Ma, overlapping the accepted age range for magmatism of the Central Atlantic Magmatic Province (CAMP). Ages for rhyolites range from 165+/-6 to 189+/-5 Ma, while the only dated granite has a well-constrained U-Pb zircon age of 159+/-3 Ma. The geochemistry of all lithologies is consistent with their eruption or emplacement in an extensional tectonic environment. The tholeiitic basalts are derived from continental lithospheric mantle and crust that is approximately 1 billion years old, suggesting an affinity with the South American portions of Gondwana. Alkali basalts found in southwestern Florida may contain a component of sub-lithospheric mantle and have compositions similar to some basalts from Liberia and Brazil. Associated silicic magmas may have been generated by intracrustal melting induced by the heat of underplated or injected mafic magmas during the waning stages of igneous activity.