GEOCHEMICAL EVIDENCE FOR TRIASSIC RIFTING IN SOUTHWESTERN FLORIDA

Mesozoic rhyolites and basalts from three drillholes penetrating the pre-Cretaceous basement of southwestern Florida were analyzed for their trace element and Sr and Nd isotopic compositions. Major and trace element abundances suggest the suite was erupted in an extensional environment, and isotopic data indicate derivation primarily from aged, enriched Precambrian continental lithosphere combined to varying degrees with an asthenospheric component. Nd model ages show no significant difference in the age of the lithosphere from which these rocks and volcanic rocks of Paleozoic age from North Florida were derived, arguing against major displacement across the peninsula, including along proposed extensions of the Jay fault and/or Bahamas fracture zone. We suggest that the geophysically inferred boundary across the peninsula, if a fault, may have had a strong normal component, consistent with the greater depth to basement south of the boundary. In this view, the southwestern Florida Mesozoic volcanic province (SFMV) may represent a part of a major Triassic rift basin associated with the breakup of Pangaea.