ABSTRACT

Tectonic interpretations of new heat-flow data from Louisiana, Mississippi, Alabama, and panhandle Florida, and radiometric dates for subsurface igneous rocks from Mississippi suggest a complex basement configuration of both continental and oceanic crust for the Gulf coastal region. Original (early Paleozoic) North American continental terrain, characterized by average heat flow (~ 1.0 heat flow units), is postulated to extend no farther south than a northwest-trending boundary linking the truncation of the southern Appalachian Mountains with the Ouachita Mountains. A northwest-trending zone of thinned, continental basement and thick, sedimentary deposits with anomalously low heat flow and Mesozoic volcanic rocks exists in southern Alabama and pinches out in northern Mississippi (Black Warrior basin and central Mississippi deformed belt). South of that belt, a zone of high heat flow (1.5 - 2.1 hfu), subsurface Mesozoic basalts, and feldspathoidal rocks characterizes northern Louisiana and west-central Mississippi. This zone is distinguished by mobilized, thermally conductive salt diapirs and alkalic igneous rocks. The Wiggins uplift, with Paleozoic granitic rocks in southernmost Mississippi and its westerly continuation in southern Louisiana, yield average heat-flow values and are interpreted to represent residual fragments of a South American continental mass that was convergent in the late Paleozoic Era and divergent during the early to middle Mesozoic Era.