Characterization of Paleozoic Terranes and Terrane Accretion at the Southeastern Margin of Laurentia

The Paleozoic growth of the eastern margin of the North American continent is exemplified by the amalgamation of a series of terranes due to the closure of intervening ocean(s) and the obduction of fragments of oceanic and continental crust. The Appalachian orogen has traditionally been described as a culmination of three distinct events including the Taconic, Acadian, and Alleghanian orogenies. While evidence of the aforementioned discrete events has been well documented in the Appalachians in general, substantiation of the effects and timing of each orogeny appears to be more ambiguous regionally, likely requiring differing tectonic models along strike of the orogenic belt. The response of Laurentia to orogenesis is important in determining the timing and extent of Paleozoic accretionary events as well as characterizing the accreted terranes themselves. Tectonic models of classically studied mountain belts including the Alps, Himalayas, and Appalachians were constructed relying heavily on identifying collisional structures formed during closure of an intervening ocean(s). The modern Pacific margin represents an alternative to collisional models termed accretionary orogenesis. Accretionary orogenesis is also variable in that there may be an advancing subduction boundary or a retreating subduction boundary (extensional accretionary orogen). This study examines the role of crustal growth in an accretionary margin along the southeastern margin of Laurentia during a time of extensive (orogen-wide) arc accretion and closure of an intervening ocean commonly associated with the Ordovician-aged Taconic orogeny. Structural, stratigraphic, geochemical and isotopic evidence suggest that the southeastern margin of Laurentia (Alabama promontory) remained open to an ocean (as an accretionary orogen) until at least the Acadian and possibly as late as the Alleghanian orogeny. The structural architecture of the terrane-bounding fault (Allatoona and Hollins-Line faults) systems and adjacent terranes and petrogenesis of arc-related volcanics and plutonic bodies provides insight into the early Paleozoic evolution of the southeastern margin of Laurentia.