IN SEARCH OF THE ALLEGHANIAN SUTURE

Recognition of subsurface Paleozoic strata in the southeastern U.S., exotic to North America, led Wilson to the then-striking conclusion that opening of the Atlantic Ocean basin left former parts of Africa stranded in the western Atlantic. Ever since, considered effort has been spent on identifying the boundary that formed between the former Laurentia and Gondwana continents in this region during the Alleghanian orogeny, including recent seismological studies in the region. Historically, no less than six major boundaries have been proposed, only three of which potentially separate Laurentia and/or accreted peri-Gondwanan terranes from the Gondwana continent, i.e. the Alleghanian suture. These three boundaries include the Central Piedmont shear zone, the Suwannee suture zone, and the Carolina-Mississippi fault.

The Central Piedmont shear zone is a major Alleghanian structure, but records shortening of previously accreted peri-Gondwanan terranes over already adjacent Laurentia. The Suwannee suture, identified as either a zone of moderately-dipping crustal-scale reflectivity or a sub-horizontal boundary defined by crustal velocity gradients, has recently been demonstrated to be a Neoproterozoic feature, and renamed the Brunswick suture zone. The Carolina-Mississippi fault cross cuts both of these structures and juxtaposes crust of Gondwanan affinity of the Suwannee terrane against crust of Laurentian or accreted terrane affinity across a relatively narrow transcurrent fault zone. However, recognition of a North American miospore assemblage in the Suwannee terrane and a shared Late Devonian tectonothermal event between Suwannee and the Laurentian margin raises the question whether there can be an Alleghanian suture in the southeastern U.S., despite widespread deformation of this age.