LINKS BETWEEN CRUSTAL BLOCKS IN THE APPALACHIAN PERI-GONDWANAN REALM

Four extensive Neoproterozoic-early Paleozoic crustal blocks that originated in a peri-Gondwanan magmatic arc setting form the eastern flank of the Appalachian orogen. They include Carolina in the southern Appalachians and Ganderia, Avalonia, and Meguma in the northern portion of the orogen. Interrelationships between these crustal blocks are important for understanding both the accretionary history of the orogen and the evolution of the Iapetus and Rheic oceans, first-order features of the Paleozoic globe.

Traditionally, Carolina and Avalonia were considered to represent a single microcontinent that accreted to Laurentia in the middle to late Paleozoic. Although they appear to share a similar lithotectonic history between c. 680-590, their latest Neoproterozoic-Paleozoic tectonic evolution is different. In particular, the Avalonian arc system ended in the late Neoproterozoic and was succeeded by a robust Cambrian-Silurian platform sequence, possibly representing a strike-slip margin. Distinct from Avalonia, the Carolina arc system terminated during late Neoproterozoic arc-arc collision; only a thin Middle Cambrian clastic sequence is preserved atop the Carolina arc sequences. Furthermore, the Avalonian platform was not deformed until the Early Devonian whereas Carolina experienced widespread Ordovician-Silurian deformation.

In contrast to the orthodox Carolina-Avalon correlation, we note more striking similarities between Ganderia and Carolina. Specifically, late Neoproterozoic magmatism and tectonism extended into the Cambrian in both Ganderia and Carolina, and both were accreted to Laurentia during the Late Ordovician-Silurian, involving a major component of sinistral transpression. In addition, a Middle Cambrian to Early Ordovician clastic sequence caps Gander arc rocks, similar to relations in Carolina. Consequently, Carolina may be more closely affiliated with Ganderia than with Avalonia. Collectively, Carolina-Ganderia may represent an extensive Neoproterozoic arc system that originated in Amazonia.

Meguma displays significant Paleozoic differences with the other blocks; a common tectonic evolution between Meguma and Avalonia cannot be inferred until the late Early Devonian, suggesting a complex and long lasting accretionary history of peri-Gondwanan terranes.