A CAROLINA-GANDERIA LINK IN THE APPALACHIAN PERI-GONDWANAN REALM: IMPLICATIONS FOR THE TERMINAL TACONIC PLATE CONFIGURATION

The Appalachian peri-Gondwanan realm encompasses the crustal blocks of Carolina, Ganderia, Avalonia, and Meguma, all of which have a Gondwanan heritage prior to their accretion to eastern North America. Interrelationships between these 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 mid to late Paleozoic. Although their lithotectonic evolution is similar between c. 680-580, their latest Neoproterozoic-Paleozoic tectonic histories diverge. In particular, the Avalonian arc system ended in the late Neoproterozoic, succeeded by a robust Cambrian-Silurian platform sequence that possibly reflects a strike-slip margin. Distinct from Avalonia, the Carolina arc system terminated c. 40 m.y later, following 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. In addition, a Middle Cambrian to Early Ordovician clastic sequence caps Ganderian arc rocks, similar to relations in Carolina. Each block was accreted to Laurentia during Late Ordovician-Silurian sinistral transpression. Consequently, we propose that Carolina is more closely affiliated with Ganderia than with Avalonia.

Collectively, elements on the Carolina-Ganderia plate(s) started interacting with the Taconic-modified Laurentian margin in the Middle to Late Ordovician after the initiation of subduction beneath Laurentia. Thus, activity related to this flip in subduction polarity overlaps in time and space with the termination of Taconic orogenesis. Subduction polarity reversal was quickly followed by the accretion of Carolina in the south, followed slightly later by the accretion of Ganderia in the north.