Final answer:
The evidence suggesting a subduction volcanic arc complex off the eastern margin of North America includes mountainous relief, igneous activity, metamorphic rocks from continental collisions, and sedimentary records from orogenic events.
Step-by-step explanation:
The evidence for the formation and approach of a subduction volcanic arc complex off the eastern margin of North America during the Ordovician includes the presence of igneous activity and mountainous relief, which are indicative of tectonic movements and processes similar to those witnessed on the western margin of South America since the Jurassic period. Additionally, the occurrence of metamorphic rocks during the Caledonide Orogeny points towards the continental collision and closure of the Iapetus Ocean; such collision events are typically associated with the formation of subduction zones and volcanic arc complexes.
In the Appalachian region, the Valley and Ridge Province contains sedimentary rocks derived from mountain-building events like the Taconic Orogeny and the Acadian Orogeny, which aligns with the pattern of an active subduction margin seen in the terrain of modern subduction zones with a history of volcanic arcs. Moreover, the Catskill clastic wedge is a Devonian sediment package sourced from the Appalachian Mountains during the Acadian Orogeny that also indicates tectonic activity likely linked to a subduction zone and a related volcanic arc.