After the formation associated to a period of crustal thining what amount of time did a long-lasting mountain building event occur?
Mount Pleasant Caldera:  It is one of few noticeable pre-Cenozoic calderas, and its formation is associated to a period of crustal thinning that followed the Acadian orogeny in the northern Appalachian Mountains. Acadian orogeny:  It was active for approximately 50 million years, beginning roughly around 375 million years ago, with deformational, plutonic, and metamorphic events extending into the Early Mississippian.
i don't know