The large-scale folding in this area was also the result of the continental collision that occurred at about 250 Ma. An extreme amount of deformation occurs in the formation of nappes. A nappe may be either a thrust sheet or a recumbent fold, that is, a fold whose limbs are almost parallel and roughly horizontal.
The effects of continental collisions appear to vary widely. The collision between India and Asia is responsible not only for the Himalaya Mountains but also for tectonics and seismicity throughout China. In contrast, the Alpine orogeny in Europe is narrowly confined. There is also observational evidence that the continental collision that resulted in the formation of the Appalachian Mountains was relatively mild. This difference in collisional orogenies may be attributed to the characteristics of the orogenic zone prior to collision. China may have resembled the western United States; that is, its lithosphere may have been very thin prior to collision, and it may therefore have been easily deformed during the collision.