With continuing constriction, the Axial Zone buckled up into a south-directed "antiformal stack". Towards the end of the subduction, a "backthrust" initiated near the actual trace of the North Pyrenean Fault, which was cutting upward into the Aquitanian crust by utilising its previously thinned, faulted nature. When the subduction process was finally blocked, parts of the northern Axial Zone and the North Pyrenean Zone with lower crustal fragments and lherzolites sandwiched in between were pushed back northward over the Subpyrenean Zone.