Middle miocene out-of-sequence thrusting and successive exhumation in the Peloritani mountains, Sicily: Late stage evolution of an orogen unraveled by apatite fission track and (U-Th)/He thermochrnology.

Apatite fission track (AFT) and (U‐Th)/He (AHe) thermochronometry are applied to constraint the thermal history of the basement rock forming the Peloritani Mountains in northeast Sicily, Italy. AFT ages range between 29.0 ± 5.5 Ma and 5.5 ± 0.9 Ma while AHe ages vary from 19.4 Ma to 3.3 Ma. Most AFT ages are younger than the overlying terrigenous sequence that, in turn, postdates the main orogenic phase. Through the coupling of the thermal modeling with the stratigraphic record, a middle Miocene thermal event is revealed. This event affected an inner‐intermediate portion of the Peloritani Mountains and is confined by the distribution of the AFT ages 15 Ma. The U‐shaped pattern of AFT ages along N-S transects across the mountain chain is consistent with burial below a thrust stack that is a few km thick, created by an out‐of‐sequence thrusting phase that affected the inner portion of the belt. The tectonic load was then removed initially by erosion enhanced by the high relief at 10-7 Ma. The difference between young AFT and AHe ages is used to infer a rate of exhumation of 0.3 mm/yr for this stage. The gap between the youngest AHe ages and the sedimentary record above indicate a final exhumation stage with increasing rates of denudation (1-3 mm/yr) since the Pliocene times due to extensional tectonics.