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 thermochronometry

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 post-dates 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 innerintermediate 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.