ALONG-STRIKE VARIATIONS IN CURVED THRUST BELTS: EXAMPLES FORM THE CENTRAL-NORTHERN APENNINES OF ITALY

The outer sectors of orogenic belts are frequently characterized by curved geometries of the thrust system architecture describing salient and recesses. These curved thrust belt patterns are most likely to be developed when the compressional deformation reworks regions that have undergone to a prior extension leading to positive inversion tectonics. Such inversion-dominated thrust belts offer a unique scenario for unravel along-strike variations and lateral changes at different scales.

The Central-Northern Apennines of Italy developed during Neogene-Quaternary time following the closure of the Alpine Tethys. The orogenic stacking involved Triassic-Miocene carbonate platform-slope-basin sequences deposited on the Adria Mesozoic continental margin and overlying Miocene-Pliocene syn-orogenic siliciclastic sediments. Significant lateral variations in structural style and stratigraphy occur along the strike of the Apennines and are mostly related to the inherited pre-orogenic setting.

Thrust-related folds, spectacularly exposed in the Central-Northern Apennines (Gran Sasso and Olevano-Antrodoco-Sibillini thrust systems) are analyzed with the aim of reconstructing their along-strike variation in thrust-related folding mechanisms and unravelling their interference fold patterns. The Central-Northern Apennines are characterized by curved thrusts and remarkable lateral variations in thrust-related folds occur. Different folding mechanisms involve the same Lower Jurassic-Miocene carbonate slope-basin multilayer and their development has been selectively controlled by contrasting styles of compressional normal-fault reactivation. Pre-thrusting normal-fault transpressive reactivation promoted fault-bend folding along the N-S and NNE-SSW oblique ramps, whereas shortcut-propagating thrusts developed fault-propagation folds along the WNW-ESE and NW-SE frontal ramps. These two laterally changing thrust-related folds interact with a characteristic interference fold pattern produced by their synchronous/in-sequence growth and interaction in the salient apex of the curved thrust system.