Thrust belt development in the central Apennines (Italy): Northward polarity of thrusting and out‐of‐sequence deformations in the Gran Sasso Chain

Abstract

The Lazio‐Abruzzi carbonate platform overrides the outermost sectors of the foreland fold and thrust belt of the central Apennines of Italy along an arcuate thrust front, which swings from E‐W to NNW‐SSE orientation. The E‐W striking, north verging thrust faults of the Gran Sasso cut in their footwall the N‐S oriented, east verging imbricates of the Marche thrust belt and the adjacent Adriatic foredeep. Our field mapping of the Gran Sasso imbricate system shows an array of six major thrust faults crosscutting each other in such a way that oblique propagation of higher thrust faults across the preexisting thrust sheets causes rethrusting of earlier imbricated units, decapitation of previous folds, and superposition of younger on older beds. Deformation in the Gran Sasso thrust belt mainly occurred between Messinian and middle Pliocene times and is partly synchronous with the development of the Marche thrust belt, thus implying that shortening resulted from a complex combination of northward and eastward propagating thrust systems. Increasing west to east shortening along the Gran Sasso thrust front indicates large, differential anticlockwise rotation by decoupling along a N‐S transpressive right‐lateral shear zone. This mechanism could have been induced by the Maiella foreland uplift, acting as a buttress against which the Lazio‐Abruzzi carbonate platform was stacked and forced to rotate anticlockwise, with consequent shortening by out‐of‐sequence thrust propagation.