Structural evolution of a fold and thrust belt generated by multiple décollements: analogue models and natural examples from the Northern Apennines (Italy)

This study analyses the role played by the mechanical proprieties of the rocks involved in a thrust system, focusing on the problem of multiple décollements and of related compressional structures. Integration of geophysical (seismic reflection profiles) and geological data and scaled sandbox models are used to study the deformation style of two areas of the Northern Apennines (Italy): the Po Plain and the Umbria-Marche Apennines. Both areas are characterised by a complex stratigraphy, consisting of décollements located at different depths that influence the geometry and kinematics of the thrust system. The main characteristic of the models presented here is the presence of two décollement horizons, situated at the base and in an intermediate level of the models. During deformation of the models, these two décollement horizons generate two sets of structures, with different geometrical characteristics and significance. Through the joint analysis of geophysical and geological data and model results, wavelengths of the compressional structures analysed show that the structural style of the two analysed areas is almost similar. Moreover, model results prove that the final configuration of the thrust system follows the general rules of evolution of a wedge deformed above a weak décollement and is largely governed by the larger, deep seated structures.