Abstract

Detailed knowledge of thrust surface geometry and the topological links between different thrusts is important for relating kinematic analysis on the small scale to structural evolution across thrust belts. The thrust surfaces outcropping between the Nera River Valley and the Rieti Basin (Umbria-Marche-Sabina Apennines, Central Italy) are characterized by geometrical irregularities, such as dip and strike variations, either original or acquired during later deformation episodes. The use of map analysis techniques indicates the existence of a close relationship between the original dip variations of thrust surfaces and the competence contrasts within the stratigraphic template: these exert a strong control on development of stepped thrust surfaces, whose flats are localized within the less competent units, such as the Late Trias evaporitic Burano Fm. and the Eocene-Oligocene marly Scaglia Cinerea Fm.. The geometrical irregularities produced during later deformation episodes are mainly responsible for along-strike variations of the thrust surfaces orientation, which describe an arcuate feature convex towards the east, and for the present distribution of the thrusting direction vectors. The radial thrusting pattern could derive from development of new structures within the footwall to previous thrusts, suggesting that compressional deformation migrated towards the east in piggy-back fashion. The application of map analysis techniques provides good information about the lithological control on thrust development and the thrusting sequence. These results provide, therefore, additional controls on constructing balanced cross sections.

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