Print this pageFault Reactivation or Truncation (or both) in Repeatedly Inverted Settings? The Kinematic Test
TAVARNELLI, ENRICO
The concept of inversion tectonics applies to regions whose evolution was characterized by a switch in deformation regime, from extension to compression, or from compression to extension. A common characteristic of inverted regions is the modification of their previous architecture by newly formed structures. Should inversion occur under brittle conditions, pre-existing fault surfaces may either be deformed by, or reactivated as, younger faults (the latter situation being likely when both early and late faults strike and dip consistently).
Because of their long history, orogenic belts generally bear the signature of one or more tectonic inversion episodes. In these situations the hanging walls of thrust faults are often affected by consistently dipping normal faults which terminate downwards against the thrust surfaces. If the stratigraphic record of syntectonic deposits is missing, this geometrical pattern alone does not constrain the relative chronology of thrusting and normal faulting, as two distinct interpretations can be made: (a) thrust faults are older and are partly reactivated as normal faults; or (b) thrust faults are younger, and truncate pre-existing normal faults. The determination of the sense of slip along the suspected reactivated faults, instead, makes it possible to distinguish between these two situations. Structural analysis in the Umbria-Marche Apennines of Italy, where fault-reactivation and fault-truncation phenomena coexist, provided an opportunity to establish a relative chronology of deformation episodes, showing that kinematic criteria represent an important tool for quantifying the effects of pre-orogenic rifting, synorogenic shortening and post-orogenic collapse in repeatedly inverted settings.