|
Dipartimento di Scienze della Terra, Università di Napoli ‘Federico II’, Largo San Marcellino 10, 80138 Napoli (NA), Italy (e-mail: stvitale{at}unina.it)
Mike Coward's seminal work on strain within thrust sheets clearly showed how understanding crustal scale deformation associated with orogenesis requires a knowledge of both: (1) deformation associated with major thrusts and/or high-strain shear zones, and (2) finite strain states within the (usually large) surrounding rock volumes. In this study, the strain variations within a major, far-travelled thrust sheet internally deformed at very low-temperature, sub-metamorphic conditions, are analysed. The studied rocks belong to the thick carbonate succession of the Apennine Platform, which constitutes a major tectonostratigraphic unit of the southern Apennines. Finite strain analysis, besides quantifying the relative importance of different deformation mechanisms and the role of matrix and object strain, points to the existence of both vertical and horizontal strain gradients. These are probably controlled by both heterogeneous shear deformation associated with NE-directed tectonic transport and sedimentary carbonate facies distribution. The relative position with respect to the main overlying tectonic contact and the occurrence of a barrier to fluid flow, represented by siliciclastic beds located at the top of the carbonate succession, are also likely to have played an important role in the development of the observed regional strain gradients. On the metre scale, deformation appears to be partitioned into domains of quasi-coaxial and dominantly non-coaxial strain, controlled by different degrees of strain localization in texturally different stratigraphic layers.
