Structures, interference patterns, and strain regime during midcrustal deformation in the Alpi Apuane (Northern Apennines, Italy)
Structures, interference patterns, and strain regime during midcrustal deformation in the Alpi Apuane (Northern Apennines, Italy) (in Styles of continental contraction, Stefano Mazzoli (editor) and Robert W. H. Butler (editor))
Special Paper - Geological Society of America (2006) 414: 79-93
- Apennines
- Apuane Alps
- continental crust
- contraction
- crust
- deformation
- Europe
- exhumation
- faults
- folds
- foliation
- geometry
- interference patterns
- Italy
- kinematics
- middle crust
- nappes
- Northern Apennines
- P-T conditions
- polyphase processes
- Southern Europe
- strain
- structural analysis
- tectonic wedges
- three-dimensional models
- Tuscany Italy
- underthrust faults
In this paper, we present results of new investigations and structural analyses on the geometries, strain patterns, and kinematics of folds in the Alpi Apuane, northwest Tuscany, Italy. The analyzed structures were formed in mid-upper crustal conditions (temperature and pressure range between 450 and 300 degrees C and 0.6 and 0.4 GPa) during underthrusting and early exhumation of a slice of Adria-derived continental crust involved in the continental subduction process. In particular, we focused our attention on the relationships between folds, localized zones of deformation, and superimposed strain patterns. Kilometer-scale fold-nappes with strongly noncylindric 3D geometries developed during the early regional scale deformation event D1, whereas later largescale noncylindric folds associated with a subhorizontal crenulation axial planar foliation refold previous structures during D2. Although the early deformation D1 can be related to an important component of noncoaxial deformation, the following D2 was instead associated with a vertical shortening and a bulk coaxial strain. The above described D1 and D2 structures developed during crustal underplating and syncontraction exhumation record strain regime partitioned through time with an over-all decrease in the noncoaxiality of deformation. This possibly reflects the movement of the unit across the deeper part of the Late Oligocene-Miocene Apenninic wedge, with a progressive increase of gravity-induced sagging in the rear part of the orogen.