The southern Tuscany represents the internal portion of the Northern Apennines. Its geological setting is particularly complicated due to two main tectonic phases: a first compressional syn-collisional phase (Late Cretaceous-Early Miocene) that led to nappe building and km-scale tectonic features; a later extensional post-collisional phase (Early Miocene-Pleistocene) led to uplift and unroofing of the thickened crust is linked to the anticlockwise Apennine rotation and Tyrrhenian Sea opening. The upper valleys of the Fiora and Albegna rivers in southern Tuscany represent a key area to reconstruct the post-collisional tectonic and sedimentary evolution of this sector of the Apennine chain. This area is characterized by a tectonic nappe stack built during the syn-collisional phase, unconformably overlain by Miocene- Pliocene depositional units, referable to a few sedimentary cycles. The sedimentary-tectonic evolution for the study area, as recognizable by field data, is the result of a sequence of different deformative and depositional events. The compressive event (Early Miocene) led to crust thickening and emplacement of the Ligurian units onto the Tuscan Nappe. Later on, a first extensional event (Early-Middle Miocene) developed low-angle normal faults. This event was responsible of a strong tectonic elision and crustal thinning, forming the «serie ridotta», characterized by a megaboudinage tectonic setting and developing structural-morphological depressions, probably seat of shallow-marine deposition. A second extensional event (Late Miocene) developed west-dipping listric normal faults, increasing the megaboudinage depressions. In the study area, the activity of west-dipping normal faults caused the deformation of the tectonic nappe stack with the development of regions with steep east-dipping attitude of bedding. In these regions east-dipping normal faults affected the steep dipping bedding, so to form structural depressions in which tectonic delaminated slices, usually Ligurian units, were emplaced. Moreover, such structural depressions represented also the basins of the Late Miocene continental-marine sedimentation. A third extensional episode (Pliocene) developed with high-angle normal faults which dissected all the previous structures. During this extensional event graben and half-graben basins formed, and the Early Pliocene marine transgression with filling of deep elongated basins parallel to the chain, developed.
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|Titolo:||Neogene post-collisional evolution of the inner Northern Apennines: inferences from the upper Fiora and Albegna valleys, (Mt. Amiata geothermal area, southern Tuscany)|
|Appare nelle tipologie:||1.1 Articolo in rivista|
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