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Alpine structural and metamorphic signature of the Sila Piccola Massif nappe stack (Calabria, Italy): Insights for the tectonic evolution of the Calabrian Arc
Author(s) -
Rossetti Federico,
Faccenna Claudio,
Goffé Bruno,
Monié Patrick,
Argentieri Alessio,
Funiciello Renato,
Mattei Massimo
Publication year - 2001
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2000tc900027
Subject(s) - geology , nappe , massif , geochronology , blueschist , shear zone , phengite , thermochronology , extensional tectonics , metamorphic rock , geochemistry , geothermobarometry , tectonics , seismology , petrology , subduction , eclogite , rift
Combined structural and petrographical investigations, coupled with 40 Ar/ 39 Ar geochronology, were carried out in the Sila Piccola Massif of the Calabrian Arc in order to define the structural geometry and map out the major structural and metamorphic breaks within the exposed nappe sequence. On the basis of the contrasting Alpine pressure‐temperature ( P ‐ T ) and structural signatures the nappe stack can be divided in two major tectonic complexes, bounded by a flat‐lying ductile to brittle extensional shear zone. The upper complex consists of a nappe‐like structure, where a major top to the east compressional shear is recorded. The lower tectonic complex consists of an ophiolite‐bearing sequence showing typical high‐ P /low‐ T parageneses (Mg‐carpholite and Na‐amphibole). The 40 Ar/ 39 Ar geochronology on phengites in equilibrium with blueschist minerals provided a minimum age estimate for the blueschist event in the lower complex rocks at the Oligocene‐Eocene boundary (around 35 Ma). Ductile to brittle top to the west extensional shear accompanied the nearly isothermal retrogression and exhumation of the lower complex rocks, reworking the previous nappe contacts with shear localization along the upper/lower tectonic complex discontinuity. The 40 Ar/ 39 Ar dating indicates that this postnappe stacking tectonic evolution took place from 30 Ma onward. It is proposed that exhumation of the deep‐seated rocks occurred below a top to the west extensional detachment active during convergence and orogenic complex formation (synorogenic extension). The age of this detachment is bracketed between 30 Ma and the post‐orogenic Neogene basin sedimentation (middle‐upper Miocene). The revised structural and metamorphic scenario is here integrated into a new tectonic evolutionary reconstruction, which involves an early high‐ P /low‐ T top to the east crustal thickening episode during the construction of the Apennine orogenic wedge (Eocene‐Oligocene), followed and overprinted by a top to the west extensional shear, probably active from the late Oligocene.