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- Title
Lithostratigraphic setting and P-T metamorphic evolution for the Dora Maira Massif along the Piedmont Zone boundary (middle Susa Valley, NW Alps).
- Authors
Gasco, Ivano; Gattiglio, Marco; Borghi, Alessandro
- Abstract
new structural and petrological study, associated with a detailed geological mapping, allowed to better understand the tectonic relationships between the Dora Maira Massif and the Piedmont Zone in the middle Susa Valley. In the study area, a thick sequence of calcschists, previously attributed to the stratigraphic cover of the Dora Maira, is interpreted as belonging to the Piedmont Zone. Four deformation phases were identified: D represents the eclogite facies stage, D developed under greenschist facies conditions, transposed the early foliation and was responsible for the development of the regional schistosity S. D is characterized by close to open folds with N dipping axial surfaces and finally, D developed macro-scale folds with E-dipping axial planes. Structural analyses allow to infer a relative timing for the tectonic contact between the two nappes which were coupled after the eclogite facies metamorphism but before the development of the S foliation under greenschist facies conditions. Petrographic investigation into metapelite samples permitted to identify two main metamorphic assemblages within the Dora Maira polymetamorphic basement: M (Phe + Pg + Cld + Grt + ChlI + Qtz + Rt) assemblage defines the S relict foliation, while M (Ms + Pg + Ab + ChlII + Qtz + Ilm ± Bt) assemblage is related to the regional foliation S. PERPLE_X pseudosection modelling allowed to reconstruct a P-T path for a garnet-chloritoid-bearing micaschist from the northern part of the Dora Maira Massif, which reached eclogite facies conditions at 18-20 kbar and 515-525°C (M/S event) and then was exhumed during increasing T (10-11 kbar and 555-565°C). The M assemblage defining the S regional foliation developed at P < 7 kbar and T < 575°C. According to the structural evolution, the tectonic coupling between Dora Maira and Piedmont Zone took place during exhumation along the subduction channel.
- Subjects
SUSA Valley (Italy); ITALY; METAMORPHIC rocks; PETROFABRIC analysis; GEOLOGICAL mapping; ROCK deformation; SCHISTOSITY; STRUCTURAL analysis (Engineering); NAPPES (Geology); METAMORPHISM (Geology); GARNET; SUBDUCTION zones
- Publication
International Journal of Earth Sciences, 2011, Vol 100, Issue 5, p1065
- ISSN
1437-3254
- Publication type
Article
- DOI
10.1007/s00531-011-0640-8