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Folded continental and oceanic nappes on the southern side of Monte Rosa (western Alps, Italy): Anatomy of a double collision suture
Author(s) -
Pleuger Jan,
Froitzheim Nikolaus,
Jansen Ekkehard
Publication year - 2005
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2004tc001737
Subject(s) - geology , nappe , ophiolite , metamorphism , gneiss , eclogite , continental collision , fibrous joint , greenschist , oceanic crust , continental margin , continental crust , geochemistry , seismology , shear zone , geomorphology , subduction , metamorphic rock , crust , tectonics , medicine , anatomy
Previous work suggested a double collision suture, including ophiolites from two oceanic basins (Valais and Piemont‐Liguria), on the southern side of Monte Rosa (Penninic Alps, northern Italy). This area was studied using field mapping, microstructural analysis, and neutron texture goniometry. After its formation and eclogite‐facies metamorphism of continental and oceanic units, the suture was deformed by four successive folding and shearing events under greenschist‐facies conditions, all of them taking place between 40 and 28 Ma. After fold retrodeformation, the following tectonostratigraphy results, from base to top: Monte Rosa gneiss (European margin), Balma serpentinite/eclogite unit (Cretaceous crust of Valais ocean), Stolemberg gneiss (Iberia‐Briançonnais continent), Zermatt‐Saas and Tsaté ophiolites (Jurassic crust of Piemont‐Ligurian ocean), Sesia nappe (continental fragment off the Adria margin). The preservation of this lithological sequence suggests that deep‐seated deformation during multiple continent collision produces heterogeneous strain and extreme thinning of nappes but their original stacking order can still be reconstructed using kinematic analysis and overprinting criteria. This is due to the ductile nature of the collisional deformation which retains the continuity of tectonic contacts.