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Finite strain and deformation within the Briançonnais Castelvecchio-Cerisola nappe of the Ligurian Alps, Italy

Journal of Structural Geology
Publication Date
DOI: 10.1016/0191-8141(92)90043-v


Abstract The structural history of the Castelvecchio-Cerisola Briançonnais nappe (Ligurian Alps, Italy) was dominated by a southwestward overthrust shear that resulted in isoclinal folding and schistosity-lineation fabric development within the nappe. This deformation was due to the intracontinental shortening related to the collision of the European and Adriatic plates during Late Cretaceous-Eocene times. Finite strain, produced during the isoclinal folding and the schistosity-lineation fabric development, was determined from quartzites, conglomerates and tuffs using Fry's method. Strain type and intensities are strongly dependent on rock type: other factors, like the proximity to the major thrusts or the position in relation to the first phase recumbent folds, seem to be of secondary importance. The quartzites and conglomerates display a constrictional strain or else they approximate to plane strain, while the pyroclastic rocks fall into the field of apparent flattening and are characterized by a higher intensity of deformation. During nappe emplacement the deformation was not accommodated by simple shear alone: the interpretation of strain patterns in the Castelvecchio-Cerisola has led to a model in which longitudinal strain was superposed on layer-parallel simple shear. Schistosity at a low angle to the major thrust faults, incremental extension directions deduced from pressure shadows, very frequent veins and stylolitic structures parallel to bedding support this hypothesis. The data presented here emphasize that subvertical thinning associated with thrust shear and a small extension perpendicular to the emplacement direction occurred in the Castelvecchio-Cerisola nappe.

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