From thickening to extension in the Variscan belt - kinematic evidence from Sardinia (Italy)

The Variscan nappe stack of SE Sardinia originated as a result of several s tages of nappe imbrication during the Lower Carboniferous phases of the Var iscan orogeny. The crustal shortening caused regional SSW-and W-directed th rusting, greenschist facies metamorphism and open-to-isoclinal polyphase fo lding. The final stage of shortening produced large-scale antiforms and syn forms, Post-collisional deformation resulted in inversion of earlier thrusts as no rmal faults, development of low-angle normal faults, and refolding of earli er foliation and thrust planes by asymmetric folds with subhorizontal axial planes. Facing directions of these latest folds are directed horizontally outward from the hinge zones of main antiforms, suggesting that they cannot be regarded as parasitic folds of the latest thickening phase, but instead are the consequence of vertical shortening during gravitational collapse o f dome-like km-scale antiforms, leading to denudation of antiformal culmina tions.