Foreland- and hinterland-verging structures in fold-and-thrust belt: an example from the Variscan foreland of Sardinia |
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| Authors: | Antonio Funedda |
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| Institution: | 1.Dipartimento di Scienze della Terra,Università degli Studi di Cagliari,Cagliari,Italy |
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| Abstract: | In the Variscan foreland of SW-Sardinia (Western Mediterranean sea), close to the leading edge of the nappe zone, nappe emplacement
caused folding and repetition of stratigraphic successions, km-scale offset of stratigraphic boundaries and an extensive brittle-ductile
shear zone. Thrusts assumed a significant role, accommodating a progressive change of shortening direction and forming complicated
thrust triangle zones. During thrust emplacement of the nappes, strong penetrative deformation affected rocks beneath the
basal thrust of the nappe stack and produced coeval structures with both foreland-directed and hinterland-directed (backthrusting)
shear sense. Cross-cutting and overprinting relationships clearly show that the shortening direction changed progressively
from N–S to E–W, producing in sequence: (1) E–W trending open folds contemporaneous with early nappe emplacement in the nearby
nappe zone; (2) recumbent, quasi-isoclinal folds with axial plane foliation and widespread, “top-towards-the-SW”, penetrative
shearing; (3) N–S trending folds with axial plane foliation, contemporaneous with late nappe emplacement; (4) backthrusts
and related asymmetrical folds developed during the final stages of shortening, postdating foreland-verging structures. Structures
at (3) and (4) occurred during the same tectonic transport “top-towards-the-E” of the nappe zone over the foreland. The several
generations of folds, thrusts, and foliations with different orientations developed, result in a complex finite structural
architecture, not completely explicable by the theoretical model proposed up to date. |
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