The role of pre-existing faults in the structural evolution of thrust systems: Insights from the Ligurian Alps (Italy) |
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| Authors: | Lorenzo Bonini Giorgio Dallagiovanna Silvio Seno |
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| Institution: | 1. Department of Arctic Geology, University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway;2. National Institute of Water and Atmospheric Research, Private Bag 14901, Wellington, New Zealand;3. Dipartimento di Matematica e Geoscienze, Università degli Studi di Trieste, 34127 Trieste, Italy;4. Dipartimento di Scienze della Terra, Università di Torino, 10125 Torino, Italy;5. Dipartimento di Fisica e Scienze della Terra “Macedonio Melloni”, Università degli Studi di Parma, Campus Universitario — Parco Area delle Scienze 157/A, I-43124 Parma, Italy;1. Dipartimento di Scienze della Terra, dell''Ambiente e delle Risorse, Università Federico II, Napoli, Italy;2. NEXT — Natural and Experimental Tectonics Research Group, Dipartimento di Fisica e Scienze della Terra “Macedonio Melloni”, Università di Parma, Italy;3. Sorbonne Universités, UPMC Univ. Paris 06, UMR 7193, ISTeP, Paris, France;4. CNRS, UMR 7193, ISTEP, F-75005, Paris, France;5. Geomodels, Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, Spain |
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| Abstract: | New structural and stratigraphic data for a selected area of the Ligurian Alps are combined in order to assess and discuss the role played by extensional structures in the southernmost segment of the Western Alps during thrusting. Restored cross-sections and field data suggest that the structural style in the external sector of the chain may depend upon the presence of pre-orogenic normal faults ascribed to three extensional events linked to different geodynamic contexts: (i) Permian post-Variscan plate reorganisation, (ii) Mesozoic rifting–drifting phases leading to the opening of the Alpine Tethys, and (iii) Eocenic development of the European foreland basins. During positive inversion in Eocene times, a thin-skinned thrust system developed in this area, followed by a thick-skinned phase. In both situations the inherited extensional structures played fundamental roles: during the thin-skinned phase they conditioned the thrusting sequence, also producing large-scale buckle folds and partial reactivations; during the thick-skinned phase the strain was compartmentalized and partitioned by pre-existing faults.The kinematic model of the external sectors of the Ligurian chain also allows the re-assessment of the Alpine evolution of the front-foreland transition, including: (i) indirect confirmation that in the Eocene the Ligurian Briançonnais and Dauphinois domains were not separated by the Valais-Pyrenean oceanic basin; (ii) that the thin-skinned phase progressively changed into thick-skinned; (iii) the assertion that there were no significant deformations from the Oligocene to the present-day, and the Corsica–Sardinia block rotation only produced a change in orientation of previously formed structures and normal fault system development. |
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