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Chronologie et évolution de la déformation de la croûte moyenne à la surface dans un prisme collisionel en décrochement - impacts sur l'aléa sismo-gravitaire: Exemple des Alpes Sud-Occidentales.

Abstract : This PhD thesis presents a multidisciplinary approach, structural, petrologic, geochronologic (Ar-Ar, fission tracks, (U-Th)/He and 10Be dating) allowing to constrain the tectonic processes (burial, exhumation, active fault...) from mid-crustal depth to the surface in the South-Western Alps. (i) Ar-Ar and thermobarometry in shear zones show that the Argentera-Mercantour massif and its attached Permian cover underwent a similar tectono-metamorphic history with a burial peak of 15-18 km at around 34 Ma due to underthrusting below the internal metamorphic unit. The exhumation path (0.8mm/an) of the massif took place in a transpressive, followed by a transtensive, regimes between 26 Ma and 5 Ma and between 5 and 0 Ma, respectively. Transpression is ascribed to Ivrea mantle body indentation while transtension is related to rotational movement of the Adriatic plate. (ii) The sedimentary cover is shortened and transported southward during the Miocene period (23-7 Ma). This displacement is directly linked to the exhumation of the Argentera-Mercantour crystalline massif. The resulting slope of the basement-cover interface due to this uplift led to decoupling and downsliding of the overlying sedimentary cover. Further, the metamorphic gap between the crystalline massif and the sedimentary cover and their structural relationship lead to propose a model of basement substitution. (iii) Since 8 Ma, cover-basement decoupling ceased as featured by similar AFT ages in both cover and basement rocks. The recent/britte tectonic regime is characterized by a main network of N140°E strike slip faults, and a minor N-S extensional component. Tectonic displacement along both these faults led to the development of the Embrunais-Ubaye transtensional domain. The initiation age of this transtensional deformation is dated at 4-5 Ma by AHe ages below the Camp des Fourches fault. (iv) This fault system still active (seismicity and landslide activity) accommodating 40-60% of counterclockwise rotation of the Adriatic plate. It resulted in offsets of the Holocene glacial morphologies, dated by 10Be on quartz at 12-13 ka , while fault surfaces are dated at 11-8 ka, and gravity features at 10 to 2 ka.
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https://tel.archives-ouvertes.fr/tel-00527515
Contributor : Guillaume Sanchez <>
Submitted on : Tuesday, October 19, 2010 - 2:49:36 PM
Last modification on : Wednesday, December 9, 2020 - 3:08:02 PM
Long-term archiving on: : Thursday, January 20, 2011 - 2:45:03 AM

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  • HAL Id : tel-00527515, version 1

Citation

Guillaume Sanchez. Chronologie et évolution de la déformation de la croûte moyenne à la surface dans un prisme collisionel en décrochement - impacts sur l'aléa sismo-gravitaire: Exemple des Alpes Sud-Occidentales.. Géologie appliquée. Université Nice Sophia Antipolis, 2010. Français. ⟨tel-00527515⟩

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