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EVOLUTION TARDI-OROGENIQUE DES CORDILLERES BETIQUES (ESPAGNE) : APPORTS D'UNE ETUDE INTEGREE

Abstract : Late-orogenic extensional metamorphic domes are often associated with sedimentary basins developed during their exhumation along major crustal shear zones. With the example of the Betic Cordilleras (Southern Spain), being one of the ideal areas to study the exhumation of metamorphic rocks, the aim of this PhD thesis was to establish a geodynamic model for the metamorphic rocks exhumation integrating both superficial (sedimentary basins) and deep (metamorphic rocks). Its aim was to compare records of both sub-surface (i.e., Sedimentary basins) by studying tectonic subsidence (i.e., S) and deep domains by studying metamorphic rocks (i.e., P-T-t); their relationships being closely linked to the extensional motion along major shear zones (Ε). The aim of the PhD was to tackle a regional problematic by comparing records of that two markers witnessing of a unique cause: the late-orogenic extension of the Betic Cordillera and the formation of the Alboran Sea and on the other hand, to propose a methodological development. The first part of this PhD plan to constrain the basin floor deformation read through the sedimentary record of two basins located structurally on the hanging wall block of major shear extensional zones by the study of subsidence curves (Articles 1 and 2). Basins were born of a meridian (i.e., N-S) extension coeval with the final exhumation stages, at least partly completed by an E-W ductile stretching. Subsidence started at the uppermost Serravallian and extended during the Late Tortonian, before a regional compressional event, some 8 My ago. The second part, mostly structural (Article 3) try to reconcile the apparent paradox between that two, almost perpendicular extension directions by studying strain evolution on the footwall block. A five-stages-succession has been described and then integrated into a structural model for metamorphic rocks exhumation. Sierra Alhamilla and Sierra de los Filabres metamorphic domes were formed in a dominant E-W stretching beneath a major extension shear zone characterised by a top-to-the-W sense of shear. Dome formation was already visible during the late stages of deformation as the shear zone was working under the greenschist facies conditions. Formation of E-W trending domes then controls locally N-S extension accompanied by basin formation in the upper crust. The third part which brings new constraints in terms of « Pressure-Temperature » and time permits to precise quantitatively the above mentioned structural model (Articles 4 and 5). The three constitutive metamorphic units of the domes are then studied by using different P-T quantification methods bringing totally new results. The geochronological part of the study brings time constraints necessary to integrate results at all scale. We used in-situ Ar/Ar Laser ablation on phengites for various textural domains showing both contrasted compositions and P-T estimates. It is thus possible to date some segments or points of the P-T path. Peak-Pressure (20kbar for the Bédar-Macael or 14kbar for the Calar Alto) are reached before 30 My, around 40My. Rapid late-orogenic exhumation then started around 30My and was realised along roughly isothermal paths until 19My. Exhumation was then completed along a HT-LP type cooling path (i.e., 60°C/km) until 8 My. Ductile-Brittle transition is crossed at around 14Ma. In the last part, results are synthetised and integrated at various time and space scales from the one of sedimentary basins to the one of the evolution of the whole Western Mediterranean area (3D evolution of lithosphere segments) through the evolution of metamorphic domes (i.e., intermediate scale). Integration at the Betic-Rif scale (i.e., taking into account the Alpujarride complex) and the Western Mediterranean area is discussed in the Article 6.
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https://tel.archives-ouvertes.fr/tel-00008744
Contributor : Romain Augier <>
Submitted on : Thursday, March 10, 2005 - 3:01:17 PM
Last modification on : Wednesday, December 9, 2020 - 3:06:01 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:20:51 PM

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  • HAL Id : tel-00008744, version 1

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Romain Augier. EVOLUTION TARDI-OROGENIQUE DES CORDILLERES BETIQUES (ESPAGNE) : APPORTS D'UNE ETUDE INTEGREE. Géologie appliquée. Université Pierre et Marie Curie - Paris VI, 2004. Français. ⟨tel-00008744⟩

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