Manioc : Portail | resultats 81 - 100 pour la recherche: Walls ( fast )

Annales de la propagation de la foi. recueil périodique. Des lettres des évêques et des missionnaires des missions des deux mondes, et de tous les documents relatifs aux missions et à l'uvre de la propagation de la foi. Tome vingt-deuxième
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Statistique générale et particulière de la France et de ses colonies avec une nouvelle description topographique, physique, agricole, politique, industrielle et commerciale T.2
Auteur(s) : Herbin de Halle, Pierre Etienne (1772-18..) Gorsse Peuchet, Jacques (1758-1830)
Auteurs secondaires : Poirson, Jean-Baptiste (1760-1831) Tardieu, Jean Baptiste Pierre (1746-1816)
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Deformation, annealing, reactive melt percolation, and seismic anisotropy in the lithospheric mantle beneath the southeastern Ethiopian rift: Constraints from mantle xenoliths from Mega
Auteur(s) : TOMMASI, Andrea Baptiste, Virginie VAUCHEZ, Alain Holtzman, Benjamin
Auteurs secondaires : Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Manteau et Interfaces ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Columbia University, Palisades

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We explore the relations between deformation, annealing, and melt percolation during rifting and the effect of these processes on seismic anisotropy by analyzing the microstructures and crystal preferred orientations (CPO) in a suite of mantle xenoliths from Mega, in the southern end of the Ethiopian rift. Previous geochemical studies on these xenoliths showed evidence for interactions with variable melt types and volumes during the rifting process. The peridotites have dominantly coarse-porphyroclastic microstructures, but coarse granular or partially recrystallized microstructures also occur. The olivine CPO, characterized by orthorhombic to fiber-[100] patterns and moderate intensities, the common occurrence of (100) tilt walls, and the predominance of <0vw> rotation axes accommodating low angle misorientations in olivine support deformation by dislocation creep with dominant activation of the [100](010) system. Annealing (static recrystallization) of variable intensity followed this deformation. Modal enrichment in pyroxenes in > 60% of the studied peridotites corroborates extensive, but spatially heterogeneous reactive melt percolation leading to refertilization of the lithospheric mantle beneath the southern Ethiopian rift. The common interstitial shapes of the pyroxenes and lack of correlation between the pyroxenes and the olivine CPOs in many samples suggest that part of the refertilization is post-kinematic. However, there is no simple relation between reactive melt percolation and annealing of the olivine deformation microstructure. Comparison with data from other xenolith localities points to changes in the metasomatic imprint in the lithospheric mantle along the East African rift system correlated with the evolution in the rift maturity. Seismic properties averaged over all samples show typical lithospheric mantle patterns with fast propagation of P- and polarization of the fast S-waves parallel to the lineation. The anisotropy is moderate (< 6% for P-waves and < 4% for S-waves), implying that aligned melt must contribute to the strong seismic anisotropy measured in the Main Ethiopian rift, north of Mega.
ISSN: 0040-1951

hal-01355918
https://hal.archives-ouvertes.fr/hal-01355918
DOI : 10.1016/j.tecto.2016.05.027

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