Linking temperature estimates and microstructures in deformed polymineralic mantle rocks

Détails

ID Serval
serval:BIB_5674A0159E53
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Institution
Titre
Linking temperature estimates and microstructures in deformed polymineralic mantle rocks
Périodique
Geochemistry, Geophysics, Geosystems
Auteur(s)
Linckens J., Herwegh M., Muntener O.
ISSN-L
1525-2027
Statut éditorial
Publié
Date de publication
2011
Peer-reviewed
Oui
Volume
12
Pages
Q08004
Langue
anglais
Résumé
To constrain deformation temperatures of mantle shear zones, we studied a strike-slip shear zone (Hilti massif, Semail ophiolite, Oman) and focused on the interaction between microstructural mechanisms and chemical equilibration processes. Quantitative microfabric analysis on harzburgites with different deformation intensity (porphyroclastic tectonite, mylonite, and ultramylonite) was combined with orthopyroxene geothermometry. The average grain size of all phases decreases with decreasing shear zone thickness. Dynamic recrystallization of porphyroclasts in combination with dissolution-precipitation and nucleation result in small-sized, chemically equilibrated pyroxenes. The composition of orthopyroxene was used to calculate deformation temperatures. In the case of the porphyroclastic tectonites, the chemical composition of orthopyroxene has been reset by diffusion yielding temperature estimates of 880-900 degrees C. The mylonites were deformed by dislocation creep of olivine and show a broad range of calculated temperatures, which result from a combination of grain size reduction and inheritance of equilibrium compositions from earlier high-temperature events and diffusion. In mylonites, diffusion profiles combined with geothermometry and grain size analysis indicate a mylonitic deformation temperature of 800-900 degrees C possibly followed by diffusion. In ultramylonites, the smallest grains (<30 mu m) reveal equilibration at temperatures of similar to 700 degrees C during the last stages of ductile deformation, which was dominated by diffusion creep of olivine. Our results provide a crucial link between temperature and evolution of microstructures from dislocation creep to diffusion creep in mantle shear zones.
Création de la notice
09/10/2011 21:09
Dernière modification de la notice
20/08/2019 15:10
Données d'usage