Deformation processes and rheology of pyroxenites under lithospheric mantle conditions
| Autor: | José Alberto Padrón-Navarta, Carlos J. Garrido, Kamal Targuisti, Andréa Tommasi, Erwin Frets, Isma Amri |
|---|---|
| Přispěvatelé: | 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), Instituto Andaluz de Ciencias de la Tierra (IACT), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC)-Universidad de Granada (UGR), Australian National University (ANU), Département de Géologie [Tétouan], Université Abdelmalek Essaâdi (UAE) |
| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: |
010504 meteorology & atmospheric sciences
Orthopyroxene [SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography Mineralogy Pyroxene Slip (materials science) Rheaology engineering.material 010502 geochemistry & geophysics 01 natural sciences Mantle (geology) Plastic deformation Microstructure 0105 earth and related environmental sciences Peridotite Dislocation creep Pyroxenite Garnet Spinel Recrystallization (metallurgy) Geology Crystal preferred orientations Deformation mechanism engineering Clinopyroxene Mantle Beni Bousera |
| Zdroj: | Journal of Structural Geology Journal of Structural Geology, Elsevier, 2012, 39, pp.138-157. ⟨10.1016/j.jsg.2012.02.019⟩ |
| ISSN: | 0191-8141 |
| Popis: | International audience; We combined microstructural observations and high-resolution crystallographic preferred orientation (CPO) mapping to unravel the active deformation mechanisms in garnet clinopyroxenites, garnet-spinel websterites, and spinel websterites from the Beni Bousera peridotite massif. All pyroxenites display microstructures recording plastic deformation by dislocation creep. Pyroxene CPOs are consistent with dominant slip on [001]{110} in clinopyroxene and on [001](100) or [001](010) in orthopyroxene. Garnet clinopyroxenites have however high recrystallized fractions and finer grain sizes than spinel websterites. Recrystallization mechanisms also differ: subgrain rotation dominates in garnet clinopyroxenites, whereas in spinel websterites nucleation and growth also contribute. Elongated shapes and strong intracrystalline misorientations suggest plastic deformation of garnet, but CPOs are weak. Clinopyroxene porphyroclasts in spinel websterites show deformation twins underlined by orthopyroxene exsolutions. Thermodynamic calculations indicate that garnet clinopyroxenites deformed at 2.0 GPa and 950-1000 °C and spinel pyroxenites at 1.8 GPa and 1100-1150 °C. The lower temperatures may explain the faster work rates implied by the finer grained microstructures in garnet clinopyroxenites. Greater stresses may have also reduced the competence contrast between garnet and pyroxene in the garnet pyroxenites and, at the outcrop scale, lowered the competence contrast between pyroxenites and peridotites, favoring mechanical dispersion of pyroxenites in the cooler lithospheric mantle. |
| Databáze: | OpenAIRE |
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