Garnet lherzolite and garnet-spinel mylonite in the Ronda peridotite

vestiges of Oligocene backarc mantle lithospheric extension in the western Mediterranean

Carlos J. Garrido*, Frederic Gueydan, Guillermo Booth-Rea, Jacques Precigout, Karoly Hidas, Jose Alberto Padron-Navarta, Claudio Marchesi

*Corresponding author for this work

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

Uplift and exhumation of vast exposures of diamond facies, subcontinental mantle peridotite in the Western Mediterranean arc are attributed to tectonic scenarios including pure extension, transpression or subduction followed by delamination-driven or rollback-driven stretching. In the Ronda peridotite (southern Spain) the strong overprint of low-pressure assemblages has precluded accurate determination of the pressure and temperature conditions for the onset of exhumation that formed the spinel tectonite and garnet-spinel mylonite domain in this massif. Here we report unequivocal petrographic evidence for the existence of prekinematic, coarse-grained garnet lherzolite assemblages from the garnet-spinel mylonite domain of the Ronda peridotite. Application of well-calibrated geothermobarometers yields prekinematic minimum equilibration conditions of 2.4-2.7 GPa and 1020-1100 degrees C, demonstrating that the Ronda peridotite equilibrated at similar to 85 km depth before shearing. We also show the existence of synkinematic garnet and spinel assemblages that overprinted garnet lherzolite assemblages at 800-900 degrees C and 1.95-2.00 GPa. The decompressional cooling path and high pressure recorded by garnet-spinel mylonites rule out their formation by near-isobaric cooling above a subduction-collision wedge or during or after the emplacement of the peridotite massif into the crust. Ronda garnet-spinel mylonites represent the vestiges of subcontinental mantle ductile shear zones formed at early stages of lithosphere extension during backarc extension in the western Mediterranean. Southward to westward retreat of the African slab during the Oligocene-Early Miocene accounts for intense backarc lithosphere extension and development of the Ronda extensional shear zone, coeval with extreme thinning of the Alboran domain overlying crust.

Original languageEnglish
Pages (from-to)927-930
Number of pages4
JournalGeology
Volume39
Issue number10
DOIs
Publication statusPublished - Oct 2011
Externally publishedYes

Keywords

  • P-T TRAJECTORIES
  • SOUTHERN SPAIN
  • STRUCTURAL PETROLOGY
  • DEFORMATION HISTORY
  • BETIC-CORDILLERA
  • SW SPAIN
  • MASSIF
  • EXHUMATION
  • INTRUSION
  • FACIES

Cite this