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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 A. Padron-Navarta and Claudio Marchesi
Garnet lherzolite and garnet-spinel mylonite in the Ronda Peridotite; vestiges of Oligocene backarc mantle lithospheric extension in the western Mediterranean
Geology (Boulder) (October 2011) 39 (10): 927-930

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 approximately 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.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 39
Serial Issue: 10
Title: Garnet lherzolite and garnet-spinel mylonite in the Ronda Peridotite; vestiges of Oligocene backarc mantle lithospheric extension in the western Mediterranean
Affiliation: Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC and UGR, Granada, Spain
Pages: 927-930
Published: 201110
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 29
Accession Number: 2011-097144
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2011276
Illustration Description: illus. incl. sect., geol. sketch map
N36°30'00" - N36°30'00", W05°15'00" - W05°15'00"
Secondary Affiliation: Universite Rennes I, FRA, FranceETH-Zurich, CHE, SwitzerlandUniversidad de Granada, ESP, Spain
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201150
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