Structural Petrology of the Ronda Peridotite, SW Spain: Deformation History |
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| Authors: | VAN DER WAL DIRK; VISSERS REINOUD L M |
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| Institution: | DEPARTMENT OF GEOLOGY, INSTITUTE OF EARTH SCIENCES, UTRECHT UNIVERSITY PO BOX 80 021, 3508 TA UTRECHT, THE NETHERLANDS |
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| Abstract: | Solid bodies of upper-mantle peridotite, emplaced in the Betic-Rifchains of SW Spain and North Morocco, show a variety of structuresdeveloped under different metamorphic conditions. These structuresand related metamorphism reflect tectonic processes in the WestMediterranean mantle during orogeny in the Betic-Rif realm.The largest of the peridotites, the Ronda massif, has preservedthree structural domains which are spatially associated withmetamorphic domains previously defined by Obata (Journal ofPetrology, 21,533–572, 1980). These structural domainsinclude: (1) porphyroclastic spinel peridotites (spinel tectonites)and mylonitic garnet-spinel peridotites (garnet-spinel mylonites),developed during progressive strain localization at ambientconditions changing from the Arigite subfacies to garnet peridotitefacies; (2) seemingly undeformed granular peridotites, developedduring a phase of extensive recrystallization affecting thespinel tectonites and garnet-spinel mylonites at Seiland subfaciesconditions, and separated from the spinel tectonites by a well-preservedrecrystallization front which forms a marked structural, metamorphicand possibly geochemical boundary probably unique to orogenicperidotites; (3) porphyroclastic plagioclase peridotites (plagioclasetectonites) developed at the expense of the granular peridotitesduring progressive shear localization allied to ductile emplacementof the Ronda massif into the crust. Our structural and microstructural data from the Ronda massifallow us to assess the relative ages of the different metamorphicfacies seen in the West Mediterranean peridotites. In orderof decreasing relative age, these are: Arigite-subfacies, garnetperidotite facies, Seiland subfacies and plagioclase peridotitefacies. In addition, the associated microstructures providesome insight into the microphysical conditions controlling thedevelopment of the different structures and, as a result, thestructural and chemical heterogeneity of the West Mediterraneanperidotites. KEY WORDS: structural geology; peridotite; Betic Cordillera; Ronda; recrystallization; strain localization
*Corresponding author. Present address: Philips Electron Optics BV, Applications Laboratory, Building AAE, PO Box 218, 5600 MD Eindhoven, The Netherlands |
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