Álvarez-Valero, A.M. and Jagoutz, O. and Stanley, J. and Manthei, C. and Maz, A.E. and Moukadiri, A. and Piasecki, A. (2014) Crustal attenuation as a tracer for the emplacement of the Beni Bousera ultramafic massif (Betico-Rifean belt). Bulletin of the Geological Society of America, 126 (11-12). pp. 1614-1624.

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Abstract

The study of petrology (fieldwork, petrography, and phase diagram modeling) and structural data of the metapelitic granulites and the southern, high-temperature exposed peridotites in the Beni Bousera massif (northern Morocco), combined with results from previous regional studies of the Alborán, suggest a new emplacement mechanism for the mantle rocks in the Betico-Rifean belt. We document two key metamorphic episodes in the granulites within a temperature window of 710-830 ± 50 °C: (1) An earlier prograde high-pressure period (from 9 ± 1.0 to 12 ± 1.0 kbar) characterized by the assemblage garnet + biotite + kyanite + K-feldspar + rutile. Pressure differences of ~3 kbar are found over a continuous crustal section of ~1.5 km of exposed granulites that indicate a signifi- cant crustal attenuation during exhumation of the ultramafic rocks; and (2) a later postkinematic low-pressure (5 ± 0.8 kbar) symplectic assemblage of cordierite + spinel + plagioclase + sillimanite. At the scale of the entire Betico-Rifean belt, two main contacts are observed as mirror images in both sides of the Alborán Sea: (1) the long axis of the high-temperature ductile contact between granulites and peridotites occurs in the west side of the Beni Bousera and Ronda massifs, coupled with (2) the consistent high-angle, east-dipping normal fault in the east parts of the belt massifs. The integration of the petrologic results with information on the rotation of both contacts reveals ductile deformation in the lower crust related to the emplacement of the ultramafic rocks in the Betico-Rifean belt along deep-reaching normal faults. The presence of the early hightemperature contact suggests that it was originally a shallow, west-dipping detachment fault developed in a back-arc environment of the east-dipping, retreating subduction zone (current western part of the Gibraltar arc). This scenario is in concordance with the tectonic evolution in western Italy, where anticlockwise Pleistocene rotations associated with northeast-directed thrusting in the Apennines-and coeval with the southeastward motion in the Calabria-Peloritani terrane-were triggered by retreat and rollback of the Adriatic-Ionian slab toward the southeast during the northwest-directed subduction beneath the Calabrian arc. © 2014 Geological Society of America.

Item Type: Article
Uncontrolled Keywords: Feldspar; Mica; Oxide minerals; Petrography; Silicate minerals; Tectonics, Crustal attenuation; Detachment fault; Ductile deformations; Pressure differences; Subduction zones; Tectonic evolution; Temperature window; Ultramafic massifs, Faulting, crustal structure; ductile deformation; emplacement; exhumation; granulite; normal fault; peridotite; petrology; subduction zone; tectonic evolution; tracer, Alboran Sea; Andalucia; Beni Bousera; Betic Cordillera; Mediterranean Sea; Morocco; Ronda Massif; Spain; Tanger-Tetouan
Subjects: Earth and Planetary Sciences
Divisions: SCIENTIFIC PRODUCTION > Earth and Planetary Sciences
Depositing User: Administrateur Eprints Administrateur Eprints
Last Modified: 31 Jan 2020 15:46
URI: http://eprints.umi.ac.ma/id/eprint/2900

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