Backarc basin inversion and subcontinental mantle emplacement in the crust: kilometre-scale folding and shearing at the base of the proto-Alborán lithospheric mantle (Betic Cordillera, southern Spain)

Abstract

To constrain the latest evolutionary stages and mechanisms of exhumation and emplacement of subcontinental peridotites in the westernmost Mediterranean, we present here a detailed structural study of the transition from granular spinel peridotite to plagioclase tectonite in the western Ronda Peridotite (Betic Cordillera, southern Spain). We show that the plagioclase tectonite foliation represents an axial surface particularly well developed in the reverse limb of a downward facing moderately plunging and moderately inclined synform at the base of the Ronda massif. The fold limbs are cut by several mylonitic and ultramylonitic shear zones with top-to-the-SW sense of shear. After restoring the middle to late Miocene vertical-axis palaeomagnetic rotation and the early Miocene tectonic tilting of the massif, these studied structures record southward-directed kinematics. We propose a geodynamic model in which folding and shearing of an attenuated mantle lithosphere occurred by backarc basin inversion during late Oligocene (23–25 Ma) southward collision of the Alborán Domain with the palaeo-Maghrebian passive margin, leading to the intracrustal emplacement of peridotites in the earliest Miocene (21–23 Ma).

Wealth of P–T–t information in medium-high grade metapelites: Example from the Jubrique Unit of the Betic Cordillera, S Spain

“…1) the peridotite bodies are tectonically interleaved with slices of metamorphic rocks (e.g., Hidas et al, 2013) belonging to the Alpujarride Complex, which is overlain by slices of the Maláguide Complex. The Jubrique Unit, from which the studied samples were taken from, is part of the westernmost Alpujarride Complex ( Fig.…”

Hyperextension of continental to oceanic-like lithosphere: The record of late gabbros in the shallow subcontinental lithospheric mantle of the westernmost Mediterranean

“…2b-c, 3c-f). These observations indicate that gabbro dikes are syn-to slightly post-kinematic relative to the stress field recorded in the plagioclase tectonite foliation and that formed in the waning stages of ductile deformation of the Ronda Peridotite prior to its intra-crustal emplacement (Hidas et al, 2013a).…”

“…2b). As in common plagioclase tectonites of the Ronda massif (Hidas et al, 2013a;Van der Wal and Vissers, 1996), spinel in the Ojén massif is rimmed as well by a subsolidus plagioclase corona. However, particularly in the vicinity of the discordant gabbroic dikes, plagioclase also occurs interstitially as elongated patches subparallel to the trace of the foliation, texturally unrelated to spinel (Fig.…”

“…1c), that belong to the western part of the Betic Cordillera. Earlier studies provide a basis to distinguish several kilometer-scale petrologic, geochemical and structural domains in otherwise coherent subcontinental lithospheric mantle sections in the Ronda and Beni Bousera Peridotites (Frets et al, 2014;Garrido et al, 2011;Hidas et al, 2013a;and references therein). Based on the correlation and structural relationship to the crustal envelope, from top to the bottom of the section these tectonometamorphic domains include : (1) overlying garnet-spinel mylonite in contact with the metamorphic crustal units (missing in the Ojén massif); (2) spinel tectonite composed of highly foliated porphyroclastic spinel peridotites; (3) granular spinel peridotite that consists of coarse grained spinel peridotites, separated from the overlying unit across a narrow (c. 200-400 m wide) and continuous (c. 20 km long) transitional zone referred to as the recrystallization front (field occurrence is less patent in the Ojén massif and the Beni Bousera Peridotite); (4) underlying, youngest plagioclase tectonite (not cropping out in the Beni Bousera Peridotite) that overprints the granular spinel peridotite domain and attests for partial equilibrium in the plagioclase lherzolite facies.…”

Late Palaeozoic to Triassic formations unconformably deposited over the Ronda peridotites (Betic Cordilleras): Evidence for their Variscan time of crustal emplacement

“…Précigout et al (2013) deduced that the Ronda peridotites were emplaced during the OligoceneMiocene just before 22 Ma. Hidas et al (2013) proposed a model for the emplacement of the Ronda Peridotites in which folding and shearing of an attenuated mantle lithosphere occurred by back arc basin inversion during the late Oligocene and a later collision during the earliest Miocene. Platt et al (2013) extensively discussed the arguments in favour of and against the possible Variscan or Miocene ages of the exhumation.…”