Antonio Azor - Profile on Academia.edu (original) (raw)

Papers by Antonio Azor

Geogaceta, 2005

inferior y medio está representado, tanto en Iberia como en Marruecos, por secuencias detríticas ... more inferior y medio está representado, tanto en Iberia como en Marruecos, por secuencias detríticas y vulcanosedimentarias formadas en un contexto de rifting. Sin embargo, la evolución de estas dos regiones se diferenció a partir del Cámbrico superior: en el sudoeste de Iberia, la actividad extensional continuó durante el Ordovícico, desarrollándose dominios oceánicos; en Marruecos, dominó durante el resto del Paleozoico inferior un régimen de plataforma débilmente extensional.

Geochronological data on the Rabat-Tiflet granitoids: Their bearing on the tectonics of the Moroccan Variscides

J Afr Earth Sci, 2010

The northern border of the Variscan Moroccan Meseta is characterized by the presence of Cambrian ... more The northern border of the Variscan Moroccan Meseta is characterized by the presence of Cambrian rocks affected by pre-Variscan deformation (the Sehoul block) thrust to the south onto Ordovician, Silurian and Devonian sediments and volcanics of the Bou Regreg corridor. A correct appraisal of the significance of this tectonic contact in the framework of the Variscan orogen needs new data on the age, geochemical features and field relationships of granitoids cropping out in the Sehoul block (Rabat granitoids) and the Bou Regreg corridor (Tiflet granitoids). Accordingly, we provide here with new geochemical data and accurate U-Pb geochronology of these granitoids, which lead us to conclude that: (i) the Rabat granitoids are Late Devonian in age (367 Ma); (ii) the Tiflet granitoids are Late Proterozoic in age (605-609 Ma) and display Andean-arc features, thus being genetically linked to the Cadomian/Pan-African subduction and forming part of the Variscan basement during the Palaeozoic; (iii) the previously accepted 430 Ma Rb-Sr age, common for the Rabat and Tiflet granitoids, which would imply a trivial Carboniferous displacement of the Sehoul thrust, must be rejected; and (iv) the Sehoul thrust might be a major Variscan boundary, perhaps hiding the Rheic Ocean suture.

La ofiolita de Bou Azzer marca la sutura del orógeno Pan-africano en el Anti-Atlas (Marruecos). E... more La ofiolita de Bou Azzer marca la sutura del orógeno Pan-africano en el Anti-Atlas (Marruecos). En esta ofiolita se ha observado una paragénesis relicta de granate y rutilo, que sugiere un episodio inicial de alta presión. Tras este episodio, la ofiolita sufrió, durante su exhumación, una retrogradación a facies esquistos verdes, al tiempo que se desarrollaba la fábrica plano-linear (S 2 , L 2 ) que domina en estas rocas. La macroestructura asociada a esta fábrica principal consiste en pliegues volcados vergentes al SW y cabalgamientos con movimiento de bloque de techo al W/SW. Estas estructuras emplazaron la ofiolita sobre rocas de la plataforma continental del Cratón Oeste Africano. Una sucesión clástica (Formación Tiddiline) aparece discordante sobre la ofiolita, las rocas de arco y los sedimentos de plataforma, estando a su vez deformada por pliegues erguidos de dirección ESE-WNW y fallas inversas. La convergencia Neoproterozoica concluyó con el desarrollo de fallas de salto en dirección izquierdo.

The evolution of a suture of the Variscan belt: the Ossa-Morena/Central Iberian boundary (south-western Iberian Massif)

The footwall structure of the Ossa-Morena/Central Iberian suture (Iberian Peninsula)

Revisiting the Variscan transpressional tectonics in the Southwestern Iberian suture

ABSTRACT The boundary between the Ossa-Morena Zone (OMZ) and the South Portuguese Zone (SPZ) in s... more ABSTRACT The boundary between the Ossa-Morena Zone (OMZ) and the South Portuguese Zone (SPZ) in southwest Iberia is a Variscan collisional suture with transpressive left-lateral kinematics, contrasting with the dextral component that characterizes most of the Variscan convergence in other regions of the Orogen. Recent work including new structural and radiometric data has improved our knowledge on the geometry and timing of deformations affecting the OMZ/SPZ suture, which can be summarized as follows: 1) Closure of the Rheic Ocean in Late Devonian time is attested by high-pressure and ophiolitic thin allochthonous units emplaced on the southern border of the OMZ. The kinematic interpretation of early stretching lineations and tectonic fabrics indicate that these units were emplaced in a tectonic regime of oblique left-lateral convergence. 2) Transient transtension in Early Carboniferous time gave way to a narrow aisle of newly-formed oceanic-like crust just over the foregoing Rheic Ocean suture, accompanied by mafic magmatism intruded/extruded at both continental sides. Radiometric dating has yielded the same age of around 340 Ma for the oceanic-like mafic protholiths and their granulite/amphibolite facies tectonic fabric, thus indicating the very ephemeral life of the oceanic-like strip. 3) Oblique convergence was resumed immediately after transtension, first causing northward obduction of the oceanic-like unit and north-verging folding in metasedimentary units of the southern border of the suture. Later on, a south-vergent regional fold was developed synchronous with left-lateral granulite-amphibolite facies shearing. Finally, shear deformation gave way to a low pitch stretching lineation, thrusting the OMZ over SPZ, concentrated on the southern limb of this regional fold and constituting a complex ductile 2-3 km-thick shear band evolving from amphibolite to greenschist facies, developing: (i) high-temperature greenschists at the southern border of the mafic oceanic-like unit, which propagated southwards progressively cooling to low-temperature greenschists; (ii) disruption of layers that produced small fishes of weakly deformed rocks, previously interpreted as sedimentary mélanges. Radiometric dating of acid volcanic rocks included in the low-grade shear zone has yielded an age of 337 Ma, putting an older limit to shearing. At late Variscan time, a brittle left-lateral shear band partially obliterated the previous syn-metamorphic shear zone. 4) Oblique convergence propagated southwards across the SPZ in Late Carboniferous time, though lateral displacements decreased rapidly in favor of shortening. This deformation has been roughly modelled as a transpressional band characterized by 40% shortening and =1 shearing. An age of 330 Ma yielded by a deformed granite at the northern part of the SPZ probably indicates the arrival of deformation at that point, while stratigraphic data suggest that deformation reached SW Portugal at around 310 Ma. To conclude, the transpressive OMZ/SPZ boundary shows strain partitioning, with left-lateral displacements concentrated in ductile to brittle shear zones affecting the suture units, and moderately oblique shortening affecting a broad zone of the SPZ foreland.

Accommodation of fault displacements by granite deformation: an example from the southwestern Iberian Massif

Tectonics, 2015

A P-wave seismic velocity model has been obtained for the Central Iberian Zone, the largest conti... more A P-wave seismic velocity model has been obtained for the Central Iberian Zone, the largest continental fragment of the Iberian Variscan Belt. The spatially dense, high-resolution, wide-angle seismic reflection experiment ALCUDIA-WA, was acquired in 2012 across central Iberia, aiming to constrain the lithospheric structure and resolve the physical properties of the crust and upper mantle.

Opposite subduction polarities connected by transform faults in the Iberian Massif and western European Variscides

Special Paper 364: Variscan-Appalachian dynamics: The building of the late Paleozoic basement, 2002

... and ophi-olitic terranes crop out (Galicia Tras-os-Montes zone), having reached granulitic an... more ... and ophi-olitic terranes crop out (Galicia Tras-os-Montes zone), having reached granulitic and eclogitic metamorphic conditions in some of the units (Arenas et al ... Silurian sequence of the Central Iberian zone (Robardet and Gutierrez Marco, 1990; Gutierrez Marco etal., 1998). ...

Tectonophysics, 2005

By confronting different geological and geophysical data, we attempt to reconstruct the Variscan-... more By confronting different geological and geophysical data, we attempt to reconstruct the Variscan-Alleghanian orogenic belt, with especial emphasis on the links between Iberia, northwest Africa, and northeast America.

Constaints on the nature of the SW-Iberia crust from wide-angle P- and S-velocity models

The SW-Iberian Peninsula was studied with the two wide-angle seismic reflection transects acquire... more The SW-Iberian Peninsula was studied with the two wide-angle seismic reflection transects acquired in 2003. Both transects cross the three tectonic provinces in the area that are part of the Variscan Belt: South Portuguesse Zone (SPZ), Ossa-Morena Zone (OMZ) and Central Iberia Zone (CIZ). The data were acquired by 650 vertical component seismographs (TEXANS seismic recorders) from the IRIS-PASSCAL Instrument Center, using explosive sources with charge sizes ranging from 500 to 1000 kg. Both Transects, A and B, are, approximately, 300 km long with station spacing of 400 m and 150 m respectively. The relatively small station spacing favored the lateral correlation of the seismic events and provided resolution enough for the identification of shear-waves arrivals. The most prominent S-wave phase recorded by the vertical component sensors corresponds to the SmS which is nearly horizontal for a velocity reduction of 4600 m/s. This phase can be followed up to normal incidence at 18 s ttwt...

Age distribution of lamproites along the Socovos Fault (southern Spain) and lithospheric scale tearing

Lithos, 2013

Metamorphism and kinematics of the early deformation in the Variscan suture of SW Iberia

Journal of Metamorphic Geology, 2012

ABSTRACT The early (Devonian) collisional stage in SW Iberia has been investigated through the an... more ABSTRACT The early (Devonian) collisional stage in SW Iberia has been investigated through the analysis of deformation in the Cubito‐Moura schists, the main lithology of an Allochthonous Complex putatively rooted in the suture between the Ossa‐Morena and South Portuguese zones. The first deformation in these schists (D1) is recorded as a S1‐L1 mylonitic fabric well preserved in early quartz veins. Subsequent D2 deformation caused the main folds and the main (S2) foliation. After restoration, the stretching lineation (L1) trends at a small angle with the Ossa‐Morena/South Portuguese suture. This trend, together with the top‐to‐the‐east kinematics determined from quartz microfabric is indicative of an oblique left‐lateral collisional scenario in SW Iberia. Chlorite–white K‐mica–quartz ± chloritoid multi‐equilibrium calculations yield P–T conditions in the range 0.9–1.2 GPa and 300–400 °C, during the first collisional stage. P–T conditions during D2 were 0.3–0.8 GPa and 400–450 °C, thus indicating an important stage of exhumation of the Allochthonous Complex during these two collisional events, after subduction of the Ossa‐Morena Zone margin under the South Portuguese Zone continental crust. In the general context of the Variscan orogen, dominated by dextral collision, the left‐lateral convergence in SW Iberia can be explained in terms of the Avalonian salient represented by the South Portuguese Zone, which would impinge between Iberia and Morocco.

Journal of Geophysical Research, 2009

1] Hypsometry is thought to be sensitive to tectonic uplift rates and lithology differences. In t... more 1] Hypsometry is thought to be sensitive to tectonic uplift rates and lithology differences. In this study we calculated hypsometric integrals (HIs) using as topographic sources two digital elevation models of 10 and 90 m of pixel resolution in the Granada basin (SE of Spain). The HI spatial distributions do not show clear spatial patterns and do not correlate with basin parameters as mean elevation or relief amplitude. However, when exploratory spatial data analysis is applied to the data distributions through local indices of spatial autocorrelation, clear hot spots are visible that improve the geologic meaning of the HI. The distributions are robust and independent of the model resolution but are scale influenced. The application of this new method to the Granada basin shows a strong correlation between the main distribution of active normal faults in the basin and the clusters of high or low HI values obtained in our analysis. Clusters with high HI values define the uplifted footwalls of these faults and regions uplifted in relation with rollover anticlines or where epeirogenic uplift has not been counteracted by local extension. Once the method was adjusted in the Granada basin, we tested its applicability in an area of known contractive tectonic activity, central Otago, New Zealand, showing that the meaning of HI values is improved by using the autocorrelation techniques.

Geochronological data on the Rabat–Tiflet granitoids: Their bearing on the tectonics of the Moroccan Variscides

Journal of African Earth Sciences, 2010

... c Département de Géologie, Faculté des sciences Ben Msik-Sidi Othmane, BP 7955, Casablanca, M... more ... c Département de Géologie, Faculté des sciences Ben Msik-Sidi Othmane, BP 7955, Casablanca, Morocco. ... area showing, from north to south, the Sehoul block, the Sehoul thrust, the Bou Regreg corridor and the Sidi Bettache Carboniferous basin (from El Hassani (1991 ...

Journal of African Earth Sciences, 2007

The Oulmès granite is a NE-SW elongated stock intruded in Ordovician metasedimentary rocks which ... more The Oulmès granite is a NE-SW elongated stock intruded in Ordovician metasedimentary rocks which crop out at the core of a regional anticlinorium of the Moroccan Variscan Meseta. The stock, dated at around 300 Ma, is made up of peraluminous two-mica granite, with subordinate amounts of muscovite leucogranite. Mineral composition and textural features of both the granite and the thermal aureole enable us to constrain the P-T conditions during magma intrusion in %250-300 MPa and %600°C at the contact between the granite and its host rock. Emplacement of the Oulmès granite postdates the main regional structures and is coeval with the late stages of Variscan compression. Prior to granite intrusion, the host rocks were affected by a main deformation phase responsible for the development of a penetrative slaty cleavage and regional-scale folds.

Geomorphology, 2009

The landscape evolution in Neogene intramontane basins is a result of the interaction of climatic... more The landscape evolution in Neogene intramontane basins is a result of the interaction of climatic, lithologic, and tectonic factors. When sedimentation ceases and a basin enters an erosional stage, estimating erosion rates across the entire basin can offer a good view of landscape evolution. In this work, the erosion rates in the Guadix-Baza basin have been calculated based on a volumetric estimate of sediment loss by river erosion since the Late Pleistocene. To do so, the distribution of a glacis surface at ca. 43 kyr, characterised by a calcrete layer that caps the basin infilling, has been reconstructed. To support this age, new radiometric data of the glacis are presented. The volume of sediment loss by water erosion has been calculated for the entire basin by comparing the reconstructed geomorphic surface and the present-day topography. The resulting erosion rates vary between 4.28 and 6.57 m 3 ha − 1 yr − 1 , and are the consequence of the interaction of climatic, lithologic, topographic, and tectonic factors. Individual erosion rates for the Guadix and Baza sub-basins (11.80 m 3 ha − 1 yr − 1 and 1.77 m 3 ha − 1 yr − 1 respectively) suggest different stages of drainage pattern evolution in the two sub-basins. We attribute the lower values obtained in the Baza sub-basin to the down-throw of this sub-basin caused by very recent activity along the Baza fault.

Geomorphology, 2012

We demonstrate that the age of 43 ka obtained for the topmost calcrete layer in the Guadix-Baza r... more We demonstrate that the age of 43 ka obtained for the topmost calcrete layer in the Guadix-Baza remains the only reliable numerical dating of the flat geomorphic surface that marks the end of the sedimentation in the basin. Consequently, the late Pleistocene to Holocene erosion rates derived from the incision of the presentday drainage network into the flat geomorphic surface remain valid. The calcrete radiometric ages reported by Díaz-Hernández and Julià (2012) in their comment are untenable due to the contamination with detrital 230 Th (not corrected with the applied U/Th technique) and the possible mix of textural elements with different ages (older inherited grains and newly formed grains). Díaz-Hernández and Julià also quote U/Th ages for travertine terraces formed later than the calcrete layer. These ages lack internal consistency probably due to systematic contamination and/or weathering of the samples. The archaeological ages reported by Díaz-Hernández and Julià are subjected to great uncertainties, but independently of the age assumed as most realistic, they are completely compatible with the age of 43 ka that we obtained for the topmost calcrete layer in the Guadix-Baza basin.