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

Papers by Antonio Azor

Research paper thumbnail of A comparison of the Neoproterozoic/Lower Palaeozoic lithostratigraphy of Morocco and southwestern Iberia. Geodynamic interpretations

Geogaceta, 2005

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Research paper thumbnail of 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.

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Research paper thumbnail of Bou Azzer 2008

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

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

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Research paper thumbnail of 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.

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

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Research paper thumbnail of Lithospheric Velocity Model across the Southern Central Iberian Zone (Variscan Iberian Massif): the ALCUDIA Wide-Angle Seismic Reflection Transect

Tectonics, 2015

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Research paper thumbnail of 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). ...

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Research paper thumbnail of The tectonic frame of the Variscan–Alleghanian orogen in Southern Europe and Northern Africa

Tectonophysics, 2005

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Research paper thumbnail of 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...

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

Lithos, 2013

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Research paper thumbnail of 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.

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Research paper thumbnail of Differentiating geology and tectonics using a spatial autocorrelation technique for the hypsometric integral

Journal of Geophysical Research, 2009

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Research paper thumbnail of 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 ...

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Research paper thumbnail of Emplacement of ellipsoid-shaped (diapiric?) granite: Structural and gravimetric analysis of the Oulmès granite (Variscan Meseta, Morocco)

Journal of African Earth Sciences, 2007

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Research paper thumbnail of Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix–Baza basin, SE Spain)

Geomorphology, 2009

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Research paper thumbnail of Reply to comment by J.L. Díaz-Hernández and R. Julià on “Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix-Baza basin, SE Spain)”

Geomorphology, 2012

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Research paper thumbnail of Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis

Geomorphology, 2010

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Research paper thumbnail of Human-driven coastline changes in the Adra River deltaic system, southeast Spain

Geomorphology, 2010

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Research paper thumbnail of A comparison of the Neoproterozoic/Lower Palaeozoic lithostratigraphy of Morocco and southwestern Iberia. Geodynamic interpretations

Geogaceta, 2005

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 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.

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Research paper thumbnail of Bou Azzer 2008

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

Bookmarks Related papers MentionsView impact

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

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 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.

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

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Lithospheric Velocity Model across the Southern Central Iberian Zone (Variscan Iberian Massif): the ALCUDIA Wide-Angle Seismic Reflection Transect

Tectonics, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of 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). ...

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Research paper thumbnail of The tectonic frame of the Variscan–Alleghanian orogen in Southern Europe and Northern Africa

Tectonophysics, 2005

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Research paper thumbnail of 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...

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

Lithos, 2013

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Research paper thumbnail of 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.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Differentiating geology and tectonics using a spatial autocorrelation technique for the hypsometric integral

Journal of Geophysical Research, 2009

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Research paper thumbnail of 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 ...

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Research paper thumbnail of Emplacement of ellipsoid-shaped (diapiric?) granite: Structural and gravimetric analysis of the Oulmès granite (Variscan Meseta, Morocco)

Journal of African Earth Sciences, 2007

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Research paper thumbnail of Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix–Baza basin, SE Spain)

Geomorphology, 2009

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Research paper thumbnail of Reply to comment by J.L. Díaz-Hernández and R. Julià on “Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix-Baza basin, SE Spain)”

Geomorphology, 2012

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Research paper thumbnail of Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis

Geomorphology, 2010

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Research paper thumbnail of Human-driven coastline changes in the Adra River deltaic system, southeast Spain

Geomorphology, 2010

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