The origin and tectono-sedimentary structure of the Alboran Basin
Resumen Abstract Índice Conclusiones
Gomez, Laura
2018-A
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The origin and tectono-sedimentary structure of the Alboran Basin
(El origen y la estructura tectono-sedimentaria de la cuenca de Alborán)
Resumen:
La presente Tesis Doctoral se fundamenta en un estudio basado esencialmente en perfiles de
sísmica de reflexión (la mayor parte adquiridos durante los proyectos TOPOMED, EVENT-
DEEP y ESCI) de la Cuenca de Alborán, situada entre las cordilleras Béticas (Sur de la Penísula
Ibérica) y Rif (Norte de Marruecos). El proceso de formación de la cuenca es aún discutido, al
igual que los posteriores procesos de deformación. He centrado este estudio en: 1) caracterizar
la estructura cortical de la cuenca, 2) definir su evolución, basándome en el estudio del registro
sedimentario, y 3) estudiar la reorganización contractiva de la cuenca. El estudio de la
reorganización contractiva lo he centrado en tres zonas: el margen de Palomares, la falla de
Yusuf y el cabalgamiento frontal de la Cresta de Alborán.
Los resultados revelan tres tipos de corteza que coexisten a lo largo de la cuenca: a) corteza
continental adelgazada, b) corteza de arco magmático y por último, c) corteza continental del
Norte de África. Las primeras evidencias de la fase extensional se localizan en la cuenca
oriental de Alborán y en la cuenca de Málaga, de edad Burdigaliense, seguidas por la creación
de un segundo depocentro en el norte de África durante el periodo Languiense-Serravaliense. El
arco magmático se formó durante el Tortoniense. Los procesos extensionales en la cuenca
ocurren hasta el Mesiniense, y a partir del Mioceno tardío-Plioceno temprano, cesa la extensión
y comienza la fase de deformación compresiva de la cuenca. El estudio de las estructuras activas
confirma que la inversión tectónica se focaliza en unas pocas fallas que marcan los límites entre
dominios corticales. El desplazamiento acumulado desde el Plioceno Inferior de dos de las
principales fallas de la Cuenca de Alborán, Yusuf y el cabalgamiento frontal de la Cresta de
Alborán, es cómo mínimo de 20 km. Este valor es cercano al valor total de la convergencia
entre las placas de Iberia y África, y por tanto confirma que actualmente la deformación se
concentra principalmente en unas pocas estructuras. Dada su importancia, es necesario realizar
un estudio de la peligrosidad de estas fallas para evaluar su potencial sísmico y tsunamogénico e
incluirlas en las bases de datos nacionales y europeas de riesgos geológicos.
Summary
In this PhD thesis I present a geological and geophysical study of the westernmost Mediterranean basin:
the Alboran Basin. This basin is located between the Iberian Peninsula and North Africa, and it is
surrounded by the Betics and Rif orogenic ranges. Along the Alboran basin, runs the boundary between the
Iberian and African tectonic plates. Although several studies have been carried out in this area, the
processes that led to the formation of the basin in the present-day compressive setting, and the prior
processes that controlled the deep structure of the basin and its later evolution still remained unclear. This
study aims to: 1) unveil the nature of the basement of the basin, 2) define a coherent seismostratigraphy for
the entire basin and analyse the evolution of the basin on the basis of the sedimentary record, 3) explore the
northeaster transition between the Alboran Basin and the Algero-Balearic Basin through the study of the
Palomares Margin, and 4) characterize two of the most prominent tectonic structures in the area that have
been poorly studied, the Yusuf Fault and the Alboran Ridge front fault. The results of this thesis will be
integrated in a geodynamic model of the area, and will help to improve the regional seismic and tsunami
hazard assessment model.
In order to perform a whole-basin scale study of the Alboran Basin, we have used a comprehensive grid of
Multichannel Seismic reflection (MCS) profiles. This seismic dataset has been acquired in the frame of
different projects, most of them acquired by our group (TOPOMED, EVENT-DEEP, and IMPULS) and
completed with vintage data (CAB, ESCI, CONRAD). The main dataset presented in this thesis comes
from the TOPOMED-GASSIS cruise (October 2011, P.I: E. Gràcia and C. Ranero). During this cruise,
new deep-penetration seismic data was acquired using leading edge technology that allows the imaging of
the basin at a crustal scale. For the first time, the new deep multichannel seismic equipment of the RV
“Sarmiento de Gamboa” was used for acquisition of the seismic survey. Two high volume G-gun arrays
(162/140 bar, 2000/2500 psi) and up to 6 km long Sercel multichannel digital streamer (408/480 active
channels) were towed behind the vessel. The result is a comprehensive dataset of multichannel seismic
profiles with unprecedented quality. This dataset allowed us to use state of the art processing and imaging
techniques to obtain a deep image of the tectonic structures, and also a relatively good resolution of the
sedimentary infill of the basin. The main steps of the processing flow in time domain include: 1)
minimum-phase conversion, 2) real geometry definition accounting for streamer feathering, 3) spherical
divergence correction, 4) predictive deconvolution in Tau-P domain (to eliminate the bubble and short
periods multiple reverberations), 5) surface consistent deconvolution, 6) Surface Related multiple
elimination (SRME) demultiple, 7) Radon filter demultiple, normal-move-out correction based on velocity
semblance analysis, 8) Dip Move Out (DMO) correction, 9) stretching mute, 10) amplitude recovery, 11)
time migration and 12) time and spatial variant band-pass filter.
To complete this study, we have also processed the EVENT-DEEP and ESCI profiles, re-processed the
CONRAD profiles, and analyzed and interpreted the whole dataset. We have performed Pre-Stack Depth
Migrations to selected profiles to obtain the real geometry of the structures, and we have also integrated
wide angle seismic (WAS), bathymetric, well and dredge data in this work.
The results reveal that three different crusts coexists in the Alboran Basin: a) a thin continental crust
underneath the West Alboran and Malaga basins, b) a magmatic arc crust in the central part of the Alboran
Sea and the East Alboran Basin, and c) the North African continental crust, below the Pytheas and Habibas
basins. The basin is configured in a fore-arc basin (West Alboran and Malaga basins), a magmatic arc
(central and east Alboran), being the back-arc of the system the easternmost part of the East Alboran Basin
and mainly, the Algero-Balearic Basin.
The seismostratigraphic study supported an early Miocene initiation of the extension in the West Alboran
and Malaga basins, followed by a Langhian-Serravallian extension in the North African margin. These
depocenters were separated by a lithospheric strike-slip fault that allows the independent evolution of each
of them, and the westward migration of the West Alboran and Malaga basins. In the Tortonian, magmatic
activity linked to the subduction system led to the formation of the volcanic arc. In the Messinian,
extensional processes ended and the contractive reorganization of the basin occurred. The present-day
active tectonic structures were mainly formed during the Pliocene, following weak lithospheric zones that
coincide with the edges of the crustal domains.
The geomorphologic and tectonic study of the Palomares margin supports that this contractive
reorganization is not a widespread process, as only few minor faults are reactivated and most of the
deformation is gathered at crustal faults. This hypothesis is confirmed by the characterizations of the Yusuf
Fault and the Alboran Ridge Front Fault. The results on both fault systems are coherent, and point out a
minimum total slip of ~20 km in a SE-NW direction since the top of the Messinian (5.3 Ma). Taking into
account the convergence rates between the Iberian and African plates, the total shortening between these
two plates since the Messinian is ~24 km, supporting that most of the strain is accommodated by these two
faults. These results highlight the importance of a further seismogenic potential characterization of the area
to improve the earthquake and tsunami hazard models in the region.
The integration of all the results presented in this thesis together with the most recent tomographic studies
(i.e., TOPOIBERIA project), offers the opportunity to review the existing geodynamic models of the area.
The main aspects that should be explored further are: i) the Iberian plate subduction below the African
plate, ii) the observed distribution of the slab, iii) the different crustal domains coexisting offshore and the
Moho depth distribution on-land, and iv) the basin evolution.
We conclude that the formation of the Alboran basin took place during the Miocene. The extensional
processes were controlled by the geodynamics and evolution of the subduction system, including the
westward slab roll-back and lithosphere tearing. At the end of the Messinian, extension in the basin
finished as a consequence of the ceased of the subduction. The Plio-Quaternary represents the
deformational stage of the basin, led by the Iberian – African plate convergence. The distribution of the
active tectonic structures in this compressive setting has been controlled by the inherited lithospheric
structure, which defines the areas of weaknesses where these faults developed.
CONTENTS
Summary 15
Presentation of this thesis 17
i. Motivation 17
ii. Objectives 18
iii. Organization of this volume 19
PART I: INTRODUCTION
Chapter 1: Basic concepts 23
1.1. Fundamentals of plate tectonics 23
1.2. Basics about subduction zones 27
1.2.1. Fore-arc basin 28
1.2.2. Magmatic arc 28
1.2.3. Back-arc basin 30
Chapter 2: Geological setting 33
2.1. The Western Mediterranean 35
2.2. The Gibraltar Arc system 39
2.2.1. The Gibraltar Arc system evolution 39
2.2.2. The Betic – Rif System 44
2.2.3. The Alboran Basin 47
*Structure and kinematics 47
*Stratigraphy 49
PART II: DATA AND METHODS
Chapter 3: Multichannel reflection data 55
3.1. Data acquisition 55
3.1.1. Acquisition parameters 57
*TOPOMED-GASSIS 57
*EVENTDEEP 58
*Cab cruise 59
*ESCI-ALB 59
*Conrad cruise 60
*Other data 61
3.2. Data processing 61
3.2.1. Processing flow in Time Domain 63
I. Pre- Processing 64
II. Deconvolution 66
II.1. Wiener predictive deconvolution in Tau-P domain 67
II.2. Surface consistent deconvolution 68
III. Multiple attenuation and velocity analysis 71
III.1. SRME 71
III.2. Velocity analysis 72
III.3. Radon demultiple 74
IV. Dip Move Out correction 76
V. Final stack 78
V.1. Final velocity analysis, trace muting and CMP
stacking 78
V.2. Zero-phase conversion 79
V.3. Quality factor amplitude correction 79
V.4.Band-Pass filtering 80
VI. Post-Stack Time Migration 80
3.2.2. Processing flow in Depth Domain 89
I. Pre-Processing sequence 90
II. Pre-Stack Depth Migration 90
III. Stacking the final section 97
Chapter 4: Wide Angle Seismic data 93
4.1. Data acquisition 93
4.1.1. Acquisition parameters 94
4.2. Data processing: Mirror imaging. 96
PART III: RESULTS
Chapter 5: Crustal domains 103
5.1. Data used in this chapter 106
5.2. Crustal domains 106
5.2.1. West Alboran and Malaga basins continental crust 106
5.2.2. Magmatic crust 112
5.2.3. North African continental crust 114
5.3. Discussion 126
5.3.1. Crustal domains 126
*Thin continental crust under West Alboran and Malaga basins 126
*Magmatic arc type crust in the East Alboran Basin 128
*Continental crust in the North African margin 130
*Crustal domains integration 130
5.3.2. Transition between domains 130
5.3.3. Basin configuration 131
5.4. In summary 133
Chapter 6: Basin evolution 135
6.1. Data used in this chapter 136
6.2. Results 138
6.2.1. Definition of seismic units 138
*Post-Messinian units 138
*Messinian units 140
*Pre-Messinian units 142
*Volcanic units 143
6.2.2. Basement characteristics 144
*West Alboran and Malaga basins 144
*Habibas and Pytheas basins 147
*South Alboran Basin 149
*East Alboran Basin and its connection with the Algero Balearic Basin 149
6.2.3. Alboran Basin stratigraphical evolution 151
*Early Miocene units: Aquitanian – Early Serravallian 151
*Late Miocene units: Late Serravallian – Messinian 153
*Plio-Pleistocene units 157
6.3. Discussion 161
6.3.1. Formation and evolution of the West Alboran and Malaga basins 161
6.3.2. Formation and evolution of the Habibas and Pytheas basins 164
6.3.3. Formation and evolution of the South Alboran Basin 166
6.3.4. Formation and evolution of the East Alboran Basin 166
6.3.5. Alboran Basin evolution 167
6.4. In summary 173
Chapter 7: The Palomares Margin 175
7.1. Geological setting of the Palomares Margin 176
7.2. Data and methods used to survey the Palomares Margin area 177
7.3. Results 178
7.3.1. Seafloor morphology 178
*Erosional features 179
7.3.2. Seismostratigraphic units 181
*Basement characteristics 181
7.3.3. Tectonic structure and stratigraphy of the Palomares margin 181
7.4. Discussion 185
7.4.1. Nature of the basement 185
7.4.2. Tectonic evolution 187
7.4.3. Halokinesis 189
7.4.4. Sedimentation and mass wasting processes 191
7.5. In summary 192
Chapter 8: The Yusuf Fault 195
8.1. Geological setting of the Yusuf Fault system 196
8.2. Data and methods used to survey the Yusuf Fault area 198
8.2.1. Seismic profiles used in this chapter 198
8.2.2. Seismic potential estimation 200
8.3. Results 203
8.3.1. Seismic stratigraphy 203
*Basement characteristics 205
8.3.2. Structure and kinematics of the Yusuf Fault 205
8.3.3. The Yusuf pull-apart basin 211
*Detailed seismic stratigraphy 211
*Basin configuration 216
8.4. Discussion 218
8.4.1. Nature of the basement 218
8.4.2. Activity of the Yusuf Fault 218
*The opening of the Yusuf pull-apart basin 218
*Seismic activity and seismogenic potential 220
*Quantification of slip 220
8.5. In summary 221
Chapter 9: The Alboran Ridge 223
9.1. Geological setting of the Alboran Ridge 223
9.2. Data and methods used to survey the Alboran Ridge area 225
9.2.1. Seismic data acquisition and processing 225
9.2.2. Shortening estimation 227
9.3. Results 229
9.3.1. Seismostratigraphic units 229
*Basement characteristics 229
9.3.2. The Alboran Ridge 231
9.3.3. Francesc Pagès, Tofiño and Xauen Banks 235
9.4. Discussion 235
9.4.1. Nature of the basement 235
9.4.2. Contractional phases 237
9.4.3. Connection between the Alboran Ridge and Francesc Pagès, Tofiño and Xauen Banks 238
9.4.4. Slip estimation 238
9.4.5. Partitioning of the deformation 240
9.5. In summary 246
PART IV: DISCUSSION
Chapter 10: Implications for geodynamic models 251
10.1. Observations to be fit 255
*Slab dimensions and geometry 255
*Magmatic activity 259
*Crustal domains 259
*Basin evolution 261
*Timing of the extension and the Pliocene contractive reorganization 263
10.2. Proposed geodynamic models: compilation and discussion 263
10.2.1. North-dipping continuous slab 264
a) The “Jolivet” model 264
b) The “Rosenbaum” model 264
c) The “Faccenna” model 266
d) The “Do Couto” model 266
*Testing the models 266
10.2.2. North-dipping slab, lithosphere tearing 269
e) The “Spakman” model 269
f) The “ van Hinsbergen” model 270
*Testing the models 271
10.2.3. South-dipping slab, lithosphere tearing 272
g) The “Gelabert” model 274
h) The “Vergés” model 274
*Testing the models 274
10.2.4. Concluding remarks 276
10.3. Lithospheric structure 278
10.4. In summary 282
PART V: CONCLUSIONS & FORWARD LOOK
Chapter 11: Conclusions 285
Chapter 12: Forward look 289
REFERENCES 295
ANNEXES
List of acronyms 323
Scientific output related with this thesis 325
.
This thesis provides new insights in the formation and deformation of the Alboran Basin. The results
shown in this thesis shed light on the geodynamic processes that governed the opening of the Alboran
Basin during the Miocene and its later evolution into a compressive setting during the Plio-Quaternary.
The most relevant findings of this research are summarized below.
12.1. Final conclusions
1) The Alboran Basin is floored by three different crustal domains: thin continental crust, magmatic
arc crust, and North African continental crust. These domains conditioned the later evolution of the
depocenters of sub-basins and the location of the present-day active tectonic structures.
2) We presented the first comprehensive seismostratigraphic analysis of the entire Alboran Basin.
Based on wells and dredge data, we have performed the correlation of units among the different
sub-basins and correlated our proposed stratigraphy with all available previous studies.
3) From the Early Miocene till the Late Miocene, the Alboran Basin was affected by extensional
processes fundamentally controlled by the slab dynamics. Extension ceased during the Late
Miocene, and since the Pliocene and during the Quaternary the Alboran Basin has been deformed
due to the Iberia – Africa tectonic plates convergence. This new stress framework produced the
contractive reorganization of the basin, focused on a few first-order structures that act as
lithospheric boundaries.
4) Present-day tectonic activity is not widespread along the basin. Instead, it is focused on few active
structures, as the Alboran Ridge, Yusuf, and Al-Idrissi fault systems and to a lesser degree the
Carboneras fault system. The estimated slip values for the Alboran Ridge and Yusuf fault systems
support that the main part of the plate convergence since the Early Pliocene have been
accommodated at these two structures.
12.2. Specific conclusions
* Deep structure
We have characterized the deep structure of the basin. The TOPOMED-GASSIS multichannel seismic
profiles have allowed for the first time a comprehensive study of the crustal configuration of the Alboran
Basin with enough resolution to identify different crustal domains and the relationships between them. We
have been able to define three different crustal domains coexisting at the Alboran Basin:
(i) Thin continental domain: Composed of metamorphic rocks, it is found below the West
Alboran Basin and Malaga Basin. The basement presents thickness variations, being <2 s
TWTT under the West Alboran Basin and ~5.5 s TWTT under the Malaga Basin. We propose
that they are part of the same crust affected by different degrees of extension. The presence of
peridotite outcrops onland together with a high-velocity anomaly following the arcuate shape
of the Betic and Rif orogens under the basin and connecting these outcrops (El Moudnib et al.,
2015), supports that along this velocity anomaly the crust under the basin is extremely thin, or
may even be floored by exhumed mantle.
(ii) Magmatic arc domain: In the central part of the Alboran Basin the crust is made of magmatic
intrusions and volcanic constructions. The basins located in this area have a volcanic basement
(Late Serravallian? – Tortonian) of ~5 s TWTT thick (~15 km). In the deepest parts, layered
reflections are seen, which are interpreted as magmatic layering. All the observations support
that this domain was formed during the subduction process and represents the volcanic arc of
the system.
(iii) North African continental domain: Offshore Algeria, the crust is defined by a metamorphic
basement of >7 s TWTT thick (~19-22 km). Towards the west, below the South Alboran
Basin, basement thickness slightly decreases to ~5 s TWTT thick (~14-16 km) and locally
volcanic intrusions increase, until forming a basin floored continental crust heavily modified
by volcanic activity. We associated this domain with the continental crust of the Africa plate.
The boundaries between these domains can be a smooth transition or a well-defined tectonic boundary.
We interpreted that these domains are the result of the extension. During the subduction process, the
crustal characteristics were gradually modified to produce the present-day configuration. The Alboran
Basin is mainly formed by a) a fore-arc basin, represented by the West Alboran Basin and the Malaga
Basin, b) a magmatic arc, represented by the central and northeaster part of the basin, and c) the North
African continental margin basins. The Alboran Basin is not a back-arc basin to the Gibraltar structural arc,
since the back-arc basin of the system corresponds to the easternmost Alboran Basin and mainly the
Algero Balearic Basin, were extension led to the formation of oceanic crust.
* Basin evolution
The different crustal domains found below the basins conditioned the later evolution of the different
depocenters of sub-basins. The correlation of the seismostratigraphic units between the depocenters allows
us to determine their evolution, at an individual scale and at the scale of the entire basin.
The basin distribution has changed within time. Extensional processes in the back-arc and magmatic
activity conditioned the location and evolution of the depocenters. The extensional formation of the
Alboran Basin took place between the Burdigalian and the Messinian. Later, during the Pliocene, the basin
evolved to a compressive stress regime. Both, the extensional displacement and the later compressional
structures provide information to reconstruct the approximate position of the depocenters through time.
The first depocenter found is the West Alboran and Malaga basins, Burdigalian in age. The lack of
deformation let us to suggest a vertical subsidence evolutionary model for this depocenter, which we
inserted that has migrated at least 300 km to the west above the slab hinge.
The second depocenter identified is formed above the North Africa margin. The Habibas and Pytheas
basins were created by strike-slip local tectonics, and were separated of the West Alboran and Malaga
basins by a lithospheric strike-slip boundary. This depocenter has remained almost in the same position
with respect to the African margin till the Pliocene.
At Late Serravallian – Tortonian, the magmatic activity that led to the magmatic arc formation conditioned
the basin evolution. New depocenters were created above the new volcanic basement.
At the Messinian, all the Alboran Basin depocenters were already formed (i.e. the West Alboran, Malaga,
Habibas, Pytheas, East Alboran and South Alboran basins). In this period, sedimentation is still
conditioned by the basement distribution and presents different characteristics for each depocenter.
The Pliocene is characterized by a change in the stress setting. Extensional processes ended, and the
Alboran Basin evolves in a compressive tectonic framework. Main tectonic structures, as the Carboneras
Fault, the Yusuf Fault, the Alboran Ridge Front fault and the Al-Idrissi Fault appeared at the boundaries
between crustal domains, being still active at the present-day. Plio-Quaternary units are similar for the
entire basin, pointing out a general subsidence for the entire basin.
* Palomares margin
The Palomares margin includes the northeaster connection between the Alboran Basin and the Algero-
Balearic Basin. It presents a complex bathymetry characterized by the presence of highs and deeply eroded
submarine canyons between them. It can be divided in (i) the continental shelf, (ii) the continental slope
and (iii) the Algero-Balearic Basin. Active processes and tectonic structures present on each area are
different, and determine their specific seafloor morphology.
A detailed analysis of the bathymetry together with the MCS profiles support that the geomorphology of
this area is mainly driven by erosional and halokinesis processes, while active faults are not clearly
identified outside of the uppermost continental slope. The tectonic activity of the structures located off-
shore seems to decrease since the Messinian. Due to this observations, we suggest that the nowadays
deformation is accommodated by onshore structures.
The sedimentary record of the margin points out an Early Tortonian formation age in relation to the
magmatic arc. Extensional processes are identified till the Late Tortonian. Since the Latemost Tortonian,
the margins evolved to a compressive regime that produces the reactivation as thrusts and/or strike-slip
faults of the previous extensional structures, especially those located in the continental slope.
* The Yusuf Fault
The Yusuf Fault is a crustal boundary that puts in touch two different crustal domains: the magmatic arc
crust, located north of it, and the North African continental crust, south of the fault. It is a right-lateral
strike-slip fault that connects toward the west with the northern Alboran Ridge transpressive fault; and
towards the east ends at the Algerian coast.
The observed deformation and the detailed analyses of the Yusuf pull-apart basin sediments allow us to
propose a post-Messinian activity for this fault. The first syn-kinematic unit is from the Early Pliocene, and
the fault is currently active.
The total slip along the Yusuf Fault has been estimated between 16 and 30 km, which within the
uncertainty is enough to accommodate the main part of the Iberian – African convergence since the
Messinian time (~24 km).
* The Alboran Ridge system
This ridge is part of a heterogeneous structure formed by the Alboran Ridge, Francesc Pagès, Tofiño and
Xauen banks. This variability is understood as result of the combination between the inherited structure,
sedimentary basins and igneous highs, and the deformation rates, increasing from west to east. The
difference between these highs is the result of strain partitioning by left-lateral strike-slip faults, being the
most important the Al-Idrissi Fault system.
The Alboran Ridge relief is a Plio-Quaternary structure. Three compressional pulses are identified: 1)
Early Pliocene (3.28 – 5.33 Ma), 2) Middle Pliocene (2.45 – 3.28 Ma) and 3) Quaternary (from 1.8 Ma till
present). Folding and faulting involved the basement and the most recent sediments, so it is still an active
structure. Shortening values measured along the Alboran Ridge are not high enough to accommodate the
Iberian and African plate convergence since ~5.3 Ma (Messinian top). We propose that this convergence
has been accommodated at a deep detachment level. Estimations of the slip needed to created the uplift
with a deep detachment provide a total slip of ~20 km. We interpreted that the detachment may be at the
Moho level, as it corresponds to the tectonic boundary between the magmatic arc crust, to the north, and
the North African margin continental crust, south of it. The accumulated slip implies that has taken most
deformation produced by convergence in this region.
* Geodynamic evolution
Through the integration of the most recent data, including the results presented in this volume, we have
evaluated existing geodynamic models and to enumerate the characteristics that should have a suitable
geodynamic model.
Most recent geophysical results do not support models that propose subduction to the north of the African
plate. Only two models (Gelabert et al., 2002; Vergés and Fernàndez, 2012) consider subduction of the
Iberia plate towards the south, although these models have not integrated a wealth of recent data.
We conclude that a geodynamic model that explains the origin and evolution of the Alboran Basin
integrate subduction a south dipping Iberian slab, that first retreats to the north and later to the west, with
an initial geometry of the subduction front able to explain the arcuate geometry of the WAB & MB since
Burdigalian times, and with lithospheric faults bounding the active subduction front, so that allow its
westward motion juxtaposing different crustal domains during the basin development.
These observations, together with the lithospheric structures, allow us to differentiate two main
evolutionary stages:
(i) The opening stage (Miocene), in which the Alboran Basin evolved as an extensional setting,
consequence of the westward migration of the subduction front and slab roll-back, and
(ii) The deformational stage (Plio-Quaternary), in which the contractive reorganization of the
basin occurred. Slab driven geodynamic processes lose importance and the driving force for
the basin evolution is the lithospheric structure in a convergence setting. The boundaries
between different lithospheric domains correspond to inherited weak zones that conditioned
the location of the main faults accommodating the Iberian and African plates convergence
(i.e. Carboneras Fault, Al-Idrissi Fault, Alboran Ridge Front fault and Yusuf Fault systems).