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Ana Crespo-Blanc

Bio: Ana Crespo-Blanc is an academic researcher from University of Granada. The author has contributed to research in topics: Flysch & Subduction. The author has an hindex of 22, co-authored 37 publications receiving 2348 citations. Previous affiliations of Ana Crespo-Blanc include University of Seville & Spanish National Research Council.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors describe the evolution of the western Mediterranean subduction zone (WMSZ) during the last 35 Myr by combining new and previous geological data, new tomographic images of the Western Mediterranean mantle, and plate kinematics.
Abstract: [1] The western Mediterranean subduction zone (WMSZ) extends from the northern Apennine to southern Spain and turns around forming the narrow and tight Calabrian and Gibraltar Arcs. The evolution of the WMSZ is characterized by a first phase of orogenic wedging followed, from 30 Ma on, by trench retreat and back-arc extension. Combining new and previous geological data, new tomographic images of the western Mediterranean mantle, and plate kinematics, we describe the evolution of the WMSZ during the last 35 Myr. Our reconstruction shows that the two arcs form by fragmentation of the 1500 km long WMSZ in small, narrow slabs. Once formed, these two narrow slabs retreat outward, producing back-arc extension and large scale rotation of the flanks, shaping the arcs. The Gibraltar Arc first formed during the middle Miocene, while the Calabrian Arc formed later, during the late Miocene-Pliocene. Despite the different paleogeographic settings, the mechanism of rupture and backward migration of the narrow slabs presents similarities on both sides of the western Mediterranean, suggesting that the slab deformation is also driven by lateral mantle flow that is particularly efficient in a restricted (upper mantle) style of mantle convection.

884 citations

Journal ArticleDOI
TL;DR: In this paper, the authors show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence and away from the trench in the case of true convergence (Aegean).
Abstract: 30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional subduction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc extension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep deformation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.

141 citations

Journal Article
TL;DR: In this paper, the authors show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence and away from the trench in the case of true convergence (Aegean).
Abstract: 30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional subduction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc extension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep deformation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.

121 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the cortical segment formed the basement of the Miocene Alboran Basin, in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes.
Abstract: The westernmost part of the Mediterranean Alpine Belt is represented by the Betic-Rif orogenic belt, around the Gibraltar Arc, which in turn surrounds the Alboran Basin. In the Betic Chain, early and middle Miocene crustal thinning of the Alboran basement is well established, as extensional low-angle normal faults and detachment faults, developed in both ductile and brittle conditions, thinned a previously thickened crust. In the Alboran Domain of the central Betics, two main extensional episodes are evidenced: a Langhian one, with a north-northwestward transport direction, followed by a west-southwestward extension, Serravallian in age. Therefore all the units heretofore considered to be thrust nappes are, in reality, extensional units bounded by low-angle normal faults. The cortical segment studied formed the basement of the Miocene Alboran Basin, in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes. The age of these sediments clearly dates the faulting. The extensional evolution during the Miocene is much more complex than the past models suggest. During the upper Miocene, these extensional systems were folded as the result of a compressive regime, which allowed them to be well exposed. Compression in the Gibraltar Arc is nearly contemporaneous with extension, and the westward migration of the compression through its footwall is related with the extensional spreading.

118 citations

Journal ArticleDOI
TL;DR: In this article, a complex tectonometamorphic evolution of the Alpujarride Complex within the internal zones of the Betics reveals a complex structural and metamorphic succession of continental collision, synmetamorphic exhumation, nappe forming in the final stage, and rifting.
Abstract: The tectonometamorphic evolution of the Alpujarride Complex within the internal zones of the Betics reveals a complex structural and metamorphic succession of continental collision, synmetamorphic exhumation, nappe forming in the final stage of exhumation, and rifting. A complex tectonic evolution is deduced from the superposition of structures observed in several Alpujarride units of the central Betics together with their metamorphic record. The following sequence of events is suggested: (1)A first stacking event (D1) is deduced from the presence of pre-S2 high-pressure-low-temperature metamorphic assemblages, (2) The synmetamorphic exhumation is inferred from the almost isothermal decompression pressure-temperature paths during which the S2 main foliation developed; the condensation of the mineral zones perpendicularly to the S2 foliation suggests large-scale vertical shortening during event D2, (3) A new stacking event (D3) is inferred from post-metamorphic thrusts and nappes, which are probably associated with kilometer-scale recumbent folds affecting the S2 main foliation, (4) A thinning event (D4), revealed by extensional fault systems, is associated with crustal spreading on the concave side of the Gibraltar Arc, which resulted in the opening of the Alboran Basin from the early Miocene (Burdigalian), (5) From late Tortonian to Pliocene a continuous N-S to NW-SE compression took place (D5). Stratigraphic, paleontological, and geochronological data suggest that event D3 could be lower Miocene in age (Aquitanian); consequently, event D1 and D2 would be pre-Miocene.

103 citations


Cited by
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Journal ArticleDOI
TL;DR: A number of tectonic events occurred contemporaneously in the Mediterranean region and the Middle East 30-25 Myr ago as discussed by the authors, which are contemporaneous to or immediately followed a strong reduction of the northward absolute motion of Africa.
Abstract: A number of tectonic events occurred contemporaneously in the Mediterranean region and the Middle East 30–25 Myr ago. These events are contemporaneous to or immediately followed a strong reduction of the northward absolute motion of Africa. Geological observations in the Neogene extensional basins of the Mediterranean region reveal that extension started synchronously from west to east 30–25 Myr ago. In the western Mediterranean it started in the Gulf of Lion, Valencia trough, and Alboran Sea as well as between the Maures massif and Corsica between 33 and 27 Ma ago. It then propagated eastward and southward to form to Liguro-Provencal basin and the Tyrrhenian Sea. In the eastern Mediterranean, extension started in the Aegean Sea before the deposition of marine sediments onto the collapsed Hellenides in the Aquitanian and before the cooling of high-temperature metamorphic core complexes between 20 and 25 Ma. Foundering of the inner zones of the Carpathians and extension in the Panonnian basin also started in the late Oligocene-early Miocene. The body of the Afro-Arabian plate first collided with Eurasia in the eastern Mediterranean region progressively from the Eocene to the Oligocene. Extensional tectonics was first recorded in the Gulf of Aden, Afar triple junction, and Red Sea region also in the Oligocene. A general magmatic surge occurred above all African hot spots, especially the Afar one. We explore the possibility that these drastic changes in the stress regime of the Mediterranean region and Middle East and the contemporaneous volcanic event were triggerred by the Africa/Arabia-Eurasia collision, which slowed down the motion of Africa. The present-day Mediterranean Sea was then locked between two collision zones, and the velocity of retreat of the African slab increased and became larger than the velocity of convergence leading to backarc extension. East of the Caucasus and northern Zagros collision zone the Afro-Arabian plate was still pulled by the slab pull force in the Zagros subduction zone, which created extensional stresses in the northeast corner of the Afro-Arabian plate. The Arabian plate was formed by propagation of a crack from the Carlsberg ridge westward toward the weak part of the African lithosphere above the Afar plume.

925 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe the evolution of the western Mediterranean subduction zone (WMSZ) during the last 35 Myr by combining new and previous geological data, new tomographic images of the Western Mediterranean mantle, and plate kinematics.
Abstract: [1] The western Mediterranean subduction zone (WMSZ) extends from the northern Apennine to southern Spain and turns around forming the narrow and tight Calabrian and Gibraltar Arcs. The evolution of the WMSZ is characterized by a first phase of orogenic wedging followed, from 30 Ma on, by trench retreat and back-arc extension. Combining new and previous geological data, new tomographic images of the western Mediterranean mantle, and plate kinematics, we describe the evolution of the WMSZ during the last 35 Myr. Our reconstruction shows that the two arcs form by fragmentation of the 1500 km long WMSZ in small, narrow slabs. Once formed, these two narrow slabs retreat outward, producing back-arc extension and large scale rotation of the flanks, shaping the arcs. The Gibraltar Arc first formed during the middle Miocene, while the Calabrian Arc formed later, during the late Miocene-Pliocene. Despite the different paleogeographic settings, the mechanism of rupture and backward migration of the narrow slabs presents similarities on both sides of the western Mediterranean, suggesting that the slab deformation is also driven by lateral mantle flow that is particularly efficient in a restricted (upper mantle) style of mantle convection.

884 citations

Journal ArticleDOI
TL;DR: In this paper, a new reconstruction of Alpine Tethys combines plate-kinematic modeling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps.

787 citations

Journal ArticleDOI
TL;DR: In this paper, a model for the Miocene evolution of the Betic-Rif mountain belts is proposed, which is compatible with the evolution of rest of the western Mediterranean.
Abstract: In recent years, the origin of the Betic-Rif orocline has been the subject of considerable debate. Much of this debate has focused on mechanisms required to generate rapid late-orogenic extension with coeval shortening. Here we summarize the principal geological and geophysical observations and propose a model for the Miocene evolution of the Betic-Rif mountain belts, which is compatible with the evolution of the rest of the western Mediterranean. We regard palaeomagnetic data, which indicate that there have been large rotations about vertical axes, and earthquake data, which show that deep seismicity occurs beneath the Alboran Sea, to be the most significant data sets. Neither data set is satisfactorily accounted for by models which invoke convective removal or delamination of lithospheric mantle. Existing geological and geophysical observations are, however, entirely consistent with the existence of a subduction zone which rolled or peeled back until it collided with North Africa. We suggest that this ancient subducting slab consequently split into two fragments, one of which has continued to roll back, generating the Tyrrhenian Sea and forming the present-day Calabrian Arc. The other slab fragment rolled back to the west, generating the Alboran Sea and the Betic-Rif orocline during the early to middle Miocene.

682 citations

01 Jan 1985
TL;DR: In this article, two classes of porphyroclast systems with monoclinic symmetry have been identified on geometrical grounds: sigma-type porphyra clasps and delta-clasps, characterized by wedge-shaped tails of recrystallized material.
Abstract: Porphyroclasts of feldspar and other relatively rigid minerals in mylonites commonly have mantles of dynamically recrystallized material that extend as tails into the matrix. The internal shape symmetry of such porphyroclasts is usually orthorhombic or monoclinic; the orientation of the porphyroclast with respect to the foliation (external symmetry) can also be described by these symmetry classes. An identical monoclinic external symmetry of most porphyroclasts in a given sample indicates non-coaxial flow in the matrix during at least the last stages of deformation. Two classes of porphyroclast systems with monoclinic symmetry have been identified on geometrical grounds. sigma-type porphyroclasts are characterized by wedge-shaped tails of recrystallized material. Median lines of the tails lie on opposite sides of, and do not cross, a marker line drawn parallel to the mean foliation. sigma-type porphyroclasts may lie isolated in a homogeneous matrix (sigma/sub a./-type) or may be in clusters associated with shear bands or S-C mylonites (sigma/sub b/-type). delta-type porphyroclasts commonly occur in ultramylonites and have highly attenuated recrystallized tails. Median lines of the tails cross the marker line adjacent to the porphyroclast which results in an embayment of matrix material adjacent to the host grain. More complex porphyroclast systems include ellipsoidal overturned delta-types,more » complex sigma - delta types and folded porphyroclast aggregates. In all cases, the symmetry of porphyroclast aggregates with respect to the foliation can be used to accurately determine the sense of vorticity in the mylonites.« less

541 citations