01 Sep 2010-Geology (Geological Society of America)-Vol. 38, Iss: 9, pp 823-826
TL;DR: In this paper, the authors present the results of dynamic modeling of the western Mediterranean that accounts for observed global positioning system (GPS) surface deformation of the Alboran Sea and surrounding Rif and Betic Mountains as the result of the combined effects of relative motion of the Eurasian and Nubian plates.
Abstract: We present the results of dynamic modeling of the western Mediterranean that accounts for observed global positioning system (GPS) surface deformation of the Alboran Sea and surrounding Rif and Betic Mountains as the result of the combined effects of relative motion of the Eurasian and Nubian plates, low strength in the Alboran Sea region and sub-lithospheric processes occurring beneath the External Rif domain. Assuming that the lithosphere behaves elastically over the short time period of the GPS observations, an elastic plate model is considered in our study, including an area of weak lithosphere (factor of 10) centered on the Alboran Sea and in which lateral boundary conditions consist of the Nubia-Eurasia oblique convergence. Sub-crustal processes are modeled by application of a horizontal traction on a small area (patch) at the base of the elastic plate. Our modeling studies demonstrate the need for sub-crustal or sub-lithospheric, southwestward-directed forcing to account for observed southwestward motion of the Rif and Betic domains. Based on the location, orientation, and small area of the traction patch, we hypothesize that forcing is associated with delamination and rollback of the subducted African continental lithospheric mantle beneath the External Rif zone, due to the pull of the oceanic part of the Western Mediterranean slab, a dynamic process that may be similar to that where the over-riding plate is driven toward the subduction zone during slab rollback.
The authors modeling studies demonstrate the need for sub-crustal or sub-lithospheric, southwestward-directed forcing to account for observed southwestward motion of the Rif and Betic domains.
The authors then discuss the implications of these model results in light of previous geodynamic models of the plate boundary zone.
TECTONIC SETTING OF THE WESTERN MEDITERRANEAN
In the western Mediterranean, the Alboran Sea is a thinned continental domain (15 km thickness; Lonergan and White 1997) surrounded by the Internal Rif and Internal Betics , which are the westernmost limit of the Alpine mountain belt (Fig. 1).
Three factors are likely to infl uence the spatial distribution of the interseismic strain 1) lateral plate driving forces due to long term Nubia-Eurasia oblique convergence, 2) low rigidity of the diffuse plate boundary zone, and 3) deep traction beneath the plate boundary due to upper mantle drag or slab traction.
The RMSs for the entire zone and for the Rif-Betics region are summarized in Table 1.
Depending on the thermal regime, the effective elastic thickness of continental plates varies from 3 to 80 km (Watts and Burov, 2003).
DISCUSSION AND GEODYNAMIC IMPLICATIONS
The authors modeling experiments include no a priori information on sub-lithospheric geometry and are designed to determine whether sublithospheric processes are needed to account for observed deformation of the western Mediterranean region.
Geodynamic models of the zone involving still active westward rollback of the western Mediterra- nean narrow slab (Gutscher et al., 2002) cannot generate such a small coupling zone confi ned to the External Rif. Spakman and Wortel (2004) suggested that the western Mediterranean slab is detached under the Betics.
The authors further suggest that the horizontal traction patch could represent the remaining coupling zone between the slab and the overlying continental lithosphere.
According to their delamination model (Fig. 3) the traction zone is expected to move to the south-southwest following propagation of the delamination front.
During the Pliocene-Quaternary, eastward subduction has died out, as suggested by the accretionary wedge sealed by undeformed sediments (Zitellini et al., 2009).
ACKNOWLEDGMENTS
The authors thank G. Bokelmann, S. Lallemand and J.L. Bodinier for their fruitful discussions, and to C. Faccenna and fi ve anonymous reviewers for their constructive comments on this manuscript.
Reilinger benefi ted from a Visiting Researcher Fellowship from the Observatoire de Recherche Méditerranéen en Environnement of Montpellier while engaged in this study.
TL;DR: In this article, a geodetic horizontal velocity field consistent at the scale of the Mediterranean and the surrounding Alpine belts is derived to discuss the boundary conditions around each major deforming area in the Mediterranean, to describe the main patterns of motion and deformation, to critically review the existing kinematics models and to finally point out the main unresolved kinematic questions.
TL;DR: In this paper, a geodynamic reconstruction of the Central-Western Mediterranean and neighboring areas during the last 50 million years was presented, including magmatological and tectonic observations.
TL;DR: In this paper, a geodynamic reconstruction of the Central-Western Mediterranean and neighboring areas during the last 50 million years was presented, including magmatological and tectonic observations.
Abstract: We present a geodynamic reconstruction of the Central–Western Mediterranean and neighboring areas during the last 50 Myr, including magmatological and tectonic observations. This area was interested by different styles of evolution and polarity of subduction zones influenced by the fragmented Mesozoic and Early Cenozoic paleogeography between Africa and Eurasia. Both oceanic and continental lithospheric plates were diachronously consumed along plate boundaries. The hinge of subducting slabs converged toward the upper plate in the double-vergent thick-skinned Alps–Betics and Dinarides, characterized by two slowly-subsiding foredeeps. The hinge diverged from the upper plate in the single-vergent thin-skinned Apennines–Maghrebides and Carpathians orogens, characterized by a single fast-subsiding foredeep. The retreating lithosphere deficit was compensated by asthenosphere upwelling and by the opening of several back-arc basins (the Ligurian–Provencal, Valencia Trough, Northern Algerian, Tyrrhenian and Pannonian basins). In our reconstruction, the W-directed Apennines–Maghrebides and Carpathians subductions nucleated along the retro-belt of the Alps and the Dinarides, respectively. The wide chemical composition of the igneous rocks emplaced during this tectonic evolution confirms a strong heterogeneity of the Mediterranean upper mantle and of the subducting plates. In the Apennine–Maghrebide and Carpathian systems the subduction-related igneous activity (mostly medium- to high-K calcalkaline melts) is commonly followed in time by mildly sodic alkaline and tholeiitic melts. The magmatic evolution of the Mediterranean area cannot be easily reconciled with simple magmatological models proposed for the Pacific subductions. This is most probably due to synchronous occurrence of several subduction zones that strongly perturbed the chemical composition of the upper mantle in the Mediterranean region and, above all, to the presence of ancient modifications related to past orogeneses. The classical approach of using the geochemical composition of igneous rocks to infer the coeval tectonic setting characteristics cannot be used in geologically complex systems like the Mediterranean area.
281 citations
Cites background from "Active surface deformation and sub-..."
...There are GPS and paleomagnetic evidences of active radial motion of the Betic and Riff nappes (Cifelli et al., 2008; Pérouse et al., 2010) and the tomography would also suggest an E-ward dipping slab (Gutscher et al., 2002; Spakman and Wortel, 2004)....
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...There are GPS and paleomagnetic evidences of active radial motion of the Betic and Riff nappes (Cifelli et al., 2008; Pérouse et al., 2010) and the tomography would also suggest an E-ward dipping slab (Gutscher et al....
TL;DR: In this article, a set of almost linear and sub-par dextral strike-slip faults, the SWIM1 Faults, that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, was mapped using a new swath bathymetry compilation available in the area offshore SW Portugal.
Abstract: The missing link in the plate boundary between Eurasia and Africa in the central Atlantic is presented and discussed. A set of almost linear and sub parallel dextral strike–slip faults, the SWIM1 Faults, that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, was mapped using a new swath bathymetry compilation available in the area offshore SW Portugal. These faults connect the Gloria Fault to the Rif–Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. The SWIM faults cut across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M ~ 8.5–8.7, and tsunami were generated, providing a new insight on its source location.
TL;DR: In this article, the authors propose a new model of delamination of the continental lithosphere for the Apennines and the Aegean arcs, supporting the hypothesis that both the Apulia/Adriatic domain and the Eastern Mediterranean Basin still belong to the former southern continental margin of the Tethys.
Abstract: [1] This paper aims at summarizing the current extent and architecture of the former Mesozoic passive margin of North Africa from North Algeria in the west up to the Ionian-Calabrian arc and adjacent Mediterranean Ridge in the east. Despite that most paleogeographic models consider that the Eastern Mediterranean Basin as a whole is still underlain by remnants of the Permo-Triassic or a younger Cretaceous Tethyan-Mesogean ocean, the strong similarities documented here in structural styles and timing of inversion between the Saharan Atlas, Sicilian Channel and the Ionian abyssal plain evidence that this portion of the Eastern Mediterranean Basin still belongs to the distal portion of the North African continental margin. A rim of Tethyan ophiolitic units can be also traced more or less continuously from Turkey and Cyprus in the east, in onshore Crete, in the Pindos in Greece and Mirdita in Albania, as well as in the Western Alps, Corsica and the Southern Apennines in the west, supporting the hypothesis that both the Apulia/Adriatic domain and the Eastern Mediterranean Basin still belong to the former southern continental margin of the Tethys. Because there is no clear evidence of crustal-scale fault offsetting the Moho, but more likely a continuous yet folded Moho extending between the foreland and the hinterland beneath the Mediterranean arcs, we propose here a new model of delamination of the continental lithosphere for the Apennines and the Aegean arcs. In this model, only the mantle lithosphere of Apulia and the Eastern Mediterranean is still locally subducted and recycled in the asthenosphere, most if not all the northern portion of the African crust and coeval Moho being currently decoupled from its former, currently delaminated and subducted mantle lithosphere.
TL;DR: In this paper, the authors constrain the depth distribution of crustal seismicity and active tectonics by means of rheological modeling on the basis of the lithospheric structure of the Gibraltar Arc.
Abstract: [1] On the basis of the lithospheric structure of the Gibraltar Arc (western Mediterranean), we constrain depth distribution of crustal seismicity and active tectonics by means of rheological modeling. Crustal yield strength and depth of the brittle-ductile transition zone (BDT) mimic the curvature of the arc with maximum depths of 12–9 km whereas in the Betics and Rif, BDT shallows eastward (to 6–5 km depth), oblique to crustal thickening. Most of the crustal seismicity (>60%) is placed within the brittle crust, decaying exponentially in the ductile crust. Active faults observed in surface geology, control the present topography of the Betics, connect in depth with scattered seismic swarms, and merge into the BDT. This horizon is interpreted as a decoupling horizon that conditions the mode of present-day deformation partitioning. Below the BDT, low-strength domains enable crustal flow under central Betics promoting stress rotation and topographic uplift.
TL;DR: Bokelmann et al. as mentioned in this paper studied waveforms of P-waves that traverse the Alboran Sea region between Spain and Morocco to better constrain upper-mantle structure under the region, and found that the dispersion is consistent with that expected from subducted lithosphere.
Abstract: [1] WestudytheAfrica-Iberiaplateboundaryinthevicinity of Gibraltar. Numerous models have been proposed for that region throughout the last decades, proposing mechanisms that range widely from continental delamination, convective removal, to subduction of oceanic lithosphere. To better constrain upper-mantle structure under the region, we study waveforms of P-waves that traverse the Alboran Sea region between Spain and Morocco. These show dispersive behavior, which, together with early arrival times, confirms the presence of an anomalous upper mantle structure under the Alboran Sea. The dispersion is consistent with that expected from subducted lithosphere. Waveforms of body waves therefore provide a way to better constrain the elusive mantle structure and dynamics of the Alboran Sea region. Citation: Bokelmann, G., and E. Maufroy (2007), Mantle structure under Gibraltar constrained by dispersion of body waves, Geophys. Res. Lett., 34, L22305, doi:10.1029/2007GL030964.
27 citations
"Active surface deformation and sub-..." refers background in this paper
...Furthermore, seismic ray dispersion shows that the slab corresponds to oceanic lithosphere material (Bokelmann and Maufroy, 2007)....