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Active surface deformation and sub-lithospheric processes in the western Mediterranean constrained by numerical models

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.

Summary (1 min read)

INTRODUCTION

  • 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.

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GEOLOGY, September 2010 823
INTRODUCTION
Deformations around transpressive plate
boundaries are thought to be due to the mechan-
ical interaction of plates (i.e., elastic strain and
associated faulting, e.g Savage and Burford,
1973), sub-crustal processes (e.g., subduction
and slab rollback, mantle delamination, Roy-
den,1993), and/or stresses induced by gravita-
tional potential energy differences (e.g., England
and McKenzie 1982). South-southwest–ori-
ented crustal motions in the western Mediter-
ranean (Fig; 1; Vernant et al., 2010) appear to
be incompatible with simple plates interaction
as they involve motion normal to the direction
of Nubia-Eurasia relative motion in a region
dominated by strike-slip and extensional tecton-
ics (for further discussion see Fadil et al., 2006
and Vernant et al., 2010), or to gravitational
potential energy differences as motion of the
Rif Mountains is directed away from the low-
lying, thinner lithosphere of the Alboran Sea.
Although the importance of subduction related
processes for the tectonic evolution of the west-
ern Mediterranean has been discussed (e.g.,
Royden, 1993; Lonergan and White 1997; Fac-
cenna et al. 2004; Spakman and Wortel 2004),
the rather localized, present-day motions of the
Betic–Alboran Sea–Rif domain have not been
subject to quantitative modeling studies. Here,
we use numerical models constrained by global
positioning system (GPS) observations and
Geology, September 2010; v. 38; no. 9; p. 823–826; doi: 10.1130/G30963.1; 3 fi gures; 1 table.
© 2010 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org.
Active surface deformation and sub-lithospheric processes in the
western Mediterranean constrained by numerical models
Eugénie Pérouse
1
, Philippe Vernant
1
, Jean Chéry
1
, Robert Reilinger
2
, and Simon McClusky
2
1
Laboratoire Géosciences Montpellier CNRS (Centre National de la Recherche Scientifi que)-Université Montpellier 2, 34095
Montpellier, France
2
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts
02139, USA
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 sur-
rounding 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 con-
sidered 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 subduc-
tion zone during slab rollback.
350° E 352°E 354°E 356°E 358°E
30°N
32°N
34°N
36°N
38°N
40°N
Alb
EURASIAN
PLATE
4 mm/yr
0 30 60 90 120 660
Depth (km)
Betics
PLATE
Observed
velocities
Boundary conditions
of the model
Mw
Internal
zone
External
zone
AH
eq
NUBIAN
Rif
Major
thrust
faults
456
Spain
Med. sea
Mo
Figure 1. Global positioning system velocities
(Vernant et al. 2010) in Nubia fi xed reference
frame and 95% confi dence ellipses. Gray ar-
rows indicate velocities consistent with Iberia
or Nubia plate motion; black arrows indicate
velocities inconsistent with either Iberia or Nu-
bia. Colored circles depict earthquakes with
Mw > 3.5 (National Earthquake Information
Center–U.S. Geological Survey, 1973–2009;
http://earthquake.usgs.gov/regional/neic/).
Major geological structures are simplifi ed
from Jolivet et. al (2008) and Zitellini et al.
(2009); red fault—Boussekkour fault; AH
eq—M = 6 Al Hoceima earthquake of 1994
(from www.globalcmt.org); Alb—Alboran
Sea. Boundary conditions of the elastic
plate model are shown in red. Inset: Tectonic
sketch of the western Mediterranean. Black
box outlines study area; Mo—Morocco; Med.
sea—Mediterranean sea; hachured areas—
Alpine orogenic belts.

824 GEOLOGY, September 2010
seismic, and other geophysical data to address
this issue and identify where these sub-crustal
processes may occur. Because the confi gura-
tion of the Nubian-Eurasian plate boundary in
the western Mediterranean and the geometry of
the subducted plate are still debated (Calvert et
al., 2000; Gutscher et al., 2002; Faccenna et al.,
2004; Spakman and Wortel, 2004), we use an
elastic plate model approach in order to evalu-
ate the role of basal traction below the crust for
active deformation, without using strong a priori
constraints on the geometry of the lithosphere in
the region. We then discuss the implications of
these model results in light of previous geody-
namic 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) sur-
rounded by the Internal Rif (Morocco) and
Internal Betics (Spain), which are the western-
most limit of the Alpine mountain belt (Fig. 1).
The tectonic evolution of the western Mediter-
ranean and the Alboran Sea has been dominated
by the long history of Nubia-Eurasia plate con-
vergence associated with the subduction of the
Neotethys Ocean (e.g., Faccenna et al., 2004).
Ideas to explain the striking topographical
symmetry of the region as well as the appar-
ently synchronous extension of the Alboran Sea
and shortening of the Betic and Rif Mountain
belts during the Neogene and Quaternary are
still debated. Current tectonic models for the
Alboran domain include four broad categories
of hypotheses: (1) backarc extension driven by
the westward rollback of an eastward subducting
slab (Royden, 1993; Lonergan and White, 1997;
Gutscher et al., 2002; Faccenna et al., 2004),
which passively falls in the mantle driven by its
own weight (subduction without convergence,
Jolivet et al. 2008) ; (2) break-off of a subducting
lithospheric slab (Blanco and Spakman, 1993);
(3) crustal extrusion due to forces transmitted
across the Eurasia-Africa plate boundary (Rebai
et al., 1992); and (4) delamination and convec-
tive removal of the lithospheric mantle root
beneath the collisional orogen (Platt and Vissers,
1989; Seber et al., 1996; Calvert et al., 2000).
Tomographic studies (Calvert et al. 2000;
Gutscher et al., 2002; Faccenna et al., 2004;
Spakman and Wortel, 2004) reveal a narrow east
dipping slab (100–200 km wide) located in the
Gibraltar Arc. Furthermore, seismic ray disper-
sion shows that the slab corresponds to oceanic
lithosphere material (Bokelmann and Maufroy,
2007). This slab seems to be detached under the
Betics (Spakman and Wortel 2004). According
to geochemical studies of igneous rocks of the
zone, beneath the Alboran Basin the slab is a
remnant part of the Tethys oceanic lithosphere,
but beneath the External Betics and Rif it con-
sists of delaminated (or subducted) continental
lithosphere (Duggen et al. 2008). The mecha-
nism responsible for the continental and oceanic
nature of the slab (delamination or continental
subduction) is still debated (Faccenna et al.
2004; Duggen et al. 2008).
Present-day tectonic processes occur within
the context of ongoing, WNW-ESE convergence
between Africa and Iberia in the Strait of Gibral-
tar (4.3 ± 0.5 mm/yr along the N116°E ± 6°
direction, McClusky et al., 2003, Fig. 1). How-
ever, the location or even existence of a discrete
Africa-Eurasia plate boundary in the Rif-Betics-
Alboran region is equivocal (Fadil et al. 2006).
The GPS velocities show signifi cant motions in
the Rif and Betics relative to Nubia and Eurasia
respectively (black arrows, Fig. 1). This south-
southwest motion of the Rif (5.4 ± 1.5 mm/yr)
in a Nubia fi xed reference frame, and to a lesser
extent the southern velocity component for sites
in the Betics with respect to Eurasia, depict more
complicated dynamics than can be ascribed to
simple crustal block interactions; or to stresses
induced by gravitational potential energy differ-
ences, since the Rif motion is not consistent with
the highest topographic gradient north of the Rif.
NUMERICAL MODEL OF THE RIF-
BETICS VELOCITY FIELD
According to Vernant et al. (2010) the GPS
velocities accurately depict the secular strain
eld and are not signifi cantly affected by either
co- or post-seismic deformation. Although the
lithosphere behaves elastically over the short time
period of the GPS observations, away from the
immediate vicinity of active faults, GPS observa-
tions are consistent with longer time period dis-
placements (from 10
3
to 3.10
6
yr and more, e.g.,
Reilinger et al., 2006). Three factors are likely to
infl uence the spatial distribution of the interseis-
mic 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.
In order to quantify the impact of these three
factors on the geodetic motion, we start with a
simple fi nite element model made of a 30-km-
thick homogeneous elastic plate driven by the
horizontal motion of the plates (Fig. 1). We
used the three-dimensional (3-D) noncommer-
cial fi nite element model software, ADELI 3D
(see http://www.dstu.univ-montp2.fr/PERSO/
chery/Adeli_web for details). Nubia plate sides
are thus locked (velocity = 0 mm/yr) and the
rigid rotation of Eurasia relative to Nubia is
applied on the Eurasian plate faces. We impose
the boundary conditions as a linear velocity
gradient on the western and eastern sides of
the model far from the study area, crossing the
diffuse seismicity between 36°N and 37°N that
defi nes the eastward prolongation of the Gloria
fault system and plate boundary zone (Fig. 1).
We estimate the fi t of the model by computing
the root mean square (RMS) residuals. This fi rst
experiment shows that crustal plate interaction
due to northwest-southeast Eurasia – Nubia
transpression explains quite well the Iberian
intra-plate motion (stations located up to the
lat. 38.2°N; Fig. 2A) and the motion of the sta-
tions located west of the Gibraltar Arc along
the Atlantic shoreline. The model velocities do
not fi t the observations in the Betics. East of the
Gibraltar Arc, signifi cant residuals of 2–6 mm/
yr are observed in the Rif (Fig. 2A). The RMSs
for the entire zone and for the Rif-Betics region
are summarized in Table 1.
In our second set of experiments, we investi-
gated the impact of a partial strength reduction
of the Alboran Sea and north Morocco sug-
gested by elevated heat fl ow (of 80–100 mW/
m
2
, e.g., Fernandez-Ibañez and Soto, 2008) on
the computed strain. Depending on the thermal
regime, the effective elastic thickness of conti-
nental plates varies from 3 to 80 km (Watts and
Burov, 2003). As average heat fl ow on continen-
tal areas is ~60 mW/m
2
, values of 80–100 mW/
m
2
may correspond to a thin mechanical litho-
sphere with strength limited to the seismogenic
zone (i.e., 6–12 km for the Alboran domain,
Fernandez-Ibañez and Soto, 2008). Therefore,
we can expect a ratio of ~10 between the Albo-
ran domain and the surrounding plates’ effective
elastic thickness. This effective elastic thick-
ness difference is equivalent to an elastic plate
of constant thickness with a factor of 10 differ-
ence in rigidity contrast (Chéry, 2008). One of
the best results is obtained with a low strength
zone limited to the region of high heat fl ow (> 80
mW/m
2
) in the Alboran Sea and adjacent areas
of the Rif (Fig. 2B and Table 1, experiment 2).
The model improves the RMS in the Betics, but
the misfi t in the Rif with respect to experiment
1 remains signifi cant, with residuals remaining
higher than the velocity uncertainties.
We ran a third set of experiments in which we
added to the previous model a horizontal trac-
tion beneath the elastic plate using a patch that
simulates the coupling between the upper plate
and the mantle at depth. We vary the patch size,
TABLE 1. SUMMARY OF THE NUMERICAL
EXPERIMENTS AND THEIR DATA FIT
Experiment
set
Weak plate
boundary
zone
Deep
traction
Best RMS*
(average)
Best
RMS
(zone)
1 NO NO 1.82 2.23
2 YES NO 1,63 1.98
3 YES YES 0.89 0.99
*RMS—root mean square.

GEOLOGY, September 2010 825
its location, and its velocity. The best model
corresponds to a traction applied to a small
surface (100 km × 50 km) located beneath the
External Rif zone at the limit of the weak plate
area (Fig. 2C). This model accounts for both the
motion toward the south-southwest observed in
the Rif and the clockwise rotation of velocity
vectors around the Gibraltar Arc. Moreover, the
traction area adjacent to the low strength region
of the Alboran Sea domain provides a signifi cant
change of the velocity fi eld in southeast Spain,
leading to close agreement of the modeled and
observed velocities in the Internal Betics.
DISCUSSION AND GEODYNAMIC
IMPLICATIONS
Our modeling experiments include no a pri-
ori information on sub-lithospheric geometry
and are designed to determine whether sub-
lithospheric processes are needed to account
for observed deformation of the western Medi-
terranean region. According to our best-fi tting
model, a traction patch applied beneath the elas-
tic plate is required to generate the unexpected
strain pattern indicated by the GPS velocity
eld (Fig. 2C), supporting the notion that either
sub-crustal or sub-lithospheric processes are
expressed in the surface displacements.
The small area of the coupling zone in our
model appears inconsistent with large-scale
mantle fl ow, and is more plausibly related to
phenomenon occurring not far from the Moho
(30 km depth in our model). Slab rollback,
that has already been proposed for the overall
formation of the Alboran Sea (e.g., Jolivet et
al., 2008), may be involved. However, geody-
namic 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. We further suggest
that the horizontal traction patch could represent
the remaining coupling zone between the slab
and the overlying continental lithosphere. This
region is located at the southern extremity of the
north-south–oriented lineament of intermediate
depth seismicity (60–120 km, Fig. 1) related to a
bend in the oceanic part of the slab (Fig. 3). This
old slab may be rolling back toward the south-
west, pulling on its upper extremities and leading
to the delamination of the lithospheric mantle in
the region of our patch. The high heat fl ow of
the region prevents the continental lithospheric
mantle from exhibiting brittle, seismic behavior.
Therefore, the patch would refl ect the interac-
tion between the delaminated African continen-
tal lithospheric mantle and the overlying plate
(Fig. 3). By analogy to subduction zones where
34°N
36°N
38°N
RMS zone = 1.98 mm/yr
352°E 354°E 356°E 358°E
RMS zone = 2.23 mm/yr
4 mm/yr
Modeled
Observed
Surface velocities :
354°E 356°E 358°E
ABC
352°E
34°N
36°N
38°N
3.6 mm/yr
RMS zone = 0.99 mm/yr
Patch velocity :
352°E 354°E 356°E 358°E
660 km
Base of the
overlying plate
Figure 3. Three-dimensional schematic diagram of the geodynamic model proposed in this
study based on tomographic studies (Calvert et al. 2000; Gutscher et al., 2002; Faccenna et
al., 2004 ; Spakman and Wortel, 2004). Base of the overlying lithosphere is schematically
represented as a plane. C.L—continental lithospheric mantle (green domain); O.L—oceanic
lithosphere (white domain). The shaded arrow represents the sinking of detached western
Mediterranean slab. Black arrow is the pull of the oceanic part of the slab at depth. Red
hachured area and red arrow are modeled traction patch (Fig. 2C) simulating the remain-
ing coupling interaction between the slab and the overlying lithosphere. Blue circles are
60–120 km depth seismicity (see Fig. 1).
Figure 2. Results of numerical modeling experiments. Boundary conditions are plotted in red in Figure 1. Shorelines are in black. RMS zone
is the root mean square calculated for global positioning system sites located in zone bound by the two dashed black lines. A: Northwest-
southeast Eurasia-Nubia transpression. Homogeneous rheology Young’s modulus E = 10
11
Pa (white domain) and Poisson’s ratio ν = 0.25.
B: Northwest-southeast Eurasia-Nubia transpression including Alboran Sea weak zone. Shaded zone: E = 10
10
Pa and ν = 0.25. C: Northwest-
southeast Eurasia-Nubia transpression including Alboran Sea weak zone and a horizontal basal traction. Rheology is the same as in B. Black
hatched area is the horizontal traction patch with a velocity of 3.6 mm/yr, 214°N directed (open black arrow), applied beneath the elastic plate
at 30 km depth.

826 GEOLOGY, September 2010
the slab is retreating, the coupling zone of our
patch would correspond to the forearc moving
toward the trench. Our modeling experiments
do not allow us to constrain the depth of the
delamination processes, which could be inside
the continental lithospheric mantle (Duggen et
al., 2008), at the Moho interface, or confi ned to
the crust at the brittle-ductile transition of the
lower crust (Gueydan et al., 2003). Since there
may not be full coupling between the depth of
the delamination and the surface, the 3.6 mm/
yr of patch displacement is the lower bound of
the delamination-induced horizontal velocities
at depth.
According to our delamination model (Fig. 3)
the traction zone is expected to move to the
south-southwest following propagation of the
delamination front. Identifying the faults that are
likely to accommodate this deep displacement is
not trivial. The surface boundaries are probably
located to the east on the northeast-southwest
trending Boussekkour fault associated with the
Al Hoceima earthquakes (Fig. 1), and to the
south on the southern thrust of the Rif, but to the
west, the locations remain unknown. During the
Pliocene-Quaternary, eastward subduction has
died out, as suggested by the accretionary wedge
sealed by undeformed sediments (Zitellini et
al., 2009). This reorganization of the tectonic
processes and the presumed south-southwest
motion of our traction patch may obscure any
surface of the western boundary. Further neotec-
tonic studies may help to clarify this point.
In conclusion, we suggest that the unexpected
velocity fi eld in the Rif-Betic zone is the result
of the combined effects of (1) long-term north-
west-southeast oblique convergence between
the Eurasian and the Nubian plates; (2) low
rigidity of the Alboran Sea domain; and (3) a
south-southwest–directed horizontal traction
applied beneath the External Rif (Fig. 2). We
suggest that this horizontal traction is due to the
rollback of the delaminated African continental
lithospheric mantle pulled by the sinking oce-
anic Western Mediterranean slab (Fig. 3).
ACKNOWLEDGMENTS
We thank G. Bokelmann, S. Lallemand and J.L.
Bodinier for their fruitful discussions, and to C. Fac-
cenna and fi ve anonymous reviewers for their con-
structive comments on this manuscript. Reilinger ben-
efi ted from a Visiting Researcher Fellowship from the
Observatoire de Recherche Méditerranéen en Envi-
ronnement of Montpellier while engaged in this study.
REFERENCES CITED
Blanco, M.J., and Spakman, W., 1993, The P-wave
velocity structure of the mantle below the
Iberian Peninsula: Evidence for subducted lith-
osphere below southern Spain: Tectonophysics,
v. 221, p. 13–34, doi: 10.1016/0040-1951(93)
90025-F.
Bokelmann, G., and Maufroy, E., 2007, Mantle struc-
ture under Gibraltar constrained by dispersion
of body waves: Geophysical Research Letters,
v. 34, p. L22305, doi: 10.1029/2007GL030964.
Calvert, A., Sandvol, E., Seber, D., Barazangi, M.,
Roecker, S., Mourabit, T., Vidal, F., Alguacil,
G., and Jabour, N., 2000, Geodynamic evolu-
tion of the lithosphere and upper mantle beneath
the Alboran region of the western Mediter-
ranean; constraints from travel time tomogra-
phy: Journal of Geophysical Research, v. 105,
p. 10871–10898, doi: 10.1029/2000JB900024.
Chéry, J., 2008, Geodetic strain across the San An-
dreas fault refl ects elastic plate thickness varia-
tion (rather than fault slip rate): Earth and Plan-
etary Science Letters, v. 269, p. 351–364, doi:
10.1016/j.epsl.2008.01.046.
Duggen, S., Hoernle, K., Kluegel, A., Geldmacher, J.,
Thirlwall, M., Hauff, F., Lowry, D., and Oates,
N., 2008, Geochemical zonation of the Miocene
Alboran Basin volcanism (westernmost Medi-
terranean): geodynamic implications: Contri-
butions to Mineralogy and Petrology, v. 156,
p. 577–593, doi: 10.1007/s00410-008-0302-4.
England, P., and McKenzie, D., 1982, A thin viscous
sheet model for continental deformation: Geo-
physical Journal of the Royal Astronomical So-
ciety, v. 70, p. 295–321.
Faccenna, C., Piromallo, C., Crespo-Blanc, A., Jo-
livet, L., and Rossetti, F., 2004, Lateral slab de-
formation and the origin of the western Medi-
terranean arcs: Tectonics, v. 23, p. TC1012,
doi: 10.1029/2002TC001488.
Fadil, A., Vernant, P., McClusky, S., Reilinger, R.,
Gomez, F., Ben Sari, D., Mourabit, T., Feigl,
K.L., and Barazangi, M., 2006, Active Tec-
tonics of the western Mediterranean: GPS
evidence for roll back of a delaminated sub-
continental lithospheric slab beneath the Rif
Mountains, Morocco: Geology, v. 34, p. 529–
532, doi: 10.1130/G22291.1.
Fernandez-Ibañez, F., and Soto, J.I., 2008, Crustal
rheology and seismicity in the Gibraltar Arc
(western Mediterranean): Tectonics, v. 27,
p. TC2007, doi: 10.1029/2007TC002192.
Gueydan, F., Leroy, Y.M., Jolivet, L., and Agard, P.,
2003, Analysis of continental midcrustal strain
localization induced by microfracturing and
reaction-softening: Journal of Geophysical Re-
search, v. 108, no. B2, p. 2064, doi: 10.1029/
2001JB000611.
Gutscher, M.A., Malod, J., Rehault, J.P., Con-
trucci, I., Klingelhoefer, F., Mendes-Victor,
L., and Spakman, W., 2002, Evidence for ac-
tive subduction beneath Gibraltar: Geology,
v. 30, p. 1071–1074, doi: 10.1130/0091-7613
(2002)030<1071:EFASBG>2.0.CO;2.
Jolivet, L., Augier, R., Faccenna, C., Negro, F., Rim-
mele, G., Agard, P., Robin, C., Rossetti, F., and
Crespo-Blanc, A., 2008, Subduction, conver-
gence and the mode of backarc extension in the
Mediterranean region: Bulletin de la Société
Géologique de France, v. 179, p. 525–550, doi:
10.2113/gssgfbull.179.6.525.
Lonergan, L., and White, N., 1997, Origin of the
Betic-Rif mountain belt: Tectonics, v. 16,
p. 504–522, doi: 10.1029/96TC03937.
McClusky, S., Reilinger, R., Mahmoud, S., Ben Sari,
D., and Tealeb, A., 2003, GPS constraints on
Africa (Nubia) and Arabia plate motions: Geo-
physical Journal International, v. 155, p. 126–
138, doi: 10.1046/j.1365-246X.2003.02023.x.
Platt, J.P., and Vissers, R.L.M., 1989, Extensional
collapse of thickened continental lithosphere;
a working hypothesis for the Alboran Sea and
Gibraltar Arc: Geology, v. 17, p. 540–543, doi:
10.1130/0091-7613(1989)017<0540:ECOTCL
>2.3.CO;2.
Rebai, S., Philip, H., and Taboada, A., 1992, Mod-
ern tectonic stress fi eld in the Mediterranean
region; evidence for variation in stress direc-
tions at different scales: Geophysical Jour-
nal International, v. 110, p. 106–140, doi:
10.1111/j.1365-246X.1992.tb00717.x.
Reilinger, R., et al., 2006, GPS Constraints on Con-
tinental Deformation in the Africa-Arabia-Eur-
asia continental collision zone and implications
for the dynamics of plate interactions: Journal
of Geophysical Research, v. 111, p. B05411,
doi: 10.1029/2005JB004051.
Royden, L.H., 1993, Evolution of retreating sub-
duction boundaries formed during continental
collision: Tectonics, v. 12, p. 629–638, doi:
10.1029/92TC02641.
Savage, J., and Burford, R., 1973, Geodetic determi-
nation of relative plate motion in Central Cali-
fornia: Journal of Geophysical Research, v. 78,
p. 832–845, doi: 10.1029/JB078i005p00832.
Seber, D., Barazangi, M., Ibenbrahim, A., and
Demnati, A., 1996, Geophysical evidence for
lithospheric delamination beneath the Alboran
Sea and Rif-Betic mountains: Nature, v. 379,
p. 785–790, doi: 10.1038/379785a0.
Spakman, W., and Wortel, M.J.R., 2004, Tomo-
graphic View on Western Mediterranean geo-
dynamics, in Cavazza, W., et al., eds., The
TRANSMED Atlas, The Mediterranean region
from crust to mantle: New York, Springer-Ver-
lag, p. 31–52.
Vernant, P., Fadil, A., Mourabit, T., Ouazar, D., Kou-
lali, A., Davila, J.M., Garate, J., McClusky, S.,
and Reilinger, R.E., 2010, Geodetic constraints
on active tectonics of the Western Mediterra-
nean: Implications for the kinematics and dy-
namics of the Nubia-Eurasia plate boundary
zone: Journal of Geodynamics, v. 49, p. 123–
129, doi: 10.1016/j.jog.2009.10.007.
Watts, A.B., and Burov, E.B., 2003, Lithospheric
strength and its relationship to the elastic and
seismogenic layer thickness: Earth and Plan-
etary Science Letters, v. 213, p. 113–131, doi:
10.1016/S0012-821X(03)00289-9.
Zitellini, N., et al., 2009, The quest for the Africa-
Eurasia plate boundary west of the Strait of
Gibraltar: Earth and Planetary Science Let-
ters, v. 280, p. 13–50, doi: 10.1016/j.epsl.2008
.12.005.
Manuscript received 14 December 2009
Revised manuscript received 20 April 2010
Manuscript accepted 27 April 2010
Printed in USA
Citations
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Journal ArticleDOI
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.

365 citations

Journal ArticleDOI
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.

356 citations

01 Aug 2012
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)....

    [...]

  • ...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....

    [...]

01 Apr 2009
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.

279 citations

Journal ArticleDOI
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.

169 citations

References
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Book ChapterDOI
01 Jan 2004
TL;DR: In this paper, the authors search for subduction remnants of the entire Cenozoic evolution in the recent global tomography model of Bijwaard and Spakman (2000) and compare these tomography results and their interpretations with those obtained in previous studies.
Abstract: During the Cenozoic, the Western Mediterranean region has experienced a complex subduction history which involved the destruction of the Late Triassic/Jurassic Ligurian ocean and the West Alpine-Tethys. Lithosphere remnants of this evolution have been detected in the upper mantle by seismic tomography imaging. However, no general consensus exists on the interpretation of these remnants/slabs in the context of Ligurian ocean and West Alpine-Tethys subduction. In this paper we search for subduction remnants of the entire Cenozoic evolution in the recent global tomography model of Bijwaard and Spakman (2000) and compare these tomography results and our interpretations with those obtained in previous studies. Next, we present an analysis of imaged mantle structure in the context of the tectonic evolution of the Western Mediterranean during the Cenozoic. Our analysis leads to the following main results:

437 citations


"Active surface deformation and sub-..." refers background or methods in this paper

  • ...This slab seems to be detached under the Betics (Spakman and Wortel 2004)....

    [...]

  • ...This southsouthwest motion of the Rif (5.4 ± 1.5 mm/yr) in a Nubia fi xed reference frame, and to a lesser extent the southern velocity component for sites in the Betics with respect to Eurasia, depict more complicated dynamics than can be ascribed to simple crustal block interactions; or to stresses induced by gravitational potential energy differences, since the Rif motion is not consistent with the highest topographic gradient north of the Rif....

    [...]

  • ...Tomographic studies (Calvert et al. 2000; Gutscher et al., 2002; Faccenna et al., 2004; Spakman and Wortel, 2004) reveal a narrow east dipping slab (100–200 km wide) located in the Gibraltar Arc....

    [...]

  • ...The GPS velocities show signifi cant motions in the Rif and Betics relative to Nubia and Eurasia respectively (black arrows, Fig....

    [...]

  • ...In the western Mediterranean, the Alboran Sea is a thinned continental domain (15 km thickness; Lonergan and White 1997) surrounded by the Internal Rif (Morocco) and Internal Betics (Spain), which are the westernmost limit of the Alpine mountain belt (Fig....

    [...]

Journal ArticleDOI
01 Feb 1996-Nature
TL;DR: In this article, the authors present an episode of active delamination of a piece of continental lithosphere, which is inferred as a high-velocity, seismically active, rigid body in the upper mantle.
Abstract: Geophysical evidence is presented for an episode of active delamination of a piece of continental lithosphere. Observations of earthquake hypocentre locations, seismic wave velocities and attenuation, Bouguer gravity, seismic reflection and drill hole data are combined with surface geology to infer the presence of a high-velocity, seismically active, rigid body in the upper mantle beneath the Alboran Sea and surrounding Betic and Rif mountain belts of the western Mediterranean region. This upper-mantle body, inferred to be the delaminating continental lithosphere, is overlain by a low-velocity, aseismic and strongly attenuating uppermost mantle, inferred to be the asthenospheric material replacing the delaminating lithosphere.

383 citations


"Active surface deformation and sub-..." refers background in this paper

  • ...…1993); (3) crustal extrusion due to forces transmitted across the Eurasia-Africa plate boundary (Rebai et al., 1992); and (4) delamination and convective removal of the lithospheric mantle root beneath the collisional orogen (Platt and Vissers, 1989; Seber et al., 1996; Calvert et al., 2000)....

    [...]

Journal ArticleDOI
TL;DR: In the oceans, the effective elastic thickness of the lithosphere, Te, is the range 2-50 km and is determined mainly by plate and load age, whereas the continents, in contrast, are characterised by Te values of up to 80 km and greater as mentioned in this paper.

356 citations


"Active surface deformation and sub-..." refers background in this paper

  • ...Depending on the thermal regime, the effective elastic thickness of continental plates varies from 3 to 80 km (Watts and Burov, 2003)....

    [...]

Journal ArticleDOI
TL;DR: An edited version of this paper was published by the American Geophysical Union (AGU) as mentioned in this paper, 2000, AGU 900024, Section 5.1.1].
Abstract: An edited version of this paper was published by the American Geophysical Union. Copyright 2000, AGU. See also: http://www.agu.org/pubs/crossref/2000/2000JB900024.shtml; http://atlas.geo.cornell.edu/morocco/publications/calvert2000.htm

317 citations


"Active surface deformation and sub-..." refers background or methods in this paper

  • ...Tomographic studies (Calvert et al. 2000; Gutscher et al., 2002; Faccenna et al., 2004; Spakman and Wortel, 2004) reveal a narrow east dipping slab (100–200 km wide) located in the Gibraltar Arc....

    [...]

  • ...…the confi guration of the Nubian-Eurasian plate boundary in the western Mediterranean and the geometry of the subducted plate are still debated (Calvert et al., 2000; Gutscher et al., 2002; Faccenna et al., 2004; Spakman and Wortel, 2004), we use an elastic plate model approach in order to…...

    [...]

  • ...…1993); (3) crustal extrusion due to forces transmitted across the Eurasia-Africa plate boundary (Rebai et al., 1992); and (4) delamination and convective removal of the lithospheric mantle root beneath the collisional orogen (Platt and Vissers, 1989; Seber et al., 1996; Calvert et al., 2000)....

    [...]

Journal ArticleDOI
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.

288 citations