Download Subduction zone evolution and deep slab structure

Subduction zone evolution and deep slab structure in the
Mediterranean
Michaela Christine Biela (319913)
E-Mail: [email protected]
Abstract
The evolution of the Mediterranean subduction zones and their deep slab structure started during the
Late Cretaceous and is a result of the relative movement of the African and European plate including
the independent motion of five microplates (Adria, Iberia, Alcapia, and Tiszia), which caused
subduction zones consuming the Tethys Ocean – a Mesozoic Ocean preserved in the Alps. This
subduction of the Alpine Tethys since Late Cretaceous caused a very complex plate-boundaryreorganization between seven (micro-) plates. Since the last 45 Ma until today the Alpine Tethys is still
consumed by four main still active subduction zones, on which will mainly be focused in this paper:
The Alps-Betics or Alpine-Betic and the Dinarides-Hellenides-Taurides subduction zones with an
eastwards- or north-eastwards-direction and the Apennines-Maghrebides and Carpathian subduction
zones with a westward-direction. The term “Alpine-Tethys” include remnants of the two JurassicCretaceous Valais and Piemont-Liguria Oceans, while the term “Neotethys” describes the creation of a
Late Paleozoic-Mesozoic Ocean due to the breakoff of Pangea.
Introduction
et al., 2004). These subduction zones
The Mediterranean is tectonically one of
consumed the previously formed Tethys
the most complex and seismically most
Ocean.
active regions in the world (Sengör, 2009).
Mediterranean was dominated by the
The main controlling factors are the
Alps-Betics
subduction of the Paleo-Tethys under
Apennines-Maghrebides, the Carpathian
Pangaea and the opening of the Central,
and
South and North Atlantic Ocean. Therefore
subduction zones (after Carminati et al.,
the tectonic of the Mediterranean is a
2004). The Dinarides, Hellenides, and
result
Taurides
of
rifting
of
the
African
and
the
During
the
or
Cenozoic
Alpine-Betic,
the
the
Dinarides-Hellenides-Taurides
are
“a
polyphase
orogeny,
Variscan
representing the coalescence of […] three
Orogeny (after Carminati et al., 2004),
subduction zones since Mesozoic times”
which started in the Paleozoic, and during
with a widespread extension development,
the Alpine Orogeny, which started in the
which resulted in a low topography in
Mesozoic.
the
comparison to the Alps (after Carminati et
Mediterranean area was dominated by
al., 2004). All four subduction zones had
three main subduction zones: “From east
different
to west the Cimmerian, the Dinarides, and
characteristics,
the Alps-Betics”, or Alpine-Betic (Carminati
Mediterranean tectonics so special. The
European
plates
In
the
after
late
the
Mesozoic
directions
which
and
different
made
the
1
Alps-Betics
or
the
Oligocene-Early Miocene” (Carminati et
Dinarides-Hellenides-Taurides subduction
al., 2012). In the eastern Mediterranean
zones
north-
deformation is very active because of the
“high
involvement of five plates in this region:
morphological and structural elevations,
Africa, Greece, Anatolia, Eurasia, and
double vergence, thick crust, involvement
Arabia. The most prominent factor in this
of
shallow
area is the “north-east-directed subduction
foredeeps” (Carminati et al., 2004). In
of Africa underneath Greece and the
contrast the Apennines-Maghgrebides and
Anatolian Plate (Eurasia)” (after Carminati
Carpathian
a
et al., 2004). Another reason for the
westward-direction and are characterized
characteristic shape of the Mediterranean
by trench retreat and “low morphological
is the individual motion of
and structural elevations, single vergence,
microplates
thin crust, involvement of shallow rocks,
Alkapecia, and Tiszia, relative to the
deep foredeeps, and a widely developed
African and European plates since Late
back-arc basin” (Carminati et al., 2004).
Cretaceous (Handy, et al., 2010).
This
the
Today’s shape of the Mediterranean is
‘westward’ drift of the lithosphere relative
mainly a result of subduction zones
to the mantle, at rates of about 49 mm per
formed during the Cenozoic. This paper
year” (Carminati et al., 2004).
will now show in detail, but on a simplified
The Mediterranean basin is divided into
view, based on the main four subduction
western, central and eastern. The central
zones, how the Mediterranean area and
and eastern Mediterranean basins are
their basins developed and will mainly
mainly relics of the Mesozoic-Cenozoic
focus on the evolution during the last 45
Tethys Ocean (after Carminati et al.,
Ma in the Cenozoic.
were
Alpine-Betic
eastwards-
crustal
rocks,
subduction
asymmetry
or
with
eastwards-directed,
deep
and
is
and
zones
“ascribed
had
to
Adria,
Iberia,
the five
Alcapia,
2004). This assumption is based on the
low heat flow (18-40 mWm-2) and the 4-8
km of sedimentary cover of the Ionian Sea
(after Carminati et al., 2004). The western
Tectonic
Mediterranean basin is the youngest and
Mediterranean
developed during the last 40-30 Ma. The
Cretaceous to Cenozoic
lithosphere is here thinned to less than 60
During 170-131 Ma the subduction of
km and the crust has a thickness of 8-15
remnant Tethyan basins was triggered by
km (Carminati et al., 2012). This is a
a “Neotethyan subduction slab along the
consequence of the “coherent system of
NE margin of the composite African-
interrelated irregular troughs, mainly V-
Adriatic slab” (Handy, et al., 2010). This
shaped that began to develop in the Late
subduction event “was linked by a sinistral
features
area
of
during
the
Late
2
transform system to E-W opening of the
the Mediterranean at 45 Ma. Therefore
Valais part of Alpine Tethys” (Handy, et al.,
figure 1 shows two different models: In a.)
2010). The effect of this subduction slab
the Neotethys, or Ionian, Ocean “is
was an intra-oceanic subduction of the
assumed to be continuous from the Ionian
Ligurian part of the Alpine Tethys during
Basin to the Maghrebian Basin” (Carminati
131-84 Ma, which coincided with Eo-alpine
et al., 2012) and b.) shows an alternative
orogenesis in the Alcapia microplate (after
with two distinct oceans: An Ionian and
Handy, et al., 2010). During 84-45 Ma the
Maghrebian Ocean (Carminati et
subduction of the Piemont and Valais
2012). Figure 2 also shows the deep slab
parts of the Alpine Tethys started and the
structure of the subduction of the oceanic
Ionian Sea slowly widened through NW
lithosphere.
translation of Adria with respect to Africa
The Cenozoic development of the Central-
(after Handy, et al., 2010).
Western Mediterranean is characterized
al.,
by a west-directed permanent subduction
zone since the Late Cretaceous (Carminati
et al., 2012). Figure 1 and 2 show the
Tectonic
features
of
the
occurrence of a continuous Alpine belt
Mediterranean area at 45 Ma
before the Apennine subduction zone
The central-western Mediterranean basin
developed (Carminati et al., 2012). The
moves from west to east and its evolution
beginning of the Apennine-Maghrebides
is connected to the three plates Africa,
and Carpathian subduction zone ranges
Adria and Europe, as seen in figure 2
from Late Cretaceous (~ 80 Ma) to Early
(Carminati et al., 2012).
Oligocene (~ 33 Ma) and is therefore
“The Alps-Betics and Dinarides belts are
neither shown in figure 1 nor in figure 2.
collisional orogens that were preceded by
the earlier […] subduction of several
branches of the Neotethys and Alpine
Tethys Ocean” (Carminati et al., 2012) and
is a result of the collision of the African
plate with Eastern and Western Europe
which happened mostly during the Eocene
(~ 55-35 Ma) (Carminati et al., 2012). This
led to the formation of a Northeast to
Southwest trending fold-and-thrust chain
(Carminati et al., 2012). Scientists are not
concurring about the existing oceans in
3
Figure 1: Geodynamic framework reconstruction of the Mediterranean at about 45 Ma. a.) Showing
the reconstruction with a continuous Ionian Ocean and b.) showing the reconstruction with two oceanic
basins (Carminati et al., 2012).
4
Figure 2: Geodynamic framework reconstruction of the Mediterranean at about 45 Ma. “The Alps were
continuous with the Betics to Gibraltar, consuming an ocean located to the west”. The formation of the
main subduction zones (Dinarides, Hellenides, Taurides) started. The Aegean extension is in progress
(Carminati et al., 2004).
Tectonic
features
of
the
Mediterranean area at 38 Ma
7 Ma later the eastern Alpine-Betic and
Dinarides-Hellenides Belts grow further,
but the Alpine-Betics slowed down. The
western
Apennines-Maghrebides
and
Carpathians Belts also start to develop
while the Neotethys Ocean is consumed.
During the development of these new
subduction zones a slab breakoff of the
former
subducted
oceanic
lithosphere
through the Alpine-Betics subduction has
to occur. Figure 3 shows the geodynamic
framework at 38 Ma.
5
Figure 3: Geodynamic framework reconstruction of the Mediterranean at about 38 Ma. Also showing
the deep slab structure in the bottom picture (Carminati et al., 2012).
6
Tectonic
features
of
the
Mediterranean area at 31-30 Ma
The
westward-directed
Apennines-
Maghrebides and Carpathians subduction
is going further “along the Alps-Betics
retrobelt, where oceanic and thinned
continental lithosphere occurred in the
foreland to the east” (Carminati et al.,
2004) and underneath the Adriatic and
Mesomediterranean plate. The ApenninesMaghrebides and Carpathian subduction
in the east is still growing further to the
west consuming the Neothethys Ocean.
Figure 4 and 5 show the geodynamic
framework reconstruction during this time.
Figure 5 also shows the deep slab
structure on a defined section trace.
Figure 4: Geodynamic framework reconstruction of the Mediterranean at about 30 Ma. “The AlpsBetics formed along the south-eastwards-dipping subduction of Europe and Iberia underneath the
Adriatic and Mesomediterrenean plates. The Apennines developed along the Alps-Betics retrobelt to
the east […] and the Carpathians started to develop along the Dinarides retrobelt” (Carminati et al.,
2004).
7
Figure 5: Geodynamic framework reconstruction of the Mediterranean at about 31 Ma. Also showing
the deep slab structure in the bottom picture (Carminati et al., 2012).
8
Tectonic
features
of
the
at about 20 Ma”, which is a result of “the
Mediterranean area at 35 Ma
Late
During the last 35 Ma until today the
counterclockwise
Adriatic and African slabs are retreating
(Carminati et al., 2004). The Apennines-
while Africa and Europe have a slowed
Maghrebides and Carpathians subduction
down convergence. The cause for this
zones are consuming further western parts
behavior is the subduction rollback of the
of the Alpine Tethys Ocean, which is
Ligurian part of the Alpine Tethys, which
visible in figure 6, which shows the
coincided
Alpine
geodynamic framework reconstruction of
orogeny. Also the very active Adriatic
the Mediterranean at 21 Ma. Figure 6
microplate
counter-
shows also the deep slab structure on a
clockwise rotation, which is caused by a
defined section during this time. In this
northward-directed push of the African
picture it is discernible that the subduction
plate, while slab pull has effected rapid
below Sardinia in the depth of around 200
rollback subduction of the Ligurian part of
km is now steeper than 10 Ma before.
with
the
started
Western
with
a
Cretaceous
to
Early
rotation
of
Tertiary
Iberia”
the Alpine Tethys and opening of the
Western
Mediterranean
ocean
basins
of
the
(Handy, et al., 2010).
Tectonic
features
Mediterranean area at 21 Ma
“The maximum amount of north-south
Africa/Europe relative motion […] was
about 135 km in the last 23 Ma, more than
five times shorter with respect to the
eastward migration of the Apennines arc
which moved eastwards more than 700 km
during the last 23 Ma” (Carminati et al.,
2012).
Therefore
the
east-directed
migration of the Apennine-Maghrebide arc
is a consequence of
Maghrebides
the Apennine-
subduction
rollback
(Carminati et al., 2012). The western
Mediterranean started mainly forming after
“the terminal convergence in the Pyrenees
9
Figure 6: Geodynamic framework reconstruction of the Mediterranean at about 21 Ma, also showing
the deep slab structure in the bottom picture (Carminati et al., 2012).
Tectonic
features
of
the
Belts are drifting further eastwards and
Mediterranean area at 15 Ma
consuming most of the eastern parts of the
6 Ma later, at 15 Ma, the Alps-Betics and
Neotethys Ocean. Figure 7 and 8 both
Dinarides-Hellenides subduction in the
show
east starts to retreat. In comparison the
reconstruction of Mediterranean at 15 Ma.
the
geodynamic
framework
Apennines-Maghrebides and Carpathians
10
Figure 7: Geodynamic framework reconstruction of the Mediterranean at about 15 Ma. The
Apennines-Maghrebides trench tend to drift eastwards. The Dinarides subduction slowed down, where
the Hellenides subduction in the south got faster. The Carpathians in the east generate the Pannonian
back-arc basin (Carminati et al., 2004).
Figure 8: Geodynamic framework reconstruction of the Mediterranean at about 15 Ma (Carminati et
al., 2012).
11
Tectonic
features
of
the
Mediterranean area at 5 Ma
At 5 Ma the Neotethys Ocean is nearly
consumed
by
the
eastwards-drifting
Apennines-Maghrebides and Carpathians
subduction zones. In comparison the
Alpine-Betics and Dinarides-HellenidesTaurides Belts in the east had a much
lower drift. Figure 9 shows the geodynamic
framework
reconstruction
of
the
Mediterranean at 5 Ma.
Figure 9: Geodynamic framework reconstruction of the Mediterranean at about 5 Ma (Carminati et al.,
2012).
12
Tectonic
features
of
the
“In the southern Apennines, the choking of
Mediterranean area today (0 Ma)
the subduction zone with the thicker
Remnants of the Mesozoic Neotethys
continental
Ocean still exist and are at present-day
platform slowed the eastwards migration of
consumed
and
the subduction hinge, whereas in the
Hellenides subduction zones (figure 10,
central and northern Apennines and in
Carminati et al., 2012) and until today the
Calabria
Apennines-Maghrebides subduction zone
including rollback of the subduction hinge
consumes old Tethyan domains by a
due to the thin continental lithosphere
speed of 25-30 mm per year (Carminati et
(Carminati et al., 2004).
al., 2004). Figure 10 also shows that Africa
Figure 11 gives an overview of the
is moving south-westwards in relation to
present-day geodynamic framework of the
Sicily.
Mediterranean showing the topography
“The recent stages of the evolution of the
and bathymetry.
Central
in
the
Apennines
Mediterranean
region
lithosphere
subduction
of
is
the
still
Apulia
active”,
are
complicated” due to a tectonic inversion,
which is “ascribed to the continuing AfricaEurope convergence (Carminati et al.,
2012).
Figure 10: Present geodynamic framework of the Mediterranean representing the main four
subduction zones: The westwards-directed Apennines-Maghrebides and Carpathians, the northeastwards-directed Dinarides-Hellenides-Taurides, and the south-eastwards-directed Alps (Carminati
et al., 2004).
13
Figure 11: Present geodynamic framework of the Mediterranean showing the topography and
bathymetry (Carminati et al., 2012).
Deep
slab
structure
of
the
Today we have shallow slabs in the Alps
Mediterranean
(~ 40°), in the Betics (~ 45°) and in the
During the last 45 Ma the deep slab
Dinarides-Hellenides (~ 25°) subduction
structure and the angle of the subduction
zones (after Carminati et al., 2012).
zones changed a lot. The Hellenides-
Steeper slabs are below the Apennines (~
Dinarides-Taurides
70°) and the Carpathians (~ 75°) (after
subduction
zone
consumed the Ionian Tethys Ocean from
Carminati et al., 2012).
east. The angle of this subduction zones
Figure 12 shows the evolution of the deep
didn’t
and
slab structure in the Mediterranean during
Maghrebides subduction zones developed
the last 45 Ma until today. At around 30
later out of the subduction of the Alps, at
Ma a slab breakoff of the Alps-Betics belt
30 Ma, consuming the Ionian Tethys
can be recognized due to the newly
Ocean from the west. In this subduction
formed
zone the more the Ionian Tethys is
Carpathians subduction zones.
changed.
The
Apennines
Apennines-Maghrebides
and
consumed the steeper is the subduction
angle.
14
Figure 12: The evolution of the Mediterranean during the last 45 Ma as a result of the three main
subduction zones: The early eastwards-directed Alpine subduction, the Apennine, and the DinaridesHellenides subduction. The Dinarides-Hellenides subduct the Tethyan Mesozoic oceanic lithosphere
(Carminati et al., 2004). At 30 Ma a slab breakoff of the Alps-betics belt can be recognized, which is
mainly caused by the new formed Apennines-Maghrebides and Carpathians subduction zones.
15
following a straight line. This gave the
Conclusion
The
extension
of
the
western
Mediterranean its present-day shape.
Mediterranean developed through relative
The still active subduction zones are the
convergence between Africa and Europe
reason that figure 13 is not the final form
at about 135 km in north-south-direction in
of the Mediterranean: The Mediterranean
the last 23 Ma, which is more than five
tectonics are still in a process of change
times slower than the migration of the
and reorganization of plate-boundaries.
Apennines arc, which was 700 km in
eastward-direction
in
the
same
time
(Carminati et al., 2004). Therefore the
migration of the Apennines arc is “a
consequence
of
the
Apennines-
Maghrebides subduction rollback, which
was generated either by slab pull or by the
‘eastwards’ flow of the mantle relative to
the lithosphere” (Carminati et al., 2004).
Figure 13 gives a summary of the tectonic
features during the last 45 Ma showing in
detail how often the direction of the four
subduction
zones
changed,
never
Figure 13: Summary of the main tectonic features of the Mediterranean during the last 45 Ma
including the related subduction zones: ”The double-vergent Alps–Betics, the single eastwardsvergent Apennines-Maghrebides […], the double-vergent Dinarides-Hellenides-Taurides and related
Aegean extension, the single eastwards-vergent Carpathians […], and the double-vergent Pyrenees”.
(Carminati et al., 2004).
16
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17