ArticlePDF Available

Pre-collisional extension of microcontinental terranes by a subduction pulley

Springer Nature
Nature Geoscience
Authors:

Abstract and Figures

Terrane accretion is a ubiquitous process of plate tectonics that delivers fragments of subduction-resistant lithosphere into a subduction zone, resulting in events such as ocean plateau docking or continental assembly and orogenesis. The post-collisional extension of continental terranes is a well-documented tectonic process linked with gravitational collapse and/or trench retreat. Here we propose that microcontinental terranes can also undergo a substantial extension before their collision with the upper plate, owing to pull from the trenchward part of the subducting plate. Forward geodynamic numerical experiments demonstrate that this pre-collisional extension can occur over a protracted phase on microcontinents that are drifting towards a subduction zone, which distinguishes the deformation from post-collisional extension on the overriding plate, as is traditionally postulated. The results show that the magnitude of pre-collisional extension is inversely correlated with the size of the microcontinental terrane and imposed convergence velocity. We find that locations along the Tethyan belts, namely, the Sesia zone and Eastern Anatolia, are evidence for this style of pre-collisional extension, as this mechanism reconciles with geothermobarometric data and kinematic analyses. The operation of this subduction pulley reveals that drifting lithospheric plates may undergo substantial tectonic events before the arrival and involvement with regular plate boundary processes.
Content may be subject to copyright.
Articles
https://doi.org/10.1038/s41561-021-00746-9
1Department of Earth Sciences, University of Toronto, Toronto, Canada. 2Eurasia Institute of Earth Sciences, Istanbul Technical University, Istanbul, Turkey.
e-mail: erkan.gun@mail.utoronto.ca
The continental lithosphere can be extended by a variety
of processes of horizontal (far field/passive rift) and ver-
tical (near field/active rift) tectonics13. For instance, the
Alpine–Mediterranean region has an array of locales of rift basins
and metamorphic exhumation in which the continental litho-
sphere undergoes extension in conjunction with plate subduction
and collision4,5. In such settings, continental lithosphere of the
back-arc (overriding) environment extends, and/or the microcon-
tinent (terrane and/or blocks) that accompanies the subducting
oceanic lithosphere undergoes an extension after the collision as
high-pressure exhumation occurs6 (Fig. 1a,b). Both mechanisms
infer that slab-pull forcing transmits stresses through the crust to
yield a trenchward retreat of the subduction (that is, the subduc-
tion rate is faster than the plate convergence)4. A key aspect of these
tectonic deformational events on the overriding continent or in the
microcontinent terrane is their temporal occurrence: the exten-
sion is contemporaneous (syn) or proceeding (post) the collision/
subduction time of the continental block. We propose that there is
another fundamental class of extensional tectonics which occurs
during the pre-collisional stages of the tectonic cycle as microconti-
nents (terranes) drift towards a subduction zone (Fig. 1c), and that
this pre-collisional episode of plate tectonic deformation has been
unrecognized.
Petrological studies in the Western Alps suggest that the burial
and exhumation of polymetamorphosed (high pressure–low tem-
perature) Austro-alpine continental crust (including eclogites) of
the Sesia–Lanzo zone (microcontinent) occurs through the devel-
opment of extensional and/or detachment faulting7 (Figs. 1 and 4a).
Notably, these events occur prior to the Eocene continent–conti-
nent collision in the Alps8. It is probable that there were overprint-
ing effects of deformation, and metamorphism in conjunction with
syn- and post-collision, but the pre-collisional timing of the main
phase of exhumation is unequivocal. This suggests an episode of
extension on the Sesia–Lanzo microcontinent prior to collision
and precludes geodynamic explanations for lithospheric stretching,
such as post-orogenic gravitational collapse9,10.
If microcontinent terranes experience an appreciable extension
prior to their continental docking at collision, this has important
implications. Terrane assembly is a fundamental step of continental
tectonics11 and accreted terranes may include intra-oceanic islands,
rifted microcontinental blocks, seamounts or oceanic aseismic ridges
and oceanic plateaus, which vary in size from a few to several thousand
kilometres12. Hence, the pre-collisional extension in such microconti-
nents could be a widespread phenomenon. For example, the entire
Alpine–Himalayas chain and North American Cordillera are intrinsi-
cally the result of an amalgamation of such a series of terranes13,14.
In this work, we explore the dynamics of how the pre-collisional
extension of microcontinents may evolve and how such events may
manifest in the metamorphic record. Computational forward mod-
els quantify the thermomechanical evolution of microcontinents
during drift and collision stages in an ocean lithosphere subduc-
tion system. The models monitor the metamorphic evolution of dis-
crete packages of crust during the convergence and collision. These
data are reconciled with petrological data of Tethyan microconti-
nent terranes in the eastern Mediterranean and Western Alps that
yielded the geological interpretations for pre-extensional collision.
The pre-collisional extension presents an unexplored and enigmatic
phase of tectonic activity in the plate subduction–collision system
that yields important new clues on the plate tectonic assembly of
the lithosphere.
Models for pre-collisional extension
To test quantitatively the deformational behaviour of microconti-
nents prior to a collision–accretion event, we used the geodynamic
numerical modelling tool SOPALE15. SOPALE is a geodynamic
code that solves plane strain deformation of viscoplastic materials
using arbitrary Lagrangian–Eulerian techniques. Extended Data
Fig. 1 and Extended Data Table 1 describe the configuration of the
Pre-collisional extension of microcontinental
terranes by a subduction pulley
Erkan Gün 1 ✉ , Russell N. Pysklywec 1, Oğuz H. Göğüş 2 and Gültekin Topuz 2
Terrane accretion is a ubiquitous process of plate tectonics that delivers fragments of subduction-resistant lithosphere into a
subduction zone, resulting in events such as ocean plateau docking or continental assembly and orogenesis. The post-collisional
extension of continental terranes is a well-documented tectonic process linked with gravitational collapse and/or trench retreat.
Here we propose that microcontinental terranes can also undergo a substantial extension before their collision with the upper
plate, owing to pull from the trenchward part of the subducting plate. Forward geodynamic numerical experiments demonstrate
that this pre-collisional extension can occur over a protracted phase on microcontinents that are drifting towards a subduction
zone, which distinguishes the deformation from post-collisional extension on the overriding plate, as is traditionally postulated.
The results show that the magnitude of pre-collisional extension is inversely correlated with the size of the microcontinental
terrane and imposed convergence velocity. We find that locations along the Tethyan belts, namely, the Sesia zone and Eastern
Anatolia, are evidence for this style of pre-collisional extension, as this mechanism reconciles with geothermobarometric data
and kinematic analyses. The operation of this subduction pulley reveals that drifting lithospheric plates may undergo substan-
tial tectonic events before the arrival and involvement with regular plate boundary processes.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles NATurE GEoSciENcE
models. A full explanation of the governing equations and formula-
tion for rheology is given in Methods and in numerous previous
applications of the SOPALE code1620.
The models test varying microcontinent widths from 120 to
600 km and three cases of convergence velocity: 0 cm yr–1 (litho-
spheric motion is driven only by the subducting ocean plate), and 2
and 4 cm yr–1 convergence velocity (as a proxy for large-scale plate
tectonics, such as ridge push). Supplementary Figs. 1 and 2 show
sets of additional test models that compare a range of different rhe-
ology parameters, a continental overriding plate and an additional
convergence rate; the Supplementary Table lists relevant modelling
parameters.
Model EXP-1 has a 120-km-wide microcontinent with a 0 cm yr–1
imposed convergent rate (Fig. 2). The left column in Fig. 2 shows
the model at 5.5 Myr when the subducting oceanic lithosphere is
consumed and the microcontinent begins to collide with the over-
riding oceanic lithosphere. By 7.1 Myr (centre column) there has
been slab break-off of the subducting lithosphere and the micro-
continent shortens. The microcontinental block largely resists being
consumed, owing to the buoyancy of the overlying continental
crust. We tracked a number of discrete crustal rock locations in the
microcontinent to reveal the pressure–temperature (PT) evolu-
tion: three from the lower crust (indicated by purple, magenta and
teal colours), and one (black) from the upper crust (Fig. 2). The
tracked rock packages were chosen primarily from the lower crust
to consider the full exhumation of the entire crust. These locations
are also horizontally distributed across the microcontinent to detect
any lateral variations of the extension that may manifest. One PT
time (PTt) path of an upper crustal rock (black) near the colli-
sion zone is also tracked. The PTt paths of the tracked rocks are
indicated in the far-right column. Solid lines show the PTt paths
of the tracked rocks for the first 5.5 Myr (Fig. 2, right column), and
dashed lines are paths between 5.5 and 7.1 Myr. The lower crustal
rocks at the centre (magenta) and the far end (teal) of the micro-
continent undergo continuous exhumation in the first 5.5 Myr of
the experiment, which corresponds to a 2.5 kbar (0.25 GPa) drop in
pressure (or ~8.7 km exhumation). The lower crustal rock package
close to the subduction zone (purple) first exhumes ~7.4 km, but
then it is rapidly buried as it becomes caught in the collision and
continental subduction. The upper crustal material at the near end
of the microcontinent (black) is buried for the first 5.5 Myr of the
model evolution, but undergoes later exhumation on a fault hanging
wall amidst the collision.
The notable behaviour of the model is the exhumation of crustal
rocks during the initial phase of plate consumption prior to colli-
sion. That is, the microcontinent undergoes pre-collisional exten-
sion as it drifts towards the plate boundary. The later events relate
to collision and depend on the proximity of the rock packages to
the collision front. For instance, near the collision front, the oro-
genically buried upper crustal material (black) starts to unroof. At
the centre of the microcontinent, the lower crustal rock package
(magenta) shows a post-collisional sequence of burial and exhuma-
tion. At the distal end of the microcontinent, the lower crustal mate-
rial (teal) is not appreciably affected by the collision and break-off
events. The lower crustal package in the subducted part of the
microcontinent (purple) continues its burial further into depths
below the lithosphere. This is a consequence of the location of the
slab break-off. The break-off happens in the subducted extent of
the microcontinent, as its lithospheric strength is lower than that of
the oceanic lithosphere21.
For EXP-2, the plate convergence velocity remains at 0 cm yr–1,
but the width of the microcontinent increases to 300 km (Fig. 2).
The experiment shows a similar evolution to that of EXP-1,
with consumption of the downgoing ocean lithosphere and drift
of the microcontinental block to the subduction zone, followed by
microcontinent collision and eventual slab break-off. The PTt
N
0 500 1,000 km
Continental block
a
Sesia BriançonnaisAdria Europe
85 Ma
d
c
Slab pull
This work
Extension
Accretion/
exhumation
b
Slab retreat
Extension
Black Sea
Aegean
Sea
Tyrrhenian
Sea
Alboran Sea
Arabian Platform
Anatolia
Pannonian Basin
Atlas Mountains
I
z
m
i
r
A
n
k
a
r
a
Adriatic Sea
Iberia
Pyrenees
Alps
Greater Caucaus
EAF
EURASIA
AFRICA
Sesia
Akdağ
Metamorphism
Exhumation
Collision
Sesia Akdağ
100 Ma
80–60 Ma
50 Ma
83 Ma
71 Ma
50 Ma
Pre-collisional extension locations
50° N
48° N
46° N
44° N
42° N
42° N
38° N
36° N
34° N
32° N
30° N
46° E44° E42° E40° E38° E36° E34° E32° E30° E28° E26° E24° E20° E18° E16° E14° E12° E10° E8° E6° E4° E2° E2° W4° W6° W8° W10° W 22° E
V
a
r
d
a
r
s
u
t
u
r
e
C
a
r
p
a
t
h
i
a
n
s
N
o
r
t
h
A
n
a
t
o
l
i
a
n
F
a
u
l
t
-
E
r
z
i
n
c
a
n
s
u
t
u
r
e
Z
a
g
r
o
s
s
u
t
u
r
e
D
e
a
d
S
e
a
F
a
u
l
t
H
e
l
l
e
n
i
c
T
r
e
n
c
h
Fig. 1 | Map showing main orogenic belts in the Alpine–Mediterranean region. Red stars indicate locations of the microcontinents that underwent
pre-collisional extensional deformation (inset). a, Tectonic setting of a microcontinent approaching a subduction trench. b, Back-arc extension on the
overriding plate due to slab retreat (modified from Brun and Faccenna6). c, Interpreted extensional tectonics of a microcontinent (continental block) in the
pro-plate, discussed in this article. d, Palaeotectonic interpretation for the Western Alps made by Rosenbaum and Lister35 with pre-accretion locations
of several microcontinents including the Sesia block. The base map in the figure was made with GeoMapApp (www.geomapapp.org) under a Creative
Commons licence CC BY 4.056. EAF, East Anatolian Fault.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles
NATurE GEoSciENcE
tracks for EXP-2 for the first 5.5 Myr follow similar paths com-
pared to those in EXP-1, but the magnitude of exhumation for the
lower crustal rocks is less than that for EXP-1. For example, for the
lower-crust rocks at the centre of the microcontinent (magenta),
this value is 1.7 kbar (0.17 GPa; ~5.9 km uplift) and it is 2.1 kbar
(0.21 GPa; ~7.4 km uplift) for the rock package at the far end of the
microcontinent (teal). Again, the important feature here is a sub-
stantial pre-collisional extension of the microcontinental block.
Break-off of the subducted slab (which occurs in the microcontinent
rather than ocean lithosphere) occurs at ~7.1 Myr, slightly delayed
with the increased microcontinent width in comparison with that of
EXP-1. The timing of this event also manifests in the PTt graphs,
in which the magenta- and teal-labelled rocks continue exhumation
to 7.1 Myr until the slab breaks off.
EXP-3 has a microcontinent increased to 450 km (Fig. 2). The
PTt paths of the tracked rock locations reveal a similar petro-
logical evolution to EXP-2, with an initial exhumation and inferred
extension of the microcontinent as it traverses towards the subduc-
tion. However, the amount of exhumation is less than that of both
EXP-1 and EXP-2. For instance, over 5.5 Myr the exhumation for
the magenta crustal package is 1.6 kbar (0.16 GPa; ~5.5 km uplift)
and the teal crustal package is 2.0 kbar (0.20 GPa; ~6.9 km uplift).
The slab break-off is further delayed compared with the previous
experiments.
800 1,000 1,200 1,400 1,600 1,800
Distance (km)
120 km300 km450 km600 km
Block
width
Slab break-off
Slab break-off
Slab break-off
Slab break-off
Lithostatic Pressure ( kbar )
Temperature (ºC)
200 300 400
4
6
8
5.5 Myr
7.1 Myr
0 100 200 300 400 50
Temperature (
0
2
4
6
8
10
Lithostatic Pressure ( kbar )
Lithostatic Pressure ( kbar )
Temperature (ºC)
200 300 400
4
6
8
5.5 Myr
7.1 Myr
Lithostatic Pressure ( kbar )
Temperature (ºC)
200 300 400
4
6
8
5.5 Myr
7.1 Myr
EXP-1
0 100 200 300 400 500
Temperature (
0
2
4
6
8
10
Lithostatic Pressure ( kbar )
EXP-2
EXP-3
0 MyrTracked crustal rocks
0 Myr
0 Myr
Initial state
Extended state
Initial state
Extended state
Initial state
Extended state
Oceanic
lithosphere
Oceanic
lithosphere
5.5 Myr
7.1 Myr
Lithostatic pressure (kbar)
4
6
8
5.5 Myr
7.1 Myr
0 100 200 300 400 50
Temperature (
0
2
4
6
8
10
Lithostatic Pressure ( kbar )
Lithostatic pressure (kbar)
4
6
8
5.5 Myr
7.1 Myr
2
4
6
8
10
Lithostatic Pressure ( kbar )
Lithostatic pressure (kbar)
Temperature (°C)
200 300 400
Temperature (°C)
200 300 400
Temperature (°C)
200 300 400
Temperature (°C)
200 300 400
4
6
8
5.5 Myr
7.1 Myr
800 1,000 1,200 1,400 1,600 1,800 2,000
Distance (km)
200
300
400
500
600
Depth (km)
0 Myr
Initial state
Extended state
EXP-4
1,400 1,500 1,600 1,700 1,800 1,900 2,000
1,400 1,500 1,600 1,800 1,900 2,000
1,700
200
300
400
500
600
Depth (km)
200
300
400
500
600
Depth (km)
200
300
400
500
600
Depth (km)
800 1,000 1,200 1,400 1,600 1,800 2,000
Distance (km)
800 1,000 1,200 1,400 1,600 1,800
Distance (km)
800 1,000 1,200 1,400 1,600 1,800
Distance (km)
800 1,000 1,200 1,400 1,600 1,800 2,000
Distance (km)
800 1,000 1,200 1,400 1,600 1,800 2,000
Distance (km)
800 1,000 1,200 1,400 1,600 1,800
Distance (km)
1,400 1,500 1,600 1,700 1,800 1,9001,300 2,000
1,400 1,500 1,600 1,700 1,800 1,900
1,300
5.5 Myr 7.1 Myr
Lithostatic pressure (kbar)
4
6
8
Fig. 2 | Model results showing the effect of microcontinent width with 0cmyr–1 imposed convergence rate. Figures from top to bottom show 120, 300,
450 and 600 km microcontinent widths (EXP-1, EXP-2, EXP-3 and EXP-4, respectively). The colour legend for the rheologies in the frames are the same
as those of the model set-up in Extended Data Fig. 1. Frames on the left show the moment at 5.5 Myr when microcontinents reach the subduction zone.
The inset figures show the initial states of the models and chosen points for PTt tracking. The initial depths of the tracked rocks are 7 km for the black,
and 28 km for the purple, magenta and teal symbols. The frames in the middle of the figure show the state of the models at 7.1 Myr when slab break-off
has happened or is about to happen. Supplementary Fig. 3 gives the corresponding second invariant of the deviatoric strain-rate tensors. The graphs on
the right show PTt paths of the tracked rocks between 0 and 7.1 Myr with 0.16 Myr subsampling intervals. The colours of the lines are the same colours
those of the tracked rocks in the figures of the left and middle columns. The solid lines represent 0–5.5 Myr and the dashed lines are the phase from 5.5 to
7.1 Myr. 1 kbar = 0.1 GPa.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles NATurE GEoSciENcE
EXP-4 has a microcontinent of 600 km width and a 0 cm yr–1
imposed convergence rate (Fig. 2). Although the PTt paths here
are generally similar to those of the previous experiments, again
there is a further decrease in the magnitude of microcontinent
exhumation and a delay in the timing of the slab break-off.
Figure 3 illustrates trends in the models: Fig. 3a shows microcon-
tinent width versus the maximum lithostatic pressure drop (essen-
tially the magnitude of exhumation) of the tracked rock packages
and Fig. 3b shows width versus the β-factor (extension factor) of
the microcontinent. In addition to the data from the models above
(solid lines), data from experiments with imposed convergence
rates of 2 cm yr–1 (long dashed lines) and 4 cm yr–1 (short dashed
lines) are included. These additional imposed convergence rates
compare when conceptual ridge-push (imposed convergence) and
slab-pull forces act together, with when slab pull is the only driving
force in the system. The graph colours correspond with the colours
of the tracked rocks in Fig. 2. For the upper crustal rocks of the
microcontinent near the collision front (black), both microconti-
nent width and convergence rate do not have any substantial effect
on the extension rate (Fig. 3a). However, as noted with the results
above, a trend shows that with increasing continent width there is
a decrease in the magnitude of the pre-collisional exhumation (and
inferred extension) for most packages of microcontinental crustal
rock. This is consistent for all the models with 0, 2 and 4 cm yr–1
convergence rates, although the extension rate is always higher in
the case of no imposed convergence rate over the 2 and 4 cm yr–1
rates. Similarly, the β-factor decreases with increasing microconti-
nent width. Also note that the change in the exhumation rate due
to the convergence rate is reduced with an increase of microconti-
nent width. In other words, the effect of convergence velocity on the
extension rates is more prominent when the microcontinent size is
smaller. This is also evident in Fig. 3b, in which, for instance, the β
extension factors are 1.40, 1.27 and 1.17, respectively, for 0, 2 and
4 cm yr–1 convergence rates at the centre of a 120-km-wide micro-
continent, but they are correspondingly 1.31, 1.21 and 1.16 for a
600-km-wide microcontinent. The extension style in our experi-
ments develops rather as a pure shear type1 than a simple shear22
because the tracked rock packages—horizontally distributed across
the tested microcontinents—do not show differences in exhuma-
tion (Fig. 3a).
Microplate extension by slab pull and a subduction pulley
Our geodynamic models demonstrate that when microcontinents
drift towards a subduction zone, they can undergo substantial
extensional deformation, as evidenced by crustal exhumation and
stretching factors (Fig. 2). This extensional deformation is present
in all of the quantitative experiments here, regardless of the size of
the microcontinent or the microcontinental terrane convergence
rate (Fig. 3). The extension rate in a microcontinent is inversely
correlated with the microcontinent width and the convergence rate.
For instance, the exhumation rate of the lower crustal rocks of a
600-km-wide microcontinent is ~40% lower compared with that
of a 120-km-wide one in the case no imposed convergent velocity.
Further models show that with a sufficient imposed convergence
velocity, the pre-collisional extension can be effectively shut off
(Supplementary Fig. 2).
We propose that a main driving mechanism for the
pre-collisional extension of the microcontinent terrane is the verti-
cal slab pull transferred across a ‘subduction pulley’ to the micro-
continent during its drift towards subduction and ultimate collision.
A mechanical analogue was superimposed on top of the subduc-
tion–microcontinent accretion system to illustrate this mechanism
(Fig. 4). Oceanic lithosphere older than 10 Myr should resist defor-
mation when tensile stress acts on it23, hence, in the mechanical sys-
tem, the ocean lithosphere is represented as semi-rigid blocks that
resist deformation (Fig. 4). There is (as yet) no evidence of exten-
sional deformational regions on oceanic plates except for back-arcs;
that is, no similar pre-collision extension of a subducting ocean
plate. However, continental lithosphere embedded within the oce-
anic lithosphere is generally weaker under the same physical condi-
tions than the oceanic lithosphere and is a preferable location for
extensional deformation and rifting21,2427. This is due to the rheol-
ogy and thickness differences between the oceanic and continental
crust. In our models, although the 30-km-thick microcontinental
crust is represented by weak wet quartzite28, the 7-km-thick oce-
anic crust is a strong Maryland diabase29. Given such differences
between the mechanical properties of the continental versus oce-
anic lithospheres, our mechanical model posits that the tensile
stress on the subducting plate is focused at the microcontinent,
which yields pre-collisional extension (Fig. 4 and Supplementary
Video 1).
120 300 450 600
0.5
1.0
1.5
2.0
Pressure drop
(P0P1) (kbar or 10–1 GPa)
Microcontinent width (km)
a
120 300 450 600
1.1
1.2
1.3
1.4
β-factor
Microcontinent width (km)
b
Fig. 3 | Plots showing the magnitudes of pre-collisional extension depending on tested parameters. a, The effect of microcontinent width and
convergence rate on exhumation rates from 0 to 5.5 Myr. The horizontal axis shows the tested microcontinent widths and the vertical axis indicates the
lithostatic pressure drop (due to unroofing or exhumation) in the selected rock locations. Teal, magenta and purple lines show the exhumation rates
of the lower crustal rocks in a microcontinent; purple represents the rocks in the front end, magenta those in the centre and teal those in the far end
of the microcontinent. The black line shows upper crustal rocks in the front of the microcontinent. The locations of these points are indicated in Fig. 2.
Convergence rates are denoted by solid, long-dashed and short-dashed lines for 0, 2 and 4 cm yr–1, respectively. b, β-factors (extension factor) for the
lower crustal rocks at the centre of the microcontinents, which depends on the convergence rates and microcontinent widths for the pre-collisional stage.
Extension factors are calculated by β=li/lf (ref. 1) (li and lf indicate initial and the final lithospheric thicknesses, respectively). Solid, long-dashed and
short-dashed lines represent β-factors for convergence rates of 0, 2 and 4 cm yr–1 , respectively.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles
NATurE GEoSciENcE
A notable phenomenon in the experiments is the location of the
slab break-off after the microcontinent accretion. Conceptually,
it is normally considered that the location of a post-collisional
slab break-off is in the subducted oceanic lithosphere at variable
depths3032; however, in our experiments break-off happens in a
subducted portion of the microcontinent instead. This is due to
the same factors discussed above: the weaker microcontinent ter-
rane is a preferential site to break compared with the oceanic plate
(of course, this is not to say that detachment could not occur in
an oceanic lithosphere in other circumstances). An intriguing
consequence of this is that it can yield a deep subduction of the
lower crust (tracked purple rock package in Fig. 2) from the first
~30–40 km subducted portion of the microcontinent (Fig. 2). This is
in accordance with previous calculations, which suggest that down-
going lithospheric mantle can carry an ~10-km-thick detached
lower crust into the asthenosphere33.
Geological record of pre-collisional extension
Pre-collisional extension is supported by geological evidence from
the Western Alps and eastern Mediterranean–Caucasus region. The
Sesia zone, as a ribbon-like microcontinent in the Western Alps,
drifted and accreted to Adria with the closure of the Ligurian–
Piemontese ocean in the Eocene34,35. The metamorphism in the
Sesia zone started ~100 million years ago (Ma) and exhumation
of the metamorphic rocks to the shallow crustal levels occurred
~60 Ma according to K–Ar cooling ages, prior the Tertiary collision
of the Western Alps8. Although there are studies that suggest the
Sesia zone thinned during Jurassic rifting36 and/or its crustal rocks
exhumed during Late Cretaceous dextral transpression37, neither of
these is able to explain why it later cooled to below 300–350 °C dur-
ing the Palaeocene38, that is, prior to collision. According to Avigad8,
Sesia pre-collisional exhumation occurred along a ductile shear
zone and showed a normal sense of kinematic motion (Fig. 5a),
as evidenced by S–C structures, mica fish and rotated porphyro-
clasts. The comparison of a calculated PTt track from one of our
experiments (EXP-3) against a variety of PTt calculations from
petrological studies in the Sesia zone indicates that the results are
compatible for the last stage of the exhumation period (Fig. 5b)3741.
The convergence rate estimations between Europe and the Adria/
middle Mediterranean plate are 1–2 cm yr–1 (refs. 42,43), which is con-
sistent with our experiments where the subduction pull creates a
~2.1 cm yr–1 convergence in EXP-3.
Additional evidence for a pre-collisional extension comes from
Eastern Anatolia in the Tethyan belt (Fig. 5c). Eastern Anatolia,
the eastward elongation of the Anatolide block, is a microconti-
nental fragment bounded by the Izmir–Ankara–Erzincan (IAE)
Subducting
oceanic plate
Slab pull
Overriding
oceanic plate
Microcontinent
Strong oceanic
lithosphere
Weak continental
lithosphere
Asthenosphere
Subducting
oceanic plate
Slab pull
Overriding
oceanic plate
Microcontinent
Strong oceanic
lithosphere
Accretion and
slab break-off
a
c
b
Fig. 4 | The mechanical analogue demonstrates the fundamental dynamics of the tectonic system. This analogue consists of a mass, pulley, dashpot and
string that connects these elements to each other. In our analogy, the elements represent slab weight (slab pull), trench, a relatively weak microcontinent
and a strong oceanic lithosphere. a, The initial state in which the microcontinent drifts towards the subduction zone. b, The microcontinent (dashpot)
extends during its journey to the trench owing to the tensional force applied by the slab pull (the mass) across the subduction zone (pulley). c, The
accretion and slab break-off, which tends to occur in the weaker microcontinent.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles NATurE GEoSciENcE
suture zone in the north and the Bitlis suture zone in the south.
Calculations based on palaeomagnetic studies again estimate a
slow convergence rate, ~1.3 cm yr–1 in the past 80 Myr, between
Africa and Eurasia for the Anatolia region44,45. On the basis of field
geological constraints and a magmatic lull, continental collision
along the IAE suture zone is constrained to have occurred by the
Palaeocene–Early Eocene46,47. However, most estimates for the con-
tinental collision along the Bitlis–Zagros suture range from the Late
Eocene to Early Miocene48,49. The basement of East Anatolia is made
up of Late Cretaceous high-temperature/low-to-middle-pressure
metamorphic rocks intruded by Late Cretaceous mafic to felsic
intrusions, and locally their non-metamorphic equivalents50,51.
The metamorphic rocks and the intrusions were exhumed to the
surface by the Maastrichtian, as deduced by unconformably over-
lying Maastrichtian reefal limestone. Crustal-scale detachment
faults juxtapose the greenschist-facies and upper amphibolite-facies
domains near Akdağ51 (G.T. et al., manuscript in preparation)
(Fig. 5c). Likewise, a crustal-scale detachment that separates
greenschist- and amphibolite-facies domains is observed in the
Taşlıçay area, which is located ~140 km to the east of the Akdağ area
(Fig. 5c). This sequence of events—exhumation completed by the
end of Late Cretaceous, and the continental collision along the IAE
Issime
Gabby
Valsesia
Val Gressoney
0 5 km
7° 40 E 7° 50 E 8° E
45° 40 N
45° 50 N
300 400
5
10
Temperature (°C)
Lithostatic pressure (kbar)
Zucali et al.39; Regis et al.40
Regis et al.40; Rubbato et al.41
Babist et al.37
500
Oberhänsli et al.38
200
This work (EXP-3)
Sesia zone
N
Triassic to Upper Cretaceous
carbonate platform
Late Cretaceous
mafic-to-acidic intrusions
Early Jurassic and Late
Cretaceous ophiolite and
melanges
Late Cretaceous
ophiolite and melanges
Post-Cretaceous
cover
Suture
Late Cretaceous
amphibolite-facies
metamorphic rocks
Late Cretaceous
greenschist-facies
metamorphic rocks
Possible detachment fault
Late Cretaceous low-to-high grade
metamorphic rocks containing
local high-pressure metamorphic rocks
Arabian Platform
East Anatolia
Eastern Pontides
Pütürge massif
Lake Van
N
IAE suture
39° E
42° E
39° N
a b
c
EMS
Metaquartzdiorite in EMS
II DK
Gneiss minuti (paraschist–
granitoid complex)
Oligocene volcanics
Ivrea zone
Oligocene intrusives
Detachment fault
Thrust
Black Sea
Aegean
Sea
Arabian Platform
Anatolia
-
Greater Caucaus
EAF
EURASIA
Akdağ
0 500 km
Tyrrhenian
Sea
Adriatic
Sea
Western
Alps
Sesia
0500 km
Detachment fault
0 5 10 km
Tasllçay
a
F
a
u
l
t
Z
a
g
r
o
s
s
u
t
u
r
e
-
E
r
z
i
n
c
a
n
s
u
t
u
r
e
I
z
m
i
r
-
A
n
k
a
r
a
H
e
l
l
e
n
i
c
T
.
N
o
r
t
h
A
n
a
t
o
l
i
a
n
F
a
u
l
t
39° N
B
i
t
l
i
s
Z
a
g
r
o
s
s
u
t
u
r
e
I
A
E
s
u
t
u
r
e
Akdag
Akdag
Fig. 5 | The geological evidence for pre-collisional continental terrane extension. a, Geological map of the Sesia zone in the Western Alps8. The
microstructures and normal-sense ductile shear zone between the eclogitic micaschists (EMS) (orange) and seconda zona Diorito–Kinzigitica (II DK)
(light blue) units suggest that Cretaceous EMS unit decompressed and exhumed before the Cenozoic collision of the Sesia microcontinental terrane.
b, Comparison of various petrological data from the Sesia zone to the calculated PTt tracks from EXP-3. c, Location and geological map of the East
Anatolia microcontinent, between the IAE and Bitlis–Zagros suture zones in Eastern Anatolia51 (G.T. et al., manuscript in preparation). The Late Cretaceous
metamorphic rocks (orange) and mafic-to-acidic intrusions (red) located near Akdağ and Taşlıçay were exhumed to the surface along the detachment
fault shown in the figure before its collision along the IAE suture zone in the Palaeocene–Early Eocene (see text for references). The greyscale location
maps were made with GeoMapApp (www.geomapapp.org) under a Creative Commons licence CC BY 4.056. Panel a adapted with permission
from ref. 8, Elsevier.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles
NATurE GEoSciENcE
suture zone occurring later (Palaeocene–Early Eocene)—indicates
a major extension in Eastern Anatolia in a pre-collisional setting.
We believe that this new pre-collisional extension idea explains
some unresolved geodynamic and petrological aspects related to
microcontinent terrane accretion processes. Until now, it has been
proposed that extension/exhumation processes take place after the
accretion of the microcontinents to an overriding plate, namely
syn- and post-collisional extension, due to gravitational collapse52
or back-arc extension4,5355.
The majority of petrological studies of extension during micro-
continent terrane accretion are interpreted as post-collisional. This
may be due to the overprinting of post-collisional metamorphism
over the pre-collisional one. Our findings suggest an alternative
hypothesis. Ultimately, the hidden or ignored pre-collisional exten-
sion/exhumation process could be important and taken into con-
sideration when investigating the tectono-metamorphic history of
microcontinental terranes.
Online content
Any methods, additional references, Nature Research report-
ing summaries, source data, extended data, supplementary infor-
mation, acknowledgements, peer review information; details of
author contributions and competing interests; and statements of
data and code availability are available at https://doi.org/10.1038/
s41561-021-00746-9.
Received: 20 April 2019; Accepted: 29 March 2021;
Published: xx xx xxxx
References
1. McKenzie, D. Some remarks on the development of sedimentary basins.
Earth Planet. Sci. Lett. 40, 25–32 (1978).
2. Şengör, A. M. C. & Burke, K. Relative timing of riing and volcanism on
Earth and its tectonic implications. Geophys. Res. Lett. 5, 419–421 (1978).
3. Turcotte, D. L. & Emerman, S. H. Mechanisms of active and passive riing.
Dev. Geotecton. 19, 39–50 (1983).
4. Royden, L. H. Evolution of retreating subduction boundaries formed during
continental collision. Tectonics 12, 629–638 (1993).
5. Jolivet, L. & Faccenna, C. Mediterranean extension and the Africa–Eurasia
collision. Tectonics 19, 1095–1106 (2000).
6. Brun, J.-P. & Faccenna, C. Exhumation of high-pressure rocks driven by slab
rollback. Earth Planet. Sci. Lett. 272, 1–7 (2008).
7. Compagnoni, R. et al. e Sesia–Lanzo zone, a slice of continental crust with
Alpine high pressure-low temperature assemblages in the Western Italian
Alps. Rend. Soc. Ital. Mineral. Petrol. 33, 281–334 (1977).
8. Avigad, D. Pre-collisional ductile extension in the internal western Alps (Sesia
zone, Italy). Earth Planet. Sci. Lett. 137, 175–188 (1996).
9. Dewey, J. F. Extensional collapse of orogens. Tectonics 7, 1123–1139 (1988).
10. Rey, P., Vanderhaeghe, O. & Teyssier, C. Gravitational collapse of the
continental crust: denition, regimes and modes. Tectonophysics 342,
435–449 (2001).
11. Price, R. A. e Cordilleran foreland thrust and fold belt in the
southern Canadian Rocky Mountains. Geol. Soc. Lond. Spec. Publ. 9,
427–448 (1981).
12. Nur, A. & Ben-Avraham, Z. Oceanic plateaus, the fragmentation of
continents, and mountain building. J. Geophys. Res. 8, 3644–3661 (1982).
13. Coney, P. J., Jones, D. L. & Monger, J. W. H. Cordilleran suspect terranes.
Nature 288, 329–333 (1980).
14. Sigloch, K., McQuarrie, N. & Nolet, G. Two-stage subduction history under
North America inferred from multiple-frequency tomography. Nat. Geosci. 1,
458–462 (2008).
15. Fullsack, P. An arbitrary Lagrangian–Eulerian formulation for creeping ows
and its application in tectonic models. Geophys. J. Int. 120, 1–23 (1995).
16. Pysklywec, R. N., Beaumont, C. & Fullsack, P. Lithospheric deformation
during the early stages of continental collision: numerical experiments and
comparison with South Island, New Zealand. J. Geophys. Res. Solid Earth 107,
https://doi.org/10.1029/2001JB000252 (2002).
17. Gray, R. & Pysklywec, R. N. Geodynamic models of mature continental
collision: evolution of an orogen from lithospheric subduction to continental
retreat/delamination. J. Geophys. Res. Solid Earth 117, B03408 (2012).
18. Göğüş, O. H., Pysklywec, R. N., Şengör, A. M. C. C. & Gün, E. Drip tectonics
and the enigmatic upli of the Central Anatolian Plateau. Nat. Commun. 8,
1538 (2017).
19. Bodur, Ö. F., Göğüş, O. H., Pysklywec, R. N. & Okay, A. I. Mantle lithosphere
rheology, vertical tectonics, and the exhumation of (U)HP rocks. J. Geophys.
Res. Solid Earth 123, 1824–1839 (2018).
20. Heron, P. J., Pysklywec, R. N. & Stephenson, R. Lasting mantle scars lead to
perennial plate tectonics. Nat. Commun. 7, 11834 (2016).
21. Vink, G. E., Morgan, W. J. & Zhao, W.-L. Preferential riing of continents: a
source of displaced terranes. J. Geophys. Res. 89, 10072–10076 (1984).
22. Wernicke, B. Uniform-sense normal simple shear of the continental
lithosphere. Can. J. Earth Sci. 22, 108–125 (1985).
23. Lynch, H. D. & Morgan, P. e tensile strength of the lithosphere and the
localization of extension. Geol. Soc. Lond. Spec. Publ. 28, 53–65 (1987).
24. Molnar, P. Continental tectonics in the aermath of plate tectonics. Nature
335, 131–137 (1988).
25. Ranalli, G. & Murphy, D. C. Rheological stratication of the lithosphere.
Tectonophysics 132, 281–295 (1987).
26. Kohlstedt, D. L., Evans, B. & Mackwell, S. J. Strength of the lithosphere:
constraints imposed by laboratory experiments. J. Geophys. Res. 100,
17587 (1995).
27. van den Broek, J. M. & Gaina, C. Microcontinents and continental fragments
associated with subduction systems. Tectonics 39, e2020TC006063 (2020).
28. Gleason, G. C. & Tullis, J. A ow law for dislocation creep of quartz
aggregates determined with the molten salt cell. Tectonophysics 247,
1–23 (1995).
29. Mackwell, S. J., Zimmerman, M. E. & Kohlstedt, D. L. High-temperature
deformation of dry diabase with application to tectonics on Venus. J.
Geophys. Res. Solid Earth 103, 975–984 (1998).
30. Davies, J. H. & von Blanckenburg, F. Slab breako: a model of lithosphere
detachment and its test in the magmatism and deformation of collisional
orogens. Earth Planet. Sci. Lett. 129, 85–102 (1995).
31. van Hunen, J. & Allen, M. B. Continental collision and slab break-o: a
comparison of 3-D numerical models with observations. Earth Planet. Sci.
Lett. 302, 27–37 (2011).
32. Freeburn, R., Bouilhol, P., Maunder, B., Magni, V. & van Hunen, J. Numerical
models of the magmatic processes induced by slab breako. Earth Planet. Sci.
Lett. 478, 203–213 (2017).
33. Molnar, P. & Gray, D. Subduction of continental lithosphere: some constraints
and uncertainties. Geology 7, 58 (1979).
34. Coward, M. & Dietrich, D. Alpine tectonics—an overview. Geol. Soc. Lond.
Spec. Publ. 45, 1–29 (1989).
35. Rosenbaum, G. & Lister, G. S. e Western Alps from the Jurassic to
Oligocene: spatio-temporal constraints and evolutionary reconstructions.
Earth Sci. Rev. 69, 281–306 (2005).
36. Manzotti, P., Ballèvre, M., Zucali, M., Robyr, M. & Engi, M. e
tectonometamorphic evolution of the Sesia–Dent Blanche nappes
(internal Western Alps): review and synthesis. Swiss J. Geosci. 107,
309–336 (2014).
37. Babist, J., Handy, M. R., Konrad-Schmolke, M. & Hammerschmidt, K.
Precollisional, multistage exhumation of subducted continental crust: the
Sesia Zone, western Alps. Tectonics 25, TC6008 (2006).
38. Oberhänsli, R., Hunziker, J. C., Martinotti, G. & Stern, W. B. Geochemistry,
geochronology and petrology of Monte Mucrone: an example of EO-alpine
eclogitization of Permian granitoids in the Sesia–Lanzo Zone, Western Alps,
Italy. Chem. Geol. Isot. Geosci. 52, 165–184 (1985).
39. Zucali, M., Spalla, M. I. & Gosso, G. Strain partitioning and fabric evolution
as a correlation tool: the example of the eclogitic micaschists complex in the
Sesia–Lanzo Zone (Monte Mucrone–Monte Mars, Western Alps, Italy).
Schweiz. Mineral. Petrogr. Mitteil. 82, 429–454 (2002).
40. Regis, D. et al. Multiple metamorphic stages within an eclogite-facies terrane
(Sesia zone, Western Alps) revealed by –U–Pb petrochronology. J. Petrol.
55, 1429–1456 (2014).
41. Rubatto, D. et al. Yo-yo subduction recorded by accessory minerals in the
Italian Western Alps. Nat. Geosci. 4, 338–342 (2011).
42. Hsü, K. J. Time and place in Alpine orogenesis—the Fermor Lecture. Geol.
Soc. Spec. Publ. 45, 421–443 (1989).
43. Hunziker, J. C., Desmons, J. & Martinotti, G. Alpine thermal evolution in the
central and the western Alps. Geol. Soc. Spec. Publ. 45, 353–367 (1989).
44. Torsvik, T. H. et al. Phanerozoic polar wander, palaeogeography and
dynamics. Earth Sci. Rev. 114, 325–368 (2012).
45. van Hinsbergen, D. J. J. et al. Tectonic evolution and paleogeography of the
Kirsehir Block and the Central Anatolian Ophiolites, Turkey. Tectonics 35,
983–1014 (2016).
46. Okay, A. I. & Şahintürk, Ö. in Regional and Petroleum Geology of the Black
Sea and Surrounding Region (ed. Robinson, A. G.) 291–311 (American
Association of Petroleum Geologists, 1997); https://doi.org/10.1306/
M68612C15
47. Schleiarth, W. K., Darin, M. H., Reid, M. R. & Umhoefer, P. J. Dynamics of
episodic Late Cretaceous–Cenozoic magmatism across Central to Eastern
Anatolia: new insights from an extensive geochronology compilation.
Geosphere 14, 1990–2008 (2018).
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles NATurE GEoSciENcE
48. Agard, P., Omrani, J., Jolivet, L. & Mouthereau, F. Convergence history across
Zagros (Iran): constraints from collisional and earlier deformation. Int. J.
Earth Sci. 94, 401–419 (2005).
49. Okay, A. I., Zattin, M. & Cavazza, W. Apatite ssion-track data for the
Miocene Arabia–Eurasia collision. Geology 38, 35–38 (2010).
50. Rolland, Y. et al. Evidence for ~80–75 Ma subduction jump during
Anatolide–Tauride–Armenian block accretion and ~48 Ma Arabia–Eurasia
collision in Lesser Caucasus–East Anatolia. J. Geodyn. 56–57, 76–85 (2012).
51. Topuz, G., Candan, O., Zack, T. & Yılmaz, A. East Anatolian plateau
constructed over a continental basement: no evidence for the East Anatolian
accretionary complex. Geology 45, 791–794 (2017).
52. England, P. & Houseman, G. Extension during continental convergence, with
application to the Tibetan Plateau. J. Geophys. Res. 94, 17561 (1989).
53. Uyeda, S. & Kanamori, H. Back-arc opening and the mode of subduction. J.
Geophys. Res. 84, 1049 (1979).
54. Heuret, A. & Lallemand, S. Plate motions, slab dynamics and back-arc
deformation. Phys. Earth Planet. Inter. 149, 31–51 (2005).
55. Göğüş, O. H. Riing and subsidence following lithospheric removal in
continental back arcs. Geology 43, 3–6 (2015).
56. Ryan, W. B. F. et al. Global multi-resolution topography synthesis. Geochem.
Geophys. Geosyst. 10, Q03014 (2009).
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
© The Author(s), under exclusive licence to Springer Nature Limited 2021
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles
NATurE GEoSciENcE
Methods
Model description. e numerical experiments were performed using the
two-dimensional plane strain viscous–plastic nite element code, SOPALE15,
which has been used to model a range of geodynamic problems16,18,20,5759. A series
of comprehensive benchmarking experiments veried the accuracy of SOPALE, in
addition to comparisons with formal geodynamic benchmark study results15,60,61.
SOPALE uses an arbitrary Lagrangian–Eulerian mesh system to solve the
governing thermomechanical equations for viscous–plastic deformation of
two-dimensional media. The numerical code assumes the crust and mantle are
incompressible viscous-plastic materials and it solves the governing equations of
the conservation of mass, momentum and internal energy15. Density is defined as a
function of temperature:
ρ
=
ρ0
[
1
α
(
T
T0
)]
where α, ρ0 and T0 are the coefficient of thermal expansivity, reference material
density and reference temperature, respectively. At each computational node, the
deviatoric stress (
σ
ij
=
min
(
σ
y
;σ
v
)
) is determined as the lesser value of either a
yield stress σy or a viscous stress σv. In this way, materials in the models deform
dynamically, essentially according to a viscous–plastic strength envelope. This can
be expressed as:
σ
ij
=
min
(
σy;σv
)
For the frictional plastic yield stress, a pressure-dependent Drucker–Prager
yield criterion was used, which is equivalent to the Coulomb criterion in plane
strain15:
σy
=
Psin ϕ
+
c0
Here, P, ϕ and c0 are the pressure, internal angle of friction and cohesion,
respectively. The viscous stress is defined as:
σv
=
2ηe
˙
I
2
where
˙
I
2
is the second invariant of the deviatoric strain rate tensor and ηe is the
effective viscosity:
ηe=
(
3
(n+1)
2n21n
n
)
fA
1
n˙
I
(
1+n
2n)
2e(Q
nRT )
In this expression, A, f, n, Q, T and R are a viscosity parameter, scaling parameter
and power exponent, and the activation energy, temperature and ideal gas
constant, respectively (the first three of which are determined from uniaxial
laboratory experiments; see the citations in Extended Data Table 1). The term
=
3
(n+1)
2n21n
n
is necessary to convert the data from uniaxial laboratory
experiments into a state of stress that is independent of the choice of coordinate
system16.
The experiment set-up has a 100-km-thick microcontinent (30 km continental
crust and 70 km lithospheric mantle) drifting towards an intra-oceanic subduction
zone with a convergence rate of 0, 2 and 4 cm yr–1, a 90-km-thick oceanic
lithosphere (7 km oceanic crust and 83 km lithospheric mantle) and sublithospheric
mantle as deep as 660 km at the closed bottom of the box (Extended Data Fig. 1).
An imposed convergence velocity, if present, is applied at the right lithospheric
boundary of the model by introducing new lithosphere into the box. The
left boundary lithosphere is fixed. An evenly distributed outward flux of the
sublithospheric mantle is prescribed in the left and right side of the model box
to compensate for the inward flux of the lithosphere from the top-right side. The
model box has a free top surface which allows the topography to evolve naturally
during the model evolution. Erosion and deposition processes are not included in
the experiments. A portion of the oceanic lithosphere is already subducted into
the asthenosphere initially, which creates a plate driving force with progressive
sinking of the oceanic lithosphere. This slab pull, in turn, causes the drift of the
microcontinent to the subduction zone. As an initial approach, differently sized
microcontinents (120, 300, 450 and 600 km) were tested to observe the effect of
the width, if any, on the deformation of the drifting microcontinent. Regardless
of the lithosphere type, either continental or oceanic, lithospheric mantle is the
same material for every plate, namely wet Åheim dunite62. Continental crust is
represented by wet quartzite28 and the oceanic crust is a Maryland diabase29. All the
rheological and physical parameters used in the experiments are listed in Extended
Data Table 1. The mantle lithosphere on the left and right boundaries of the model
set-up has relatively high cohesion values (300 MPa) to prevent deformation at the
model box boundaries in case of the presence of imposed convergence velocities.
These cohesion values were initially chosen for practical reasons and they do not
have any significant effect on the pre-collisional extension of microcontinents, as
evidenced by our supplementary test models (Supplementary Figs 1 and 2).
Data availability
The data—the outputs of the numerical experiments—that support the findings of
this study are available at https://doi.org/10.5683/SP2/9RDQYB.
Code availability
The SOPALE modelling code was developed by the Dalhousie University
Geodynamics group; this is not a freely available open-source code.
Documentation for the code and the address of the developer research group may
be found at http://geodynamics.oceanography.dal.ca/sopaledoc.html.
References
57. Göğüş, O. H. & Pysklywec, R. N. Near-surface diagnostics of dripping or
delaminating lithosphere. J. Geophys. Res. 113, B11404 (2008).
58. Göğüş, O. H. Geodynamic experiments suggest that mantle plume caused
Late Permian Emeishan Large Igneous Province in Southern China. Int. Geol.
Rev. https://doi.org/10.1080/00206814.2020.1855602 (2020).
59. Memiş, C. et al. Long wavelength progressive plateau upli in Eastern
Anatolia since 20 Ma: implications for the role of slab peelBack and
Breako. Geochem. Geophys. Geosyst. 21, e2019GC008726 (2020).
60. Buiter, S. J. H. et al. e numerical sandbox: comparison of model results for
a shortening and an extension experiment. Geol. Soc. Lond. Spec. Publ. 253,
29–64 (2006).
61. Buiter, S. J. H. et al. Benchmarking numerical models of brittle thrust wedges.
J. Struct. Geol. 92, 140–177 (2016).
62. Chopra, P. N. & Paterson, M. S. e role of water in the deformation of
dunite. J. Geophys. Res. Solid Earth 89, 7861–7876 (1984).
63. Hirth, G. & Kohlstedt, D. L. Water in the oceanic upper mantle: implications
for rheology, melt extraction and the evolution of the lithosphere. Earth
Planet. Sci. Lett. 144, 93–108 (1996).
Acknowledgements
This research was enabled in part by support provided by SciNet and Compute Canada
(www.computecanada.ca). A modified version of the SOPALE (2000) software was used
to run numerical models. The SOPALE modelling code was originally developed by P.
Fullsack at Dalhousie University with C. Beaumont and his Geodynamics group. We
used Ö. F. Bodur’s script to plot the PTt paths. Funding for this research was provided
by an NSERC Discovery Grant (RGPIN-2019-06803)-RNP and TÜBİTAK grant
(114Y226) to G.T.
Author contributions
E.G. designed and carried out the numerical experiments and interpreted the results
with R.N.P. O.H.G. and G.T. helped with the geological background of the Alpine–
Mediterranean region. E.G. and R.N.P. developed ‘the subduction pulley’ hypothesis and
wrote the manuscript with inputs and comments from all the authors.
Competing interests
The authors declare no competing interests.
Additional information
Extended data is available for this paper at https://doi.org/10.1038/s41561-021-00746-9.
Supplementary information The online version contains supplementary material
available at https://doi.org/10.1038/s41561-021-00746-9.
Correspondence and requests for materials should be addressed to E.G.
Peer review information Nature Geoscience thanks Wim Spakman and the other,
anonymous, reviewer(s) for their contribution to the peer review of this work. Primary
Handling Editor: Stefan Lachowycz.
Reprints and permissions information is available at www.nature.com/reprints.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles NATurE GEoSciENcE
Extended Data Fig. 1 | Initial conditions of model EXP-2. The figure shows dimensions, geometry, materials, geotherm, Eulerian and Lagrangian grid
dimensions, and convergence velocity direction. The upper left side of the model box is fixed. The imposed velocity, if present, is applied at the location
of the blue arrow by introducing new oceanic lithosphere into the box. Orange arrows show evenly distributed outward flux to compensate inward flux.
The red line on the right shows the change of geotherm with depth. The inset table lists experiment numbers according to microcontinent widths and
convergence rates.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
Articles
NATurE GEoSciENcE
Extended Data Table 1 | The rheological parameters used in experiments EXP-1 to EXP-8
Material properties: 1. wet quartzite28; 2. wet Åheim dunite62; 3. Maryland diabase29; and 4. dry olivine63.
NATURE GEOSCIENCE | www.nature.com/naturegeoscience
... The geological record from the eastern Mediterranean and western Alps indicates that drifting microcontinental terranes underwent extensional deformation prior to their collision at the Tethyan subduction zone (Avigad, 1996;Gün et al., 2021;Topuz et al., 2017). It has been suggested that such pre-collisional extension may be the consequence of a "subduction pulley" (Figure 3c) where the subducted slab pulls on the lithosphere and localizes deformation at a weaker microcontinent embedded in the ocean plate (Gün et al., 2021). ...
... The geological record from the eastern Mediterranean and western Alps indicates that drifting microcontinental terranes underwent extensional deformation prior to their collision at the Tethyan subduction zone (Avigad, 1996;Gün et al., 2021;Topuz et al., 2017). It has been suggested that such pre-collisional extension may be the consequence of a "subduction pulley" (Figure 3c) where the subducted slab pulls on the lithosphere and localizes deformation at a weaker microcontinent embedded in the ocean plate (Gün et al., 2021). The syn-drift tectonics observed in the Pacific may be a plate-scale process akin to these in the Tethyan realm. ...
... For the Manihiki Plateau, it has been suggested that the extensional Suvarov and unnamed troughs and grabens reflect a change in the Pacific plate motion and slab-pull regimes (Pietsch & Uenzelmann-Neben, 2016). We agree (Gün et al., 2021). (d) Stretching factor (current ocean plateau width/initial width) evolution plots of EXP-1 to 4. Experiments show a similar plateau extension development regardless of the initial distance from trench. ...
Article
Full-text available
The paradigm of plate tectonics holds that ocean plates are rigid during drift and only experience tectonic deformation at subduction zones, but new findings from the Pacific challenge this idea. Geological and geophysical evidence from the Ontong Java, Shatsky, Hess, and Manihiki oceanic plateaux indicates that extensional deformation during plate drift is a widespread phenomenon across the Pacific plate. These anomalously thick oceanic plateaux are weaker regions of the ocean lithosphere and more prone to tectonic deformation. Numerical geodynamic models demonstrate that a slab pull force from distant subduction plate boundaries can be effectively transmitted to oceanic plateaux through strong ocean lithosphere and cause substantial extension during plate drift. Our findings reveal that a wide expanse of the Pacific has experienced syn‐drift plate tectonics linked to pull from the western Pacific subduction factory.
... Subsequently, to examine the effects of convergence velocity (u c ), we perform several experiments with values that are lower than in the reference experiment (4.5 cm yr 1 ): 3.0, 1.5, and 0.5 cm yr 1 (models 8-10). It is well known that in natural collisional settings, the presence of a small continental block (microcontinent) extending along the passive margin can add complexity not only to the architecture of the original passive margin but also to the resulting collisional orogen (Eskens et al., 2024), potentially affecting the processes of slab breakoff and tear propagation (Gün et al., 2021;Handy et al., 2010). We therefore complete our modeling set with experiments containing a microcontinent for both convergence-perpendicular (i.e., α is 0°; model 11) and oblique passive margin (i.e., α is 7.5°and 15°; models 12-13). ...
... In contrast to all previous experiments, in which the collision phase always begins after the complete detachment of the entire oceanic plate along strike, model 11 (passive margin obliquity of 0°in the presence of the microcontinent; Figure 7) shows an earlier collision between the microcontinental block and the right continental plate (Figure 7b-ii), when the tearing of subducting slab has not yet reached its terminal point in the back segment of the convergence zone (Figures 7b-i). In other words, the presence of the microcontinent leads to a synchronous continental collision and slab breakoff, as also reported in a previous study by Gün et al. (2021). Moreover, the existence of the microcontinent appears to delay slab breakoff (by ∼0.86 Myr) in the back segment compared to the front segment, which includes the microcontinent area. ...
Article
Full-text available
The horizontal propagation of slab detachment (slab tearing) is known to control lateral migration of the mountain uplift along the collisional belt. However, along‐strike differential collision due to an oblique passive margin geometry can make the topography response more complex. In this study, we employ 3D thermomechanical modeling to distinguish between the lateral migration of the mountain topography driven by slab tearing and oblique continental collision itself. In our models, slab breakoff is triggered by the transition from oceanic to continental subduction, occurring earlier on one side of the passive margin than on the other due to the initial oblique configuration. However, once slab breakoff has begun, it spreads horizontally in the form of tearing at high velocity (∼38–118 cm yr⁻¹), and associated topographic uplift also propagates with the same velocity. In contrast, the along‐strike migration of subsequent continental collision and related topographic uplift propagation is typically much slower (∼2–34 cm yr⁻¹). Similarly, the vertical magnitude of surface uplift caused by slab tearing is higher (up to 10 mm yr⁻¹) than the following collision phase (<4 mm yr⁻¹). The parametric analysis reveals that slab tearing velocity and the associated horizontal propagation of mountain uplift depends on obliquity angle and slab age, whereas the migration of collision‐induced topographic growth is controlled by the convergence velocity and obliquity angle. Finally, we show that presence of microcontinental block detached from the passive margin leads to spatial and temporal transition from horizontal to vertical slab tearing and more intense syn‐collisional mountain building.
... Subduction of the oceanic lithosphere into the mantle exerts slab pull force on the trailing plate, the prime force that drives plate tectonic motions (Forsyth & Uyeda, 1975). In general, subduction may continue until the trailing passive margin and continental lithosphere enter the trench and some 5-15 Myr later, detachment of slab (i.e., break-off) occurs, and the subduction is terminated (Gün et al., 2021;Hafkenscheid et al., 2006;Wortel & Spakman, 2000). The termination of subduction has far-reaching geodynamic consequences, one of which is the initiation of changes in plate motions that may ignite a plate tectonic chain reaction (Gürer et al., 2022). ...
... These geological as well as seismic tomography observations suggest that the down-going oceanic slab has detached from the trailing, most likely stretched continental, Sinai Microplate. Such slab tearing along the oceanic-continental transition zone at around 200 km depth has previously been predicted by numerical models (Gün et al., 2021;van Hunen & Allen, 2011). We note that although detached at depth from the leading oceanic slab, the tomographic images suggest that the shallow subducted continental lithosphere (i.e., <200 km depth) is still being attached to the subducting oceanic lithosphere found west of Cyprus (part of the Nubian Plate). ...
Article
Full-text available
The detachment (i.e., break‐off) of down‐going subducting oceanic slabs is a major geodynamic event with far‐reaching consequences, one of which is the reduction of the slab pull force acting on the trailing plate. We investigate the motion of the Sinai Microplate where a recent (∼1 Myr ago) slab break‐off occurred along its sole converging plate boundary (Cyprian Arc) with the overriding Anatolia Microplate. Based on new bathymetric mapping, high‐resolution seismic reflection imaging, geodetic and earthquake data, we show that Sinai is actively moving in a northwest direction with respect to Nubia. Our results indicate that despite the recent slab break‐off, Sinai has and is still being pulled (or pushed) toward the overriding Anatolia Microplate. The continued convergence possibly occurs because of a persistent slab pull force, a suction force induced by the down‐going detached slab and/or by the upper mantle flow induced by the Afar Plume.
... Based on our seismic models and other geophysical evidences, we propose that the anisotropic structures observed in the SCB may demarcate a set of continental fragments that were accreted through successive orogenic events. Such continental fragments exhibit different tectonic responses to long-term evolution (e.g., Heron et al., 2023;Gün et al., 2021), and our new multiscale seismic approach presented in this study illustrates its potential to provide deep constraints that can enhance comprehension of these processes. ...
Article
Full-text available
... Accretion and subduction zone jumps are impacted by the width and rheological structure of allochthonous terranes, the thickness of the crust, convergence rates, boundary convergence forces, mantle convection, pre-existing weak zones, rheological strength and the thermal structure of passive continental margins, and the geometry of subduction zones (e.g., Cloos, 1993;Nikolaeva et al., 2010Nikolaeva et al., , 2011Marques et al., 2013Marques et al., , 2014Buiter, 2012, 2014;Moresi et al., 2014;Vogt and Gerya, 2014;Leng and Gurnis, 2015;Wan et al., 2019;Kiss et al., 2020;Gün et al., 2021;Yan et al., 2021Yan et al., , 2022Zhong and Li, 2022). However, past studies only considered the dynamics of continental accretion (e.g., Moresi et al., 2014), the subduction initiation of the passive continental margin without the collision process (e.g., Marques et al., 2013Marques et al., , 2014, or a single phase of subduction zone jump (e.g., Yan et al., 2021). ...
Article
Full-text available
The accretion of future allochthonous terranes (e.g., microcontinents or oceanic plateaus) onto the southern margin of Asia occurred repeatedly during the evolution and closure of the Tethyan oceanic realm, but the specific geodynamic processes of this protracted convergence, successive accretion, and subduction zone initiation remain largely unknown. Here, we use numerical models to better understand the dynamics that govern multiple terrane accretions and the polarity of new subduction zone initiation. Our results show that the sediments surrounding the future terranes and the structural complexity of the overriding plate are important factors that affect accretion of multiple plates and guide subduction polarity. Wide (≥400 km) and buoyant terranes with sediments behind them and fast continental plate motions are favorable for multiple unidirectional subduction zone jumps, which are also referred to as subduction zone transference, and successive terrane-accretion events. The jumping times (∼3−20+ m.y.) are mainly determined by the convergence rates and rheology of the overriding complex plate with preceding terrane collisions, which increase with slower convergence rates and/or a greater number of preceding terrane collisions. Our work provides new insights into the key geodynamic conditions governing multiple subduction zone jumps induced by successive accretion and discusses Tethyan evolution at a macro level. More than 50 m.y. after India-Asia collision, subduction has yet to initiate along the southern Indian plate, which may be the joint result of slower plate convergence and partitioned deformation across southern Asia.
... Based on our seismic models and other geophysical evidences, we propose that the anisotropic structures observed in the SCB may demarcate a set of continental fragments that were accreted through successive orogenic events. Such continental fragments exhibit different tectonic responses to long-term evolution (e.g., Heron et al., 2023;Gün et al., 2021), and our new multiscale seismic approach presented in this study illustrates its potential to provide deep constraints that can enhance comprehension of these processes. ...
Article
Full-text available
The lithospheric architecture of the South China Block (SCB) is crucial to understanding the formation and evolution of this distinctive and highly reworked continental lithosphere with over 3 billion years of tectonic history. However, due to a lack of high‐resolution geophysical datasets, a detailed picture of the SCB lithosphere is absent, and fundamental questions regarding its formation, assembly, and subsequent reworking processes are actively debated. Assuming that unique deformation patterns due to such tectonic processes can be mapped by seismic anisotropy, we present a new crustal radially anisotropic shear‐wave velocity model along a 1500‐km seismic transect that spans the major tectonic domains of the SCB to characterize the past deformation processes. The new seismic models show significant lateral variations in seismic anisotropy and velocity, suggesting that the SCB consists of several separated (micro)continental blocks or terranes that likely have different origins and have survived the prolonged deformation history since the early formation of these continental fragments. Combining available geophysical datasets, we link individual crustal domains of distinct anisotropy to constrain the multiphase deformation processes of the SCB, including the early formation of the Proto‐Yangtze and Cathaysia Blocks, the assembly of the SCB, and the subsequent reactivation of the interior and extensive deformation that have formed the Basin‐and‐Range style tectonics in the Cathaysia Block. We suggest that relict continental fragments have played critical roles in the formation and reactivation of the SCB lithosphere.
... Despite advances in understanding the coupling between mantle convection patterns and plate motions (e.g. Zhong et al. 2007Zhong et al. , 2008Li and Zhong 2009;Yoshida andSantosh 2011, 2014;Yoshida 2016;Heron 2019;Gün et al. 2021;Langemeyer et al. 2021;Wolf and Evans 2021), the tectonic and kinematic descriptions of these geodynamic scenarios in the context of supercontinent cycles are lacking. Here, we propose new tectonic definitions for interior and exterior oceans that acknowledge the improved understanding of coupled supercontinent and convective mantle dynamics, thus allowing for the consistent identification of supercontinent formation by introversion and/or extroversion. ...
Article
Supercontinent amalgamation is described by the end-member kinematic processes of introversion - closure of interior oceans; extroversion - closure of exterior oceans; or orthoversion - amalgamation 90° from the centroid of the previous supercontinent. However, supercontinent formations are often ascribed to contradictory mechanisms; for example, Pangea has been argued to have formed by introversion from Pannotia/Gondwana, and extroversion from Rodinia. Conflicting interpretations arise partly from attempting to define oceans as interior or exterior based on paleogeography, or the age of the oceanic lithosphere relative to the time of supercontinent breakup. We define interior and exterior oceans relative to the external subduction ring, and associated accretionary orogens that surround amalgamated supercontinents. All oceans within the continental dominated cell and internal to the subduction ring are interior oceans. The exterior ocean is separated from the interior oceans by the subduction ring and bordered by external accretionary orogens. Wilson cycle tectonics dominate the interior continental cell, conversely, subduction of the exterior ocean is doubly vergent and lacks continent-continent collision. For the exterior ocean to close, the subduction ring must collapse upon itself, leading to the collision of external accretionary orogens. Employing this definition, Rodinia formed by extroversion, but all other supercontinents formed by introversion.
Article
Full-text available
The Eastern Anatolian Plateau (EAP), approximately 2000 m above sea level, is located between the Eastern Pontides to the north, the Arabian Platform to the south, and the Iranian Plateau to the east. It is characterized by approximately 6 km-thick Maastrichtian to Quaternary volcano-sedimentary cover which unconformably overlies continental and oceanic basement units. Overall, the outcrops of the pre-Maastrichtian basement are rare and include both continental and oceanic units. This led to drastically different interpretations of the nature of the pre-Maastrichtian basement as (i) the oceanic accretionary complex or (ii) continental crust and overlying ophiolitic mélange. This synthesis deals with the relationships between continental and oceanic units in light of the recent geological, geophysical, and geochemical studies. Geophysical studies consistently indicate the presence of a spatially thickened continental crust with a lateral variation ranging from 38 to 52 km. Seismological models estimate lithospheric thicknesses to be in the range of 70–80 km, suggesting the presence of a rather thinned lithosphere. The pre-Maastrichtian continental units include late Cretaceous high-T/low-P metamorphic rocks, which are intruded by late Cretaceous basic to acidic intrusions at the base. Protoliths of the high-T/low-P metamorphic rocks can be closely correlated with those of the Anatolide-Tauride Block, probably representing the metamorphosed equivalents of the Anatolide-Tauride Block. The continental crustal nature is also testified by the presence of metasyenite to -granite with igneous crystallization ages of 430–440 Ma. The Late Cretaceous ophiolitic mélanges with locally intact tracks of ophiolite and overlying forearc deposits tectonically sit over the Late Cretaceous high-T/low-P metamorphic rocks. These ophiolitic mélanges probably form part of the North Anatolian ophiolitic belt, related to the İzmir-Ankara-Erzincan suture. Maastrichtian to Quaternary volcano-sedimentary rocks overlie both the continental crustal and tectonically overlying oceanic units, representing probably collisional and postcollisional basin fills. Available geological, geochemical, and geophysical data suggest a pre- Maastrichtian basement that comprises a continental crustal domain and an overlying ophiolitic mélange beneath the Masstrichtian to Quaternary cover. Keywords: Eastern Anatolian Plateau, accretionary complex, continental crust, high-T/low-P metamorphism, Turkey
Article
Full-text available
Abstract: The Eastern Anatolian Plateau (EAP), approximately 2000 m above sea level, is located between the Eastern Pontides to the north, the Arabian Platform to the south, and the Iranian Plateau to the east. It is characterized by approximately 6 km-thick Maastrichtian to Quaternary volcano-sedimentary cover which unconformably overlies continental and oceanic basement units. Overall, the outcrops of the pre-Maastrichtian basement are rare and include both continental and oceanic units. This led to drastically different interpretations of the nature of the pre-Maastrichtian basement as (i) the oceanic accretionary complex or (ii) continental crust and overlying ophiolitic mélange. This synthesis deals with the relationships between continental and oceanic units in light of the recent geological, geophysical, and geochemical studies. Geophysical studies consistently indicate the presence of a spatially thickened continental crust with a lateral variation ranging from 38 to 52 km. Seismological models estimate lithospheric thicknesses to be in the range of 70–80 km, suggesting the presence of a rather thinned lithosphere. The pre-Maastrichtian continental units include late Cretaceous high-T/low-P metamorphic rocks, which are intruded by late Cretaceous basic to acidic intrusions at the base. Protoliths of the high-T/low-P metamorphic rocks can be closely correlated with those of the Anatolide-Tauride Block, probably representing the metamorphosed equivalents of the Anatolide-Tauride Block. The continental crustal nature is also testified by the presence of metasyenite to -granite with igneous crystallization ages of 430–440 Ma. The Late Cretaceous ophiolitic mélanges with locally intact tracks of ophiolite and overlying forearc deposits tectonically sit over the Late Cretaceous high-T/low-P metamorphic rocks. These ophiolitic mélanges probably form part of the North Anatolian ophiolitic belt, related to the İzmir-Ankara-Erzincan suture. Maastrichtian to Quaternary volcano-sedimentary rocks overlie both the continental crustal and tectonically overlying oceanic units, representing probably collisional and postcollisional basin fills. Available geological, geochemical, and geophysical data suggest a pre- Maastrichtian basement that comprises a continental crustal domain and an overlying ophiolitic mélange beneath the Masstrichtian to Quaternary cover. Keywords: Eastern Anatolian Plateau, accretionary complex, continental crust, high-T/low-P metamorphism, Turkey
Article
Full-text available
Subduction initiation is a pivotal process in plate tectonics. Models of subduction initiation include the collapse of passive margins, oceanic transform faults, inversion of oceanic core complexes, and ridge failure but have ignored the potential effects of continental crust relicts within the oceanic crust. In this paper, we explore the role of microcontinents on subduction initiation through two-dimensional thermo-mechanical numerical modeling. We consider three scenarios with variable ages of oceanic crust surrounding the microcon-tinent and parametrically examine the microcontinent characteristics (size, crustal thickness , thermal gradient, and rheology), oceanic plate age, and convergence rates. Results suggest that moderate-size (≥300 km) microcontinents can nucleate subduction initiation at the junction between continental and oceanic plates. A large part of the microcontinent would be dragged into the subduction zone, and the subsequent asthenosphere upwellings would incorporate part of the microcontinent. Our numerical models add a new hypothetical scenario for subduction initiation, especially for those places where a young and buoyant plate subducts beneath an older and denser oceanic plate. Moreover, they can explain the origin of exotic crust materials and ultrahigh-pressure minerals in supra-subduction zone ophiolites.
Article
Full-text available
Stratigraphic, petrological and geophysical studies suggest that the Late Permian (~ 260 Ma) Emeishan Large Igneous Province in southern China may be formed by mantle plume activity. However, the plume impingement hypothesis remains controversial since interpretations based on volcano-stratigraphic analyses around plume induced domal uplift/inner zone suggest that the volcanism occurred under submarine environment rather than elevated sub-aerial (above sea level) conditions, usually associated with the dynamic topography effects of the ascending mantle plumes. Here, 2-D numerical and 3-D scaled laboratory (analogue) plume experiments are used to explore the coupled dynamics of plume-mantle-lithosphere interaction and their evolution of surface topography characteristics. Experimental results show that the initial (plume incubation) phase is characterized by rapid, transient domal uplift above the plume axis, subsequently, as plume head flattens, there is short wavelength topographic variation (ie. subsidence and uplift occurs synchronously) due to the shear stress imposed onto the base of the lithosphere and loss of gravitational potential energy. The surface depressions predicted by the plume models, next to the plume axial/inner/uplift zone, may explain the deposition of submarine volcanics at Lake Erhai, Dali in the western side and Xiluo and Daqiao in the eastern side, which may resolve the plume controversy for the formation of Emeishan Large Igneous Province. Notably, while experimental results from these two different techniques show some differences, (e.g much bigger plume head for the laboratory experiment), the overall characteristics of the predictions have robust similarities. For instance, the extension above the plume axis may explain the enigmatic cause of the Panxi rift system, in the middle of the inner zone where giant dyke swarms radiate from, and mafic magma underplatings in the lower crust has been described by seismological studies.
Article
Full-text available
Microcontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions, and a “proto‐microcontinent,” in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back‐arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and their formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for their formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in‐situ subduction‐related microcontinents is meager (an area of 0.56% and 0.28% of global, non‐cratonic, continental crustal area and crustal volume, respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.
Article
Full-text available
Stratigraphic evidence is used to interpret that the East Anatolian Plateau with 2 km average elevation today was below sea level ~20 Ma and uplift began in the northern part. The presence of voluminous volcanic rocks/melt production across the plateau—younging to the south—corroborates geophysical interpretations (e.g., high heat flow and lower seismic velocities) that suggest progressive removal of the slab subducting under the Pontides. Here, we conduct numerical experiments that investigate the change in the surface uplift as a response to slab peel‐back and potential break‐off processes under subduction‐accretionary complexes as well as continental lithosphere. Model results show similar types of tectonic behavior and magnitudes of uplift‐subsidence in both oceanic and continental removal processes, and they satisfactorily explain 1.5 km of plateau rise and a ~280 km wide asthenospheric upwelling zone beneath Eastern Anatolia over 18 Myr timescale. Parametric investigation for varying plate strength and convergence velocities show that such model parameters control the amount of surface uplift (1 to 3 km), the width of the asthenospheric upwelling zone, and the potential timing/depth of break‐off of the steepening/peeling slab. Experiments show that slab break‐off develops during the terminal phase, which may correspond to only a few million years ago. Therefore, the long wavelength plateau uplift and magmatism over the Eastern Anatolian‐Lesser Caucasus region since 20 Ma is controlled by progressive slab peel‐back and resulting mantle dynamics. The slab break‐off process (if it happened) has yet an indiscernible role.
Article
Full-text available
We compiled geochronology data from 87 published studies within the Anatolia orogen (32.5°E–44°E) to investigate the spatial and temporal patterns of continental magmatism during the final stages of Neotethys Ocean closure. The number and diversity of studies compiled here collectively provide a thorough characterization of magmatism (>700 ages) in the Anatolia orogen since the Late Cretaceous (ca. 100 Ma). Our new compilation reveals that magmatism was episodic and occurred in three distinct magmatic episodes punctuated by two orogen-wide magmatic lulls. We used regional-scale insights into the timing, location, composition, and evolution of magmatism revealed by our compilation to evaluate the tectonic and geodynamic processes responsible for each widespread magmatic lull, and to test and refine existing geodynamic models for Anatolia. We interpret the first orogen-wide magmatic lull (ca. 72–58 Ma) to have been the result of Maastrichtian to Paleocene collision of the Kırşehir and Anatolide-Tauride blocks with the Pontides arc along the Izmir-Ankara-Erzincan suture zone and synchronous collision of the Bitlis-Pütürge massif with the southern-margin of the Anatolide-Tauride blocks along the Bitlis suture zone. Magmatic quiescence during the second magmatic lull (ca. 40–20 Ma) was variably related to terminal subduction and Arabia slab break off along the Bitlis suture zone in the east, and Cyprus slab flattening due to postcollisional southward retreat of the Cyprus trench in the west, each triggered by middle to late Eocene Arabia collision. Postcollisional Neogene–Quaternary magmatism was most likely caused by lithospheric delamination and slab tearing/rollback in the Eastern and Central Anatolia volcanic provinces, respectively.
Article
Full-text available
Numerical modelling results indicate that mantle lithosphere rheology can influence the pressure-temperature-time (P-T-t) trajectories of continental crust subducted and exhumed during the onset of continental collision. Exhumation of ultra-high pressure (~35 kbar)/high temperature (~750C) metamorphic rocks is more prevalent in models with stronger continental mantle lithosphere (e.g., dry) whereas high pressure (~9-22 kbar)/low temperature (350C – 630C) metamorphic rocks occur in models with weaker rheology (e.g., hydrated) for the same layer. In the latter case, the buried crustal rocks can remain encased in ablatively subducting mantle lithosphere, reach only moderate temperatures and exhume by dripping/detachment of the lithospheric root. In this transition from subduction to a dripping style of ‘vertical tectonics’, burial and exhumation of crustal rocks are driven without imposed far-field plate convergence. The model results are compared against thermobarometric P-T estimates from major (ultra-)high pressure metamorphic terranes. We propose that the exhumation of high pressure/low temperature metamorphic rocks in Tavşanlı and Afyon Zones in western Anatolia may be caused by viscous dripping of mantle lithosphere suggesting a weaker continental mantle lithosphere, whereas (ultra-)high pressure exhumation (e.g., Dabie Shan-eastern China and Dora Maira-western Alps) may be associated with plate-like subduction. In the latter case, the slab is much stronger and deformation is localized to the subduction interface along which rocks are buried to >100 km depth before they are exhumed to the near surface.
Poster
Full-text available
The uplift of Central Anatolia over the last 8-10 m.y. is associated with a broad 1 km plateau, with higher elevations at the north (Pontides) and the south (Taurides) margins. A number of geophysical, petrological and geological evidence suggests that the Central Anatolian (Kırşehir) arc root was removed 10 Myrs ago. To investigate the role of potential arc root removal process in the style of drip tectonics, a series of numerical experiments are conducted. Model predictions are tested against a range of geological and geophysical observables from Central Anatolia. Numerical models demonstrate that an arc root removal event has a distinct spatial and temporal effect in the crust resulting in plateau uplift > 1 km. The vertical loading and crustal deformation change during drip evolution. Lithospheric rheology and plate convergence can significantly modify the magnitude and length scale of the uplift. This drip tectonics process is in good agreement with the geologic evidence for the broad plateau uplift of Central Anatolia, as well as seismic data showing thin or missing lithosphere and a remnant structure characteristic of a removal event. While this research focuses on the Late Cenozoic geodynamic evolution of Central Anatolia, the outcome of this work may have general implications for the development of other orogenic areas where compelling documentation on drip tectonics has been interpreted (e.g., Central Andes, Tibet, Sierra Nevada, Colorado plateau, Mediterranean Alpides).
Article
Full-text available
Lithospheric drips have been interpreted for various regions around the globe to account for the recycling of the continental lithosphere and rapid plateau uplift. However, the validity of such hypothesis is not well documented in the context of geological, geophysical and petrological observations that are tested against geodynamical models. Here we propose that the folding of the Central Anatolian (Kırşehir) arc led to thickening of the lithosphere and onset of “dripping” of the arc root. Our geodynamic model explains the seismic data showing missing lithosphere and a remnant structure characteristic of a dripping arc root, as well as enigmatic >1 km uplift over the entire plateau, Cappadocia and Galatia volcanism at the southern and northern plateau margins since ~10 Ma, respectively. Models show that arc root removal yields initial surface subsidence that inverts >1 km of uplift as the vertical loading and crustal deformation change during drip evolution.
Article
Full-text available
The East Anatolian plateau (Turkey) is extensively covered by Neogene to Quaternary volcanic-sedimentary rocks, and is characterized by an attenuated lithospheric mantle. Its pre-Neogene basement is commonly considered to consist entirely of Late Cretaceous to Oligocene oceanic accretionary complexes, formed at the junction of several continental blocks. Here we report on three main exposures of the pre-Neogene basement in this region. The exposed areas consist mainly of amphibolite- to granulite-facies metamorphic rocks, including marble, amphibolite, metapelite, metagranite, and metaquartzite. An upper amphibolite– to granulite-facies domain is equilibrated at ~0.7 GPa and ~800 °C at 83 ± 2 Ma (2). U-Pb dating of magmatic zircons from the metagranite yielded a Late Ordovician–early Silurian protolith age (444 ± 9 Ma, 2). The detrital zircons from one metaquartzite point to a Neoproterozoic–early Paleozoic provenance. Ophiolitic rocks tectonically sit on the metamorphic rocks. Both the metamorphic and ophiolitic rocks are in turn unconformably covered by lower Maastrichtian clastic rocks and reefal limestones, suggesting that the whole exhumation process and juxtaposition with the ophiolitic rocks had occurred by the early Maastrichtian. Several lines of evidence, such as (1) the absence of any indication of a former high-pressure metamorphism in the metamorphic rocks, (2) the allochthonous nature of the ophiolitic rocks, (3) the presence of metagranite with a Late Ordovician–early Silurian protolith age, and (4) the Neoproterozoic–early Paleozoic provenance of detrital zircons in the metaquartzite (in contrast to the dominance of late Paleozoic–Mesozoic crystalline rocks in the adjacent continental blocks) indicate a substantial component of continental basement beneath the Neogene to Quaternary cover. Thus, the loss of the lithospheric mantle probably resulted from lithospheric foundering processes beneath the plateau, rather than just slab steepening and break-off.
Article
Turcotte, D.L. and Emerman, S.H., 1983. Mechanisms of active and passive rifting. In: P. Morgan and B.H. Baker (Editors), Processes of Continental Rifting. Tectonophysics, 94: 39–50. In this paper we obtain two solutions relating to the alternative active and passive hypotheses for continental rifting. Active rifting assumes the impingement of a mantle plume on the base of the continental lithosphere. We determine the rate of lithosphere thinning due to this impingement. We conclude that it takes 50–75 million years to thin the continental lithosphere to the base of the crust; the long length of time required appears to rule out this lithospheric erosion mechanism as a viable mechanism for complete lithospheric thinning. We suggest that diapiric penetration is the mechanism by which hot mantle rock reaches the base of the continental crust at a rift. We have also obtained values for the tensional stresses generated by the diapiric penetration of hot asthenospheric rock into the lithosphere. The stress levels are obtained as functions of lithospheric and crustal thinning factors. These stresses may lead to rift propagation and the splitting of a continent.