Continental collision mountain belts: the Arabia-Eurasia system

1
Continental collision mountain belts the
Arabia-Eurasia system
Paolo Ballato, 11-02-2009
2
Today's class contents
1) Continental collision a brief outlook
(definition, causes, implications..)
2) How is tectonics deformation accommodated
within the Arabia-Eurasia collision zone?
3) A case study from the Alborz mountains, an
intracontinental mountain belt linked to
Arabia-Eurasia collision (the record from
foreland basin deposits)
a) When did the deformation related to
continental collision
start in the Alborz mountains?
b) How did deformation evolve?
c) What can we learn from foreland basin deposits
(i.e. climate vs tectonic) ?
3
PART 1
1) Continental collision a brief outlook
(definition, causes, implications..)
4
Pre-collisional setting
Lower plate
Upper plate
Prior to a continental collision, the landmasses
are separated by oceanic crust, formed during an
earlier episode of sea-floor spreading As the
continental blocks converge, the intervening sea
floor (lower plate) is subducted beneath the
upper plate The descending oceanic slab
generates a volcanic arc Upper plate deformation
is limited (tectonics stress is not transferred
far away from trench) and shortening is mainly
accommodated along plates interface (accretionary
wedge)
India-Asia convergence rate decreased from 160
to 50 mm/yr in the last 70Ma
www2.bc.edu/kafka/ge180.f03/PT_4.ppt
5
Collisional setting
As the continental lithosphere of the lower plate
approaches the upper plate subduction terminates,
suturing occurs, and continents are
amalgamated Tectonics stress is progressively
transferred to the upper plate, where deformation
is accommodated across a broad region (thousands
of km from the suture zone). Possibly
reactivation of structures forming old orogenic
belts A fold and thrust belt develops in the
lower plate Mountain range/ranges are formed and
several km of crust can be exhumed
www2.bc.edu/kafka/ge180.f03/PT_4.ppt
6
Why does continental collision occur?

• Oceanic lithosphere (3.3-3.2 g/cm3)
• crust (density ca. 2.9 g/cm3)
• mantle (density ca. 3.3 g/cm3)

• Continental lithosphere (3.1-3.2 g/cm3 )
• crust (density ca. 2.7 g/cm3)
• mantle (density ca. 3.3 g/cm3)

Cloos, 1993
Oceanic lithosphere is denser than continental
lithosphere, so it tends to sink (subduction)
into the asthenosphere when convergence takes
place
When the continental crust reach the subduction
zone the buoyancy forces oppose resistance to the
slab pull forces subduction ends and the
pulling slab will break off sinking into the
asthenosphere
7
How is it tectonics deformation absorbed in the
upper plate?
1) Crustal thickening (exhumation)
2) Extrusion tectonics (lateral transport of
crustal blocks)
Tapponnier et al., 1982, 1986
8
3) Large scale folding (lithospheric buckling)
Burg et al, 1999
Difficult to demonstrate.is it an efficient
mountain building process?
4) Intra-collision zone subduction (subduction
of denser microplates located in the collision
zone)
Matte et al, 1997
9
PART 1..Summarizing
1) Continental collision occurs when plate
convergence cannot absorbed anymore via
subduction process
2) Continental collision takes place because
buoyancy forces do not allow large amount of
continental subduction
3) During continental collision tectonics
deformation is not anymore localized along the
plate margin (accretionary wedge), but affects a
large area in the upper plate and propagate
cratonward in the lower plate (fold and thrust
belt)

• 4) Deformation in the upper plate is absorbed via
  
• Crustal thickening
• Lateral extrusion of rigid blocks
• Possibly via lithospheric buckling
• Intra-collision zone subduction

5) Intracontinental deformation is generally
localized along crustal weakness (i.e. old
orogenic belts)
10
PART 2
2) How is tectonics deformation accommodated
within the Arabia-Eurasia collision zone?
11
The Arabia-Eurasia collision zone
Caucasus
Black Sea
Eurasia
Aspheron
Casp
Anatolia
T-I plateau
Kopeh Dagh
Alborz
Aegean
Central Iran
Cyprus
Hellenic
Zagros
Lut
Helmand
Nubia
Makran
Red Sea
Arabia
Owen FZ
Gulf of Aden
India
Eastern African Riften
Somalia
12
Arabia-Eurasia system from oceanic subduction to
continental collision
Opening of the Gulf of Aden
McQuarrie et al., 2006
13
Active tectonics of the Arabia-Eurasia collision
zone seismicity
Reilinger et al., 2006
14
Active tectonics of the Arabia-Eurasia collision
zone quantifying present-day deformation with
GPS data
Subduction of a denser microplate (Southern
Caspian Basin)
Westward extrusion of Anatolia (escape tectonics)
Crustal thickening
Reilinger et al., 2006
15
Active deformation in North Iran
Alborz
Intra-collision zone subduction
South Caspian Basin crust is thinner and denser
than adjacent regions
Brunet et al., 2003
Guest et al., 2007
16
The Arabia-Eurasia collision zone kinematics
model GPS based
Black numbers 3 strike (3) dip slip White
numbers plate velocities
Reilinger et al., 2006
17
Active deformation takes place along crustal
heterogeneity (i.e. old suture zone and orogenic
belts)
Horton et al., 2008
18
PART 2..Summarizing
1) Deformation is accommodated along seismic
belts (mountain chains and large intracontinental
strike-slip faults) bounding aseismic blocks

• 2) Deformation in the upper plate is absorbed via
  
• Crustal thickening (Zagros, Alborz, Caucasus,
  etc.)
• Lateral extrusion of rigid blocks (Anatolia and
  smaller crust blocks)
• Possibly via lithospheric buckling (Alborz-South
  Caspian basin system?)
• Intra-collision zone subduction (South Caspian
  basin)

3) Intracontinental deformation is localized
along crustal weakness like inherited structures
(paleosutures and old orogenic belts)
19
PART 3
3) A case study from the Alborz mountains, an
intracontinental mountain belt linked to
Arabia-Eurasia collision (the record from
foreland basin deposits)
a) When did the deformation related to
continental collision start in the Alborz
mountains?
b) How did deformation evolve?
c) What can we learn from foreland basin deposits
(i.e. climate vs tectonic) ?
20
Foreland basin anatomy and sedimentary facies
distribution
Grain-size decrease
Tectonic load (crustal shortening and thickening
exhumation of crustal section)
Plate deflection (flexural subsidence)
DeCelles and Giles, 1996
Coarse-grained facies are generally confined in
proximity of the fold and thrust belt
front. However in some cases they can prograde
into the foreland for tens of kmWhy?
21
Lateral and vertical sedimentary facies evolution
in a foreland basin system syn-thrusting
progradation of coarse-grained facies
Stable thrust front
Progradation of gravel facies during a major
thrusting phase
Distance from the thrust front (km)
Burbank et al., 1988
22
Lateral and vertical sedimentary facies evolution
in a foreland basin system post-thrusting
progradation of coarse-grained facies
Time (Ma)
Flemings and Jordan 1990
23
Lateral and vertical sedimentary facies evolution
in a foreland basin system climatic forcing
Zhang et al., 2001
24
Simplified tectonostratigraphy of the Alborz
Mountains
36 Ma (end of magmatism)
The Alborz range is characterized by a complex
crustal fabric, with inherited structures related
to both compression and extension since Paleozoic
time
Guest et al., 2006
25
Central Alborz Mountains
ca. 6 mm/yr of shortening
ca. 4 mm/yr of left-lateral shearing
Modified after Geological maps of Tehran, Semnan,
Saveh, Sari, Qazvin and Amol 1 250 000,
Geological Society of Iran, and Guest et al., 2006
26
Eyvanekey stratigraphic section
ASTER satellite image, bands 731-RGB
27
Unit 1
Unit 1C braided river dep. system
N
S
Unit 1B distal river dep. system
Unit 1A playa lake dep. system
S
N
28
Unit 2
Unit 2B braided river dep. system
S
N
29
Unit 3
Unit 3C alluvial fan dep. system
3C
3B
30
Stratal geometric relationship
ASTER satellite image, bands 321-RGB
31
Magnetostratigraphy
Main prerequisites
Normal Polarity
Fine-grained lithologies
Continuous sedimentation
Reverse Polarity
Independent age constrains
Reference MPTS
32
Magnetostratigraphy
In 75 of samples a Characteristic Remanent
Magnetization (ChRM) was isolated
Ballato et al., 2008
33
Magnetostratigraphic Correlation
Ballato et al., 2008
34
Sediment accumulation rates
Coarse-grained sed.
Fine-grained sed.
Coarse-grained sed.
Fine-grained sed.
Coarse-grained sed.
Fine-grained sed.
Ballato et al., 2008
35
6.2 Ma
PART 3..Concluding
Sed.acc.rate 0.65 mm/yr
7.5 Ma
a) When did deformation related to the
Arabia-Eurasia continental collision start in the
Alborz mountains?
Sed.acc.rate 0.58 mm/yr
At ca. 17.5 Ma the basin records a sharp increase
in sedimentation rate (0.04 to 0.58 mm/yr). This
increase reflect onset of flexural subsidence
related to crustal shortening and thickening
17.5 Ma
Sed.acc.rate 0.04 mm/yr
36 Ma
36
Tectonic vs climate retrogradation of
coarse-grained facies
Increase in slip rate 100 increase in
subsidence and sed. flux
Decrease in precipitation -50 decrease in sed.
flux
Post-perturbation
Post-perturbation
Pre-perturbation
Pre-perturbation
Pre-perturbation
Post-perturbation
Pre-perturbation
Pre-perturbation
Facies retrogradation
Facies retrogradation
Sediment flux
Sediment flux
Time (Myr)
Time (Myr)
Time (Myr)
Distance from fault (Km)
Time (Myr)
Distance from fault (Km)
In both cases retrogradation of sedimentary
facies is recorded in the basin. However, when
precipitation decrease the sedimentation rate
does not change since there is no perturbation in
subsidence
Densmore et al., 2007
37
Tectonic vs climate progradation of
coarse-grained facies
Decrease in slip rate -50 decrease in
subsidence and sed. flux
Increase in precipitation 50 increase in sed.
flux
Post-perturbation
Post-perturbation
Pre-perturbation
Pre-perturbation
Pre-perturbation
Post-perturbation
Pre-perturbation
Post-perturbation
Facies progradation
Facies progradation
Time (Myr)
Sediment flux
Sediment flux
Time (Myr)
Time (Myr)
Distance from fault (Km)
Time (Myr)
Distance from fault (Km)
In both cases progradation of sedimentary facies
is recorded in the basin. However, when
precipitation increase the sedimentation rate
does not change since there is no perturbation in
subsidence
Densmore et al., 2007
38
Unit 1
39
Stratal geometric relationship
ASTER satellite image, bands 321-RGB
40
Unit 2
41
Unit 3
42
PART 3..Concluding
a) How did deformation evolve?
The locus of deformation moved forth and back,
without a predictable pattern on a time scale
ranging from 2 to 0.6 Ma
b) What can we learn from foreland basin deposits
(i.e. climate vs tectonic) ?
In a medial-distal part of a foreland basin high
sediment accumulation rates coincide with
fine-grained sediments and reflect an increase in
subsidence due to tectonic loading
Low sediment accumulation rates coincide with
coarse-grained sediments and reflect decrease in
subsidence related to intraforeland uplift
Progradation of coarse grained sediments during a
moderate to high subsidence rate seems be related
to an increase in sediment flux possibly
triggered by enhanced precipitation
43
Thank you
With the contribution of Angela Landgraf, Manfred
Strecker, Cornelius Uba, Norbert Nowaczyzk, Anke
Friedrich, and many others