S. Sobolev, GFZ Potsdam

“Geodynamic modeling and integrative interpretation” group in the GFZ Potsdam

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

F ig . 1

A frican plate

A rabian plate

Surface topography at t=16 Myr (105 km strike-slip motion)

Boundary weak zone

3D model of the Dead Sea evolution

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

Depth, km

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Factors controlling subduction orogeny in Central Andes

Stephan Sobolev and Andrey Babeyko GFZ Potsdam

Outline

Geological time scale model (Myr) of interaction of the subducting and overriding plates

time zoom

Human time scale model (yr)

S. Sobolev, GFZ Potsdam

Brasilian shield

thick (50-70 км) hot and felsic crust

Subandean thin-skin deformation zone

3 cm/yr

Andean Orogeny

The high-mountain belt has been formed only during the last 30 Myr and only in the central part of the South America plate margin.

Nazca plate

5 cm/yr

S. Sobolev, GFZ Potsdam

Pattern of Central Andean Deformation (21°S)

Elger, Oncken & Glodny, in prep.

S. Sobolev, GFZ Potsdam

Which processes are responsible for the tectonic shortening in CenozoicTransfer function

Pardo-Casas and Molnar (1987)

Silver et al. (1998)

Lamb and Davis (2003)

Oncken, personal communication

S. Sobolev, GFZ Potsdam

Key questions

Why only in Cenozoic and why only in the Central Andes?

How important are plate kinematics and plates coupling in the Andean orogeny?

Model testable predictions?

S. Sobolev, GFZ Potsdam

2-D Thermomechanical Modelling

Explicit finite element algorithm

Basic calculational cycle:m ·d /dt = V F F

- solution of full dynamic equation of motion- calculations in Lagrangian coordinates- remeshing when grid is too distorted- no problems with highly non-linear rheology

General model setupComplex visco-elasto-plastic rheologyT=0, =0xz = zzT or , 0 xz zz = , - Archim.force T/z = const T/x=00xz = T/x=00xz = V xV x

Governing equations:

tLAxTxtTC plasticityCoulombMohrordtdG xvKtp gxxptv

ijijiip ijijij ii ijijiiinert

)(2121

)3(2,1,0

igxx

pi

j

ij

i

,i

i

x

vK

dt

dTK

dt

dp

;2

1ˆ

2

1ijij

ij

dt

d

G

),(/1)(/1),(/1/1 TTT Pdifdisl

0sin1

sin12

sin1

sin131

c

31 sg

Ax

TTx

xdt

dTC ijij

ii

ip

)),((

Momentum conservation equation:

Mass conservation equation and constitutive laws:

visco-elastic body

Mohr-Coulomb failure criterion

non-associated shear flow potential

Energy conservation equation including shear heating term:

2-D Thermomechanical Modelling

Implimentation: Finite element, LAgrangian, Particle Explicit , code LAPEX-2D,2.5D,3D

S. Sobolev, GFZ Potsdam

Large-scale model setup

fertile peridotite

depleted peridotite

felsic upper crust

V2

Dynamic subduction channel with special rheology

depleted peridotite

gabbro

V1

Pz sediments

h1

z

h2

S. Sobolev, GFZ Potsdam

V1

V2

Friction angle 10° ( = 0.17)

Effect of interplate friction

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Large-scale model

Evolution of the lithospheric structure in the best fit model

Friction angle 3° ( = 0.05)

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Large-scale model

Evolution of the lithospheric structure in the best fit model

Evolution of the density distribution in the best fit model

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Large-scale model

Evolution of the lithospheric structure in the best fit model

Evolution of the temperature distribution in the best fit model

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Cumulative strain distribution in the best fit model

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Topography in the

best fit model

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Tectonic shortening in the best fit model

0 10 20 30 40T im e, M yr

0

100

200

300

400

Sho

rten

ing,

km High converg. rate

Active delamination

Subandian thrusting

South America acceleration

S. Sobolev, GFZ Potsdam

Effect of the overriding velocity

10 15 20 25 30 35Time, Myr

0

100

200

300

400

Sho

rten

ing,

km

fr=0.05, V=2-3 cm/yr (best fit model)

fr=0.05, V=1 cm/yr

S. Sobolev, GFZ Potsdam

Effect of friction

10 15 20 25 30 35Time, Myr

0

100

200

300

400

Sho

rten

ing,

km

fr=0.05, V=2-3 cm/yr (best fit model)

fr=0.005, V=2-3 cm/yr

S. Sobolev, GFZ Potsdam

Brasilian shield

Nazca plate

5 cm/yr

3 cm/yr

High overriding rate

fr=0.03-0.05

Friction and trench fill

Model prediction

S. Sobolev, GFZ Potsdam

locking at high friction

z

h1

h2

locking at low friction

Change of the friction coefficient by 5-10 times should result in the change of the locking depth by 15-25 km

Friction and locking depth Model prediction

S. Sobolev, GFZ Potsdam

Brasilian shield

Nazca plate

3 cm/yr

shallow

locking

deep

locking

no sediments in the trench - high friction

a lot of sediments in the trench - low

friction

Model prediction

5 cm/yr

S. Sobolev, GFZ Potsdam

7 6 º W 7 4 º W 7 2 º W 7 0 º W 6 8 º W 6 6 º W 6 4 º W3 8 º S

3 6 º S

3 4 º S

3 2 º S

3 0 º S

2 8 º S

2 6 º S

1 0 0 k m

a l p a r a i s o 3 / 3 / 8 5 M w 7 . 9

1

2

3

4

5

6

7

8

9

1 0

1 1

1 2

1 3

1 4

1 5

1 6

1 7

1 8

1 9

2 0

2 1

2 2

2 3

2 4

2 5

2 6

2 7

2 8

2 9

3 0

3 1

3 2

3 3

3 4

3 5

3 6

3 7

3 8

3 9

4 0

4 1

4 2

4 3

4 4

4 5

4 6

4 7

4 8

4 9

5 0

5 1

5 2

5 3

5 4

5 5

5 6

5 7

5 8

5 9

6 0

6 1

6 2

6 3

6 4

6 5

6 6

6 7

6 8

6 9

7 0

7 1

7 2

7 3

7 4

7 5

7 6

7 7

7 8

6 5 m m /y r ( N 7 7o E )

A n g e r m a n n e t a l . , 1 9 9 9

S c a l e

D a ta

M o d e l

2 0 2 m m / y r

Klotz et al., 2003

S. Sobolev, GFZ Potsdam

Brasilian shield

Nazca plate

3 cm/yr

33 km deep

locking

50 km deep

locking

5 cm/yr

S. Sobolev, GFZ Potsdam

Brasilian shield

Cenozoic Central Andean orogeny was likely controlled by both:

plate kinematics (high speed of the overriding of South America)

and climate (high friction in the subduction channel in the arid Central Andes).

3 cm/yr

High overriding rate

fr=0.03-0.05

Conclusions 1

Nazca plate

5 cm/yr

S. Sobolev, GFZ Potsdam

Human time scale: GPS data

S. Sobolev, GFZ Potsdam

-1200 -800 -400 0

D istance, km

-4

-2

0

2

4

6

Vx,

cm

/yr

N U V EL-1A

Stable SA

G eological data last 10 M yr

G PS

Trench

G PS

S. Sobolev, GFZ Potsdam

-1200 -1000 -800 -600 -400 -200 0

D istance, km

-4

-2

0

2

4

6

Vx,

cm

/yr

long-term m odel

N U V EL-1A

Stable SA

G eological data last 10 M yr

G PS

Trench

G PS

S. Sobolev, GFZ Potsdam

Zooming in Time

Mln. years years

Friction coefficient (fr) =0.03 fr=0.03+-0.0015

S. Sobolev, GFZ Potsdam

Friction down 0.0525 0.0475

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Friction up 0.0475 0.0525

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ PotsdamS. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

Friction down 0.0525 0.0475

S. Sobolev, GFZ Potsdam

S. Sobolev, GFZ Potsdam

-1200 -1000 -800 -600 -400 -200 0

D istance, km

-4

-2

0

2

4

6

Vx,

cm

/yr

long-term m odel

N U V EL-1A

Stable SA

G eological data last 10 M yr

G PS

Trench

G PS

df=0.1f (0.005)

S. Sobolev, GFZ Potsdam

-1200 -1000 -800 -600 -400 -200 0

D istance, km

-4

-2

0

2

4

6

Vx,

cm

/yr

long-term m odel

d f=0.2 f

N U V EL-1A

Stable SA

G eological data last 10 M yr

G PS

Trench

G PS

df=0.1f (0.003)

(0.010)

S. Sobolev, GFZ Potsdam

Conclusions 2

The same thermo-mechanical model can explain both geological-scale and human-scale deformations in the Central Andes