S. Sobolev, GFZ Potsdam “Geodynamic modeling and integrative interpretation” group in the GFZ...

S. Sobolev, GFZ Potsdam

“Geodynamic modeling and integrative interpretation” group in the 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

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-8

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-6

-5

-4

-3

-2

-1

0

1

Depth, km



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)


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


Pattern of Central Andean Deformation (21°S)

Elger, Oncken & Glodny, in prep.


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


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?


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


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


V1

V2

Friction angle 10° ( = 0.17)

Effect of interplate friction



Large-scale model

Evolution of the lithospheric structure in the best fit model

Friction angle 3° ( = 0.05)



Large-scale model


Evolution of the density distribution in the best fit model



Large-scale model


Evolution of the temperature distribution in the best fit model



Cumulative strain distribution in the best fit model



Topography in the

best fit model



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


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


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


Brasilian shield

Nazca plate

5 cm/yr

3 cm/yr

High overriding rate

fr=0.03-0.05

Friction and trench fill

Model prediction


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


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


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


Brasilian shield

Nazca plate

3 cm/yr

33 km deep

locking

50 km deep

locking

5 cm/yr


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


Human time scale: GPS data


-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


-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 PS

Trench

G PS


Zooming in Time

Mln. years years

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


Friction down 0.0525 0.0475



Friction up 0.0475 0.0525


S. Sobolev, GFZ PotsdamS. Sobolev, GFZ Potsdam


Friction down 0.0525 0.0475



-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 PS

Trench

G PS

df=0.1f (0.005)


-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 PS

Trench

G PS

df=0.1f (0.003)

(0.010)


Conclusions 2

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

S. Sobolev, GFZ Potsdam “Geodynamic modeling and integrative interpretation” group in the GFZ...

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