BENCHMARK (IMEDL 2004)BENCHMARK (IMEDL 2004)

L. L. Lavier, G. Manatschal, O. Müntener.

Dynamic modeling of riftingDynamic modeling of rifting Physical approach (parameter space Physical approach (parameter space

analysis).analysis).

Use of the physical parameterization to Use of the physical parameterization to interrogate the geology (Benchmark interrogate the geology (Benchmark exercise?).exercise?).

What’s working and what’s not.What’s working and what’s not.

What is needed to improve the geological What is needed to improve the geological approach?approach?

RheologiesRheologies ElasticElastic

Visco-elastic MaxwellVisco-elastic Maxwell(Non-Linear Creep Laws)(Non-Linear Creep Laws)

Elasto-PlasticElasto-Plastic(Mohr-Coulomb, the material (Mohr-Coulomb, the material

has both cohesional and has both cohesional and frictional strength)frictional strength)

Some background…

FLAC, Fast Lagrangian analysis of FLAC, Fast Lagrangian analysis of continua (Podlatchikov, Poliakov).continua (Podlatchikov, Poliakov).

Self-consistent dynamic model of the lithosphere Self-consistent dynamic model of the lithosphere (state of stress, strain, strain rate, viscosity, (state of stress, strain, strain rate, viscosity, temperature).temperature).

Spontaneous localization of shear zones. Spontaneous localization of shear zones.

Takes into account the weakening phenomena on Takes into account the weakening phenomena on faults (non-associative plasticity).faults (non-associative plasticity).

Can model a brittle (elasto-plastic) media coupled Can model a brittle (elasto-plastic) media coupled to a ductile (non-linear visco-elastic).to a ductile (non-linear visco-elastic).

More realistic rendering of geological states.More realistic rendering of geological states.

Two Controlling Parameters:

-The thickness of the brittle Layer, H.

-The rate and the amount ofweakening on the fault.

Two Controlling Processes:

-The elastic-plastic bending of the brittle layer as the fault offset (Force % to the thickness square).

-The weakening on the fault (Force % to the thickness).

THICK BRITTLE LAYER.

THIN BRITTLE LAYER.

Lithospheric deformationLithospheric deformation SINGLE FAULTSINGLE FAULT

LOCALIZING LOCALIZING (fault weakens).(fault weakens).

Weakening on faults by Weakening on faults by strength loss (cohesion strength loss (cohesion and/or friction loss).and/or friction loss).

Weakening by thermal Weakening by thermal necking.necking.

Weakening by magmatism Weakening by magmatism (dyking).(dyking).

MULTIPLE FAULTSMULTIPLE FAULTS

DELOCALIZING DELOCALIZING (fault strengthens).(fault strengthens).

Elastic and Plastic bending Elastic and Plastic bending of a brittle layer to buildup of a brittle layer to buildup topography.topography.

Viscous strengthening in Viscous strengthening in the ductile layer by cooling the ductile layer by cooling or higher strain rates.or higher strain rates.

DETACHMENT FAULTING AND MANTLE EXHUMATION:DETACHMENT FAULTING AND MANTLE EXHUMATION:MID-ATLANTIC RIDGE (with Roger Buck).MID-ATLANTIC RIDGE (with Roger Buck).

FORMATION OF A SINGLE NORMAL FAULT BY EXTENDING AN ELASTIC PLASTIC LAYER

Dynamic Modeling ApproachDynamic Modeling Approach

Use of the physical parameterization with constraints Use of the physical parameterization with constraints from geological reconstruction.from geological reconstruction.

What are the initial and boundary conditions?What are the initial and boundary conditions?

What processes control the evolution of deformation in What processes control the evolution of deformation in the plate and at the plate boundary?the plate and at the plate boundary?

What forces are needed to drive deformation?What forces are needed to drive deformation?

Comparison of the model to data.Comparison of the model to data.

In this magma poor environment, In this magma poor environment, what is the role of detachment what is the role of detachment

faulting?faulting? Constraints from reconstructions (Alps and Iberia Constraints from reconstructions (Alps and Iberia

abyssal plain).abyssal plain).

What are the initial and boundary conditions?What are the initial and boundary conditions?

What processes control the evolution of What processes control the evolution of deformation at the ocean-continent transition?deformation at the ocean-continent transition?

What forces are needed to drive deformation and What forces are needed to drive deformation and mantle exhumation at continent-ocean transition?mantle exhumation at continent-ocean transition?

2D example…

UPWARD VS. DOWNWARD CONCAVE FAULTINGUPWARD VS. DOWNWARD CONCAVE FAULTING

Initial conditionsInitial conditions

1cm/yr

Model spaceModel space

We vary the initial temperature of the We vary the initial temperature of the mantle.mantle.

Temperature dependent melt fraction is Temperature dependent melt fraction is modeled. Increasing melt fraction modeled. Increasing melt fraction decreases both the density and viscosity decreases both the density and viscosity of the mantle.of the mantle.

The parameters controlling fault formation The parameters controlling fault formation in the brittle layer are also varied.in the brittle layer are also varied.

asymmetric extensionasymmetric extension

EVOLUTION OF THE DEFORMATIONEVOLUTION OF THE DEFORMATION

Thinning of the continental crust (≤10 km) and mantle exhumation over 4.3 myr

The force needed to stretch the The force needed to stretch the lithosphere is large (>2e13 Nm-1)lithosphere is large (>2e13 Nm-1)

The force is dominated by bending of the strong brittle The force is dominated by bending of the strong brittle parts of the lithosphere (lithospheric mantle)parts of the lithosphere (lithospheric mantle)

The asymmetry is possible when the detachment fault The asymmetry is possible when the detachment fault becomes very weak.becomes very weak.

The serpentinized mantle (weak plastic) controls the strain The serpentinized mantle (weak plastic) controls the strain history (listric faulting vs. concave downward faulting).history (listric faulting vs. concave downward faulting).

The topography developed is unrealistic.The topography developed is unrealistic.

The depth extent of the detachment is too large (i.e. the The depth extent of the detachment is too large (i.e. the temperature is too low or the mantle is much weaker).temperature is too low or the mantle is much weaker).

EVOLUTION OF THE DEFORMATIONEVOLUTION OF THE DEFORMATION

RIFTING: KINEMATIC CONSTRAINTSRIFTING: KINEMATIC CONSTRAINTS

How does the crust thins down to 10km How does the crust thins down to 10km before the exhumation of the mantle?before the exhumation of the mantle?

What is the effect of preexisting weakness What is the effect of preexisting weakness (suture zone, orogeny) in the lithosphere?(suture zone, orogeny) in the lithosphere?

What is the role of the lower crust if it is What is the role of the lower crust if it is partly composed of gabbros?partly composed of gabbros?

What is the role of the role of the strength What is the role of the role of the strength of the mantle (wet or dry)?of the mantle (wet or dry)?

Initial conditionsInitial conditions

The mantle is serpentinized when it is uplifted close to the surface (depth < 10 km for a temperature < 500 °C) and along the shear zones (high plastic strain; friction coefficient = 0.2).

Model spaceModel space

We vary the initial strength of the mantle.We vary the initial strength of the mantle.

We vary the strength of the lower crust.We vary the strength of the lower crust.

The parameters controlling fault formation The parameters controlling fault formation in the brittle layer are also varied.in the brittle layer are also varied.

Gabbro-Rich Lower Crust

Weak Mantle (wet)

ASYMMETRIC

- The crust is thinned down to 25 km.

- The mantle is exhumed along a rolling hinge.

- Serpentinized mantle occurs when the mantle is exhumed.

EVOLUTION OF THE DEFORMATIONEVOLUTION OF THE DEFORMATION

Total force needed for stretchingTotal force needed for stretching

Asymmetric

ConclusionsConclusions The strong gabbro rich lower crust keeps the The strong gabbro rich lower crust keeps the

deformation distributed and the topography deformation distributed and the topography small. It also allows for the initial uniform small. It also allows for the initial uniform stretching of the lithosphere.stretching of the lithosphere.

Serpentinization and weakening both control the Serpentinization and weakening both control the final asymmetry. final asymmetry.

A weak (wet) mantle reduces the thickness of the A weak (wet) mantle reduces the thickness of the brittle lithosphere and the force needed to stretch brittle lithosphere and the force needed to stretch it. it.

A strong mantle with a preexisting weakness A strong mantle with a preexisting weakness leads to the formation of a symmetric rift.leads to the formation of a symmetric rift.

What doesn’t work?What doesn’t work?

The gabbroic bodies may be distributed The gabbroic bodies may be distributed heterogeneities and very strong since they heterogeneities and very strong since they are likely to be generated in the Permian are likely to be generated in the Permian (Ivrea body).(Ivrea body).

The initial thickness of the crust should be The initial thickness of the crust should be maximum 30 km.maximum 30 km.

The resolution of the models is too low. The resolution of the models is too low.

Snoke et al., 1999

Ivrea bodyIvrea body

Ductile shear zones in the lower crust

Do we have to take into account Do we have to take into account the Permian Collapse?the Permian Collapse?

NewFoundland and melt NewFoundland and melt generation?generation?

ConclusionsConclusions We want vary the strength and extent of the We want vary the strength and extent of the

gabbroic bodies in the lower crust gabbroic bodies in the lower crust (heterogeneities).(heterogeneities).

Using this approach is walking on a thin line. Using this approach is walking on a thin line. Heterogeneities can impose the physical behavior Heterogeneities can impose the physical behavior and therefore not teach anything about the and therefore not teach anything about the physics.physics.

It must remain a study of the physical processes. It must remain a study of the physical processes. If not the method becomes a “mélange If not the method becomes a “mélange approach”.approach”.

Iterative process between the geologists and the Iterative process between the geologists and the modelers. Between the models and the data.modelers. Between the models and the data.

CURRENT WORKCURRENT WORK

Modeled thermal history and PTt paths can be Modeled thermal history and PTt paths can be compare to data.compare to data.

Increase the model resolution and improve Increase the model resolution and improve modeling technique (mesh refinement + implicit modeling technique (mesh refinement + implicit solvers) (with Wolfgang Bangerth at UT).solvers) (with Wolfgang Bangerth at UT).

Model melt migration and compaction (with Chad Model melt migration and compaction (with Chad Hall at Caltech)Hall at Caltech)

3D dynamic model of lithospheric deformation 3D dynamic model of lithospheric deformation (with Mike Gurnis at Caltech).(with Mike Gurnis at Caltech).

I have a dream…I have a dream…PTt and thermal history

Melt percolation and compaction

Lower crustal flow and faulting

3D dynamic modeling

Was this phase of extension similar Was this phase of extension similar to the Basin and Range?to the Basin and Range?

1. 1. Lower crustal front propagationLower crustal front propagation

16 Myr.

STRONG THRUST FAULT OR LARGE THICKENING.

WEAK THRUST FAULT OR LESS THICKENING.

Particle PathsParticle Paths

MODEL RESULTS NEAR THRUST FOOTWALL

MODELS OF MELT FLOWMODELS OF MELT FLOW

With C. Hall at Caltech

WHAT DOES IT TAKE TO DO WHAT DOES IT TAKE TO DO THAT IN 3D?THAT IN 3D?

GEOFRAMEWORK TO COUPLE CODES TOGETHER GEOFRAMEWORK TO COUPLE CODES TOGETHER (MANTLE CONVECTION AND LITHOPHERIC (MANTLE CONVECTION AND LITHOPHERIC DEFORMATION)DEFORMATION)

1- Pythia (Python bindings)1- Pythia (Python bindings)

2- StGermain (VPAC).2- StGermain (VPAC). FLAC 3D (SNAC).FLAC 3D (SNAC).

New numerical techniques. New numerical techniques.

                             

   

                                

                                                                                                                                                               

         

 

SIMULATION OF MULTI-SCALE DEFORMATION IN GEOPHYSICS (with Mike Gurnis at Caltech).

GEOFRAMEWORK PROJECT.

Numerical Method (Flac3D).Numerical Method (Flac3D). Explicit Finite Difference Scheme.Explicit Finite Difference Scheme.

FLAC takes advantage of the fact that finite FLAC takes advantage of the fact that finite difference equations can be derived for elements difference equations can be derived for elements of any shape (Wilkins, 1964) like finite elements.of any shape (Wilkins, 1964) like finite elements.

No costly iteration process needed even for No costly iteration process needed even for nonlinear constitutive laws.nonlinear constitutive laws.

Need to have some Need to have some a prioria priori idea of the system idea of the system behavior to make sure the solution is stable.behavior to make sure the solution is stable.

3D localization first tests3D localization first tests

Coupling between lithosphere and Coupling between lithosphere and astenosphere. astenosphere.

Red Sea test case.Red Sea test case.

Mesh refinement techniques at UT Mesh refinement techniques at UT with Wolfgang Bangerth.with Wolfgang Bangerth.

ConclusionsConclusions THIS TYPE OF STUDIES IS DIRECTED AT UNDERSTANDING THIS TYPE OF STUDIES IS DIRECTED AT UNDERSTANDING

AND QUANTIFYING THE FACTORS, PHYSICAL PROCESSES AND QUANTIFYING THE FACTORS, PHYSICAL PROCESSES AND FORCES DRIVING PLATE TECTONICS.AND FORCES DRIVING PLATE TECTONICS.

THEY PROVIDE A DYNAMIC IMAGE OF THE EVOLUTION OF THEY PROVIDE A DYNAMIC IMAGE OF THE EVOLUTION OF THE DEFORMATION AT PLATE BOUNDARIES.THE DEFORMATION AT PLATE BOUNDARIES.

THEY CAN ALSO PROVIDE CONSTRAINTS ON SUCH THEY CAN ALSO PROVIDE CONSTRAINTS ON SUCH PROBLEMS AS THE THERMAL EVOLUTION OF BASINS AND PROBLEMS AS THE THERMAL EVOLUTION OF BASINS AND SEDIMENT SOURCE AND SINK.SEDIMENT SOURCE AND SINK.

GEOFRAMEWORK IS NOW A SCIENCE APPLICATION IN THE GEOFRAMEWORK IS NOW A SCIENCE APPLICATION IN THE TERAGRID FRAMEWORK WITH TACC (Texas Advanced TERAGRID FRAMEWORK WITH TACC (Texas Advanced Computer Center).Computer Center).

POSSIBILITY OF INTEGRATING GEODYNAMIC MODELING POSSIBILITY OF INTEGRATING GEODYNAMIC MODELING WITH KINEMATIC MODELS FOR STUDIES IN THE SOUTH WITH KINEMATIC MODELS FOR STUDIES IN THE SOUTH ATLANTIC. ATLANTIC.

ApproachApproach

Reconstruct the stratigraphy, morphology and Reconstruct the stratigraphy, morphology and paleo-water depth through time (backstripping + paleo-water depth through time (backstripping + palinspastic reconstruction).palinspastic reconstruction).

2D and 3D numerical Modeling of the Tectonic 2D and 3D numerical Modeling of the Tectonic and Thermal History of the Margins.and Thermal History of the Margins.

Combine Reconstructions and Tectonic and Combine Reconstructions and Tectonic and Thermal constraints from numerical models to Thermal constraints from numerical models to determine the maturation and migration of determine the maturation and migration of hydrocarbons.hydrocarbons.

West African MarginWest African Margin

Kinematical approachKinematical approach

Successful at constraining the Successful at constraining the tectonic and thermal history during tectonic and thermal history during the post-rift phase of margins’ the post-rift phase of margins’ formation.formation.

The assumptions for the syn-rift The assumptions for the syn-rift history are too simplistic.history are too simplistic.

Opening of the South AtlanticOpening of the South Atlantic Need for seismic refraction data (Harm Van Avendonk). Need for seismic refraction data (Harm Van Avendonk).

Collaboration with GXT.Collaboration with GXT.

Constraints from the geology and plate reconstructions.Constraints from the geology and plate reconstructions.

Great variability in styles of rifting. 2D numerical models of Great variability in styles of rifting. 2D numerical models of extension along the conjugate margins. Focus on the extension along the conjugate margins. Focus on the thermal state and the possible heterogeneities in rheology thermal state and the possible heterogeneities in rheology with depth.with depth.

3D model of the opening with initial conditions taking into 3D model of the opening with initial conditions taking into account the great geological variability along the pan-account the great geological variability along the pan-African belt. African belt.

What is the future of geodynamic What is the future of geodynamic modeling?modeling?

2D models of the conjugate margins. 2D models of the conjugate margins. Study similar to the Iberian-New Founland Study similar to the Iberian-New Founland conjugate margins.conjugate margins.

3D models of the opening of the South-3D models of the opening of the South-Atlantic (including geological constraints Atlantic (including geological constraints from plate reconstructions and rheological from plate reconstructions and rheological and crustal heterogenities).and crustal heterogenities).

Parameter space analysis.Parameter space analysis.