Lucie Tajčmanová, Evangelos Moulas, Yuri Podladchikov

Heidelberg University

Mechanically-controlled rock-microstructures: Witnesses of the long-term stress-state in the

continental lithosphere

Motivation: Modelling of geodynamic processes

Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

CURRENT AIMS: Understanding processes in the Earth

interior Mitigation measures, e.g. earthquakes

May et.al., 2013 & Crameri et al., 2012

Rheology: an extrapolation problem

CURRENT UNCERTAINTY:

Rheology extrapolated from lab over 10 orders of magnitude

Rheology: an extrapolation problem

4Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

No predictive power for geo-material towards high stresses.Constraint under geological conditions is missing.

Geological conditions

PLAGIOCLASE – the most abundant mineral in the Earth’s crust

Rheology: an extrapolation problem

PLAGIOCLASE – the most abundant mineral in the Earth’s crust

5Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

=> This questions our understanding of geodynamic processes!

Groningen gas field (Netherlands)

6Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

• Only 1-2 orders of magnitude difference in extrapolation, i.e. years vs. months

• Close to the surface

• Elastic vs. creeping behavior problem

=> How confident are we for conditions in the lower crust?

Any hope for a constraint at geologically

relevant conditions?

7Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

Any hope???

Mechanically-controlled microstructures

Witnesses of the long-term stress state in the lithosphere!

Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

Inclusion

(e.g. coesite)

Host (e.g. garnet)

Korsakov et al. 2007

Inclusion-host environment

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Pressure and stress directly measured by state-of-the-art analytical methods.

Dienstag, 20. November 20189

Departement/Institut/Gruppe

Unconventional Rheometry:

Chemical potential and equilibrium

temperature

pressure

composition c

Little bit of background first

aRTTPi ln),(0

Compositional vs. pressure variations

Chemically- controlled Mechanically- controlledfast viscous relaxation and

slow chemical diffusionslow viscous relaxation

and fast chemical diffusion

The effect of pressure variation on chemical redistribution

12Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

Equilibrium under external force: pressure variations

Gases Liquids

Hydrocarbons reservoirs

The effect of pressure variation on chemical redistribution

13Lucie Tajčmanová, Heidelberg University, GermanyMUSCLE

Polymers Solids???

Equilibrium under external force: pressure variations

Currently and active research

Inclusion

(e.g. coesite)

Host (e.g. garnet)

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D b 10th 2014 Lucie Tajčmanová ETH Zurich

aRTTPi ln),(0

The effect of pressure variation on the chemical redistribution

Ky=HP

Mx=LP

Equilibrium under pressure gradients: Unconventional barometry

Dienstag, 20. November

201815

Departement/Institut/Grupp

e

Unconventional Rheometry: Key steps of the alternative approach

Dienstag, 20. November 2018 16Departement/Institut/Gruppe

Unconventional Rheometry: Key steps of the alternative approach

1/ Chemically zoned mechanically-controlled microstructure, e.g. inclusion-host environment

Ky=HP

Dienstag, 20. November 2018 17Departement/Institut/Gruppe

3/ Classical mechanics: from stress decay to effective stress exponent (n)

2/ Classical mechanics: From pressure to stress decay

Unconventional Rheometry:

Dienstag, 20. November 2018 18Departement/Institut/Gruppe

Ky=HP

Mx=LP

Plagioclase rim

4/ Results: From composition to apparent stress exponent and critical stress

( )(log )c

rr

(log )(log )

rrappn

non-constant power-law exponent

Unconventional Rheometry:

Results & Comparison

Usually, rock samples are subject to either constant stress or constant strain rate

Results & Comparison

Usually, rock samples are subject to either constant stress or constant strain rate

Results & Comparison

Usually, rock samples are subject to either constant stress or constant strain rate

Results & Comparison

Usually, rock samples are subject to either constant stress or constant strain rate

Results & Comparison

Usually, rock samples are subject to either constant stress or constant strain rate

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D b 10th 2014 L i T jč á ETH Z i h

Concluding remarks:

Mechanically-controlled microstructures provide information on the long-term stress state in the lithosphere

New approach to infer rheology directly from natural samples, for naturally relevant T, grain size and time scale.

Independent of conventional constitutive laws: based on equilibrium thermodynamics and classical mechanics

Constraint for the extrapolation – an inspiration also for olivine and pyroxene