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
8
Pressure and stress directly measured by state-of-the-art analytical methods.
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)
14
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
24
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
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