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Deformation (Dominant salt deformation mechanism (Glide - High temp /…
Deformation
Dominant salt deformation mechanism
Glide - High temp / stress
Creep - lower stress i.e. < 10 MPa ?
Dominantly: solution-precip
(@ lower temp)
(Other creep @ T>300°C)
Salt
strength
Wet salt - so weak its creep curve plots @ 0 MPa on central axis
Salt has virtually no frictional resistance
∴ Very susceptible to creep
Deformation mechanism (general recap)
Solution precipitation creep
pressure solution - reprecipitation
Glide - dislocation glide
moving/deforming lattice via glide on individual crystal planes
Creep
Dislocations overcome obstacles by jumping over them
Qom Kuh
Central Iran
Salt extrusion, Central Iran
Slightly asymmetric fountain
feeding allochthonous salt from a stem plunging steeply NE
Salt Glacier
salt pierced surface
began to flow down topographic gradient (hill)
complex deformation during upwelling/glide downhill
Deformation mechanisms
wrt Z (general)
Frictional deformation
governed by pressure
mostly upper 10s km
f( Byerlee's law) ∴ temp insensitive
Temp-activated creep
dictated by temperature
dry limestone
starts creep ~ 8 km
since calcite deforms by creep @ 250°C
(via twinning & dislocation creep)
Creep
strength
= deviatoric strength required to drive salt flow
@ representative strain rate
i.e. 10^-14 s^-1
Pore pressure coefficient λ
= ratio between pore pressure & lithostatic pressure
i.e. dry rock λ = 0 vs highly overpressurised λ = 0.82
Conditions natural salt flow
Pressure: -3 to - 8 MPa
Temp ~50 - 400°C
Shear
modulus
Elastic descriptor
Tells us how strong salt is from elastic perspective