Salt Structures
Diapir
Salt dome formation
= buoyancy driven
Salt
structures
whole suite of salt structures
form due to gravitational instability
when buoyant force of salt > weight of overburden keeping salt in place
= body which gravitationally moves upward & intrudes the overburden
body typically salt/magma/water-saturated mud
Salt diapir
= salt mass that has
flowed upward ductilely
discordantly pierced overburden
E.g.s Salt Structures
Salt volumes in crust take on variety of geometries
Elongated - salt pillows & anticlines
bend & uplift overburden passively
Localised & plug-like - salt stocks
Elongate but look like stocks in ⊥ cross-section = salt walls
N. Germany
Extensive salt bodies i.e. salt walls / pillows / diapirs
= part of Zechstein deposits
Dasht-E Kavir
Salt Domes
Dasht-E Kavir, Iran - Great Salt Desert
Salt domes piercing the surface
Size: several km across
S. of Caspian Sea
Salt dome features, Iran
Rose up to surface displacing everything around it
Internal folding evident in salt body
evince constriction before welling up to surface
Some pierce the surface - forming salt glaciers
Salt
Glacier
Significant deformation of sediments in between salt bodies
Salt dome significance
may trap hydrocarbons within them
given salt body is impermeable to hcs
= rare salt flow formed when a
--> rising diapir in a salt dome breaches the surface
= Salt flowing out of a diapir (salt plug) above sea level
Flow toward highest dip direction
Flow in Iran = weather dependent
Salt Glacier Deformation
In dry regions (Iran) def mechanism = f ( fluid availability)
Flow - when salt is wet i.e. rainy periods
Wet conditions favour plastic deformation
Brittle deformation (jointing) - when salt is dry
Salt flowing downhill
Deforms by folding
--> Due to non-constant velocity field
(velocity increases from base upward)
Salt
dome
Sedimentary strata uplifted by rising salt
to form massive dome around the salt body
If salt pierces overburden - begins to flow down gravitational potential down side of dome
What drives
salt flow?
Underground: stress gradients drive salt flow
At surface: gravitational potential drives salt flow