Theory
A mushroom-shaped or plug-shaped diapir made of salt, commonly having an overlying cap rock. salt domes form as a consequence of the relative buoyancy of salt when buried beneath other types of sediment. The salt flows upward to form salt domes, sheets, pillars and other structures. Hydrocarbons are commonly found around salt domes because of the abundance and variety of traps created by salt movement and the association with evaporite minerals that can provide excellent sealing capabilities.
alt diapirs are typically developed in e.g. deformed epicontinental basins with basal salt layer in the sedimentary sequence (e.g. Zagros basin, Iran). The salt diapirs are often associated with extensive oil traps and their shapes and evolution is being extensively studied by research groups of oil-companies. We are rather interested in the microscale processes of salt deformation responsible for its longtime viscous flow.
The selected salt diapir in southern Iran (Kuh-e-Namak) probably represents the most well exposed salt dome, which is still active. It pierces the crest of a WNW-ESE trending “whale-back” anticline, where the anticline is cross-cut by a NNW-SSE trending deep seated Kazerun fault (Talbot, 1979). The Hormuz salt (precambrian to cambrian in age) rises from the basal layer through a 5 km thick phanerozoic sedimentary sequence and flows down on both flanks of the anticline. The lateral salt motion on Kuh-e-Namak was measured to be on the order of metres per year (Talbot and Jarvis, 1984), however it must be much slower according to more recent and accurate measurements done on diapirs on islands in Persian gulf (Bruthans et al., 2006). It is interesting that salt domes resemble in shape some volcanic domes, but their times of emplacement differ by several orders (104-106 yrs for salt, only few months for volcanic domes). The previsously horizontally layered salt sequence has been mobilized in permian due to extensional deformation controlled by deep-seated Kazerun fault (opening of the Tethys ocean). From eocene to recent the whole Zagros basin is subjected to N-S compression given by the convergence of Arabian and Iranian plates, which produces fold and thrust belts forming the Zagros mountains (Bahroudi, 2003; McQuarrie, 2004).
The salt rocks occuring on the surface shows complex fold patterns and layer alternations which have formed due to superpositon of at least 3 fold generations (Talbot, 1979; Talbot and Jacskon, 1987). In our work, we are mainly interested in the microphysical processes that are responsible for the viscous flow of salt at atmospheric conditions. Our approach comprises structural, microstructural and AMS analysis.
The Kuh-e-Namak salt dome is being investigated in close cooperation with the following geoscientific institutions: IPSG (Institute of petrology and structural geology, Prague), EOST (Ecole et Observatoire des Sciences de la Terre, Strasbourg), CGS (Czech geological Survey, Prague).
Schematic tectonic evolution of Kuh-e-Namak salt diapir (Zagros mountains, Southern Iran):
A mushroom-shaped or plug-shaped diapir made of salt, commonly having an overlying cap rock. salt domes form as a consequence of the relative buoyancy of salt when buried beneath other types of sediment. The salt flows upward to form salt domes, sheets, pillars and other structures. Hydrocarbons are commonly found around salt domes because of the abundance and variety of traps created by salt movement and the association with evaporite minerals that can provide excellent sealing capabilities.
alt diapirs are typically developed in e.g. deformed epicontinental basins with basal salt layer in the sedimentary sequence (e.g. Zagros basin, Iran). The salt diapirs are often associated with extensive oil traps and their shapes and evolution is being extensively studied by research groups of oil-companies. We are rather interested in the microscale processes of salt deformation responsible for its longtime viscous flow.
The selected salt diapir in southern Iran (Kuh-e-Namak) probably represents the most well exposed salt dome, which is still active. It pierces the crest of a WNW-ESE trending “whale-back” anticline, where the anticline is cross-cut by a NNW-SSE trending deep seated Kazerun fault (Talbot, 1979). The Hormuz salt (precambrian to cambrian in age) rises from the basal layer through a 5 km thick phanerozoic sedimentary sequence and flows down on both flanks of the anticline. The lateral salt motion on Kuh-e-Namak was measured to be on the order of metres per year (Talbot and Jarvis, 1984), however it must be much slower according to more recent and accurate measurements done on diapirs on islands in Persian gulf (Bruthans et al., 2006). It is interesting that salt domes resemble in shape some volcanic domes, but their times of emplacement differ by several orders (104-106 yrs for salt, only few months for volcanic domes). The previsously horizontally layered salt sequence has been mobilized in permian due to extensional deformation controlled by deep-seated Kazerun fault (opening of the Tethys ocean). From eocene to recent the whole Zagros basin is subjected to N-S compression given by the convergence of Arabian and Iranian plates, which produces fold and thrust belts forming the Zagros mountains (Bahroudi, 2003; McQuarrie, 2004).
The salt rocks occuring on the surface shows complex fold patterns and layer alternations which have formed due to superpositon of at least 3 fold generations (Talbot, 1979; Talbot and Jacskon, 1987). In our work, we are mainly interested in the microphysical processes that are responsible for the viscous flow of salt at atmospheric conditions. Our approach comprises structural, microstructural and AMS analysis.
The Kuh-e-Namak salt dome is being investigated in close cooperation with the following geoscientific institutions: IPSG (Institute of petrology and structural geology, Prague), EOST (Ecole et Observatoire des Sciences de la Terre, Strasbourg), CGS (Czech geological Survey, Prague).
Schematic tectonic evolution of Kuh-e-Namak salt diapir (Zagros mountains, Southern Iran):
Economic Importance
[size=12]Salt domes supply industrial commodities, including fuel, minerals, chemical feedstock, and storage caverns. Giant oil or gas fields are associated with salt domes in many basins around the world, especially in the Middle East, North Sea, and South Atlantic regions. Salt domes are also used to store crude oil, natural gas (methane), liquefied petroleum gas, and radioactive or toxic wastes]
Salt domes are largely subsurface geologic structure that consists of a vertical cylinder of salt embedded in horizontal or inclined strata. In the broadest sense, the term includes both the core of salt and the strata that surround and are “domed” by the core. Major accumulations of oil and natural gas are associated with salt domes in the U.S., Mexico, the North Sea, Germany, and Romania; domes along the Gulf Coast contain large quantities of sulfur. Salt domes are also major sources of salt and potash on the Gulf Coast and in Germany, and they have been used for underground storage of liquefied propane gas. Storage “bottles,” made by drilling into the salt and then forming a cavity by subsequent solution, have been considered as sites for disposal of radioactive wastes.]
The salt that forms these deposits was laid down in prehistoric times, mainly in places where inland seas
]were periodically connected and disconnected from oceans. As these seas are cut off from the main body of water, the water evaporates, leaving immense salt pans. Over time, the salt is covered with sediment and becomes buried. Since the density of salt is generally less than that of surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes, sheets, pillars and other structures as it rises. If the rising salt diapir breaches the surface, it can become a flowing salt glacier. In cross section, these large domes may be anywhere from 1 to 10 kilometers across and extend as far ]
Geometry
]One example down as 6.5 kilometers.of an island formed by a salt dome is Avery Island in Louisiana]