Institute of Geophysics of the CAS, v. v. i.

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Salt domes in Iran

Salt domes in Iran

Infra-Cambrian and Cambrian evaporite Hormuz Formation that deposited originally on the epicontinental margin of Gondwana represent a major décollement layer in the recently deforming fold-thrust wedge of the Zagros Mountains (McQuarrie, 2004). The salt diapirs in Zagros display a range of morphologies from salt pillows above basement faults, blind reactive diapirs, downbuilt emergent diapirs to mature extrusions producing fountains or namakiers.

The flow of salt in salt glaciers remains enigmatic (Desbois et al., 2012), although the fine-grained nature of rock salt in salt glaciers and input of water from rainfall (Desbois et al., 2010) are considered as the major factors in facilitating the rock salt recrystallization (Urai et al., 1986). Major goal of our work is to identify deformation mechanisms, and systematically quantify microfabrics in actively extruding salt fountains to address the long-term flow behavior of rock salt.

For this purpose, the Kuh-e-Namak (Dashti) salt diapir in southern Iran was selected for detailed field survey and sampling. This diapir represents a unique ‘natural laboratory’ of salt deformation due to its excellent exposure and consists of a dome and two glaciers (namakiers) that flow downslope on both flanks of the Zagros anticline. Both namakiers display clear finite deformation gradient towards their snouts. The diapir pierces the crest of a WNW-ESE trending “whale-back” Zagros anticline, where the anticline is cross-cut by a NNW-SSE trending segment of a deep seated Kazerun fault (Talbot, 1979). The Hormuz salt (Precambrian and Cambrian) at Kuh-e-Namak (Dashti) salt dome rises from the basal layer through a 6 km thick Phanerozoic sedimentary sequence.

 

Large sheath fold in layered extruded Hormuz salt forming the northern salt glacier of the Kuh-e-Namak (Dashti) diapir. For scale see the man figure in the middle of the photograph.

Microstructural analysis of rock salt from comprises quantitative textural analysis using the PolyLX statistical toolbox (PolyLX) and Electron Backscattered Diffraction (EBSD) of crystallographic preferred orientation. We employ gamma-irradiation of the specimens that elucidates numerous microstructural features in the thin-sections that can be interpreted in terms of deformation mechanisms. We recently focus on the influence of fluid and solid inclusion impurities on the rock salt flow. This research is conducted by joint cooperation with the institute of Structural Geology, Tectonics and Geomechanics at RWTH Aachen University.

Schematic tectonic evolution of Kuh-e-Namak salt diapir (Zagros mountains, Southern Iran). .

Publications:

* Desbois, G., Urai, J. L., Schmatz, J., Závada, P. & de Bresser H. (2012). The distribution of fluids in natural rock salt and understanding deformation mechanisms, in Bérest, Ghoreychi, Hadj-Hassen & Tijani, eds, Mechanical Behavior of Salt VII, Taylor and Francis Group, London, pp. 3–12.

* Desbois, G., Závada, P., Schleder, Z. and Urai, J. L. (2010). Deformation and recrystallization mechanisms in actively extruding salt fountain: Microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size (Qum Kuh, central Iran), Journal Of Structural Geology, 32(4), 580-594. DOI:10.1016/j.jsg.2010.03.005.

Team: Prokop Závada

Co-workers: Guillaume Desbois and Janos Urai (GED-RWTH Aachen), Karel Schulmann (CGS), Ondrej Lexa (IPSG), Jakub Haloda (CGS), Patricie Týcová (CGS), František Hrouda (IPSG, Agico, Int.), Mahmoud Rahmati Ilkhchi (GSI Teheran)

References:

* Desbois, G., Urai, J., and de Bresser, J. H. P, (2012), Fluid distribution in grain boundaries of natural fine-grained rock salt deformed at low differential stress (Qom Kuh salt fountain, central Iran): Implications for rheology and transport properties. Journal of Structural Geology 43, 128-143.

* Desbois, G., Zavada, P., Schleder, Z. & Urai, J. L. (2010), Deformation and recrystallization mechanisms in actively extruding salt fountain: Microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size (Qum Kuh, Central Iran), Journal Of Structural Geology 32(4), 580–594.

* McQuarrie, N. (2004). Crustal scale geometry of the Zagros fold–thrust belt, Iran. J. Struct. Geol.,26(3),519-535. Urai, J., Spiers, C., Zwart, H. & Lister, G. (1986), Weakening of rocksalt by water during long term creep, Nature 324, 554–557.

* Urai, J. L., Schléder, Z., Spiers, C. J. & Kukla, P. A. (2008), 5.2: Flow and transport properties of salt rocks, in R. Littke, U. Bayer, D. Gajewski, H. J. Brink & I. Winter, eds, Dynamics of complex intracontinental basins: The Central European Basin System, Springer, pp. 2-5. Talbot, C.J., (1979). Fold trains in a glacier of salt in southern Iran. J. Struct. Geol.. 1, 159-181.