Scaled physical models of folds An applicatin for potash explorations in salt domes

Category Economic geology & mineral exploration
Group GSI.IR
Location 21th symposium on geosciences
Holding Date 21 May 2008

   Abstract:
      Pohl Kuh or Sar Pohl is a 7*2*0.72 km extrusion of Hormuz salt in the Zagros thrust fold belt. It is an Iranian Salt Mountain near coast of the Persian Gulf 60 Km west of Bandar Abbas. The main problem of Pohl has been that chemical analysis of secondary potassium minerals collected from the rivers indicated (by qualitative and quantitative analysis) that potash must be present in the mass(Aftabi,2001)and then potash layers explored by potash group in the GSI(Aftabi, Jahangiri, Nabian & Vaezipoor, 2002;2003).
   The local stratigraphies at Pohl (Salt Mountain with potash) in terms of the traces of axial surfaces of three suites of flow folds have many irregularities. The traces of early F1 folds are refolded by later F2 folds and both traces refolded by the axial surfaces of upright F3 folds.
   This probably developed from a pillow of salt that trended N-S before the eastern Zagros into two pull apart basins. Other analogue models explained the internal and external structure of Pohl.
   Marker layers with two different types of colored stratigraphies were built into source layers of viscous transparent fluid (PDMS) and then extruded through a pulled apart vent with or without a collar. The results modeled the internal flow folds seen in extrusive salt diapirs in Iran. Such models are useful for the exploration of potash layers in such extrusions and also simulate the evolution of flow folds seen in the metamorphic rocks exposed in the cores of orogenic belts. Curtain folds
   In general two processes occurred in all models: extrusion out of the vent (at a rate controlled by the load), and gravity spreading at a rate controlled by the height of the extruded fluid). Each phase of extrusions is recorded by an individual upright fold which is refolded to a recumbent fold by gravity spreading above the vent.
   The number, spacing and tightness of flow folds in bodies extruded through a vent of constant size are found to relate to the loading (+/-unloading) history of the models. Episodes of loading were varied in value, time and number and interspersed with episodes of unloading. Other variables tested were size and shape of the vent, the competence contrast of marker layers and also irregularities in the source layer (bubbles etc) Collars around the vent change the shapes of the extrusion and their internal folds. Fold trains in the eroded extrusions are indistinguishable with extrusions that have not been eroded. Resurgence after the extrusion level has fallen beneath the rim, results in a separable overlying extrusion. The models here in this report are simple pattern for understanding the folds in salt domes in common. We did not model the folds near potash areas of Pohl but simple patterns reported here is a key for potash explorations and understanding of salt and potash structures.

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