Complex Mushroom Diapirs of Great Kavir, Iran

Pedram Aftabi
Geological Survey of Iran, Tehran, Iran

The field and new modeling study suggest the internal structures in exposed mushroom diapirs are more complex than have been illustrated before (e.g domes 22-20-21-27-28 of Jackson et al., 1991- and x of Richter-Burnburg, 1981).

Profiles through salt extrusions in Northern Great Kavir (and Qum) and simple analogue models suggest that steady viscous extrusion gravity spreads in the uppermost part over sub-horizontal surface results in a series of recumbent to overturned folds. Each significant increase in extrusion rate therefore imposed a new outward verging similar-type flow fold in the upper limb of the basic namakier propagation fold (NPF). The spacing between these folds are related to the time of tectonic stress and rest(0.5 m to 10 m). These types of folds formed in the viscous extrusion (e.g Qum Kuh) during 42000 years (rate 82 mm a-1)and also seen in overhanging internal mushrooms. The central white salt in the domes of Kavir area have intruded lateraly to the URF diapiric formation and have formed the same structures. The gypsum rim and salt layers folded as train of overturned to recumbent folds with updip layering (salt) and tight updip (dips to centre) pseudostratigraphy.

Measurements, suggest salt stocks, canopies, overhangs, and glaciers records the driving forces.

Minor to major joints and shear zones between less than 0.5 m to more than 6 km long indicate brittle failure of overhanging mushroom diapirs of Kavir by regional stress field. Fractures with length more than 100m called master at Qum Kuh.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005