Download Chah-e Deev: a model of sinkholes development in center of Iranian

Chah-e Deev: a model of sinkholes development in center of Iranian Plateau
Sohrabi*, A., Nadimi**, A., & Hajihashemi***, M.,
* Zamin Pajuhan Kuhestan Geological Institute, P.O. Box 81655-195, Isfahan, Iran
[email protected]
** Department of Geology, Faculty of Science, University of Isfahan, P.O. Box 81746-73441, Isfahan, Iran
*** Islamic Azad University, Dolatabad Branch, Isfahan, Iran
Researches in vertical caves and sinkholes are rare and usually restricted to speleological explorations because of
difficult access. The systematic methodology of work in the caves and sinkholes has not been established. Scientific studies
of these areas require speleological exploration, which can often include the discovery of new caves and passages, as well
as careful documentation (Kambesis, 2007) such as cave surveys, exploration reports, photographs and morphological
descriptions of the cavities. The exploration of large vertical caves and sinkholes in Europe began in the late 1970s with the
publication of several speleological studies on the Alps, Slovenia, the Pyrenees and the Picosde Europa Mountains
(Ballesteros et al., 2011).
Three general types of sinkholes have been classified that are collapse, subsidence and solution sinkholes.
Progression of the sinkholes is related to effects of water and structures in rocks. Groundwater percolating through the zone
of aeration slowly dissolves the carbonate rock and enlarges its fractures and bedding planes. Gradually subsiding sinkholes
commonly form where slow dissolution takes place, mostly along joints, fractures and faults in the rocks. Chah-e Deev
sinkhole is one of the best examples of subsidence sinkholes that formed along brittle structures in the northeast of Isfahan
in central part of Iranian plateau that has been introduced for the first time.
Iran provides one of the best examples of a youthful stage of continent-continent collisions in the world. The
collision between the Arabian and Eurasian plates followed by the closure of the Neo-Tethys Ocean resulted in the
development of Zagros orogen, which is the main deformation belt in this area (e.g., Stöcklin, 1968). The climax of the
orogeny is indicated by the Zagros Mountains uplifts during the Late Neogene. This uplifting motion has created the
present morphology of Iranian Plateau.
In vast areas of Iran, several caves and karstification phenomena have been recognized and described during recent
years. These areas including Zagros, Alborz and central Iran mountains are partly made of karst stones, which are the main
source of providing drinking water in arid and semi-arid states of the country. These phenomena have been studied in
sedimentology, hydrogeology, hydrocarbon and touristic aspects. Researches that investigate the relationship between karst
and tectonics are rare in Iran. Nadimi and Sohrabi (2009) have studied Kalahrood cave in north Isfahan and showed that
brittle deformation and karstification processes have created a suitable area for cave formation.
In this research, we have two goals. Firstly, we are going to introduce and describe a sinkhole in the north Isfahan
city and secondly introduce role of tectonics in formation of Chah-e Deev sinkhole.
Chah-e Deev sinkhole area is located in southwestern margin of the Urumieh-Dokhtar Magmatic Arc (UDMA) and
its distance is about 55km from Isfahan. The area is surrounded by high and uplifted mountains of UDMA to the northeast
and the Sanandaj-Sirjan Zone flats to the southwest. The oldest exposed rocks in the Chah-e Deev area are yellowish
dolomite of middle Triassic that have exposure in northeastern margin of the area and separated by a NW-SE-trending
reverse fault. The area is covered by shales with intercalations of sandstones and ammonite limestones of Upper Triassic.
Several generations of alluvial fans and vertically eroded recent alluvial deposits indicate uplifting of the area. In the Chahe Deev area, the fault pattern consists of NW-SE and NE-SW- trending faults. These faults dissect older rocks and have
made a brittle area that created a suitable area for forming of a sinkhole.
The Chah-e Deev sinkhole has 35m width and about 56m depth that is formed on top of a hill and is 2221m higher
than sea level (see figure). Walls of the sinkhole are vertical and several sets of vertical joints that can be seen in the rocks.
Two steeply dipping dextral strike-slip faults have conjugated each other on the surface and have made a crushed zone. A
major fault plane was observed in the floor of the sinkhole that has made the northern wall of the hole and has sinistral
strike-slip component of movement (see figure). The structural observations show that tectonic processes are the first and
major factor for formation of Chah-e Deev sinkhole and also for determining its location.
Chah-e Deev sinkhole is the best and most unique example of sinkholes in central Iran. Based on this research in the
Chah-e Deev sinkhole, we have considered two main stages for tectonic evolution and formation of the sinkhole. First,
during the Zagros collision and start of strike-slip movements in Zagros collision zone after Pliocene, several fault sets
were formed. Conjugation of these faults and their branches and joints has created a crushed zone in Chah-e Deev area,
northeast Isfahan. Second, after formation of the faults and joint, uplifting of the area and activity of groundwater and
solving of Upper Triassic limestones in the lower part of the sinkhole, created some karsts and small caves and these places
were filled during subsidence the sinkhole.
Location of the studies area and Zagros orogen structural zones are shown in small map. A) Chah-e Deev Sinkhole on top
of a hill. B) Cross section of the sinkhole. C) Plane and slickenlines of a sinistral strike-slip fault in bottom of the sinkhole.
D) strike-slip faults of upper part of the sinkhole.
References:
1. Ballesteros, D., Jimenez-Sanchez, M., Garcia-Sansegundo, J., and Giralt, S., (2011) Geological methods applied to speleogenetical research in
vertical caves: the example of Torca Teyera shaft (Picos de Europa, northern Spain), Carbonates Evaporites, 26, 29-40.
2. Kambesis, P., (2007) The importance of cave exploration to scientific research, Journal Cave and Karst stud. Nat. Speleol. Soc., 69, 46-58.
3. Nadimi, A., and Sohrabi, A., (2009) Role of Tectonics in Forming of the Kalahrood Cave, North Isfahan, Iran, European Geosciences Union, General
Assembly, Vienna, Austria, Vol. 11, EGU-3936-1.
4. Stöcklin, J., (1968) Structural history and tectonics of Iran; a review, American Association of Petroleum Geologists Bulletin, 52, 7, 1229–1258.