GeoLines (Praha), 7 (1998) 3 Salt Plugs in the Eastern Zagros, Iran: Results of Regional Geological Reconnaissance Pavel BOSÁK1, Josef JAROŠ2, Jiøí SPUDIL3, Petr SULOVSKÝ4 and Vladimír VÁCLAVEK5 1 Geological Institute, Czech Academy of Sciences, Rozvojová 135, 165 02 Praha 6, Czech Republic; e-mail: [email protected] 2 Institute of Geology and Paleontology, Faculty of Natural Sciences, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic 3 GET Ltd., Korunovaèní 29, 170 00 Praha 7, Czech Republic, e-mail: [email protected] 4 Department of Mineralogy, Petrology and Geochemistry, Masaryk University, Kotláøská 2, 611 37 Brno, Czech Republic; e-mail: [email protected] 5 Pod Spoøilovem 2779, 141 00 Praha 4, Czech Republic ABSTRACT. Regional reconnaissance study of salt plugs cov- temperature is needed to start the glacier flow. Unbreached ered the area of about 50,000 square kilometers (coordinates salt plugs were discussed. Their occurrence is highly limited. It 53o50' to 56o30' E and 26o30' to 28o15‘N). Altogether 68 salt is shown, that “collapse structures” are connected rather with plugs were characterized from the viewpoint of their position other processes than solution collapse after leached salt. Tec- in the structure of area, morphological and evolution stages, tonic effects, erosion and pedimentation took part substantial- rock content and mineralization. ly in the formation of cauldrons. Linear cauldrons are connect- Prevailing amount of plugs lies in the flanks of anticline ed with tension regime in the apical zone of anticlines. Primary folds and is bounded to fold plunges and sigmoidal bends, where and secondary rim synclines have not been yet detected. The the most favorable conditions are established for the salt plug origin of salt plugs was multicyclic process active at least since intrusion. The position of plug is highly influenced by base- Paleogene. The distribution of exotic blocks in plugs was rein- ment tectonics, too. terpreted from satellite images and air photos, indicating that Hydrogeological works proved the existence of regional and the delineation and deciphering of their lithologies is some- local aquifers. Upper regional aquifers are situated in the Ba- times possible when the field knowledge is available. khtyari Formation filling most of synclines, the lower is con- The soliferous Hormoz Complex was deposited in Upper nected with Paleogene limestone units. The weathered zone of Precambrian (Riphean-Vendian) to Middle Cambrian on rifted salt plugs shows its own hydrogeological regime and aquifers. continental margins of Arabian Plate in a rectangular basin Groundwater is highly mineralized, sometimes even in the up- limited by deep (crustal) faults. New fossils have not been found. per aquifer. Waters can be classified as brackish to brines. Nu- The Hormoz Complex represents product of deposition in merous are warm springs accompanied with hydrogen sulfide. evaporitic basin with multicyclic nature and repeating hori- Salt plugs were classified into three structural-morpholog- zons of salts and other evaporites within carbonate-clastic-vol- ical groups (circular, linear and combined). According to size, canosedimentary accumulations. The percentage and thickness plugs are distinguished as small (below 4 km in diameter) and of gypsum and especially of salt decreased from the center of large. Activity of plugs was divided into three traditional groups, the basin towards its margins. Predominance of acid volcanics i.e. active, passive and ruins, each of groups being subdivided and volcanoclastics is bound to the southeastern part of the into three subgroups. Completely new criteria were adopted to region close to the Oman line. estimate the activity in the most objective manner. Salt glaciers originated in surficial conditions by increased creep caused by KEY WORDS: salt plugs, diapirism, lithology, tectonics, hy- the hydratation of salts. Movement of glaciers can be very fast drogeology, Hormoz Complex, Zagros Fold Belt, Southeastern if supplied in salt from plug vent. No anomalously increased Iran. 4 GeoLines (Praha), 7 (1998) 1. Introduction (P. Bosák) The geological exploration of salt plugs in the southeastern Iran and DURST apparatuses. Spatial information was enhanced by (Bandar Abbas area) was performed by the staff of the former (i) local optimization, (ii) first horizontal derivation, and (iii) GMS (Geoindustria GMS) exploration company from October Laplace operator. Spectral information was enhanced by (i) cal- 1992 to January 1993 (P. Bosák, J. Spudil, P. Sulovský and V. culations of ratios of individual spectral bands, (ii) principal Václavek). The study was concentrated to the geology, struc- component analysis, and (iii) production of color composite ture and position of famous salt plugs and for their economic images. Black-and-white products at the scale of 1:250,000 were geological potential. The study was ordered by the Ministry of produced as the principle material for photogeological inter- Plan and Budget, Tehran, Islamic Republic of Iran. pretation and planning of field operations. Air photos at the The exploration was divided into two important phases. The scale of about 1:60,000 (rows M 111-M 114, M 261-M 263, M first one was concentrated to detailed remote sensing analysis 287, M 295-M 300 and M 306 were taken in 1956 and 1957 by of the area (1991-1992) which was finished by the Final Report American companies) covered nearly whole studied territory, on Remote Sensing Phase (Bosák et al. 1992). The second phase nevertheless they could be used only for photogeology owing (1992/1993) was represented by the field reconnaissance com- to their age and substantially changed surface situation and in- pleted by the final report (Bosák et al. 1993). frastructure. On the other hand, they allowed to study changes This contribution deals dominantly with the results of the of relief and plugs which started within nearly 40 years. Limit- field phase of the study utilizing general results of the remote ed amount of air photos at the scale of about 1:20,000 were sensing analysis. It was edited by P. Bosák. The descriptive chap- available for some salt plugs and their surroundings (Puhal, ters were contributed by all authors taking part in the field phase Zendan, Do-Au and Qalat-e Bala), and for the Khanet Surkh and by Josef Jaroš. Responsible authors of respective chapters Anticline. and subchapters are mentioned in the text only. Altogether, 68 identifiable salt plugs and salt veins (Salz- Acknowledgement: We acknowledge the field cooperation of gang) occur on the surface (Fig. 1, Tabs. 18 and 19). Only 6 the staff of the Ministry of Plan and Budget, Tehran, Islamic sites were not visited during field operations or seen from heli- Republic of Iran. The chemical analyses of groundwater were copter. Other plugs were visited: (1) by car field trips (with performed in the Laboratory of Water of the Ministry of Power field routes on foot), (2) during helicopter landing (with field in Bandar Abbas (Islamic Republic of Iran). The chemical anal- foot trips, 7 sites), (3) by boat (with field trips on foot and/or yses of evaporates from groundwater and a part of chemical car, 2 sites), (4) by combined car trips/helicopter landing (3 analyses of rocks were performed in laboratory of MEGA Co. sites), (5) by combined car/boat trip (1 site, and (6) by car/foot in Strá• pod Ralskem (Czech Republic). The organic carbon trips, helicopter landing and boat/foot trips(1 site). Helicopter and hydrocarbons were analyzed in organic geochemical lab- reconnaissance covered 10 sites. Some salt plugs were surveyed oratory of the Czech Geological Institute, Brno (Czech Repub- by several visits (cf. Tab. A2 in the Appendix). During explora- lic). Thin sections and a part of chemical analyses of rocks tion works, study of groundwaters, springs and surficial streams were made by the GEMATRIX Ltd., Èernošice (Czech Repub- were carried out, too. lic). Digital processing of remote sensing data was performed Remote sensing analysis was performed before the start of by Mr. Jindøich Rejl, now with Agency of Nature Conservation the field reconnaissance. Following cosmic photos were uti- and Landscape Protection of the Czech Republic, Praha (Czech lized: LANDSAT MSS (digital, path: 160 and 161, row: 41, Republic) and Mr. Stanislav Saic in the Department of Image photos taken on May 15, 1984 [160/41] and April 29, 1987 Processing, Institute of Information Theory and Automatiza- [161/41]) and LANDSAT TM (digital, path: 160, row: 41 and tion, Academy of Sciences of the Czech Republic, Praha (Czech 42 floating), both types produced by LANDSAT/EOSAT (USA), Republic). Drawings were finished by Mr. Miroslav Morch, now SPOT XS (digital, path k: 162, row J: 296, photo taken on May with Timex Ltd. Zdice and by Mr. Josef Forman, Institute of 20, 1988) produced by SPOT IMAGE (France), and KFA 1000 Geology, Academy of Sciences of the Czech Republic, Praha (spectrozonal, analog type of data, film no. 0086, photo no. (Czech Republic). The help of all institutions and persons is 17586, photo taken on September 1, 1990) produced by acknowledged. The text was carefully and critically read and SOYUZKARTA (Russian Federation). Data were processed commented by Prof. Dr. Manfred Fürst (Hallstadt, FRG); his using specialized system of image analysis PERICOLOR 2001. contribution is especially acknowledged. Data were visualized on PHOTOMATION 1700, RECTIMAT GeoLines (Praha), 7 (1998) 5 2. Geographical data (P. Bosák, J. Spudil and V. Václavek) The studied area lies in the southern part of the Islamic Republic region and the sea level changes are documented by both river of Iran near the northern shore of Khalij-e Fars (Persian Gulf). and marine terrace systems. Several levels of terraces in the area The studied region covers the area of about 50,000 km2, and it is of Kuh-e Shu lie at +100 to +80 m, +60 m, +30 m, +15 to +10 m limited by coordinates: 26o30'-28o15' N and 53o50'-56o40 (Fig.