structural control on the salmas geothermal region

1 Introduction In recent decades, exploration of geothermal reservoirs

has been a controversial subject because of their role as a green source of energy (Brogi et al., 2005; Dilek et al., 2009; Dezayese etal., 2010; Faulds et al., 2010; Chambefort et al., 2014; Fauzi et al., 2015; Ebigbo et al., 2016; García and Díaz, 2016; Hammond and Bell, 2016 ?). Tectonic studies for geothermal prospects area are considered and handled in two aspects: first is the geodynamic setting of the reservoir, and second is a structural pattern of the exploration area (Meixner et al., 2016). From the geodynamic point of view, the heat regime of the area is regarded as the most important factor with the need to address related tectonic phenomena, which can be a source of heat. For example, if located an active volcano in the geothermal prospects region, the magmatic event can provide heat source for propagation of geothermal reservoir, for this reason the formation and

related futures are considerable notice. So, in order to decipher these unknowns, a comprehensive understanding about regional tectonics is definitely needed (Yamamoto et al., 2017; Yukutake et al., 2010). High heat flow is one of the most important characteristics for the formation of geothermal reservoirs. In continental crusts the high heat flow can be found in the surrounds of active magmatic arcs (Norini et al., 2015; (Alizadeh & Jangjoo, 2017) Roulleau et al., 2017). In Iran, the Urumieh-Dokhtar magmatic arc is the NW-SE trending magmatic events that related to the subdauction of Neo-Tethys oceanic crust under Iranian microcontinent. This magmatic arc lie parallel to the Zagros suture and Sanandaj-Sirjan Zone. This region is also known as a prospective area in the hosting of the geothermal reservoirs (Fig. 1a) (Jahangiri, 2007).

In addition, of younger volcanic complexes, magmatic bodies with ages up to 1 million years are also addressed as probable geothermal reservoirs ( Verdel et al., 2011;

Structural Control on the Salmas Geothermal Region, Northwest Iran, from Fractal Analysis and Paleostress Data

Mahdi BEHYARI1, *, Javad NOURALIEE2 and Davar EBRAHIMI2

1 Department of Geology, Faculty of Sciences, Urmia University, 57153165, Urmia, Iran 2 Renewable Energy Department, Niroo Research Institute (NRI), Tehran, Iran Abstract: The Salmas geothermal field is located in NW Iran. Subduction of Neo-Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic-Arc. Fractures and faults in the convergent zone have created path-ways for the circulation of geothermal fluid. Fracture concentration in the Salmas geothermal field has been characterized using of the fractal method and creation of a fracture density map that shows the highest concentration in the central part of the study area. The permeability of fractures has been evaluated by analyzing their orientation in respect to the paleostress axes. Also, the fractal analyzing result indicates the maximum fractal dimension (1.96) is around the thermal spring outlet. Paleostress analyzing revealed that in the central part of the study area, σ1 axes orientation is S90°W/10° and the σ2 dip is near to the vertical in this stress field, where strike slip faults can be propagated. In the SE part near the recharge of the thermal springs, the σ3 plunge increases to 70˚ and σ1 orientation is N15°E/20°, in this local tectonic regime thrust fault developed. Fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs in the Salmas geothermal field. Regarding the paleostress data fracture with N-S direction such as the F1 fault zone (parallel to the σ1 axes), a suitable pathway for deep circulation of geothermal fluid flow has been created. Key words: lineament extraction, fractal method, geothermal field, paleostress, Salmas, NW Iran

Vol. 92 No. 5 pp.1728–1738 ACTA GEOLOGICA SINICA (English Edition) Oct. 2018

* Corresponding author. E-mail: [email protected], [email protected]

© 2018 Geological Society of China

Oct. 2018 Vol. 92 No. 5 1729 ACTA GEOLOGICA SINICA (English Edition) http://www.geojournals.cn/dzxben/ch/index.aspx http://mc.manuscriptcentral.com/ags

Roulleau et al., 2017). Concerning structural patterns, investigation is

concentrated on more local and small-scale structures such as faults, fractures, folding and crushes zones. Each of these structures can influence circulation and transportation of the magma and geothermal fluid

(Roulleau et al., 2017). Fluid flow within the crust is important in a magmatic system because of its impressive role in the descent of cold water through the faults and fractures, heating at depth and final ascension of hot water in fractures and faults until recharge on the surface (Dezayes et al., 2010; Faulds et al., 2010; Yukutake et al.,

Fig. 1. Revised geological map of Salmas geothermal region after (khodabandeh, 1992). (a), Position of study area on the structural zone Map, study area is located between Sannandaj-Sirjan metamorphic zone and Urmia-Dokhtar magmatic Arc (Eocene Volcanic). (b), Structural map of study area and rock unit in the study area with location of outlet of hot water spring, Qtr: Quaternary Travertine, Qt: Quaternary Alluvium, Mms: Miocene marl, sandstone and shale, Pd: Permian Dolomite, Prd: Dolomite and limestone, El: Cambrian marl and sandstone, Ebt: Cambrian shale and dolomite, Ez: Cambrian shale and sandstone, Peksch: Pre-Cambrian shale and schist, Pek: Pre-Cambrian Slate phyletic shale, am: Am-phibolite with dioritic protolith, lm: Limestone, Cm: Ultramafic Rocks (color mélange), gr gh: Goshchi granite, Mt am: Amphibolite with some schist, Mt d: dioritic gabbro ,Mt gn: Gneiss with schist, Mt gr: Metagranite, Mt m: crystalized limestone, Mt mt: Meta-rhyolite, Meta-basalt, Mt sh: Biotite, amphibole schist with some gneiss, Mt r: Meta-rhyolite and meta-rhyodacite, Mt rsh: Alternatione of schist and amphibolite.

1730 Vol. 92 No. 5 Oct. 2018 ACTA GEOLOGICA SINICA (English Edition) http://www.geojournals.cn/dzxben/ch/index.aspx http://mc.manuscriptcentral.com/ags

2010; Fauzi et al., 2015; Hammond and Bell 2013; 2016; Meixner et al., 2016; Roulleau et al., 2017; Asghari et al., 2018) . Also, lineament and fracture spatial orientation are critical because of their effect on the secondary permeability and fluid circulation of geothermal reservoirs.

Fractal analysis is an effective tool for quantitative evaluation of the fracture pattern because of its reliability in revealing and detecting the fracture accumulation and distribution (Babadagli, 2001; Park et al., 2010; Fagereng, 2011; Kruhl, 2013; Pérez-Flores et al., 2017).

Permeability of fractures is closely linked with their spatial orientation related to the main regional stress axes (Pérez-López et al., 2005; Heuberger et al., 2010; Pérez-Flores et al., 2017;). Therefore, evaluating stress orientation is fundamental to the study of geothermal fields (Pérez-Flores et al., 2017) and so, in this research, we tried to find the principle stress axis orientation by using the geometrical analysis of structures. Actually, the orientation of structures such as faults with slickenline, conjugate fault, foliation and dikes is applied to reveal the direction of the main stress axes in the study area (Navabpour et al., 2007). Finally, regarding the determined directions of the stress axes, the impact of the structure is assessed in the formation of the Salmas geothermal field. 2 Regional Geology

The study area is located in northwestern Iran and according to the sedimentary-structural zoning of the country (Stocklin, 1968), it falls into the metamorphic and ophiolitic Sanandaj-Sirjan Zone (khodabandeh, 1992).

The oldest exposed rock units in the study area are metamorphosed amphibolite and greenschist. This complex is deformed in dynamo-thermal conditions, and is the most important metamorphism phase in the study area, within greenschist and amphibolite facies. Granite-diorite plutonic masses were intruded into the metamorphic complex. Fine-grained detrital deposits of the late Precambrian Kahar Formation have a fault contact with the metamorphic complex (Behyari et al., 2017). In, overlying sediments weighed down the Kahar unit, which caused slight deformation to propagate (to slate grade) because of the force of burial. An major unconformity indicates a wide gap through the late Ordovician, Silurian, Devonian and Carboniferous in the area (khodabandeh, 1992).

Permian units have a significant thickness in the study area and overlie the older unit unconformably or against the metamorphic rocks with thrust faults (Fig. 1b). The lithologies of the overlying Cretaceous rocks consist of

shale, sandstone and limestone units that have been slightly deformed (khodabandeh, 1992).

The Paleo-stress axes orientation provided adequate space to allow the emplacement of the batholithic Ghoshchi Granite, which penetrated into the older rock units, deformed them and propagated different contact metamorphic minerals.

In the late Cretaceous, mafic oceanic rocks had been broadly formed in the area and are covered by greenschist metamorphic rocks, huge masses of pillow basalt, dibasic dikes, a gabbro-diorite plutonic complex, pink pelagic limestone and shale. Between the late Cretaceous and the Paleocene, an ophiolitic mélange was abducted and has widespread exposure in the study area ( Hassanipak and Ghazi, 2000; Ballato et al., 2010; Agard et al., 2011; Azizi et al., 2011; Mouthereau et al., 2012). This complex caused metamorphism up to greenschist facies. In the Palaeocene, thick deposits such as conglomerate, breccia, shale and sandstone with pelagic and hemi-pelagic propagated interlayers (khodabandeh, 1992).

During the Plio-Pleistocene, tectonic stresses caused the development of folding in the sediments that were deposited in Miocene and Pliocene basins. This folded complex was then covered by series of lava, pyroclastics, formed during Quaternary volcanic activity, and other Quaternary sediments.

Another considerable tectonic event in the study area is travertine spring exposure along the fracture zone (Verdel et al., 2011). There are six warm springs in the Salmas region; their temperature varies from 23–29 degrees Celsius and their cumulative flow rate is about 6 l/s. Also, there are several travertine outcrops in the Salmas region. Because of the abovementioned surface manifestations, we believe that there is at least a geothermal reservoir in the deeper parts of this region (Nouraliee and Ebrahimi, 2016). 3 Tectonics and Structure 3.1 Lineament extraction and fracture distribution pattern

The fracture distribution pattern results from fracture automatic extraction from ASTER satellite images. In the first step, an RGB image combination of three bands is prepared from the ASTER satellite image. One and two bands were used because of having more natural colors (R:2 G:1 B:1). Then, a Sobel filter was applied for edge enhancement on the satellite images and after selecting appropriate parameters, lineaments were extracted from all three bands (Masoud & Koike, 2006; Raghavan, Masumoto, Koike, & Nagano, 1995; Ramli, Yusof, Yusoff, Juahir, & Shafri, 2010).


In the next step, the lineament layer is converted to a union layer and a lineament map is derived from this data. To distinguish the main joint sets and their direction, rose diagrams of lineation length and frequency were plotted. Results revealed that lineation with a N–S trend are the most frequent. Considering lineament length, they are almost dispersed, but NE–SW and N–S sets are longer. Extracted lineaments from satellite images were merged with the faults detected in field work. These lineaments and faults layers decompose into single vertexes and by interpolating these vertexes, a density map was generated.

In the study area, lineament density can be divided into four zones based on differences in the principal stress axes orientation, and fractal analysis conducted for each zone (Fig. 2). In Zone A of the study area the least density of fractures is observed, few faults are detected and thermal springs are also absent. In Zone B, a high distribution of lineament exists. In faulted parts of the area and especially in Permian limestone, fractures are more abundant than in the igneous part to the east of the study area. In the dense part of this fractured area one of the thermal springs is recharged. In Zone C, a high density of fractures is

Fig. 2. Fracture density map of Salmas geothermal region and depicted location of thermal spring. This map revealed that the thermal springs are located on the high fractured zone. With attention to the rose diagram of length and frequency, the fractures with N-S trend are the most frequent structures in the region. Also Fractal Square used for counting of fractures in the different dimension represent on the map.


frequent but thermal spring outlets are absent. Zone D is the main area for the hosting of thermal springs. Alongside faults and breccia regions, a dense fracture network is formed and some thermal springs also exist in this section of the Salmas geothermal region.

3.2 Fractal analysis

The lineaments extracted from satellite images and combined with regional faults were used to calculate fractal dimension and detect the fracture influence on the productive geothermal field.

A fracture distribution map presents a qualitative description of the fractures, but fractal geometry analysis is used to gain a quantitative approach for them. Most of the geological features have various variables so that finding their relationship is too complex for mathematical methods. For example, the relationship between rock grain size and earthquakes, or topography caused by faults and folds are these kind of relationships (Turcotte, 1997). Recently, numerous studies have been published addressing the application of fractal geometry for evaluating fault properties such as fault length, intensity, displacement, aperture, and their distance (Babadagli, 2001; Fagereng, 2011; Kruhl, 2013; Park et al., 2010).

The concept of fractal analysis is based on calculation of fractal dimension for each of the geometric elements. Fractal dimension can be in decimal numbers, so this method is an unrestricted approach to the measuring of natural phenomena (Turcotte, 1997; Volland & Kruhl, 2004). Fracture fractal distribution or fractal dimension is related to the development of the faulting activity in the study area. Many fractal models are proposed for the analysis of the faults distribution on the earth’s crust. Comparing them, the clearest for fault fractal distribution is the b coefficient that gives the best results (Fagereng, 2011; Kruhl, 2013; Pérez-López et al., 2005).

In this research, the square counter method was used for calculation of fractal dimension. The prepared lineaments map of the study area is divided into four squares (A, B, C and D) of 11.4 km dimension to analyze the fractures fractal. The plotted network covers all the study area (Fig. 2). In the fractal analysis, each of these squares is evaluated individually and the fractal dimension is calculated for all of them (Da to Dd). Then, each square with 11.4 km length is divided into four squares having 5.7 km sides; this process continued five times. The squares can be divided into a feed-forward cycle. The log-log curve of N (number of squares that contain fractures) is based on 1/R (length of each square) for each section and its slope is chosen as the fractal dimension of fracture X (Table 1).

Regarding the calculated fractal dimension, it is

revealed that four sections have different values. The high fractal dimension of a section fracture implicates the intensity of the fractures density. In Zone (A) the least value of fractal dimension is detected and that is in concordance with the fractures density map (Fig. 3a). In Zone C, fractal dimension increased to 1.91 because of fault propagation (Fig. 3c). In the (B) and (D) sections there are high values of fractal dimension and a considerable frequency of the fractures (Fig. 3b, d). In Zone D, the highest amounts of fractal dimension and also several thermal springs exist. The fractal dimension value indicates that in this section thermal springs are in close relationship with fracture density and logically faults played an important role in the formation of the geothermal reservoirs. So, for this reason in the next step geometrical and kinematic analyses of the faults were conducted in the study area.

3.3 Geometric and kinematic analysis of structures

Structures in the Salmas geothermal region can be generally divided into brittle and ductile categories. Brittle ones mainly include faults and conjugate fractures; ductile and semi-ductile comprise shear zones, folds and their related foliations. The brittle structures usually cut ductile ones and are relatively younger. They are used for kinematic analysis to detect the main stress axes in the study area.

Faults can be divided into two sets based on geometry and spatial orientation: the first set has a N–S trend and second set has NE–SW orientation. When these faults intersect with each other, the consequent fracture density increases and facilitates the thermal fluid flow in the deeper parts of the crust. According to the field studies, the geometric characteristics of the major faults, which influence geothermal reservoir formation, can be described as follows.

The F1 fault trend is almost N010E and located adjacent to Salmas thermal spring. The length of this fault in the satellite image is detectable up to 5 km. This fault caused the formation of a valley with the same direction (Fig. 1). Structural data on the fault plane in the valley show a dip

Table 1 Fractal analysis data. Length of the square in different dimensions and number of squares, which contain fractures in each zone

R (km) Log 1/R N A N B N C N D 14.50 −1.16 1 1 1 1 7.25 −0.86 4 4 4 4 3.62 −0.56 16 16 16 16 1.81 −0.26 57 82 62 75 0.90 0.05 220 226 219 234 0.45 0.35 740 894 788 904Fractal Dimension 1.90 1.96 1.91 1.96

R: length of each square, N: number of square contain faults or fracture in each square


of about 70° to 85°. Kinematic analyses on the fault plane such as fault step and slickensides confirmed that there is a left lateral displacement on the fault zone. Subsidiary valleys that are cut by F1 also have sinistral movement. Based on the relative age detection rules and the observation that F1 cuts other faults in the area, it can be regarded as the youngest one. The width of its crush zone is about 5 m to 7 m. In some locations, subsidiary faults are added to the major fault zone, and crush zone width increased. Several cold springs are observed alongside this fault and indicate that the crush zone acts as a continuous network with fluids circulating within it. The dimension of F1 has no effect on the crustal thermal regime in this region, but it provides a pathway for fluid flow.

The F2 is an E–W trend fault, located 1 km south of the thermal spring; it is cut by the F1 fault. In the F1 fault valley, evidence of F2 is also observed. Its dip is about 50° to 60° and the fault plane dip is to the north. This is not a single fault but observed as a set of parallel fractures all cut by F1. Considering the collected data from slickensides, folds are formed by the thrust component of F2 and most of the structures are semi-ductile. The major structures consist of microfolds, drag folds and also foliation and subsidiary thrusts faults parallel to the main thrust. The width of the crush zone of F2 is about 10 m and thermal springs are not observed around it, but only some weak seepage of water from fracture of rocks can be

seen. The F3 fault is one of the most effective faults in the

study area and its fault zone contains the fractured area. It separates the colored mélange basin from the metamorphic units with a sharp difference clearly observable between two sides of this fault (Fig. 1, Fig. 4b). Its impact in the fracture density maps is also revealed and the fracture density increases within the fault zone (Fig. 2). The F3 fault also affected the fractal analysis result and increased the fractal dimension in the F3 fault zone.

Regarding the tectonic setting of NW Iran ophiolites, the age of the metamorphic units has been predicted as before the Cretaceous (Azizi et al., 2011; Hassanipak and Ghazi, 2000). The fault movement mechanism was thrusting in the early stages. Its direction is almost E–W, which changed to the NE–SW in some locations. The fault movement mechanism was evaluated using evidence such as fault step and slickenside. The rake of the striation on the fault plane is about 10˚W and the fault mechanism is a right lateral strike slip (Fig. 4a–b).

Foliations are other structures propagated broadly in the study area. They have been formed perpendicular to the maximum stress axis and, consequently, they can be used as an indicator of secondary permeability in the rock units. Fractures and faults that are parallel to the foliation (i.e. perpendicular to maximum stress axis) were squeezed and then permeability was decreased in that direction.

Fig. 3. Calculated fractal dimensions for the four zones of the Salmas geothermal region. Horizontal axes are the logarithm of the length of each square and vertical axes is the number of squares that contain fractures. In the equation of a line the X coefficient is fractal dimension.


Foliation data acquisition in the study area indicates various spatial orientations of the foliated plane. Their dip is also variable in different parts of the region and shows a wide range, between 20˚ to 80˚ degrees.

Some evidence of semi-ductile deformation is detected in the study area. Rock fragments such as limestone wrap in the soft fabrics like schist. These rotations indicate that there are non-coaxial ductile deformation and high-temperature conditions in the shear zone. Regarding the direction of porphyroclast rotation, the shear sense in the semi-ductile shear zone is sinistral. Micro-folds can also be seen in chert and sometimes show signs of flow indicating that they were formed in the flexural flow and shear conditions.

In the central and eastern parts of the study area, highly deformed shear zones with NE–SW strike have been propagated. Amphibolites and basalts are deformed and caused the formation of prominent structures such as refolding (Fig. 5a), ptygmatic folds and quartz veins boudin (Fig. 5a–b). The axial plane of the folds formed in the amphibolite layers is recumbent and also refolding occurred in the recumbent axial plane. From the geothermal point of view, it must be noted that all ductile or semi-ductile structures in the shear zone are cut and displaced by N–S brittle faults. Therefore, a new brittle deformation phase influenced the study area. 3.4 Paleostress and principal stress axes:

Besides geodynamic and geomechanical properties, spatial orientation and type of structure is affected by the direction of the main stress axis (Saintot & Angelier, 2002). So, the spatial orientation of the main stress axes, consequently the local compressional and tensional stress field, constitutes notable importance both in categorizing structures and analysing their effect on the formation of geothermal reservoirs (Pérez-Flores et al., 2017). To achieve this aim, and to determine the paleostress principal stress axes, using fault plane data and

slickensides direction can be addressed as the best tool (Navabpour et al., 2006; Pérez-López et al., 2005; 2017). These features are applied to the F1 and F2 faults for detecting the paleostress data and compressional and tensional stress axes. Conjugate faults or other structures were applied to detect the stress direction. Considering to this principle that the bisector of the acute angle between two conjugate faults is indicated σ1 direction, and the bisector of the obtuse angle between the two conjugate faults, stands for σ 3, so regarding these principles and the abundance of conjugate faults in this geothermal region, the paleostress axes direction can be determined. Also, with attention to this fact that the foliation developed perpendicular to maximum stress axis and the strike of the dikes is parallel with the maximum stress (Magee et al., 2012), these structures also have been used to determine paleostress direction.

Data used in the S1 station are mainly based on the foliation spatial orientation measurements. In spite of having wide diversity, the foliation dips are almost toward the SW. After analysing the structural data, it is revealed that NE–SW is the direction of maximum stress and its position is N 33°E/16. In the S2 station interpretations were carried out based on conjugate faults. Two fault sets are observed here with different directions: N30°E/75°NW and E20°S/80°SW; considering these directions, the main stress axis direction is expected to be NE–SW with a N 65°E/27° trend. The revealed direction in the S2 station is almost parallel to the first station. The S3 station is located at the central part of the study area and conjugate faults are also the most frequent recorded structures.

The direction of these faults is measured as N45°W/80°NE and S75°W/80°SE. In this station, the position of the main stress axis is N77°W/18°. Performing the same procedure, the maximum stress position in different stations is detected at S4, S5, S6, S7 and S8 as S88°W/02°, N26°W/60°, N20°W/60°, E90°S/20°and S16°W/09°, respectively (Fig. 6).

Fig. 4. F3 fault zone in the Salmas geothermal region. (a), F3 fault is a right lateral strike slip fault which acts as a divider between ophiolite and metamorphosed intrusion units. Stereonet showed orientation of principal stress axes calculated from fault plane slip data. (b), Fault step and slickenlines on the F3 fault plane.


4 Discussion

Density of fractures and orientation relationship with direction of compressional and tensional stress field were applied to evaluate their potential to create a pathway for fluid flow because of the primary permeability. Fractures with a perpendicular orientation to the maximum stress field are squeezed impeding the connection of the fracture network. Our paleostress data analyzed with Win-Tensor 4.0 (Delvaux, 2012) and the data demonstrate that in the central part of the study area, where s2, s3 and s4 stations are located, the average maximum stress axis orientation is S90° W/10°. In this zone under such a stress field, structures are commonly characterized by strike slip faults with thrust component, such as F3. Therefore, in this area, fractures with E–W orientation (parallel to maximum stress), due to proper aperture, are the proper path for fluid circulation. In contrast to this, fractures with N–S orientation have been squeezed and have low permeability and so cannot play an important role in the geothermal system.

Due to the proximity of thermal springs to S1, S7 and

S8 stations, the paleostress axes direction and fracture density and orientation are more important than at other stations. In those stations, σ1 is near to horizontal and, according to Anderson theory, thrust faults and a transpression shear zone can be developed in this type of the stress field (Anderson, 1951). On average, the maximum stress axis orientation is N15E/20˚. This fracture with the N–S direction is effective in the preparing a pathway for fluid around a thermal spring. The F1 fault with a 350°–170° strike and fractures along this fault have an important role in the fluid flow. In the S5 and S6 stations, the σ1 plunge increases and reaches to near vertical. On average, the maximum stress orientation is N50W/70. This stress regime is proper to the propagation of normal faults with a strike slip component and transtensional shear zones. In this region, it is revealed that tensional regime of normal faults is an important factor in the circulation of underground fluid.

Ophiolite obduction in the study area implies that this region is located in the Zagros suture zone. A collision tectonic event affected paleostress axes and age of the palestress tensor contemporaneous with this event in the

Fig. 5. Refolding in the amphibolite rock unit. (a) ductile structure such as refolds or folded veins cut by brittle faults (b) Poly folded quartz veins, (c) Refolding white layer cut brittle faults.


late Oligocene and early Miocene (20 Ma) (Hassanipak and Ghazi, 2000; Ballato et al., 2010; Agard et al., 2011; Azizi et al., 2011; Mouthereau et al., 2012). In the eastern parts of the study area density of the fractures is higher than other parts of the region. Also, fractal analyses of faults and fractures confirm that the fractal dimension of the eastern section is 0.5 more that the western section of the Salmas geothermal region. The fracture direction study has revealed that there are different trends in the region but N–S and NE–SW trends are the most frequent ones. Despite this fact, fracture abundance in the study area is unable to prove the [reason for] the considerable permeability.

The F1 fault trend is almost N–S and can be addressed as one of the most important structures in the development of the geothermal reservoirs. Considering the fault effect in the study area, the stress direction experienced local shift in the study area. In the western section the stress direction is almost E–W and there are fewer fractures. 5 Conclusions

We used a lineament and fracture density map to

demonstrate the concentration of faults and related

fractures in the Salmas geothermal field. Lineaments were extracted from satellite images, combined with recognized faults from our field studies. The prepared map reveals that thermal springs outlets are located in the high fracture density zone.

To gain a quantitative distribution of fractures in the study area, we used fractal geometry analysis. Our results show that where thermal springs have exposure, increased fractal dimension reaches to 1.96, so these data indicate that the geothermal system in the study area is controlled by structures and the fractures pattern.

Field investigation and observation show that various structures have been affected in the study area; the youngest is brittle faults, which cut all ductile structures. Also, the spatial orientation of the structures shows wide variations in ranges and implies change in the orientation of the principal stress axes.

Paleostress analysis carried out in the study area to find relationships between the orientation of fractures and stress axes characterize that the set of fractures have a role in the fluid circulation in deeper parts of the geothermal system. Our data indicates that in the S1, S7 and S8 stations, σ3 orientation is near vertical and σ1 is in a N–S direction for these fractures with N–S orientation such as

Fig. 6. Fault slip data, conjugate faults and foliation orientation inferred to paleostress axes. Stereographic projection faults with slip line in the fault plane. Blue arrow indicates main compression direction and red arrows show the maximum tension direction. Gravimetric data also revealed along the F1 fault occurred distinct variation on the gravity of the rock units.


fractures in the F1 zone having an important role in increasing permeability and fluid circulation in the geothermal system. In the S5 and S6 stations, σ1 is near to the centre of the stereonet. This regime is proper for development of normal faults and where there is extension of the normal fault it can play an important role in the fluid transfer. In the S2, S3 and S4 stations, the σ2 plunge is near to vertical and strike-slip faults are propagated under these conditions. The σ1 direction is E–W for this F3 fault and fractures with the same orientation are essential elements in the evolution of geothermal system.

The results of this study demonstrate that in the Salmas geothermal field, fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs.

Acknowledgements

This work was supported financially by Urmia University and the Renewable Energy Department of the Niroo Research Institute (NRI). The authors would like to express their appreciation and gratitude to Professor Degan Shu, Dr Lian Liu and Dr Susan Turner for their editorial work, and two reviewers for making constructive comments and valuable suggestions, all of which have definitely improved the quality of this work.

Manuscript received Mar. 21, 2018 accepted May. 15, 2018

edited by Susan Turner and Fei Hongcai References Agard, P., Omrani, J., Jolivet, L., Whitechurch, H., Vrielynck,

B., Spakman, W., and Wortel, R., 2011. Zagros orogeny: A subduction-dominated process. Geological Magazine, 148(5–6): 692–725. doi:10.1017/S001675681100046X.

Alizadeh, A., and Jangjoo, F., 2017. Wedge‐Shaped Pop‐Up Structure in the Eslami Peninsula, Lake Urmia, Northwestern Iran. Acta Geologica Sinica(English Edition): 91(4): 1264-1269.

Asghari, G., Alipour, S., Azizi, H., & Mirnejad, H., 2018. Geology and mineral chemistry of gold mineralization in Mirge‐Naqshineh occurrence (Saqez, NW Iran): Implications for transportation and precipitation of gold. Acta Geologica Sinica (English Edition), 92(1): 210–224.

Anderson, E.M., 1951. The dynamics of faulting and dyke formation with application to Britain (2nd ed.). Oliver and Boyd, Edinburgh, 1–206,.

Azizi, H., Chung, S.-L., Tanaka, T., and Asahara, Y., 2011. Isotopic dating of the Khoy metamorphic complex (KMC), northwestern Iran: A significant revision of the formation age and magma source. Precambrian Research, 185(3): 87–94.

Babadagli, T., 2001. Fractal analysis of 2-D fracture networks of geothermal reservoirs in south-western Turkey. Journal of Volcanology and Geothermal Research, 112(1): 83–103.

Ballato, P., Uba, C. E., Landgraf, A., Strecker, M. R., Sudo, M., Stockli, D. F., and Tabatabaei, S. H., 2010. Arabia-Eurasia continental collision: Insights from late Tertiary foreland-basin evolution in the Alborz Mountains, northern Iran. Geological Society of America Bulletin, 123(1–2): 106–131. doi:10.1130/B30091.1

Behyari, M., Mohajjel, M., Sobel, E. R., Rezaeian, M., Moayyed, M., and Schmidt, A., 2017. Analysis of exhumation history in Misho Mountains, NW Iran: Insights from structural and apatite fission track data. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 283(3): 291–308.

Brogi, A., Lazzarotto, A., Liotta, D., Ranalli, G., and Group, C.W., 2005. Crustal structures in the geothermal areas of southern Tuscany (Italy): insights from the CROP 18 deep seismic reflection lines. Journal of Volcanology and Geothermal Research, 148(1): 60–80.

Chambefort, I., Lewis, B., Wilson, C., Rae, A., Coutts, C., Bignall, G., and Ireland, T., 2014. Stratigraphy and structure of the Ngatamariki geothermal system from new zircon U–Pb geochronology: Implications for Taupo Volcanic Zone evolution. Journal of Volcanology and Geothermal Research, 274: 51–70.

Delvaux, D., 2012. Release of program Win-Tensor 4.0 for tectonic stress inversion: statistical expression of stress parameters. Paper presented at the Geophysical research abstracts.

Dezayes, C., Genter, A., and Valley, B., 2010. Structure of the low permeable naturally fractured geothermal reservoir at Soultz. Comptes Rendus Geoscience, 342(7): 517–530.

Dilek, Y., and Sandvol, E., 2009. Seismic structure, crustal architecture and tectonic evolution of the Anatolian-African Plate Boundary and the Cenozoic orogenic belts in the Eastern Mediterranean Region. Geological Society of London Special Publication, 327: 127–160. doi:10.1144/SP327.8.

Ebigbo, A., Niederau, J., Marquart, G., Dini, I., Thorwart, M., Rabbel, W., and Clauser, C., 2016. Influence of depth, temperature, and structure of a crustal heat source on the geothermal reservoirs of Tuscany: numerical modelling and sensitivity study. Geothermal Energy, 4(1): 5.

Fagereng, Å., 2011. Fractal vein distributions within a fault-fracture mesh in an exhumed accretionary mélange, Chrystalls Beach Complex, New Zealand. Journal of Structural Geology, 33(5): 918–927.

Faulds, J. E., Coolbaugh, M. F., Benoit, D., Oppliger, G., Perkins, M., Moeck, I., and Drakos, P., 2010. Structural controls of geothermal activity in the northern Hot Springs Mountains, western Nevada: The tale of three geothermal systems (Brady’s, Desert Peak, and Desert Queen). Geothermal Resources Council Transactions, 34, 675–683.

Fauzi, A., Permana, H., Indarto, S., and Gaffar, E. 2015. Regional structure control on geothermal systems in West Java, Indonesia. Proceedings of the World Geothermal Congress, Melbourne, Australia, 19–25 April 2015.

García, K., and Díaz, D., 2016. Three-dimensional geo-electrical structure in Juncalito geothermal prospect, northern Chile. Geothermics, 64: 527–537.

Hammond, W.C., and Bell, J.W.2013. Structural controls on geothermal reservoir deformation at Stillwater, Nevada. From InSAR and GPS Data, GRC Transactions, 37: 11–15.

Hassanipak, A., and Ghazi, A.M., 2000. Petrology, geochemistry and tectonic setting of the Khoy ophiolite, northwest Iran:


implications for Tethyan tectonics. Journal of Asian Earth Sciences, 18(1): 109–121.

Heuberger, S., Célérier, B., Burg, J.-P., Chaudhry, N.M., Dawood, H., and Hussain, S., 2010. Paleostress regimes from brittle structures of the Karakoram–Kohistan Suture Zone and surrounding areas of NW Pakistan. Journal of Asian Earth Sciences, 38(6): 307–335.

Jahangiri, A., 2007. Post-collisional Miocene adakitic volcanism in NW Iran: Geochemical and geodynamic implications. Journal of Asian Earth Sciences, 30(3): 433–447.

Khodabandeh, A.A., 1992. Salams 1:100000 Geological Map. 4966. Geological survey and mineral exploration of iran (GSI).Tehran, Iran.

Kruhl, J.H., 2013. Fractal-geometry techniques in the quantification of complex rock structures: a special view on scaling regimes, inhomogeneity and anisotropy. Journal of Structural Geology, 46: 2–21.

Magee, C., Stevenson, C., O'Driscoll, B., Schofield, N., and McDermott, K., 2012. An alternative emplacement model for the classic Ardnamurchan cone sheet swarm, NW Scotland, involving lateral magma supply via regional dykes. Journal of Structural Geology, 43: 73–91.

Masoud, A., and Koike, K., 2006. Tectonic architecture through Landsat-7 ETM+/SRTM DEM-derived lineaments and relationship to the hydrogeologic setting in Siwa region, NW Egypt. Journal of African Earth Sciences, 45(4): 467–477.

Meixner, J., Schill, E., Grimmer, J.C., Gaucher, E., Kohl, T., and Klingler, P., 2016. Structural control of geothermal reservoirs in extensional tectonic settings: an example from the Upper Rhine Graben. Journal of Structural Geology, 82: 1–15.

Mouthereau, F., Lacombe, O., and Vergés, J., 2012. Building the Zagros collisional orogen: timing, strain distribution and the dynamics of Arabia/Eurasia plate convergence. Tectonophysics, 532: 27–60.

Navabpour, P., Angelier, J., and Barrier, E., 2006. Paleostress and brittle tectonic evolution from continental passive margin to continental collision: a case study of the High Zagros Belt of interior Fars, Iran. The Middle East Basin Evolution Conference, Abstracts.University of Milan. Milan, 34–37.

Navabpour, P., Angelier, J., and Barrier, E., 2007. Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province). Tectonophysics, 432(1): 101–131.

Norini, G., Groppelli, G., Sulpizio, R., Carrasco-Núñez, G., Dávila-Harris, P., Pellicioli, C., and De Franco, R., 2015. Structural analysis and thermal remote sensing of the Los Humeros Volcanic Complex: Implications for volcano structure and geothermal exploration. Journal of Volcanology and Geothermal Research, 301: 221–237.

Nouraliee, J., and Ebrahimi, D., 2016. Geochemical studies in Salmas geothermal region. Renewable Energy Department, Niroo research Institute (NRI), Tehran, Iran. Internal report in Persian.

Park, S.-I., Kim, Y.-S., Ryoo, C.-R., and Sanderson, D., J., 2010. Fractal analysis of the evolution of a fracture network in a granite outcrop, SE Korea. Geosciences Journal, 14(2): 201–215.

Pérez-Flores, P., Veloso, E., Cembrano, J., Sánchez-Alfaro, P.,

Lizama, M., and Arancibia, G., 2017. Fracture network, fluid pathways and paleostress at the Tolhuaca geothermal field. Journal of Structural Geology, 96: 134–148.

Pérez-López, R., Paredes, C., and Muñoz-Martín, A., 2005. Relationship between the fractal dimension anisotropy of the spatial faults distribution and the paleostress fields on a Variscan granitic massif (Central Spain): the F-parameter. Journal of Structural Geology, 27(4): 663–677.

Raghavan, V., Masumoto, S., Koike, K., and Nagano, S., 1995. Automatic lineament extraction from digital images using a segment tracing and rotation transformation approach. Computers & Geosciences, 21(4): 555–591.

Ramli, M., Yusof, N., Yusoff, M., Juahir, H., and Shafri, H., 2010. Lineament mapping and its application in landslide hazard assessment: a review. Bulletin of Engineering Geology and the Environment, 69(2): 215–233.

Roullea2u, E., Bravo, F., Pinti, D. L., Barde-Cabusson, S., Pizarro, M., Tardani, D., and Takahata, N., 2017. Structural controls on fluid circulation at the Caviahue-Copahue Volcanic Complex (CCVC) geothermal area (Chile-Argentina), revealed by soil CO 2 and temperature, self-potential, and helium isotopes. Journal of Volcanology and Geothermal Research, 341: 104–118.

Saintot, A., and Angelier, J., 2002. Tectonic paleostress fields and structural evolution of the NW-Caucasus fold-and-thrust belt from Late Cretaceous to Quaternary. Tectonophysics, 357(1): 1–31.

Stocklin, J. 1968. Structural History and Tectonic of Iran: A Review. American Association of Petroleum Geologists Bulletin, USA, 52: 1229–1258.

Turcotte, D.L., 1997. Fractals and chaos in geology and geophysics. Cambridge: Cambridge University Press, pp.

Verdel, C., Wernicke, B.P., Hassanzadeh, J., and Guest, B., 2011. A Paleogene extensional arc flare‐up in Iran. Tectonics, 30(3): 1–20.

Volland, S., and Kruhl, J.H., 2004. Anisotropy quantification: the application of fractal geometry methods on tectonic fracture patterns of a Hercynian fault zone in NW Sardinia. Journal of Structural Geology, 26(8): 1499–1510.

Yamamoto, Y., Hamada, Y., Kamiya, N., Ojima, T., Chiyonobu, S., and Saito, S., 2017. Geothermal structure of the Miura–Boso plate subduction margin, central Japan. Tectonophysics, 710: 81–87.

Yukutake, Y., Tanada, T., Honda, R., Harada, M., Ito, H., and Yoshida, A., 2010. Fine fracture structures in the geothermal region of Hakone volcano, revealed by well-resolved earthquake hypocenters and focal mechanisms. Tectonophysics, 489(1): 104–118.

About the first author Mahdi BEHYARI: Male, is an assistant professor in the

Department of Geology, Urmia University, Iran. He specialized in structural geology and tectonics. His works concern progressive deformation in the ductile shear zone in the W and NW Iran. He is now interested to utilize strain ellipsoid shape in the shear zone as an index for the evolution of the ductile shear zone.

structural control on the salmas geothermal region

Documents