Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey

Accepted Manuscript Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey Gulcan Sarp PII: DOI: Reference:

S1367-9120(14)00522-7 http://dx.doi.org/10.1016/j.jseaes.2014.11.017 JAES 2178

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

23 May 2014 1 October 2014 11 November 2014

Please cite this article as: Sarp, G., Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey, Journal of Asian Earth Sciences (2014), doi: http://dx.doi.org/10.1016/j.jseaes.2014.11.017

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Tectonic controls of the North Anatolian Fault System (NAFS) on the geomorphic evolution of the alluvial fans and fan catchments in Erzincan pull-apart basin; Turkey Gulcan Sarp Geological Engineering Department, Suleyman Demirel University, 32260 Isparta, Turkey *Corresponding author. e-mail: [email protected], [email protected]

Abstract The Erzincan pull-apart basin is located in the eastern section of the North Anatolian Fault System (NAFS). The tectonic evolution of this basin is mostly controlled by strike slip master faults of the NAFS. This study examines the topography–structure relationships in an effort to evaluate the tectonic signatures in the landscape, paying special attention to recent tectonic activity. In the study, the main focus is on the tectonic controls of the NAFS on the geomorphic evolution of alluvial fans and fan catchments in the Erzincan pull-apart basin. The observations of the amount of tilting of the alluvial fans (β) and its relation with morphometric (Asymmetry Factor (AF), Hypsometric Integral (HI), Fractal analysis of drainage networks (D)) properties of the fan catchments provide valuable information about the tectonic evolution of the basin area. The results of the analyses showed that the alluvial fan and fan catchment morphology in the pull-apart basin are mainly controlled by the ongoing tectonic activity of the NAFS. The fault system in the basin has controlled the accommodation space by causing differential subsidence of the basin, and aggradation processes by causing channel migration, channel incision and tilting the alluvial fans.

Keywords: Alluvial fans, Tectonic activity, Morphometric indices, Erzincan basin, North Anatolian Fault System

1. Introduction Alluvial fans are a common feature in many arid and semi-arid regions and provide a significant record of Quaternary tectonics and climate change (Birkeland, 1999; Bull, 1977, 1991). Alluvial fans are commonly built outwardly from the long, high-angle, fault-bounded basin margins such as the Dead Sea rift (Sneh, 1979), the Salton basin of southern California (Van de Kamp, 1973), the East Anatolian pull-apart basins in Turkey (Hempton and Dune, 1984), and the North Anatolian pull-apart basins in Turkey (Sengor et al., 2005; Barka et al., 2000). Among others, these basins usually have a strongly elongated shape typically forming half grabens, in which one side of the basin undergoes significantly more subsidence than the other (Blair, 1987) and have syndepositional fault motion (Colella, 1988). Alluvial fans have been built outwardly from basin margins by high gradient feeder channels that flow transverse to the basin axis. The geomorphic evolution of alluvial fans is controlled by fan catchment characteristics, tectonics and climate (Harvey et al., 2005). The catchment characteristics influence mainly the size and slope of alluvial fans (Bull, 1962; Hooke, 1967). Tectonic forces influence the fan morphology by controlling the accommodation space and, therefore, the sequential organization of the detrital sediments (Ethridge and Wescott, 1984; Silva et al., 1992; Calvache et al., 1997; Barrier et al., 2010). They are easily differentiated from the neighboring fluvial environments by characteristic fan morphology. Morphometric indices have been broadly used as a tool to identify and characterize sectors deformed by active faults (Keller and Pinter, 1996; Pedrera et al., 2009; Perez-Peña et al., 2010). The morphometric properties of alluvial fans and fan catchments have been successfully applied

in large-scale geographical studies. Gorur (1992) studied a tectonically controlled alluvial fan which developed into a marine fan-delta at a complex triple junction: the Miocene Gildirli formation of the Adana Basin in Turkey (Fig. 1a). Singh and Tandon (2007) studied the effects of the past and ongoing deformation on two fans that occur in the Pinjaur dun, in northwestern Himalayan foothills. Goswami et al. (2009) studied the tectonic controls on the geomorphic evolution of alluvial fans in the Piedmont Zone of Ganga Plain in India. Gómez-Villar et al. (2006) analyzed the factors which influence the presence or absence of tributary-junction fans in the Iberian Range in northern Spain. Saqqa and Atallah (2013) studied the development of alluvial fans at the foot of the fault-controlled eastern mountainous chain in Wadi Araba Desert in Jordan. Sarp and Duzgun (2012) tested the spatial significance of the morphometric indices in tectonically active Bolu pull-apart basin in order to evaluate the tectonic activity of the opposite sides of the basin margins. Sarp (2014) analyzed the tectonic and geomorphic history of the Bingöl pull-apart basin based on morphometric features (Fig. 1a). The North Anatolian Fault System (NAFS) is one of the most well-known tectonically active strike–slip faults in the world. It forms the boundary between the Eurasian and Anatolian plates. The fault zone extends from eastern Turkey to the Aegean Sea in the shape of an arc parallel to the Black Sea coast (Ketin, 1948; Ambraseys, 1970; Barka, 1992; Yilmaz et al., 2002) (Fig. 1a). The offset and slip rate of the NAFS vary from place to place because of a number of different fault segments that join or bifurcate the NAFS (Saroglu, 1988). In a detailed morphotectonic study of the central and eastern NAFS, the geologically-constrained Neogene slip rate of 6.5 mm/yr (over 13 Myr) has been succeeded by a higher Holocene slip rate of about 20 mm/yr (Hubert-Ferrari et al., 2002), which is consistent with the contemporary GPS-determined rate (McClusky et al., 2000). Several Neogene–Quaternary tectonic basins are formed within or

adjacent to the NAFS. According to Barka and Gulen (1988), the continental clastic deposits of these basins clearly exhibit the tectonic signature of the initiation of the fault zone. The Erzincan pull-apart basin is developed along the eastern part of the NAFS. The duration and morphometric evolution of the basin are disputed in Tatar et al. (2013). It was initially interpreted as a simple pull-apart basin at a releasing step-over by Sengor (1979) and Hempton and Dunne (1984). According to recent studies, however, the Erzincan basin does not show a simple pull-apart shape and its complex multi-phase development has been attributed to both movements along the interfering segments of the NAFS and the Ovacik fault (Linneman, 2002; Grosser, 1998). Tectonic models proposed to explain the basin range from simple rhomboidal pull-apart to a complex multi-phase evolution. To help constrain the age and tectonic regime(s) forming the basin, a palaeomagnetic and geochronologic study of volcanic domes which occur mainly in proximity to strike-slip faulting along the northern margin of the basin was carried out by Tatar et al. (2013) and it was proposed that the Erzincan basin is segmented as a mature basin by strike-slip cross faults. In this study the tectonic influences of the NAFS on the morphometric evolution of the alluvial fans and fan catchment morphology in the pull-apart basin is investigated to evaluate mature stage of the basin. The results of the study reveal that ongoing tectonic activity of the NAFS have mainly controlled the morphometric evolution of the alluvial fans and fan catchment morphology. 2. Geological and tectonic setting of the basin area The Erzincan pull-apart basin is situated in the eastern part of the NAFS, and the shape and the sedimentary fill of the basin were developed under the control of the tectonically active strike

slip motion of the fault system (Fig. 1a). The basin area is 15 km wide and 50 km long (Avsar et al., 2013). Several small volcanoes which formed during the pull-apart opening are aligned along the margins of the basin, usually along the northeastern margin (Barka and Gulen, 1989). These volcanoes and hot springs suggest high heat flow and the thinning of the crust (Aydin and Nur, 1982). The pull-apart basin is bounded by the Kesis Mountains in the north and by the Munzur Mountains in the south. The Kesis Mountains are characterized by the Refahiye complex (Fig. 1b), which contains ophiolites with large amounts of serpentinite and metamorphic rocks. The Refahiye complex is overlain by the Paleocene-Eocene aged Sipirkoy formation, which is composed of siliciclastic and carbonate sedimentary rocks (Rice et al., 2009). To the south of the Erzincan basin, the basement rocks consist of Upper Triassic to Lower Cretaceous carbonates of the Munzur formation (Ozgul and Tursucu, 1983), which was called the Munzur Dag unit by Rice et al. (2009). The Karayaprak Melange is a 4-km-thick, variably tectonized mixture of blocks consisting of serpentine, basalt, radiolarite, massive limestone and volcaniclastic sedimentary rocks. The Sutpinar formation consists of a 1.500 m thick, upwardcoarsening succession of mixed carbonate siliciclastic sedimentary rocks and subordinate volcanic rocks. The basement rocks on both sides of the basin are covered by Miocene deposits that outcrop extensively in the west and north of the Erzincan basin and include limestone, marls, green clays, evaporites and fluvial deposits (Tuysuz, 1993; Westaway and Arger, 2001; Kocyigit, 2003; Rice et al., 2009) (Fig. 1b). The Erzincan Basin is filled by continental sediments comprising Plio-Quaternary alluvial sediments lying over a ∼700 m thick Pleistocene-Holocene conglomerate (Irrlitz, 1971;

Kocyigit, 1989, 1990; Barka, 1992). The conglomerates are composed of ophiolitic mélange clastics and carbonates. These conglomerates are supplied by the alluvial fans as well as recent debris flow and coarse-grained braided stream deposits compose these fans (Hempton and Dune, 1984). The central part of the basin is filled mostly by silts, sands and gravels (Barka and Gulen, 1989). The NAFS bordering its Quaternary plain is characterized by numerous subparallel faults with components of both strike-slip and normal-slip (Fig. 1b). Master faults bound the basin and are characterized by an overlap of 32 km and a right-stepping separation of 13 km. The mapped surficial faults within the basin strike roughly NW–SE, paralleling the northern part of the basin which is limited by the active segment of the NAFS. 7 km to the east of Erzincan, the NAFS consists of a series of subparallel faults having a total length of 22 km and an average strike of N133°. At the eastern end of the basin, the main segment of the NAFS strikes eastward (N113°) approximately 10 km, then joins yet another segment with a minor change in strike (N106°) and extends 85 km W-SW of Erzincan (Aktar et al., 2004). Subparallel linear fault scarps occur on the north and south margins and are very degraded, particularly those of the south margin. The north margin of the basin is steeper (15°-20°) than the south margin and topographic and stream profiles are segmented by several faults (Hempton and Dune, 1984). Fig. 1. 3. Methods The method of the study consists of data collection, alluvial fans mapping, determination of amount of tilting of the alluvial fans (β), morphometric analysis of fan catchments using morphometric parameters (Asymmetry Factor (AF), Hypsometric Integral (HI), Fractal analysis

of drainage networks (D)) and finally the investigation of the strength and direction of the relationship between β and AF, HI, and D with the Pearson correlation coefficient at a confidence level of 95%.

3.1. Data collection This step involves the preparation of input data. Topographic and geologic maps at 1:25.000 scale and SPOT 5 imagery, having a spatial resolution of 5 m (nadir), from March 2004 constitute the main data used in the study. The Digital Elevation Model (DEM) data are generated from topographic maps with a cell size of 10 m using Triangular Irregular Network (TIN). The Root Mean Square Error (RMSE) of the data is 1.14 m. The drainage networks and fan catchment boundaries are extracted from the DEM data by calculating the flow directions at all points using D8 (eight direction) method (Hogg et al. 1997; Maidment, 1993). This method expected flow direction from each grid cell to one of its eight neighbors, either adjacent or diagonal, in the direction of the steepest downward slope. The extracted drainage networks and catchment boundaries are depicted in Fig. 2. Fig. 2

3.2. Alluvial fans mapping The fan surfaces were mapped from the panchromatic band of SPOT 5 imagery. Several 3-D perspective views were generated by draping the satellite data over the DEMs, for different vertical exaggeration factors (ranging from 1 to 25) of the z-value, sun azimuth and sun angles. Then old and active alluvial fan boundaries are delineated based on their morphological characteristics. The extracted old and active alluvial fan boundaries are depicted in Fig. 2.

3.3. Tilting of the alluvial fan (β) To quantify the amount of tilting of the alluvial fans, a morphometric technique developed by Pinter and Keller (1995) has been applied. The basic principle behind this technique is that in the absence of tilting an alluvial fan can be described as a symmetrical half-cone with topographic contours on the surface defining concentric semicircles. But in case of tilting, the contours on the surface will represent segments of ellipses with their long axes oriented parallel to the direction of tilting (Pinter and Keller, 1995). This methodology assumes that the surface of the fan has not experienced significant deposition since tilting started, because active deposition will continually anneal the fan and restore its concentric, untilted conical geometry (Burbank and Anderson, 2001). The angle of tilt of the fan (β) can be calculated using the following equation;

⎡ ⎧

2

⎫⎤

⎪⎛ b ⎞ ⎪ β = arccos ⎢ ⎨ ⎜ ⎟ sin 2 α + cos 2 α ⎬ ⎥ ⎢ ⎪⎝ a ⎠ ⎣ ⎩

⎪⎭ ⎥ ⎦

(1)

Where α is the original depositional slope, which is derived by measuring the slope along the minor axis of the ellipse, b is half of the length of the minor axis of the ellipse, and a is half of the length of the major axis of the ellipse (Fig. 3). These dimensions and the amount of tilting can be estimated from the analysis of topographic contours on alluvial fans. Initially, a best fitting ellipse is overlain on that portion of each contour that lies on the fan surface. Fig. 3.

3.4. Morphometric analysis of fan catchments 3.4.1. Tilting of the fan catchments (AF) AF is a way to evaluate the existence of tectonic tilting at the scale of a drainage basin. The method may be applied over a relatively large area (Hare and Gardner, 1985). AF is calculated as; AF =

(Ar

/ At )x 100

(2)

Where Ar is the area of the basin to the right (looking downstream) of the trunk stream, At is the total area of the drainage basin. AF is sensitive to changes in inclination perpendicular to the stream direction. AF significantly greater or smaller than 50 shows the influence of active tectonics/lithologic control or differential erosion, as the stream slipping down bedding plains over time (El Hamdouni et al., 2008). AF closes to 50, if there is no or a little tilting perpendicular to the direction of the trunk channel. In tectonically active topography, the landforms are characterized by relatively steep, mountainous sides and flat floors. The steep sides are created by displacement on faults such that the valley floor moves down relative to the surrounding margins, or, conversely, the margins move up relative to the floor. This movement results in basin tilting and causes the river to migrate latterly and deviate from the basin midline. Also, the structural control of the orientation of bedding may play a vital role in the growth of basin asymmetry (Cox, 1994).

3.4.2. Hypsometric integral (HI) of the fan catchments HI measures the proportions of high and low areas in the basin, giving a value for the degree of relief evolution (Mayer, 1990; Keller and Pinter, 1996). The index value helps to differentiate tectonically active and inactive areas. HI is calculated as;

HI=

MeanElevat ion − MinimumEle vation MaximumEle vation − MinimumEle vation

(3)

HI values range from 0 to 1. Values close to 0 indicate highly eroded tectonically inactive regions, whereas those close to 1 indicate slightly eroded tectonically active regions (Pedrera et al., 2009). HI values provide valuable information not only on the erosional stage of a basin but also on the tectonic, climatic, and lithological factors controlling it (e.g. Moglen and Bras 1995; Willgoose and Hancock 1998; Huang and Niemann 2006).

3.4.3. Fractal analysis (D) of drainage networks Evaluating drainage systems in the context of surface deformation is getting more and more important because they represent the witnessing of erosive and tectonic processes which may have disconnected, linearized and changed the dendritic behavior of the drainage system (Shahzad, et al., 2010). The drainage patterns are characterized by irregularities with self-similar characteristics. The concept of fractals given by Mandelbrot (1983) has been applied in various fields, including drainage pattern analysis. In the present study, the fractal characteristic of drainage patterns is investigated using the box-counting method in order to quantify the prevailing tectonic patterns. In this study, the fractal dimension drainage network is calculated using a box counting method in order to quantify the prevailing tectonic patterns. This method allows unbiased statistics of drainage patterns and helps to understand the linearity, heterogeneity and connectivity of drainage patterns. A self-similarity structure following a fractal distribution would exhibit a power-law relationship between the number of objects larger than a specified size and the size itself such that,

N (r) ~ r -D

(4)

Where; N(r) is the number of boxes that a drainage line enters, r is the measure of one side of a square box and D is a fractal dimension or more specifically a capacity dimension (Hirata, 1989; Mandelbrot, 1983). In case of the drainage system, the computation involves the division of a square area of length R enclosing the system into a regular square grid of boxes of length r (Hirata, 1989). D of a drainage line segment is computed by dividing the square area of length R enclosing the system into a regular square grid of boxes of length r, which is the measure of one side of a square box. The box-counting method used for measuring the D of the drainage lines is depicted in Fig. 4. The procedure is repeated for different values of r and the D is estimated as the slope of the linear fit on the plot between log10N (r) and log10 (r) (Turcotte, 1986). Fig. 4. Due to rough appearances of drainage systems over many length scales, drainage lines can be regarded as fractal, and the geometrical irregularity of drainage systems can be quantified by the D; larger D values are associated with more irregular geometry (Sukmono et al., 1997). The low D values correspond to highly linearized drainage patterns and thus correspond to high vulnerability to surface deformation. Similarly, the regions with a high D value represent the dendritic drainage behavior, which are less affected by surface deformation (Gloaguen et al., 2008). In general, higher D values correspond to less deformed regions, whereas lower values of D represent highly deformed regions.

3.5. The strength and direction of the relationship between the angle of tilt of the fan (β) and drainage basin asymmetry (AF), drainage basin hypsometry (HI), fractal dimension of drainage lines (D) The strength and direction of the relationship between β and AF, HI, and D is statistically tested with the Pearson correlation coefficient under the null hypothesis of no correlation present between β and AF, HI, and D at a confidence level of 95%. The Pearson correlation coefficient for continuous (interval level) data ranges from -1 to +1. A positive correlation indicates that both variables increase and decrease simultaneously, whereas a negative correlation indicates that as one variable increases, the other one decreases, and vice versa. 4. Results In the pull-apart basin area, the alluvial fans and fan catchments in Group 1 and Group 2 have similar physiographic and litho-tectonic settings. The strike slip movement along the NAFS caused some alluvial fans to be dislocated from their original sites (Fig. 5). Thus, the surface of the fans has not experienced significant deposition because of tilting. The amount of tilting of Group 1 and Group 2 alluvial fans is measured by fitting an ellipse on each contour that lies on the fan surface as given in Fig. 5. The original depositional slope of the fans, the lengths of major and minor axes of the resulting best-fitting ellipse are given in Table 1. Substituting these values in the above equation, the tilt in the fans is calculated. In Group 1, β values range from 0.81° to 4.21° and in the Group 2 from 1.15° to 5.00°. According to the spatial distribution of β values, in Group 1 high and medium β values are mainly placed in the central part of the basin margin. On the other hand, in Group 2 low and medium β values are clustered in the central part of the basin margin. These irregularities are most plausibly related to geomorphic variations among alluvial fans which are controlled by tectonics. The clustered distribution of high β values is mainly

related to the presence of high tectonic controls on the alluvial fans. On the other hand, the clustered distribution of low β values is associated with relatively moderate to less tectonic controls. Fig. 5.

Table 1. AF values of the fan catchments establish the lateral tilting of the catchments with respect to the main water course. In Group 1, the AF values range from 35.19 to 69.69 and in Group 2, from 19.44 to 75.01. Those AF values significantly greater or smaller than 50 indicating the tectonic influence of the fault system are mainly placed in the center and SE of the Group 1 and Group 2 fan catchments (Fig. 6a). HI values in Group 1 range from 0.420 to 0.587 and in Group 2 from 0.422 to 0.549. HI values close to 0 indicate highly eroded tectonically inactive regions, whereas those close to 1 indicate slightly eroded tectonically active regions (Pedrera et al., 2009). According to the map of HI values, moderate activity is observed in Group 1 and Group 2 fan catchments (Fig. 6b). In Group 1, D values range from 1.007 to 1.407 and in Group 2 from 0.956 to 1.193. These low values indicate the existence of controlling processes, i.e. erosion and uplift on the tectonic evolution of the fan catchments (Guillermo et al., 2004). In Group 1 (fan catchments 12-4-10-11-12), D values are relatively higher (1.199–1.407) when compared to the other fan catchments (Fig. 6c). The clustered distribution of D values suggests variability in the structural control in the pull-apart basin area. Low D values, located in the middle part of Group 1 and Group 2, correspond to highly linearized drainage patterns and thus correspond to high

vulnerability to surface deformation based on the fact that rivers tend to linearize under tectonic forcing (Shahzad et al., 2010). High D values, observed in the NW and SE of Group 1 and Group 2, show that here the patterns are more dendritic and are controlled by erosion processes and thus show low vulnerability to surface deformation. Fig. 6. The Pearson correlation coefficient between β and AF in Group1 and Group 2 is 0.71 and 0.63 respectively, which indicates a moderate high correlation. This means that when β increases in value, AF also does like this in the basin area. Similarly, when β decreases in value, AF also decreases in value. The tectonic activity of the NAFS affects not only β but also AF of the fan catchments in the pull-apart basin area. This tectonic effect on β and AF is higher in Group 1 than Group 2. The significance of the Pearson correlation coefficient is tested at a 95% confidence level. In Group 1 and Group 2, the P-Value is 0.0097 and 0.0089 respectively, and the result is significant at p < 0.05 (Table 2). At a 95% confidence level, the null hypothesis is rejected due to large significance values. The Pearson correlation coefficient between β and HI in Group 1 and Group 2 is 0.58 and 0.51 respectively, which indicates a moderate positive correlation. This means that the tectonic activity of the NAFS in the pull-apart basin area affects not only β but also HI of the fan catchments. The tectonic activity affected on the fan catchments would result in more sediment being eroded and supplied to a fan, whereas a steeper fan would cause aggradation on the distal end (Silva et. al., 1992). In contrast, tectonic subsidence can lower the gradient of fans and cause the fan to become larger in the area (Viseras et. al., 2003). The tectonic effect of the NAFS on β and HI is higher in Group 1 than in Group 2. The significance of the Pearson correlation

coefficient is tested at a 95% confidence level. In Group 1 and Group 2 the P-Value is 0.0481 and 0.0436 respectively. The result is significant at p < 0.05 (Table 2). At a 95% confidence level, the null hypothesis is rejected due to large significance values. The Pearson correlation coefficient between β and D in Group 1 and Group 2 is -0.77 and -0.67 respectively, which indicates a negative correlation. This means that when β increases in value, then D will decrease in value, and vice versa. The result of this correlation indicates that in the pull-apart basin area the tectonic activity of the NAFS affects not only β but also D of the drainage network of the fan catchments. This tectonic effect on β and D is higher in Group 1 than in Group 2. The significance of the Pearson correlation coefficient is tested at a 95% confidence level in Group1 and Group 2. The P-Value is 0.0034 and 0.0045 respectively, and the result is significant at p < 0.05 (Table 2). At a 95% confidence level, the null hypothesis is rejected due to large significance values. Table 2. 5. Discussion The geomorphic evolution of alluvial fans is controlled by fan catchment characteristics, tectonics and climate (Harvey et al., 2005). Tectonics primarily influences the fan morphology by controlling the accommodation space (Silva et al., 1992; Ferrill et al., 1996; Calvache et al., 1997; Viseras et al., 2003). In the pull-apart basin area, the alluvial fans and fan catchments on the opposing sides of the pull-apart basins have similar physiographic settings. However, ongoing tectonic activity and varying rates of displacement along the strike-slip fault system would cause displacement of the alluvial fan sediments or folding of the fan sediments.

The geomorphologic and morphotectonic features of faults located within the PlioQuaternary deposits of the pull-apart basin are generally not clear owing to the unconsolidated character of the sediments, although they become clearer towards the margins of the basin where stream offsets and small scale faults within alluvial fans and pumice quarries are observed on the northern margin of the basin (Tatar et al., 2013). In the basin a sequence of alluvial fans and fan catchments are cut by NW–SE striking faults (Fig. 2). The Erzincan pull-apart basin is defined as in a mature stage pull-apart by Tatar et al. (2013). In the mature stage of evolution, strike-slip and normal faults join to bound the pull-apart basin completely (Rahe et al., 1997). The migration of boundary faults toward the basin center as cross-basin strike-slip faults is considered to be a contributing factor towards the extinction process of a pull-apart basin (Rahe et al., 1998; Gürbüz and Gürer, 2009). That caused some alluvial fans and fan catchments to be dislocated from their original sites. The northern margin of the pull-apart basin displays more morphological features which are characteristic of a pull-apart basin margin compared with the southern margin (Tatar et al., 2013). The difference between the spatial distributions of β, AF, HI and D values on the opposite sides of the basin is compatible with this basin characteristic. In the Erzincan pull-apart basin, the mapped surficial faults strike roughly NW–SE, paralleling the northern part of the basin which is limited by the active segment of the NAFS (Aktar et al., 2004). This is well-defined by geomorphology, and is evident as sharp lineaments on satellite images (Fig 2). 7 km to the east of Erzincan, the NAFS consists of a series of subparallel faults having a total length of 22 km and an average strike of N133°. At the eastern end of the basin, the main segment of the NAFS strikes eastward (N113°) approximately 10 km, then joins yet another segment with a minor change in strike (N106°) and extends 85 km W-SW

of Erzincan (Aktar et al., 2004). The tectonic activity of these faults is one of the forces controlling the changes in the geomorphological features and morphometric parameters of the basin. Significant relationships between β and AF, HI, and D observed in the eastern end of the basin are consistent with these mapped surficial faults. In the basin, the drainage patterns observed in metamorphic and sedimentary rocks mainly exhibit a dendritic drainage pattern, as if streams were downcutting into a large expanse of homogeneous rock. This occurs because the differences in lithology in complex metamorphic rock are expressed at too small a scale to control drainage. Towards the pull-apart basin area this pattern changes into a linear pattern which can be associated with the fault or fracture zone. High D values observed in the basin also fit with the mapped surficial faults. The tilting of alluvial fans on the opposite side of the basin margins is also supported by the drainage patterns on the fan catchments.

6. Conclusion

The present study relies primarily on the tectonic controls of the NAFS on the geomorphic evolution of the alluvial fan and fan catchments in the Erzincan pull-apart basin. In the basin area the alluvial fans have different morphological characters as well as aggradation processes. The strike slip movement of the NAFS caused alluvial fans to be dislocated from their original sites. The neotectonic activity of the NAFS in the basin area affects not only the geomorphic evolution of alluvial fans but also fan catchments characteristics. Subsidence and uplift related to movements along various faults strongly influence β and AF, HI, D. The strength and direction of the relationship between β and AF, HI, and D seem to be the signature of cross faulting within the center of the pull-apart basin, which accommodates the ongoing extension

within the present basin. The applied methods are useful tools for detecting the ongoing deformation in the pull-apart basin area. The morphometric analysis of the alluvial fans and fan catchments in the basin area also helps to identify the blind faults covered by sediments, allows the relative activity of different faults to be compared. This analysis could be used in similar pull-apart basin areas that are affected by strike-slip fault motions. References Aktar M., Dorbath, C., Arpat, E. 2004. The seismic velocity and fault structure of the Erzincan basin, Turkey, using local earthquake tomography. Geophys. J. Int. 156, 497–505. Ambraseys, N.N., 1970. Some characteristic features of the North Anatolian Fault Zone. Tectonophysics 9, 143–165. Avşar, Ü., Türkoğlu, E., Unsworth, M., Çağlar, İ., Kaypak, B., 2013. Geophysical Images of the North Anatolian Fault Zone in the Erzincan Basin, Eastern Turkey, and their Tectonic Implications. Pure and Applied Geophysics 170, 409-431. Aydin, A., Nur, A., 1982. Evolution of pull-apart basins and their scale independence. Tectonics 1, 91–105. Barka A., Akyuz, H.S., Cohen, H. A., Watchorn F., 2000. Tectonic evolution of the Niksar and Tasova–Erbaa pull-apart basins, North Anatolian Fault Zone: their significance for the motion of the Anatolian block. Tectonophysics 322, 243–264. Barka, A. A., Gulen, L., 1989. Complex Evolution of the Erzincan Basin (Eastern Turkey). Journal of Structural Geology 11, 275–283.

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Figure Captions Fig. 1. (a) Simplified map showing major plates and their boundary faults in the Eastern Mediterranean region and location of the study area; (b) Simplified neotectonic map showing tectonic and geological units of the Erzincan pull-apart basin area (modified from Rice et al., 2009 and Avşar et al., 2013).

Fig. 2. Alluvial fans and fan catchments overlaid on panchromatic band of SPOT 5 imagery (30% transparent) and DEM (vertical exaggeration factors 10 m.).

Fig. 3. Geometric model of tilted alluvial fans and its crossections. 2a and 2b are the major and minor axes of the ellipse respectively (modified from Keller and Pinter, 1996; Burbank and Anderson, 2001).

Fig. 4. The box counting method for measuring the fractal dimension of the drainage lines. The r is measure of side of a square box, and N(r) is number of boxes containing at least one or any part of drainage lines (shaded gray) (modified from Roy et al., 2012; Sarp, 2014).

Fig. 5. Topographic contours and best-fitting ellipses on the alluvial fans of Group 1 in (a); and Group 2 in (b). Contour interval is 10 m.

Fig. 6. Fan catchment asymmetry (AF), fan catchment hypsometry (HI) and fractal dimension of drainage lines (D).

Table Captions Table 1. Depositional slope of the fans, lengths of major and minor axes of the best-fitting ellipses and β values. Fan No 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Fan Slope (degree) 4.87 6.06 5.19 4.66 4.22 5.50 3.97 5.90 4.06 6.71 3.44 3.00 4.11 2.05

Major axes Length (2a) (km) 1.23 2.29 1.76 1.52 1.59 1.88 1.84 2.23 2.13 3.35 1.91 2.15 3.63 5.45

Minor axes Length (2b) (km) 0.99 1.76 1.66 1.38 1.07 1.22 1.79 1.88 2.04 2.86 1.76 1.91 3.38 2.43

β Fan (degree) No

Fan Slope (degree)

2.82 3.89 1.81 1.98 3.44 4.21 0.81 3.14 1.15 3.53 1.40 1.40 1.40 1.81

4.16 6.11 2.34 3.33 3.55 4.08 4.22 3.25 3.60 2.39 4.92 4.38 3.78 2.48

15 16 17 18 19 20 21 22 23 24 25 26 27 28

Major axes Length (2a) (km) 2.76 3.11 3.19 2.81 1.91 1.62 1.11 1.80 2.75 1.53 1.51 1.35 2.13 2.96

Minor axes Length (2b) (km) 2.19 1.77 2.57 2.27 1.38 1.15 1.03 1.60 2.21 1.29 0.93 1.10 1.47 2.18

β (degree) 2.56 5.00 1.40 1.98 2.43 1.62 1.62 1.40 2.14 1.15 3.89 2.56 2.69 1.62

Table 2. Pearson's correlation coefficient (R) between (β) and (AF), (HI), (D).

AF β

Pearson's correlation coefficient P-Value

Group 1 HI

D

AF

Group 2 HI

D

0.71

0.58

-0.77

0.63

0.51

-0.67

0.0097

0.0481

0.0034

0.0089.

0.0436

0.0045

Figure_1

Figure_2

Figure_3

Figure_4

Figure_5

Figure_6

Highligths: 

The tectonic influence of the NAFS in the Erzincan pull-apart basin is analyzed.



Alluvial fans and fan catchments of the basin area is investigated.



Fan tilting concept and Morphometric Indices are applied to basin area.



The relationship between β and AF, HI, D is statistically tested.



The alluvial fans and fan catchments are mostly controlled by the NAFS.