Neo-Tectonism and Quantitative Morphotectonic Analysis of Roste Valley at Imbricated-Suture Zones, Kurdistan Region, Iraq

Abstract


Introduction
The neo-tectonism or active tectonic deals with the crustal movement and deformation that occurred in the recent past in geologic time and may still be occurring today (Stewart, 2005).During the Cenozoic Era, the onset of the neotectonics period depend on the significant changes in the evolution of tectonic conditions that happened for the last time in that region (Stewart, 2005).The landforms are continuously modified and changed at any period on the earth under the influence of two forces, first one is the endogenic internal force, which drives from the interior of the earth (uplifting, subsiding, folding, and faulting) including both paleo and neotectonics activity, and the other is the exogenic external forces, which derives from the surface of the earth (weathering, erosion, transportation, and deposition).The combination of two forces is referred to as a geomorphic process.(Keller and Pinter, 1996).The geomorphic process is responsible of any change and modification in the landforms, these changes are identified and determined through applying a set of geomorphic indices which have a direct relation with active tectonic deformation (El hamdouni et al., 2008).
The Roste valley is located in the Imbricated and Zagros Suture Zone, NE of Erbil city, in the north bounded by Hassan-bag and Hasarrost mountain, in the north-east by Halgurd mountain, and in the south-west bounded by Tanoun (Spibalis) anticline.Nearly 128 km far from Erbil city, latitude from 36.6174983 to 36.7400068 northing and longitude from 44.6363368 to 44.8349798 easting, with the area, is about 172.5 Km 2 and the main Roste river is approximately 19.43 Km in length (Fig. 1).Therefore, according to the tectonic settings of the studied area, the effect of tectonism indicated by various Imbrication and sheet thrusting faults, triangular facets along the range of mountains through fault uplift which is the geomorphic features formed by active faults (Balogun. et al., 2011).The linear or axial valleys in the study area are associated with faulting.The water gap and abandoned alluvial fan are also an indicator for neotectonics (Sissakian et al., 2020).Due to high relief, steepness, and rugged mountains, the climatic condition (raining and snowing) facilitates the surface processes (erosion and weathering) and plays important role in the modification of the surface form of the study area.The effect of geomorphic (surface and internal) processes is reflected through the variety of landforms.Since the study area is located in the Imbricate and Suture Zone, the endogenic forces (tectonic activity) have prevailed over exogenic forces in the evolution of the study area.
The degree of neo-tectonism can be determined and calculated through morphotectonic analysis, which is concerned with the study of landform evolution through the effect of tectonic process and the study of tectonic impact in the modification of landforms (Burbank and Anderson, 2009).The morphotectonic study was carried out through using morphotectonic indices which are applied as an important and effective tool in the evaluation of the tectonic deformation of the Valley basin (Keller and Pinter, 1996;Bull and McFadden, 1977).However, quantitative morphotectonic analysis allows us simply to differentiate various landforms and applying (Morphotectonic indices) which is useful for defining the tectonic activity levels of an area (Keller and Pinter, 1996).
The area was studied by many researchers for tectonic, geomorphologic, and geochemical purposes among them including the work of Le Garzic et al. (2019) describes the tectonic evolution of Zagros orogeny, Koshnaw et al. (2021) studied the Neo-Tethys Ocean closures and Zagros Mountain orogeny Sissakian et al. (2020) studied the lateral propagation of Tanoun anticline.The main objective in this research is to better understand the recent tectonic activity in the evolution of Roste valley through morphotectonic analysis and calculation of the Index of relative active tectonics.

Materials and Methods
The morphotectonic study of Roste valley is based on the fieldworks and the GIS technique including determination of contact between formations through measuring coordinates (GPS) of the formations contact and plotting all points in ArcGIS software and thrusting surfaces also determined through measuring coordinates (GPS) of the thrust surfaces between (Naopurdan, Walash Groups and Qandil series), and plotting them in ArcGIS software and drawing a geological map of the study area.
Measurement of elevation and coordination of river terraces in the Roste gorge, observation of geomorphic and tectonic features which indicate active tectonism.The Neotectonics assessment and morphotectonic analysis are done through applying morphotectonic indices which are sensitive to any neotectonics activity.The Satellite imagery (3D World Imagery Wayback in ArcGIS Earth software, June 2017) and digital elevation model used in this study including ALOS PALSAR (12.5m),Aster (30m), Sentinel (30m) with the following software's (ArcGIS 10.8, ArcGIS pro-2.8,Arc Earth and Global mapper and Google earth).

Geological and Tectonic Settings
The geological settings are summarized in terms of tectonics, geomorphology, and stratigraphy.The study area is located in the Unstable Shelf in the Imbricated Zone and Suture Zone, this zone is characterized by tectonic complexity, due to Late Cretaceous oceanic crust (Ophiolite) obduction onto the margin of the Arabian plate (Le Garzic et al., 2019).Highly uplifted and mountainous area characterized by a steep slope, deep V-shaped valley, with the mixed dendritic and parallel drainage pattern where dendritic type indicates soft lithology (Walash and Naopurdan Groups) and erosion is the dominant process, whereas a parallel one indicates hard lithology (Aqra-Bekhma formation NE limb of Tanoun anticline and Govanda formation) and indicates that the tectonic process is dominant (Mukherjee and Jha, 2011).The main landforms include klippe of Qandil Series in Suture Zone and window thrusting of Naopurdan Group near Sreshma village (Figs. 2 and 4), perched syncline, cuesta and hogback, structural ridge, and an eroded core anticline.The stratigraphic successions are disrupted by thrust fault in Imbricated Zone, bringing the Sarki and Sehkaniyan formations over the Qamchuqa Cretaceous rocks in the truncated syncline (Le Garzic et al., 2019), the exposed formations including Sarki, Sehkaniyan, Sargelu, Naokelekan, Barsarin, Chia Gara, Balambo, Sarmord, Qamchuqa, Aqra, Bekhma, Shiranish, Tanjero, Govanda and Redbed series formations in Imbricated Zone and volcanosedimentary rocks of Walash and Naopurdan Groups and Metamorphosed rocks of Qandil series in Suture Zone, (Fig. 2).

Tectonic Evolution
The study area passes through several tectonic phases from sub-hercynian to Valahian and Pasadenian phases.The Late Triassic and Jurassic basins were restricted from the neo-Tethys Ocean and identified with the deposition of the Baluti, Sarki, Sehkaniyan, Naokelekan and Barsarin formations.According to (Mustafa and Tobia, 2020) the Chia Gara formation was deposited from the Late Jurassic (Tithonian) to the Early Cretaceous (Berriasian) age.From the middle Jurassic to early Cretaceous period the Arabian margin was identified with the formation of a rift basin; this basin was filled with the sediments of Qulqula radiolarian formation (Fig. 3a).At the end of the Tithonian, the isolated basin in the north-eastern marginal part of Arabian plate changed to more open marine environment which defined by the deposition of carbonates of the Balambo formation which laterally changed into marls of Sarmord and Qamchuqa massive limestone (Le Garzic et al., 2019).This period was associated with the development of the volcanic arc on the Sanandaj-Sirjan terrane.
During pre-Campanian, the sub-hercynian tectonic phase was associated with the developed passive margin in the northeastern part of the Arabian Plate (Trifonov and Sokolov, 2018) due to Neo-Tethys Ocean opening (Fig. 3b).The tectonic process was periodic until the Late Cretaceous, where the tectonic stress was increased (Znad et al., 2020).The sub-hercynian phase followed by the Laramide phase during the Late Cretaceous (Campanian-Maastrichtian) the onset of ophiolite obduction over the margin of the Arabian plate result in the folding of the Mesozoic sedimentary cover as a detachment fold one of them is the Tanoun (Spibalis) anticline (Le Garzic et al., 2019), and development of flexural foreland basins.the foreland flexural basin filled with the deposition of Aqra-Bekhma, Shiranish and Tanjiro formations (Ahmed, 2021), (Fig. 3c).
During Paleocene and Eocene, the sheet thrusting continued toward the foreland onto the Arabian margin.Development of volcanic arc of Naopurdan Group and back-arc basins of the Walash group in (Paleogene) Paleocene and Eocene epoch (Aziz et al., 2021), with the magmatic activity which intrudes volcanic component and ashes into the existing deposits (Fig. 3d).The Oligocene and Miocene collision results in the shortening and thrusting propagated and transferred from basal detachment to the overlying sedimentary covers and tightening the present anticlines (Le Garzic et al., 2019).According to (Le Garzic et al., 2019) the south-west limb of the Tanoun (Spibalis) anticline is cut by a north-east dipping thrust fault resulting in the formations of the faulted detachment fold (Fig. 5), this thrust is branched from the Paleozoic detachment surface and forming (Baluti secondary detachment surface) and from this Baluti detachment surface Imbricate thrusting is propagated to the earth's surface (Fig. 3e).The recent study done by (Khoshnaw et al., 2021) shows the age of Redbed series (Merga Group) and they assumed to be deposited during Late Miocene epoch.The collision between the Arabian and Iranian Plate (Sanandaj-Sirjan) and the final closure of the Neo-Tethys Ocean associated with the emplacement and thrusting of Walash-Naopurdan volcano-sedimentary rocks on the Arabian margin at the Miocene epochs (Fig. 3f).
However, in the Middle to Late Miocene, the compressional stress is renewed along the Suture Zone of neo-Tethys (Jassim and Goff, 2006).The metamorphosed rock (schist and calc-schist) of the Qandil Series emplaced (Out-of-Sequence thrusting) onto the Arabian plate (Ali et al., 2017), (Fig. 3f).This Age corresponds to the Styrian orogenic phase which marks the onset of folding in the main Zagros thrust zones and the complete closure of Neo-Tethys Ocean.The Late Miocene and end of this epoch are associated with the Attic tectonic phase, the impact of this phase is indicated in the Higher Zagros (Trifonov and Sokolov, 2018), and advanced sheet thrusting into the foreland area over Qulqula radiolarian and Oceanic crust (ophiolite).The present morphology of the study area (Fig. 3g), after extensive erosion, shows the Qandil series as the Klippe landforms and develops an eroded core anticline.The recent orogenic phase Valahian and Pasadenian phases are indicated in the Zagros piedmont zones (0.9 Ma), (Trifonov and Sokolov, 2018).From the Miocene to the present day several local or secondary thrust faults propagated from the main thrust sheets of the Zagros nappes (Fig. 4).

Migration of Roste Rivers
The Roste river in the study area influenced and migrated over a period of time under the action of Neotectonics activity.When the river migrated leaves behind the terraces that mark the previous location of the rivers.The river terraces show variation in tectonic or climatic conditions, which is the reason for switching rivers from degradation to aggradation or conversely (Burbank and Anderson, 2009).The migration of the Roste river leave 7 levels of terraces in the Imbricated Zone across the oblique faults in the core of Tanoun (Spibalis) anticline (Fig. 6).The first level of river terraces is 783 m above sea levels and the present location of river 737 m above sea levels, it means the river incised by 46m.The horizontal distance between the first river terraces and the present location of the river is nearly 100 m. (Figs. 7 and 8).The Roste river is located in the zone of high tectonic deformation as compared to the large rivers like Tigris, the Tigris river is located in the Low Folded Zone and Mesopotamian Plain, where cut bank erosion and point bar deposition are abundant rather than the leaving river terraces, but the Roste river in the study area leave the 7 levels of terraces because of existence of the oblique fault movement since the Neogene age, the oblique fault migrated the river stage by stage and at each stage leave levels of terraces (Fig. 8).
The river terraces are present only in the NW side of the river because the hanging wall moves downward in addition to the strike-slip movement toward the NE side of the river, the deposited terraces in the NE side are eroded with each stage of fault movement, this results in the preservation of the river terraces only in one side of the river.
The size of the clasts ranges from sand to boulder size and is composed of igneous, metamorphic, and sedimentary particles, the igneous and metamorphic particles sourced from Zagros nappes of Walash, Naopurdan Groups, and Qandil Series.The clasts are cemented with calcite, silt, and sand, this indicates that the seven levels are terraces not slope deposits.The particle shapes or form is mostly rounded with small amounts of angular particles, this indicates that most of the particles are derived from distant sources, and this is another indication of the existence of the levels of river terraces.

Morphotectonic Indices
In this study, we use morphotectonic indices which have a direct relationship with the active tectonics, and are used to determine active tectonic intensity (Keller and Pinter, 1996).These morphotectonic indices is regarded as a powerful tool for determining active tectonic deformation.For this purpose, the study area is divided into 18 subbasins (Fig. 11) using automated watershed delineation and extraction tools in Global mapper software (Fig. 9).The method of analysis for each indices is illustrated in Fig. 10.

Hypsometric Integral and Curve
The hypsometric integral is the ratio of the variation between mean and minimum elevations to the variation between maximum and minimum elevations.An effective tool for determining the degree of disequilibrium in the balance among the erosive and tectonic forces (Keller and Pinter, 1996).The hypsometric integral is calculated with the following equations: HI = (Mean height -Minimum height)/(Maximum height -Minimum height) (1) The value of HI is classified into three classes Class 1: High Value (HI > 0.5) indicates low erosion and high neo-tectonic activity (young stage), Class 2: Medium value (0.4 < HI < 0.5) indicates that this area is in equilibrium between erosion and tectonic process (equilibrium stage), Class 3: Low value (HI < 0.4) showing that erosion is the dominant process in this area with a low active tectonic activity (old stage), (El hamdouni et al., 2008).The calculated values are shown in Table 1.The distribution of the HI classes are shown in Fig. 16a.
The hypsometric curve defined as the distribution and arrangement of elevation over the area of the land, and is calculated by the plotting the relative height of the basins (h/H) against the relative area of the basins (a/A).Where the H is the total heigh (relief) within the basins (maximum elevation minus minimum elevation), h is the elevation values above the minimum height, a is the area above the given contour line and A is the total area of the basins.The convex curve indicates young stage where mainly controlled by tectonic activity, the S shaped curve represents equilibrium stage where there is a balance between tectonic and erosion activity and the concave curve indicates the old stage where the amount of erosion process is more than the tectonic activity (Fig. 13).

Stream Length Gradient Index (SL)
The SL index proposed by Hack, (1973) is useful for describing stream gradient conditions and analyzing the relationship between commonly recent tectonic activity which changes the slope gradient, surface topography, the resistance of rock to erosion processes, and the length of streams.The high value indicates that the drainage flow through an active uplifted area with more resistant rock, whereas the low value defines rivers or streams which flow through an area that is composed of less resistant rock and soft lithology (Mathew, 2016;Keller and Pinter, 1996).The SL can be expressed as the following: Where (∆ℎ/∆) is the slope of the channels, and L is the length of the stream from upstream to the midpoint (Fig. 10).The SL value is calculated for all subbasins at the horizontal distance of 100 m (interval) between all points (Fig. 12).The SL value categorized into three classes: Class 1: SL > 500 indicate high active tectonism, Class 2: 300 < SL < 500 indicate medium active tectonism, Class 3: SL < 300 indicate low active tectonism (El hamdouni et al., 2008).
The SL Plot against the river profile shows the locations of Knick points which are developed along the main Roste river and other streams, these Knickpoints formed as a result of either structural factor (faulting) or lithological variation (Fig. 14).The high values of SL index are found in the Suture Zone, particularly in (Naris and Sariprsawl) subbasins, and the lowest values are along the main Roste river (Fig. 12).The calculated values are shown in (Table 2), and the distribution of (SL) classes are shown in (Fig. 16b).

Valley Floor Width to Valley Height Ratio (Vf)
According to Keller and Pinter (1996), the Vf index is expressed as:  = (2 × )/(( − ) + ( − )) (3) Where Vfw is the width of the valley floor, Eld is the elevation of the left valley divide, Erd is the right valley divide elevations, and Esc is the elevation of the valley floor.The low value indicates a Vshaped valley associated with high active tectonic settings and a high rate of uplifting, whereas the high value represents a U-shaped valley typically a glacial valley, with low active tectonic settings, and a low rate of uplifting (Keller and Pinter, 1996).To indicate the neotectonics activity (Vf) is categorized into the following classes: Class 1 (Vf ≤ 0.5) high tectonic control V-shaped valley, Class 2 (0.5 < Vf < 1) moderate tectonic controls and Class 3 (Vf ≥ 1) low tectonic controls U-shaped valley (El hamdouni et al., 2008), the calculated values are shown in the (Table 3).The distribution of (Vf) classes are shown in (Fig. 16c).

Asymmetry Factors (Af)
The drainage line developed in response to active tectonics reflects the deformation directions, which refers to tectonic tilting caused by faulting or folding.Consequently, one side of the drainage area is larger than the other side (Mathew, 2016).The asymmetry factor is calculated as the following:  = (/) 100 (4) Where Ar is the area to the right of the stream (Downstream facing); Atis the total area of the drainage basin.The Af is classified into three classes to describe tectonic tilting as follow: Class 1 (Af > 65 or Af < 35) high tilting, Class 2 (57 < Af < 65 or 35 < Af < 43) moderate tilting, and Class 3 (43 < Af < 57) low tilting (El hamdouni et al., 2008), the calculated values are shown in Table 4.The distribution of Af classes is shown in Fig. 16d

Mountain Front Sinuosity (Smf)
Is the measurement of the balance among the tectonic processes that produce the straight mountain front and erosional processes that tend to produce a sinuous mountain front.The straight front is associated with an active mountain range bounded by faults (high active tectonism), whereas the sinuous front reflects (low active tectonism) (Keller and Pinter, 1996).The Smf measured in the foot of mountain (Mahmood and Gloaguen, 2012), where characterized by the presence of triangular facets and/or breaking in the slope.The mountain front sinuosity is expressed as: Where Smf is the mountain front sinuosity, Lmf is the mountain front length along the mountain foots at the break of slope, the Ls is the straight-line along Lmf.The Smf is categorized into three classes to define active tectonic intensity; Class 1 (1.0 -1.09) high neo-tectonism, Class 2 (1.1 -1.16) medium neo-tectonism, Class 3 (> 1.16) low neo-tectonism (El hamdouni et al., 2008), the calculated values are shown in (Table 5).The distribution of (Smf) classes are shown in (Fig. 16e).

Basin Shape Index (Bs)
The shape of the drainage basin is another indicator to define Neotectonics activity (Keller and Pinter, 1996), this index is expressed as: where Bl is the length of the basin measured from head-water to river mouth, Bw is the width of the basin measured from the widest portion of the basin, the high value represents the elongated basin associated with the high tectonism, whereas the low value indicates the circular basin and low tectonic activity (Tepe and Sözbilir, 2017;Keller and Pinter, 1996).Bs are classified into the following classes: Class 1 (Bs ≥ 1.77) elongate basin with high active tectonism; Class 2 (1.76 ≥ Bs ≥ 1.21) moderate tectonism associated with elongate to circular basins and Class 3 (Bs ≤ 1.20) Low tectonic activity with circular basins (Mahmood and Gloaguen, 2012) (Table 5) (Fig. 16f).6).The distribution of IRAT classes shows the variable range of tectonic activity (Fig. 17   The moderate IRAT values are reflected in subbasins, that are in equilibrium to the old stages, semielongated to elongated shape, low sudden change in the gradients (Knickpoint), sinuous mountain front, V to U shaped valley, and the low tectonic tilting.

Conclusions
The Roste valley, based on tectonic position is situated in the Imbricated and Suture Zone, tectonic force (endogenic) is the main and important factor in the modification of the study area.The Tanoun (Spibalis) anticline developed as a detachment fold in the Late Cretaceous as the result of Ophiolite obduction, during the middle Miocene a thrust fault has crossed the SW limb of Tanoun anticline forming faulted detachment fold.The Roste river migrated across the sinistral oblique fault in the Imbricated Zone within the Jurassic formations in the core of Tanoun anticline and leaving seven levels of river terraces, which indicates neotectonics activity.The difference in the elevation and distance are 46m and 100m respectively.The main basin or valley is divided into 18 subbasins for quantitative morphotectonic analysis.The result of morphotectonic analysis of the study area shows that the Suture Zone reflects more neotectonics activity as compared to the Imbricated Zone.
However, the variation in the tectonic intensity in the two zones is related to high relief and gradient in the Suture Zone, along with the impact of sheet thrusting of metamorphosed Qandil series, Walash and Noupurdan volcano-sedimentary rocks.The SL curve shows the location of the Knick points on the main Roste river and other streams within all subbasins, each peak of the SL curve indicates the Knick point (abrupt change in slope).In the Roste gorge, the subbasin shows various Knick points that developed in response of imbrication in the core of the Tanoun anticline.The drainage in the other subbasins also show Knick points (break in slope) and this change is related to two reasons either structural and lithological factors.
The IRAT map of the Roste valley shows different ranges of tectonic activity from moderate to very high, generally, the moderate tectonic activity (Chambarok and Chomansmail Agha subbasins) in the Imbricated Zone and (Mama Khatibyan, and Simelan subbasins) in the Suture Zone, and is located in the middle of the Roste valley, whereas very high tectonic activity is located near the valley divide in the Suture Zone (Mawan, Neris, Sariprsawl, and Piromar) Subbasins, the other remaining subbasins in the study area shows the high tectonic activity in the Imbricated and Suture Zones.However, the overall neotectonics activity in the Suture zone is higher than in the Imbricated zone, Where the very high active tectonic subbasins only found in the Suture zone.

Fig. 1 .
Fig.1.Location map of the study area

Fig. 2 .
Fig.2.a) a Geological map; b) a 3D cross-sectional view of the study area, and the depth data obtained from(Le Garzic et al., 2019)

Fig. 3 .
Fig.3.Continued, f) Advanced sheet thrusting and out-of-sequence thrusting of Qandil series over Walash and Naopurdan group; g) Present-day subduction of Sanandaj-Sirjan with the Arabian plate.

Fig. 4 .
Fig.4.Field photograph shows a) The Zagros nappes and the Naopurdan window thrusting (Naopurdan Group overthrusted by Walash Group, part of Walash Group eroded and the Naopurdan Group form the window thrusting) near Sreshma village; b) The local thrusting within Walash and Qandil series, the black arrow indicates thrusting plane and directions.

Fig. 6 .
Fig.6.a) Satellite image shows the oblique fault cut across the Sarki and Sehkaniyan Formations in the Roste gorge subbasins, Simelan road near the Rawandz river within the Imbricated Zone; b) Field photograph showing the vertical (Black arrow) and horizontal (White arrow) displacements of the oblique fault within Sarki and Sehkaniyan Fns, in the Roste gorge.

Fig. 7 .
Fig.7.Field photograph of 7 levels of river terraces in the Roste gorge, within the Jurassic formation, core of Tanoun anticline.

Fig. 8 .
Fig.8.Block diagram shows the migration stages of Roste river (a to h) across the oblique fault.

Fig. 9 .
Fig.9.Flow chart shows the method of subbasin extraction using Global Mapper software.

Fig. 11 .
Fig.11.Map shows the main subbasins of the Roste valley

Fig. 12 .
Fig.12.Map showing SL index values in all subbasins within the study area

Fig. 14 .
Fig.14.The longitudinal profile of stream and river of 18 subbasins versus SL index.Where distance and elevation are in (meters) extracted from digital elevation model (DEM).

Fig. 15 .
Fig.15.Map shows the location of Smf measurements ).The values of IRAT depends upon morphotectonic indices (HI, SL index, Vf, Af, Smf and Bs).The applied geomorphic indices are very sensitive to any change or activity in tectonic conditions.The study area consists of all classes and indicating that the Roste valley active zone in tectonic condition.

Fig. 16 .
Fig.16.Maps shows distribution of indices class and their related tectonic intensity, a) Hi, b) SL index, c) Vf ratio.

Fig. 16 .
Fig.16.Continued, Maps shows distribution of indices class and their related tectonic intensity, d) Af, e) Smf, f) Bs.

Table 1 .
The resulted values and tectonic classes of HI

Table 2 .
The resulted values and tectonic classes of SL index .

Table 3 .
The calculated values and related tectonic classes of Vf index

Table 4 .
The calculated values and related tectonic classes of Af (*) means that this subbasins has no mountain front sinuosity.

Table 5 .
Representing the values and related tectonic classes of Smf and Bs