STRUCTURAL ANALYSIS OF FOLDS SYSTEM AND RELATED MESOSTRUCTURES IN THE AREA WEST OF IRBED, JORDAN

The study area is located in the northwestern highlands of Jordan. It is located few kilometers to the west of Irbid city and about 10 kilometers east of Jordan Valley. The aim of the study is to analyze the folds system and the related mesostructural elements. The outcropping rocks in the study area are of Late-Cretaceous age, the measured structural elements were taken from outcrop hills, road cuts and quarries. The main structural elements in the study area are folds and fractures (faults and joints). Folds are mainly anticlines, which characterized by gently dipping strata (5º–20º), and gently plunging hinge lines (3º–18º). Hinge lines of minor folds are mainly plunging toward SW and WSW, some folds are plunging either toward NNW, SSE, NNE, NE and SSW. The interlimb angles of the folds range between 136º–165º, so they are classified as gentle folds. About 2800 fracture measurements were taken from nine stations of the study area. The major trend of the fractures is NW-SE, in addition to minor trends in NNW-SSE, WNW-ESE and NE-SW. It is observed that the main trend of the fractures is normal to the hinge lines of the folds in stations 3,5 and 8, in which they parallel to the NW-SE compression direction of the Dead Sea stress system . In station -6 the main trend of the fractures is subparallel to the fold axis. Station-6 shows an over thrust fault (NNE-SSW) sub-parallel to the fold axis (NNW-SSE) in which both are resulted from ESE–WNW compression of the SAS. In stations 1 and 4, the main trend of the fractures is neither parallel nor perpendicular to the fold axes, this indicates that the fractures are post-formational structures i.e. formed in later stages of the formation of the folds. Some folds were truncated by major faults which indicate that the folding phase was followed by faulting phase. The study area has been affected by both stress fields in the region, these are the SAS since the Turonian to Oligocene, and the Dead Sea stress since Middle Miocene to Recent.


INTRODUCTION
The structural pattern of Jordan was affected by the opening of the Red Sea and the Gulf of Aden, and the left movement along the Dead Sea transform fault (Fig. 1).The regional tectonics of the continental part of Arabian Plate (including Jordan) has been studied throughout macrostructures by many authors, but few analyses of the regional tectonics based on mesostructures (Diabat et al., 2004;Diabat, 2015).The Fold structures in Jordan were explained by many researchers.Examples of structures related to the Syrian Arc Fold Belt (SAF) are Ajlun Dome, Koura Basin, Amman-Hallabat structure (Abed, 2000), fold structures found in Jordan between the Jordan Valley and the basalt Plateau (Atallah and Mikbel, 1992); they are the Halawa-Al Husun, Ibbin-Hausha and Bal'ama-Al Mafraq fold belts (Fig. 2), and also in south Jordan.The major trend of these fold axes is NE to ENE.These folds were formed by SE and SSE compressive stresses, due to the northward movement of the Arabian plate.In northern Jordan, the area east of the Jordan Valley was studied by Mikbel andZacher (1981&1986).Through the fieldwork, they explained many compressional fold belts formed as a result of SE-NW compressional stresses acting since the late Cretaceous.Fold are also found in southern Jordan; Petra -Shaubak and Diylagha-Ail structures are two examples of them (Abu Taimeh, 1988;Atallah, 1992) (Fig. 2).
Mesostructures are considered to be accurate indicators of the paleostress and strain orientation (Angelier,1979(Angelier, ,1989;;Delvaux et al.,1995).Eyal and Reches (1983) presented a study based on mesostructural analysis and found two major stress systems in the Levant area, they are the Syrian Arc Stress System (SAS), trending ESE and responsible for the formation of the Syrian Arc Fold Belt (SAF).The second system is the Dead Sea Stress System (DSS) trending SSE and responsible for the horizontal displacement along the Dead Sea Transform.
The study area is located in the northwestern highlands of Jordan according to Bender (1974).
It is located few kilometers to the west of Irbid city and few kilometers east of Jordan valley.
It includes Zahar, Kufr Yuba, Bayt Yafa, Dayr Yousef and Samue towns, where Late Cretaceous rocks are well exposed in many quarries and outcrop hills.The study area covers about 70km 2 which is bounded by the coordinates: 32 o 30'00" -32 o 35' 00" N and 35 o 45' 00" -35 o 50'00" E (Fig. 3).In general, the area is hilly and cut by many Wadis and their tributaries.A digital elevation map of the study area is produced (Fig. 3).The map shows the elevation of the study area ranges from 300 m above sea level (a.s.l.) in the northwestern parts to 750 m (a.s.l) in the southern parts.The aims of this study are to analyze the fold systems and the related mesostructural elements (e.g., faults, joints), in addition, to deduce the stress fields in the study area.Throughout most of Jordan, the Wadi As Sir Formation (Turonian) represents the topmost part of the Ajlun Group and is disconformably overlain by the white chalk of the basal Belqa Group (Powell, 1989).The Wadi As Sir Formation is a very distinctive, white to very light gray limestone, which weathers brown, microcrystalline and thinly bedded with very thin marl parting, fractured, medium hard concretionary, become chalky at the top and base, it can easily be defined from the overlying marl of the base of Ghudran Formation.
Wadi As Sir Formation crops out only in the most southern part of the study area (Fig. 4).
Ghudran Formation represents the lowermost part of the Belqa Group; it consists of about 15 m chalky limestone, and 15 m of limestone and chalky limestone in the upper half.The formation is cropping out in the western and southern parts of the study area (Fig. 4).Amman Formation consists of medium to thin bedded, locally thick chert, silicified limestone, limestone, and phosphatic chert layers at the top.The base of Amman Formation (Santonian) lies conformably on top of the Wadi Umm Ghudran Formation, it crops out in many localities in the area and is usually consistent in lithology throughout the area of outcrop.Thin chert beds, phosphatic chert and a few thin phosphatic beds characterize the uppermost part.A characteristic feature of the Amman formation is the undulating structure of its beds.It is widely spreading in the study area (Fig. 4).

Tectonic Setting
There are two main trends of the fold belts in Jordan; the first one is NNE-SSW and the other is ENE-WSW (Atallah, 1992).The first fold trend could be formed as a result of SE-NW compression, responsible for the formation of the Dead Sea Transform (DST); this trend coincides with the Riedel model of fractures associated with major strike-slip fault system.
Whereas the second trend is most probably part of the SAS (Sahawneh and Atallah, 2002).
The Syrian Arc forms a conspicuous S-shaped fold-thrust belt (Fig. 1).The tectonic evolution of the Syrian Arc fold-thrust belt had been markedly influenced by the opening and closing of the Neo-Tethyan Ocean around the margins of the Afro-Arabian plate.The opening of the Neo-Tethys, in the Eastern Mediterranean region, started in the Late Permian (Garfunkel and Derin, 1984;De Ruiter et al., 1994;Ricou, 1995;Robertson et al., 1996 andSharland et al.,2001).The study area lies within the Highlands east of the northern segment of the Dead Sea Transform (DST).The northern segment of the DST is the Jordan Valley active strikeslip fault (Fig. 1).It extends from the northwestern of the Dead Sea to the southeastern of lake Tiberias with a general N-S trend (Diabat, et al., 2015).The Jordan Valley, between the sea of Galilee to the north and the Dead Sea to the south, is a long and narrow depression that is part of the Syrian-African Rift system (Garfunkel and Derin, 1984).

Fig. 5. General lithostratigraphic units of the study area
This system extends from southern Africa through east Africa and the Red Sea to southern Turkey (Freund et al., 1970;Garfunkel, 1981;Horowitz, 2001).The sinistral DST is 1100 Km long and connects the Gulf of Aqaba-Red Sea spreading system to the convergence zone in the Taurus-Zagros Mountain.The DST is the major tectonic feature controlling the geological and geomorphological evolution of the region since the Miocene (Garfunkel, 1981).The Dead Sea Transform (DST) fault is the most prominent structure in Jordan that resulted from the northward faster movement of the Arabian Plate relative to that of the African Plate, in relation to the Red Sea opening (Quennel,1958;and Grafunkel, 1981).The Dead Sea Transform fault is left lateral, comprised of a zone of en echelon strike-slip faults.
Motion on the Dead Sea Transform initiated in the Miocene and has a cumulative lateral displacement of about 107 km (e.g., Quennell,1958;Freund et al.,1970 andGarfunkel,1981).
The displacement along the Dead Sea has been the major source for the stress stored in the rocks along with the transform, resulting in internal deformation of plates adjacent to it (Eyal, 1996).The Dead Sea Transform is the major tectonic feature controlling the stratigraphic and structural evolution region since the Miocene (Zain El deen et al.,2002).

METHODOLOGY
This study concentrated on detailed field measurements of the various structural elements such as folds and fractures (mainly joints).The data were taken from nine main measurement stations; S1, S2, S3,.... and S9 (Fig. 4).Each measurement station consists of quarries, road cuts or clear outcrops.These stations are selected due to easy reaching and the abundant data which are found in parts of the study area.Orientations of 2800 meso-scale fractures (joints and faults), in addition to many bedding planes to determine the fold hinge lines in each measurement station that measured in the field.Most of the fractures are considered as joints which lack any shear indicators on their surfaces.The fractures that have striations on their surfaces (faults) were used to compute the stress tensors using the TENSOR program (Delvaux, 1993;Sperner et al., 2003).The stereographic projection and rose diagrams are used in data analyzing, whereas the produced lineaments map and DEM (Fig. 3) used the following techniques and software: -Google earth for projection coordinates of the study area to overlay with lineament map.
-Using Coral draw x5 2010 to draw vertical and horizontal geological cross-sections.

RESULTS
The study area has been sub-divided into nine main stations, located west of Irbid city and named S1, S2,…,and S9 with new described folds (Fig. 6) and Table (1).A NW-SE crosssection (A-B) was drawn to show the general view of folds in the study area (Fig. 7).

Station 1
The data of this station were collected from Amman Silicified limestone and Al-Hisa Phosphorite Formation, which is about 4 km west of Irbid city (Fig. 5).Ten bedding planes The data of this station were collected from Wadi Umm Ghudran Formation, which is about 6 km west of Irbid (Fig. 5).Eighteen bedding planes were measured in the field and represented as stereographic projection, which determined hinge line, axial plane and profile plane (Fig. 10).It shows symmetric anticline with a slightly plunging hinge line towards SSW (10º/189º).
The interlimb angle is 161º showing a gentle anticline (Fig. 11).It also observed slightly plunging small anticline and syncline affected by faulting (Fig. 12).The data were collected from Wadi Umm Ghudran Formation, which is about 7 km west of Irbid city (Fig. 4).Twenty bedding planes were measured in the field and represented as stereographic projection which determined hinge line, axial plane and profile plane (Fig. 13a).
It shows symmetric anticline with slightly plunging hinge line towards WSW (03º/ 244º).The interlimb angle is 150º showing a gentle anticline.Six hundred fracture measurements mainly joints were collected from this station.A NW-SE main trend is observed in the rose diagram (Fig. 13b).Horizontal slickenlines with a dextral sense of movement were measured on some fault planes oriented WNW-ESE (Fig. 14a   The data of this station were collected from Wadi As Sir Formation, which is about 3 km west of Irbid city (Fig. 4).Fourteen bedding planes were measured in the field and represented thru stereographic projection and determined hinge line, axial plane and profile plane (Fig. 15 a).
It shows slightly plunging symmetric anticline towards NNE (04º/ 022º).The interlimb angle is 136º showing a gentle anticline.A fault zone was observed with a sinistral sense oriented NNW-SSE (Fig. 16).This indicated by the tilting of strata particularly at the eastern side of the fault which has dragging and steeper dip than the left side.The data of this station were collected from Wadi Umm Ghudran Formation, which is about 10 km west of Irbid (Fig. 4).Fourteen bedding planes were measured in the field and represented thru stereographic projection and determined hinge line, axial plane and profile plane (Fig. 17a).It shows slightly plunging symmetric anticline towards SW (03º/ 223º).The  The data of this station were collected from Wadi As Sir limestone Formation, which is about 8 km southwest of Irbid city (Fig. 4).Fourteen bedding planes were measured in the field and represented as stereographic projection and determined hinge line, axial plane and profile plane (Fig. 18 a).Figure (19) shows the eastern limb of the anticline.It shows symmetric slightly plunging anticline towards SSE (11º / 176º) (Fig. 18 a).The interlimb angle is 142º showing a gentle anticline.Six hundred fracture measurements mainly joints were collected from this station.A N-S main trend is observed in the rose diagram and two minor trends oriented NNW and NNE (Fig. 18b).It is also observed horizontal slickenlines indicating a strike-slip movement in Wadi As Sir Formation and an overthrust fault in Umm Ghudran Formation (Fig. 20).This indicates that a permutation of principal stress axes i.e Ơ2 and Ơ3 was locally changed.

Station7
The data of this station were collected from Wadi Umm Ghudran Formation, which is about 4 km west of Irbid city (Fig. 4).About ten bedding planes were measured in the field and represented as stereographic projection and determined hinge line, axial plane and profile plane.It shows symmetric slightly plunging anticline towards WSW (05º /258º) (Fig. 21).The interlimb angle is 148º showing a gentle anticline.

Station 8
The data of this station were collected from Amman Silicified limestone and Al-Hisa Phosphorite Formation, which is about 5 km from Irbid city (Fig. 4).Twenty-three bedding planes were measured in the field and represented as stereographic projection and determined hinge line, axial plane and profile plane (Fig. 22a).It shows slightly plunging symmetric anticline towards WSW (05º / 236º).The interlimb angle is 165º showing a gentle anticline.
About three hundred fracture measurements mainly joints were collected from this station.A NW-SE main trend is observed in the rose diagram (Fig. 22b).Listric normal fault was observed in this station (Fig. 23).The data of this station were collected from Amman Silicified limestone and Al-Hisa Phosphorite Formation, which is about 9 km NW of Irbid city (Fig. 4).Twenty-four bedding planes were measured in the field and represented as stereographic projection and determined hinge line, axial plane and profile plane of anticline (Fig. 24a) and syncline (Fig. 24b).It shows slightly plunging symmetric anticline towards NNW (07º / 321º).The interlimb angle is 160º showing a gentle anticline.The syncline is also symmetric and plunging toward (11º / 048º) with an interlimb angle of 148º.It also observed small highly fractured anticline at the northeastern limb of the major anticline (Fig. 25).

LINEAMENTS
The word "lineament" was introduced by Hobbs (1904) to characterize the spatial relationships of landscape features that included (1) crests of ridges or boundaries of elevated areas, (2) the drainage lines, (3) coast lines, and (4) boundary lines of formations, of petrographic rock types, or of lines of outcrops."(Hobbs, 1904).Any linear feature of the landscape which possesses an abnormal degree of regularity whether straight or gently curving, is generally believed to be the surface expression of some structural feature in the bedrock e.g., faults, folds,...etc.Experience and careful judgment are required to distinguish a diagnostic linear from random river stretches, hills, and similar results of random erosion (Lueder, 1959).A lineament map of the study area is produced (Fig. 26   discontinuities (Fleuty and Waever, 1975;Scholz and Engelder, 1976;Engelder and Scholz, 1976;Petit, 1987;Doblas et al., 1997;Doblas, 1998;Fry, 1999).Inversion of fault-slip data is based on the Wallace and Bott hypothesis (Wallace, 1951;Bott, 1959), which stating that fault-slip occurs parallel to the direction of the maximum shear stress.
Analysis of the fault-slip data restricted only to station-3 of the study area in which a quarry of Wadi As Sir Formation has slickenlines.The analysis was performed using the win-TENSOR program of Delvaux (2003).Results show that a dominance of strike-slip tensors which indicate three orientations; the first is characterized by E-W compression and N-S extension (Fig. 27), the second is characterized by NW-SE compression and NE-SW extension (Fig. 28), and the third tensor is characterized by NNW-SSE compression and ENE-WSW extension (Fig. 27).The tensors characterized by NNW-SSE to NW-SE compression and ENE-WSW to NE-SW extension are compatible with the established regional Dead Sea Stress pattern in the region (Eyal and Reches, 1983;Eyal, 1996;Diabat et al., 2004).The tensor characterized by E-W compression and N-S extension is compatible with the Syrian Arc stress field.Stress axes orientation of fault-slip measurements in station-3 (Fig. 29) shows compression σ1 (SHmax) and tension σ3 (Shmin).

DISCUSSION
The study area is located at the western parts of Irbid City.The formations that outcrop in the study area are of Late Cretaceous (Turonia-Maastrichtian).The data were collected from nine measurement stations of the study area.The structures in the study area include; folds, faults (e.g., strike-slip, normal and thrust), and joints.

Minor Folds
Folds which are mainly anticlines in the study area characterized by gently dipping strata (5º-20º) and gently plunging hinge lines (fold axes) (3-18).The interlimb angles of these folds lie in the range between 120º to 180º.This implies that they are classified as gentle folds (136º-165º), and this means there were no highly intensive compressional stresses during their

Fig. 4 .
Fig. 4. Geological map shows the locations of station measurements in the study area (after, Moh'd, 2000)

Fig. 6 .
Fig. 6.Geological map shows the location of station measurements and the new described folds in the study area

Fig
Fig. 15.a) Stereonet diagram shows the trend of hinge line is 04º/ 022º b) Rose diagram of 200 joints in station4 mainly joints were collected from this station.A NW-SE main trend is observed in the rose diagram (Fig.17 b).

Fig. 17
Fig. 17. a) Stereonet diagram shows the trend of hinge line is 03º/ 223º b) Rose diagram of 800 joints in station5 Station 6

Fig. 24 .
Fig. 24.Stereonet diagrams of Zahar; a) anticline, the trend of hinge line is a)07º / 321º and b) syncline, the trend of hinge line is 11/ 048º a) and the rose diagram of the lineaments shows a major trend oriented NW-SE and two minor trends oriented N-S and NE-SW (Fig.26 b).The NW-SE trend reflects the main trend of the fractures in the study area, and the NE-SW trend reflects the main trend of the fold axes, whereas the N-S trend may reflect both minor trends of the fractures and fold axes in the study area.

Fig. 26
Fig. 26.a) Lineament map of the study area, b) rose diagram shows the orientation of the lineaments

Fig. 27 .Fig. 28 .
Fig. 27.Stress tensor related SAS shows E-W compression and N-S extension.Stereogram (Schmidt net, lower hemisphere) with traces of fault planes, observed slip lines and slip senses.Inward arrows indicate compression, outward arrows indicate tension, circle is σ1, triangle is σ2 and the square is σ3 orientation.
formation.Hinge lines of minor folds are mainly plunging toward SW and WSW, some folds are plunging either toward NNW, SSE, NNE, NE and SSW.The difference in the plunging direction and orientation of the hinge lines is due to the differences in the stress fields and/ or to local variations in the stresses belong either to the same stress field.To interpret the results reasonably, a direction model is produced to show the relation of our results with the main stress fields in the region e.g., the DSS field and the SAS (Fig.30).According to figure (30); the folds in stations(3, 5, 7, 8, and 9) are related to the DSS field, whereas folds in stations (2and 4) are related to SAS field.Those folds in stations (1 and 6) are affected by local stresses or by block rotation.

Fig. 30 .
Fig. 30.A model to show the main stress fields in the region e.g., the Dead Sea stress field (DSS) and the Syrian Arc stress field (SAS), and the related folds; DSF related to the DSS field and SAF related to SAS field Fractures About 2800 fractures (small faults and joints) were measured in different stations of the study area along road cuts and quarries and represented as rose diagram (Fig. 31).The fractures show a major NW-SE trend in addition to minor trends in NNW-SSE, WNW-ESE and NE-SW.

Fig. 31 .
Fig. 31.Rose diagram represents strikes of all measured fractures in the study area, showing a main trend swinging about NW-SE To interpret the results, rose diagrams represent the strike measurements in each station were displayed on the geological map (Fig. 32).It is observed that the main trend of the fractures is NW-SE (e.g., S1, S3, S5, and S8), whereas the main trend is NNW-SSE (e.g., S4) and N-S (e.g., S6), may be an indicator to a clockwise rotation in stations (S4) and (S6).

Fig. 32 .
Fig. 32.Rose diagrams of the strike measurements in each station displayed on the geological map