Paleostress analysis of the Cretaceous rocks in the eastern margin of the Dead Sea transform, Jordan

Journal of African Earth Sciences 38 (2004) 449–460

www.elsevier.com/locate/jafrearsci

Paleostress analysis of the Cretaceous rocks in the easternmargin of the Dead Sea transform, Jordan

Abdullah A. Diabat a, Mohammad Atallah b,*, Mustafa R. Salih c

a Institute of Earth and Environmental Sciences, Al al-Bayt University, Al Mafraq, Jordanb Department of Earth and Environmental Sciences, Yarmouk University, Irbid, Jordan

c Department of Geology, Sana’a University, Sana’a, Yemen

Received 14 August 2002; accepted 22 April 2004

Available online 17 June 2004

Abstract

This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea

transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by

rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes (r1, r2 and r3) and the ratio of the

principal stress differences (R) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first

is characterized by NNW–SSE compression and ENE–WSW extension and related to Middle Miocene-Recent sinistral movement

along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW–ESE compression and NNE–

SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the

Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Paleostress; Tensor; Dead Sea transform; Syrian Arc

1. Introduction

The Dead Sea transform (DST) is one of the major

morphotectonic features of the Middle East and is the

source for most historical and recent earthquakes. It

represents the boundary between the Sinai micro plate

and the Arabian plate (Fig. 1). In Jordan, the transform

consists of three morphotectonic segments: Wadi Araba

in the south, Dead Sea in the middle and Jordan Valleyin the north. Though it has many features of an exten-

sional rift, many evidences indicate that it is a transform

linking the Red Sea, where sea floor spreading takes

place to the south, with a continental collision zone

in the Taurus-Zagros mountain belt in the north

(Garfunkel et al., 1981).

The tectonic stress field due to the regional driving

forces acting on a portion of the lithosphere is modifiedby the deformational processes that take place within

the lithosphere. Thus, the observed tectonic stress field

* Corresponding author.

E-mail address: [email protected] (M. Atallah).

0899-5362/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jafrearsci.2004.04.002

reflects the dynamic conditions existing now, but someof its characteristics are also inherited from conditions

created by earlier tectonic evolution, in particular lateral

heterogeneities and zones of weakness (Delouis et al.,

1993). During the last few decades, several techniques

for paleostress analysis have been devised and modified

using both numerical and graphical methods. Such

methods are based on the stress–shear relationship

described by Wallace (1951) and Bott (1959).The displacement along the DST has probably been

the major source for the stress stored in the rocks along

this transform, resulting in seismic activity and internal

deformation of plates adjacent to it (Garfunkel, 1981;

Eyal, 1996). East of the DST paleostresses were deduced

from the general orientation of folds and faults (Burdon,

1959; Mikbel and Zacher, 1981; Atallah, 1992) and by

tectonic stylolite (e.g. Salameh and Zacher, 1982), whilewest of the DST, paleostresses were deduced from the

analysis of the mesostructures (Eyal and Reches, 1983;

Eyal, 1996; Eyal et al., 2001). The latter proved the

existence of two stress fields since the Late Cretaceous,

one is responsible for the formation of the Syrian

Arc (Syrian Arc Stress field, SAS), and the other is

mail to: [email protected]

Fig. 1. (a) Plate tectonic setting of the Dead Sea transform. (b) General geological and structural map of the area east of the DST (simplified after

Bender, 1968).

450 A.A. Diabat et al. / Journal of African Earth Sciences 38 (2004) 449–460

responsible for the formation of the DST (Dead Sea

Stress field, DSS). There are no previous studies based

on the analysis of fault-slip data in Jordan, except for

Zain Eldeen et al. (2002). The aim of this study is

reconstructing the first paleostress results in 12 stations

(Fig. 2) at the eastern margin of the DST. The basic

assumption of the paleostress analysis is that any planar

discontinuity in a rock may be activated as a faultregardless of its origin.

2. Geological setting

The study area is located at the eastern rim of the

Dead Sea transform. It comprises 12 sites concentratedin three areas, NW Jordan, east of the Dead Sea, and

NE of Aqaba (Fig. 1). Cretaceous rocks cover more

than 60% of Jordanian land (Bender, 1968). The thick-

ness decreases from north to south and from west to

east. Two different facies of Cretaceous sedimentation

are recognized in Jordan: Lower Cretaceous composed

mainly of sandstone, and Upper Cretaceous consisting

mainly of limestone. The Lower Cretaceous sandstone

unconformably overlies older strata (Jurassic and Tri-

assic in north and central Jordan and Silurian, Ordovi-

cian and Cambrian in south Jordan). Upper Cretaceouscarbonaceous rocks are composed mainly of alternating

beds of limestone, marl, marly limestone, chalk, chert

and phosphate. Few normal and strike-slip faults cut the

area east of the DST (Fig. 1).

3. Faults and slickensides

In this study the term slickenside was used for the

polished surface formed by frictional sliding and the

Fig. 2. Location of the fault-slip data measurements east of the DST (1, 2, etc. are station numbers).

A.A. Diabat et al. / Journal of African Earth Sciences 38 (2004) 449–460 451

groove lineations (striations or scratches) on the slic-

kensides are called lineated slickensides or slickenlines.445 fault planes with their slickenlines were measured

east of the DST (Al-Diabat, 1999). The measured faults

have various lengths (i.e. few centimeters up to 100 m).

Strike-slip faults represent more than 60% of the total

measured faults. The major trends of these faults are

WNW–ESE and NNE–SSW. The dip angle ranges from

65� to 90� (Fig. 3a). Normal faults have shorter traces in

the field and they are less abundant than strike-slipfaults. They represent about 30% of the total measured

faults and trend WNW–ESE and NW–SE. Their dip

angle ranges from 60� to 90� (Fig. 3b). Reverse faults are

generally rare and do not exceed 10% of the total mea-

sured faults. They trend ENE–WSW with two minor

sets trending ENE–WSW and WNW–ESE. There are

two dip group values: 70–90� and 40� (Fig. 3c).The measured faults have slickenlines on their sur-

faces; the strongest and most clear being horizontal, on

the sub-vertical strike-slip faults. Some of the slickenside

on a few slickolite faint oblique slickenlines were ob-

served superimposed on previously formed horizontal

slickenlines. Vertical slickenlines were also observed on

many slickenside surfaces. In some cases they aresuperimposed on horizontal slickenlines. A convenient

way to determine the slip orientation on faults is pro-

vided by the observation of slickenlines on slickenside

surfaces. The attitude of slickenlines in addition to

associated features as mineral steps and tension gashes

have been used to determine the orientation of slip and

the sense of relative motion allowing the reconstruction

of the paleostress in the area under investigation.

4. Paleostress analysis

4.1. Field measurements

The fault-slip data were collected by measuring fault

planes and slickenlines on these fault planes at 12 sta-

tions (Al-Diabat, 1999). The measurements at eachstation included the attitude of the fault plane, trend and

plunge of slickenlines, motion along these planes (Fig.

4). 445 fault-slip data were collected from sub-horizontal

Fig. 4. Plunge and azimuth of the measured slickenlines (A: 250 lines

on strike-slip faults, B: 130 lines on normal faults and, C: 30 lines on

reverse faults).

Fig. 3. Dip (left) and strike (right) of (a) 271 strike-slip faults; (b) 137

normal faults and; (c) 37 reverse faults in the study area.


strata of the Upper Cretaceous limestone (Wadi As Sir

Formation). This formation was selected because it was

affected by the stress system responsible for the forma-

tion of the Syrian Arc and the DST and post-date

known older stress regimes (Paleozoic and Pre-

cambrian). Furthermore, it is exposed along the DST

from north to south and can be documented in detail in

quarries (fresh slickensides). The term station in thisstudy means a group of quarries, valley sides or road

cuts located at different sites ranging in area from 1 to

10 km2.

4.2. Stress inversion method

Fault plane and slickenline orientations, including

slip senses are used to compute the reduced paleostress

tensors (r1, r2, r3 and R): the principal stress axis r1

(maximum compression), r2 (intermediate compression)

and r3 (minimum compression) and the ratio of prin-

cipal stress differences R ¼ ðr2 � r3Þ=ðr1 � r3Þ. Thesefour parameters are determined using successively an

improved version of the Right Dihedron method of

Angelier and Mechler (1977), and a rotational optimi-

zation method, using the TENSOR computer program

developed by Delvaux (1993). For faults, the angular

deviation between observed slickenlines and computed

shears is minimized, together with the maximization of

friction coefficients for each fault plane (for detailssee Delvaux, 1993; Delvaux et al., 1995, 1997).

4.3. Stress tensor determination

A total of 445 fault-slip data were measured in the

field, out of which 330 measurements found to be usefulin stress determination. The computed stress tensors in

this study explained 74% of the numerous striations

observed. According to the slip deviation angle between


theoretical striations derived from the computed meanstress tensor, homogeneous populations of faults have

been obtained from each station separately. All the

WNW–ESE compression trends are compatible with the

Syrian Arc stress field (SAS), and those trending NNW–

SSE are compatible with Dead Sea stress field (DSS).

The following is a representation of the results in each

station.

4.3.1. Station 1

Seventy-eight measurements were carried out inquarries located NNW of Irbid (Fig. 2). Fifty fault

planes with their slickenlines have been used in com-

putation. Three stress tensors were obtained from the

whole fault population: the first stress tensor gives the

maximum principal stress axis (r1) 08/118, the interme-

diate principal stress axis (r2) 78/349, and the minimum

principal stress axis (r3) 09/210; with stress ratio (R)

equals 0.30. The tensor belongs to the pure strike-slipsystem. It indicates a WNW–ESE compression and

NNE–SSW extension. The second stress tensor is char-

acterized by r1: 60/314, r2: 30/142 and r3: 04/050 with

R ¼ 0:27. This tensor belongs to pure extension system,

and indicates ENE extension. The third stress tensor is

characterized by r1: 39/209, r2: 40/076 and r3: 26/323

with R ¼ 0:75. It indicates NNW–SSE extension with

oblique principal stress axes.

4.3.2. Station 2

Eighty fault-slip measurements were used in com-

puting 108 measurements from quarries located SSW of

Irbid (Fig. 2). The movements along the measured faults

are of strike-slip (dominant) and dip-slip nature. The

sense of motion is determined based on calcite steps,

tension gashes on fault planes and stratigraphic sepa-

ration. We observed vertical and oblique striationssuperimposed on horizontal striations in the area. Five

stress tensors were separated from the total fault pop-

ulation: the first one is characterized by r1: 07/140, r2:

77/018, and r3: 11/232 with R ¼ 0:37. It belongs to a

pure strike-slip system and indicates NNW–SSE com-

pression and ENE–WSW extension. The second one is


with R ¼ 0:50. It belongs to pure strike-slip system (asthe first one), indicating WNW–ESE compression and

NNE–SSW extension. The third tensor is characterized

by r1: 60/145, r2: 26/297 and r3: 12/034 with R ¼ 0:75.It belongs to an extension system, and indicates NNE–

SSW extension. The fourth tensor is characterized by r1:

52/035, r2: 29/260 and r3: 22/157 with R ¼ 0:56. It

belongs to a pure extension (as the third one), but

indicates NNW–SSE extension. The last one, is char-acterized by r1: 22/275, r2: 16/012 and r3: 62/135 with

R ¼ 0:5. This tensor indicates WNW–ESE compression,

and belongs to a pure compressive system.

4.3.3. Station 3

Sixty measurements were carried out in the quarries

west of station 2 (Fig. 2), including 44 fault-slip mea-

surements of both strike-slip and normal faults. Two

stress tensors were separated from the total fault pop-

ulation: the first is characterized by r1: 01/335, r2: 80/

241 and r3: 10/065 with R ¼ 0:33. It belongs to a pure

strike-slip system, and indicates NNW–SSE compres-

sion and ENE–WSW extension. The second tensor ischaracterized by r1: 80/102, r2: 10/282 and r3: 00/012

with R ¼ 0:1. This stress subset indicates a major NNE–

SSW extension and a minor WNW–ESE extension, so

it belongs to a radial extension system.

4.3.4. Station 4

Thirty-nine measurements were carried out in the

quarries NNW of Ajlun (Fig. 2). The movements along

fault planes are of both strike-slip and dip-slip nature.

Thirty-four measurements were used during computa-

tion. As a result, four stress tensors were separated from

the total fault population. The first one is characterizedby r1: 00/107, r2: 86/014 and r3: 04/196 with R ¼ 0:5. Itindicates WNW–ESE compression and NNE–SSW

extension, and thus belongs to a pure strike-slip system.

The second tensor is characterized by r1: 08/335, r2: 80/

121 and r3: 05/244 with R ¼ 0:88. It indicates ENE–

WSW extension and minor NNW–SSE compression.

This tensor belongs to an extensional strike-slip system.

The third tensor is characterized by r1: 60/192, r2: 19/318 and r3: 22/056 with R ¼ 0:55. It indicates ENE–

WSW extension, and belongs to a pure extension

system. The last one is characterized by r1: 29/129, r2:

29/237 and r3: 47/003 with R ¼ 0:63. It indicates

WNW–ESE compression, and belongs to an oblique

compressive system.

4.3.5. Station 5

Eighteen fault-slip measurements were carried out in

the quarries and in road cut north of Jerash along

Amman–Irbid highway (Fig. 2). Fourteen measure-ments of strike-slip faults were included in the compu-

tation and separated from the total fault population.

The stress tensor which has been obtained is character-

ized by r1: 01/326, r2: 84/228 and r3: 06/056 with

R ¼ 0:25. It indicates NNW–SSE compression and

ENE–WSW extension and belongs to the compressive

strike-slip system.

4.3.6. Stations 2, 3, 4 and 5

These stations display similar stress tensors and thus

the data were grouped to test the whole fault population

data and compare the results with the tensors obtainedfor each of the primary subsets. The obtained stress

tensor is characterized by r1: 03/336, r2: 87/174 and r3:

01/066 with R ¼ 0:33. It belongs to the pure strike-slip


system, and indicates NNW–SSW compression andENE–WSW extension (Fig. 5).

4.3.7. Stations 1, 2 and 4

These stations indicate the same stress tensors, thusthey are grouped and tested for new stress tensor. The

new tensor is characterized by r1: 02/119, r2: 83/009 and

r3: 07/210 with R ¼ 0:34. It belongs to the pure strike-

slip system, and indicates WNW–ESE compression and

NNE–SSW extension.

4.3.8. Stations 1 and 4

A new stress tensor has been obtained from grouping

similar stress subsets of two stations 1 and 4. It is


with R ¼ 0:35. It indicates ENE–WSW extension andbelongs to the pure extension system.

4.3.9. Stations 1 and 2

The similar stress tensors of these stations have beengrouped, and tested for a new stress tensor. This stress


09/148 with R ¼ 0:31. It indicates NNW–SSE extension,

and belongs to the pure extension system.

4.3.10. Station 6

Sixteen measurements from this station were col-

lected along a monoclinal structure dipping 65� WNW

east of Dead Sea (Fig. 2). Despite the scarcity of data,

two stress tensors were separated from the whole fault

population. The first tensor is characterized by r1: 54/

359, r2: 27/134 and r3: 22/235 with R ¼ 0:57. Thisindicates ENE–WSW extension, and it belongs to a pure

extension system. The second is characterized by r1: 22/

Fig. 5. Example of stress inversion results in north Jordan (stations 1,

2, 3, 4 and 5).

344, r2: 26/086 and r3: 55/220 with R ¼ 0:56. It indicatesNNW–SSE compression and belongs to a pure com-

pressive system.

Since the limestone bedding is steep in this area, it has

been rotated to a horizontal position. As a consequence

the new orientation of the principal stresses become as

follows: the first has r1: 09/332, r2: 76/204 and r3: 06/

062. The second has r1: 22/165, r2: 57/030 and r3: 20/

264. The two tensors belong to the strike-slip system,but the compressional and extensional directions remain

in the same orientation before and after rotation (cor-

rection). Because there are no sufficient evidences on the

timing of the tilting and the slip, the two probabilities

are presented.

4.3.11. Station 7

Eleven measurements were carried out in quarries

northwest of Karak, east of Dead Sea (Fig. 2). The

fault-slip data show an oblique stress tensor. This may

be due to block rotation or to error in the measurement.

So it is excluded from the analysis.

4.3.12. Station 8

Nine fault-slip measurements were carried out north

of Karak (Fig. 2). The stress tensor is characterized by

r1: 02/097, r2: 83/200 and r3: 07/007 with R ¼ 0:46. Itbelongs to a pure strike-slip system, and indicates E–W

to WNW–ESE compression and N–S to NNE–SSWextension.

4.3.13. Station 9

Only nine measurements of strike-slip faults have

been carried out SSE of Petra (Fig. 2). They give a stress

tensor characterized by r1: 17/334, r2: 66/201 and r3: 17/069, with R ¼ 0:50. It indicates NNW–SSE compression

and ENE–WSW extension, and it belongs to a pure

strike-slip system.

4.3.14. Station 10

Thirty-nine fault-slip data of this station were carriedout in south of Gharandal, east of Wadi Araba (Fig. 2).

Twenty-six measurements of strike-slip faults have been

used in the computation of the stress tensor. This stress


04/056 with R ¼ 0:50. It belongs to pure strike-slip and

indicates NW–SE compression and NE–SW extension.

4.3.15. Station 11

Fifty fault-slip data of this station were carried out

NNW of Quweira (Fig. 2). Thirty-five fault-slip mea-

surements of both strike-slip (dominant) and dip-slip

(rare) faults were included in the computation. Four

stress tensors were deduced from the whole fault pop-ulation. The first tensor is characterized by r1: 35/120,

r2: 55/311 and r3: 05/213 with R ¼ 0:53. It belongs to

pure strike-slip, and indicates WNW–ESE compression

Fig. 6. Example of stress inversion results in south Jordan (stations 9,

10, 11 and 12).Fig. 7. Representative paleostress tensor east of the DST.

Table 1

Results of the reduced Paleostress tensors from fault-slip data of the studied stations

Station N Nt. R (a) Principal stress axes Q R0 Shmax Tensor type

r1 r2 r3

1 12 78 0.30 8.93 08/118 78/349 09/210 B 1.70 118 Pure strike-slip

22 0.27 11.36 60/314 30/142 04/050 B 0.27 142 Pure extension

16 0.75 6.0 39/209 40/076 26/323 A 0.75 Oblique extension

2 31 108 0.37 10.75 07/140 77/018 11/232 A 1.63 140 Pure strike-slip

19 0.50 11.37 07/294 83/106 01/204 B 1.5 294 Pure strike-slip

9 0.75 12.66 60/145 26/297 12/034 B 0.75 297 Pure extension

15 0.56 6.95 52/035 29/260 22/157 A 0.56 260 Pure extension

5 0.50 1.5 22/275 16/012 62/135 C 2.5 275 Pure compression


7 0.32 7.29 52/028 14/278 34/179 B 0.32 278 Pure extension

8 0.35 15.05 55/127 27/264 20/005 C 0.35 264 Pure extension

15 0.10 15.76 80/102 10/282 00/012 B 1.10 282 Radial extension

4 10 39 0.88 9.15 08/335 80/121 05/244 B 1.12 335 Extension strike-slip


9 0.55 4.8 60/192 19/318 22/056 B 0.55 318 Pure extension

5 14 18 0.25 7.37 01/326 84/228 06/056 B 1.75 326 Compression strike-slip

2, 3, 4, 5 68 0.33 9.23 03/336 87/174 01/066 A 1.67 336 Pure strike-slip

1, 2, 4 38 0.34 12.08 02/119 83/009 07/210 A 1.66 119 Pure strike-slip

1, 4 31 0.35 13.72 70/313 20/141 02/050 A 0.35 141 Pure extension

1, 2 34 0.31 15.56 81/317 02/058 09/148 A 0.31 058 Pure extension

6 7 16 0.57 5.67 54/359 27/134 22/235 0.57 134 Pure extension

5 0.56 3.32 22/344 26/086 55/220 B 2.56 344 Pure compression






4 0.40 6.09 58/148 32/324 02/056 C 0.40 324 Pure extension

4 0.30 7.74 01/132 04/222 86/028 C 2.30 132 Pure compression

12 12 17 0.10 7.46 25/148 65/317 05/056 B 1.90 148 Compression strike-slip

9, 10, 11, 12 66 0.37 12.33 13/328 75/176 07/060 A 1.63 328 Pure strike-slip

All 127 0.37 11.43 04/330 84/202 05/061 A 1.63 330 Pure strike-slip

N ¼ net data number representing the tensor; Nt.¼ total data measured; R¼ stress ratio ðr2 � r3Þ=ðr1 � r3Þ; a¼mean slip deviation angle;

Q¼ quality ranking (as defined by Delvaux et al., 1997); R0 ¼ tensor type index (as defined by Delvaux et al., 1997); Shmax ¼maximum horizontal

shear.


Fig. 8. Distribution of the stress field that is characterized by NNW–SSE compression (black arrow¼r1) and ENE–WSW extension (white

arrow¼r3) in the study area.


and NNE–SSW extension. The second is characterized

by r1: 22/357, r2: 60/130 and r3: 19/258 with R ¼ 0:64.It belongs to the same system as the previous one, but

indicates NNW–SSE compression and ENE–WSWextension. The third tensor is characterized by r1: 58/

148, r2: 32/324 and r3: 02/056 with R ¼ 0:4. It indicatesENE–WSW extension and belongs to a pure extension

system. The last one is characterized by r1: 01/132, r2:

04/222 and r3: 86/028 with R ¼ 0:3. It indicates NW–SE

compression, and it belongs to a pure compression

system.

4.3.16. Station 12

Seventeen measurements were carried out at the

eastern edge of Wadi Araba, about 30 km north of

Aqaba (Fig. 2). Twelve fault-slip measurements of

strike-slip faults at this station have been extracted from

the whole fault population. The only stress tensor is

characterized by r1: 25/148, r2: 65/317 and r3: 05/056with R ¼ 0:1. It indicates NNW–SSE compression and

ENE–WSW extension and thus belongs to a compres-

sional strike-slip system.

4.3.17. Stations 9, 10, 11 and 12

Grouping the similar stress tensors of these stations

gives a more consistent new tensor. This tensor ischaracterized by r1: 13/328, r2: 75/176 and r3: 07/060

with R ¼ 0:37. It indicates NNW–SSE compression and

ENE–WSW extension and thus belongs to a pure strike-


slip system (Fig. 6). The above results with all parame-ters of the reduced stress tensors are provided in Table 1.

5. Discussion and conclusions

Stress tensor of the various stations along the whole

length of the DST with relatively similar deviation an-

gles were grouped with each other and new representa-tive stress tensor was obtained (Fig. 7).

To interpret the results easily, the reduced stress

tensors are displayed with the orientation of both hori-

zontal maximum principal stress (Shmax) and horizontal

minimum stress axes (Shmin) on maps (Figs. 8 and 9). As

a result, two main paleostress fields since Late Creta-

ceous are identified. The first is characterized by WNW–

ESE compression and NNE–SSW extension. It includestwo paleostress regimes, one with predominantly strike-

slip faulting (strike-slip regime) and the other with

predominantly dip-slip normal faulting (extensional

regime) which corresponds to S1 and n1, respectively

Fig. 9. Distribution of the stress field that is characterized by WNW–ES

arrow¼r3) in the study area.

(Fig. 10, Table 2). The second paleostress field is char-acterized by NNW–SSE compression and ENE–WSW

extension; it includes two stress regimes, one with

dominating strike-slip faulting and the other with nor-

mal faulting, which corresponds to S2 and n2, respec-tively (Fig. 10 and Table 2). The first paleostress field

is restricted mainly to north Jordan (east of Jordan

Valley), while the other paleostress field is found in all

other stations (Table 2). This may be due to scarcity ofdata collected from the south. This means that the SAS

could be found in southern Jordan, as recognized by

Eyal and Reches (1983) and Eyal (1996) west of the

DST. It is also noted that both normal and strike-slip

faulting of each paleostress field have nearly the same

orientation of r3 axis, while r1 and r2 axes change

according to the stress regime. Associations of stress

regimes of each stress field, which is frequent, can beexplained by stress axes permutation. Permutation of

stress axes r1 and r2 or r2 and r3 commonly occur

during tectonic events. Fig. 10 shows such changes from

predominantly strike-slip to predominantly normal

E compression (black arrow¼ r1) and NNE–SSW extension (white


faulting modes (r1=r2 permutation), for a single stage(i.e. S1=n1 and S2=n2), and a distinct stress field. This

figure also shows local permutations of r2 and r3 from

predominantly strike-slip to reverse faulting mode (i.e

S1=I1 and S2=I1) for both stress fields. It is also clear that

permutation of r2 and r3 for the same normal faulting

mode is possible (e.g. n2=n3; Fig. 10), such permutation

is of local effect (Table 2).

The stress field characterized by NNW–SSE com-pression and ENE–WSW extension is associated with

the 105 km sinistral displacement along the DST and the

opening of the Red Sea since Early Miocene to Recent.

The stress field characterized by WNW–ESE compres-

sion and NNE–SSW extension could be associated with

the formation of the Syrian Arc fold belt that started

during the Turonian or it may be due to an anticlock-

Fig. 10. The mean orientation of the principal stresses of the main stress reg

strike-slip regime belongs to DSS, n1: extensional regime belongs to SAS, n2unknown stress field, I1: compressional regime belongs to the both stress fie

wise rotation of the first stress field. Eyal and Reches(1983) suggested that: (1) the NNW–SSE (DSS) field is a

younger stress field and responsible for the formation

of the Dead Sea transform and (2) the WNW–ESE trend

(SAS) field is older and responsible for the formation of

the Syrian Arc.

In addition to the above main stress fields, a local

paleostress tensor characterized by vertical r1 and nearly

N–S oriented r3 is responsible for the formation of E–Wtrending normal faults and N–S elongation at station 3.

This is the youngest event as these faults cut the previous

ones, and it may have been active since the post-Middle

Pliocene (Ron and Eyal, 1985). Another local paleo-

stress tensor was found east of the Dead Sea at station 7.

This is characterized by oblique stress axes, possibly due

to tilting of fault blocks. East of Wadi Araba (station

imes in the study area, where S1: strike-slip regime belongs to SAS, S2:: extensional regime belongs to DSS, n3: extensional regime belongs to

lds.

Table 2

Average results of paleostress tensors

Tensor

symbol

Stress field Axis r1 Axis r2 Axis r3 Station Nt.

Trend Plunge Trend Plunge Trend Plunge

S1 SAS 110 03 015 85 018 04 1, 2, 4, 8 50

S2 DSS 150 05 016 84 060 05 2, 3, 4, 5,

6,9,10 12

147

n1 SAS 295 83 114 07 023 02 1, 2, 3 40

n2 DSS 320 70 140 20 050 01 1, 2, 3, 4, 6,

11

38

I1 Both 125 12 036 05 150 75 2, 4, 11 20

n3 Unknown 317 81 058 02 148 09 1, 2 34

S1 � S2: predominantly strike-slip fault sets; n1 � n3: predominantly normal fault sets; I1: predominantly reverse fault sets; 1, 2: station number as

defined in text; Nt.: number of fault-slip data representing the tensor; SAS: Syrian Arc stress; DSS: Dead Sea stress.

Fig. 11. Stress trajectory map of the dominant stress field east of the

DST (i.e. DSS).


11), a stress tensor with N–S compression and E–W

extension of pure strike-slip type has been identified.

This may be due to clockwise rotation of the regional

stress tensor as a result of continuous compressional

stresses. The stress tensor marked by NNW–SSE

extension with r1 vertical in north Jordan can be ex-plained by the reactivation of the dextral faults or it

belongs to unknown stress field (Table 1). To interpret

results of paleostress analysis on a regional scale, it is

necessary to compare paleostress tensors of a single

tectonic event or a distinct paleostress field. To achieve

this a map of stress trajectories is produced based on

maximum horizontal shears (Fig. 11). This map shows a

general NNW–SSE compression and ENE–WSWextension with slight rotation along some stations of the

study area.

The trend of compressional stresses (r1 ¼ 150�) is

responsible for the development of conjugate strike-slip

faults, and the northward movement of the Arabian

plate since the Oligocene (i.e. since the first opening of

the Red Sea). One set of these faults is parallel to the

western Arabian plate margin namely the major sinistralfaults, while the other set makes an acute angle with

the plate margin (Al-Diabat, 1999).

As a result of these compressional stresses and the

continuous sinistral movement, extensional stresses were

formed during the relaxation period or during reacti-

vation of stresses, they mainly affected the dextral set.

Reactivation of stresses caused vertical movement on

the preexisting dextral faults, as indicated from thesuperimposed of new vertical slickenlines on the older

horizontal slickenlines of the dextral strike-slip faults.

In conclusion, the current results are compatible with

the previous paleostress results, especially those at the

western margin of the DST (e.g. Eyal and Reches, 1983;

Eyal, 1996) defining two distinct stress fields. The older

one (SAS) is characterized by E–W to ESE–WNW

compression, whereas the younger stress field (DSS) ischaracterized by N–S to NNW–SSE compression. Our

results are also compatible to some extent with the

paleostress results based on tectonic stylolites carried


out in Jordan by Salameh and Zacher (1982), indicatingtwo dominant paleostress directions; the older Shmax

trends 130–140�, whereas the younger Shmax trends 170�.

Acknowledgements

The authors would like to thank Mrs. Julia Sahawneh

for drafting the figures. We thank two anonymousreviewers for their comments and improvement of the

manuscript.

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Paleostress analysis of the Cretaceous rocks in the eastern margin of the Dead Sea transform, Jordan

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