ORIGINAL PAPER

Petrogenesis of lamprophyre and associated diabase dykes in WadiMandar-Um Adawi area, South Sinai, Egypt

Waheed I. Elwan1& Shehta E. Abd Allah1

Received: 3 November 2017 /Accepted: 1 May 2018 /Published online: 10 May 2018# Saudi Society for Geosciences 2018

AbstractThe mafic dykes in Wadi Mandar-Wadi Um Adawi area are as follows: (1) calc-alkaline lamprophyre (i.e., kersantite andspessartite), (2) diabase, and (3) alkaline lamprophyre (i.e., camptonite). The field relations reveal that the emplacement ofcalc-alkaline lamprophyres preceded the diabase dykes, while alkaline lamprophyres emplaced later than the diabase dykes.Calc-alkaline are basaltic andesite, basaltic trachyandesite to basalt, while the diabase dykes and alkaline lamprophyres arebasaltic in composition. These dykes are characterized by metaluminous character. Calc-alkaline lamprophyres and diabasedykes show transitional affinity from calc-alkaline to alkaline, while the alkaline lamprophyres exhibit more strong alkalinecharacter. The mafic dykes were crystallized under temperature 1100–1150 °C and pressure 3–5 kbars in a high oxygen fugacityconditions. Fe-Ti oxides in the dykes are represented by ilmenite and Ti-magnetite. The chemistry of the sulfides hosted in thosemafic dykes suggests a magmatic-hydrothermal origin for these minerals. The geochemical behavior of high field strengthelements and large ion lithophile elements in these dykes excludes the derivation of diabase or alkaline lamprophyre either bypartial melting or fractional crystallization from calc-alkaline lamprophyre. The parental magmatic sources of the studied dykeswere generated from crustal material with addition of mantle-derived melt during the post-collisional stage. The mafic dykes inWadiMandar-Wadi UmAdawi area were generated from different magmatic sources by partial melting and subsequent fractionalcrystallization. In addition, the crustal contamination/assimilation process has a prominent role in the magmatic evolution ofdiabase and alkaline lamprophyre dykes.

Keywords Lamprophyre . Diabase . South Sinai . Arabo-Nubian shield

Introduction

One of the main characteristic features of the southern Sinaimassif, as in many other parts of Arabo-Nubian Shield, is theunusual density of dykes including lamprophyre as minor in-trusions. The dyke system in Sinai is thought to be part of thePrecambrian basement, which include from oldest to youn-gest: (1) island arc calc-alkaline granitoids (820–740 Ma;Bentor 1985; Stern and Hedge 1985; Moghazi 1999), (2)syn-collision medium to high-K calc-alkaline granitoids(670–635 Ma; Greenberg 1981; Moghazi 2002;), (3) post-collision alkaline granitoids (640–610 Ma; Jarrar et al. 2003,

2008), (4) dykes and veins, and (5) within-plate alkaline andperalkaline granites (600–550 Ma; Liégeois 1998). Eyal andEyal (1987) recognized three different episodes of dyke em-placements in Sinai and Eastern Desert: (1) a metamorphosedsyn-tectonic dykes (800–650 Ma); (2) unmetamorphosedpost-orogenic dykes (591–459 Ma; Halpern and Tristan1981; Stern and Manton 1987; Stern and Voegeli 1987;Schandelmeier et al. 1994); and (3) Neogene dykes (30–12 Ma; Meneisy 1990; Camp and Roobol 1992), which arerelated to Red Sea rift system. Many workers consider that thedykes in the Egyptian basement reflect a transitional periodfrom compressional subduction to extension-relatedmagmatism (Abdel-Rahman 1996; Mohamed et al. 2000).Shafranek (1978) described the following sequence of dykesin southeastern Sinai: (1) spessartite dykes trending NNE, (2)kersantite and spessartite dykes trending ENE, (3) diabasedykes trending NE-SW, (4) camptonite dykes trending NNE,and (5) diabase dykes trending WNW. Kabesh et al. (1978)related the calc-alkaline lamprophyre (CAL) and alkaline

* Waheed I. Elwanwibraheem@hotmail.com

1 Geology Department, Faculty of Science, Zagazig University,Zagazig, Sharkia 4459, Egypt

Arabian Journal of Geosciences (2018) 11: 223https://doi.org/10.1007/s12517-018-3585-4

lamprophyre (AL) to the same magmatic source, whileLehmann (1977) and Basta et al. (1985) supposed that theyare totally unrelated. This paper presents new geological data,mineral chemistry, and new geochemical data that allow amuch broader perspective for the lamprophyre and diabasedykes at Wadi Um Adawi-Wadi Mandar area, southeasternSinai.

Geological setting

The basement rocks at Wadi Mandar-Wadi Um Adawi areaare represented by older syn-collisional and younger post-collisional granites (i.e., syeno-monzogranites, alkali-feldspar granites, and alkali granites). The dykes in the areaare represented by mafic dykes, including lamprophyre dykes(LPD) and diabase dykes (DBD). They form dyke swarmscutting syeno-monzogranites in different directions (Fig. 2a,b). The alkali-feldspar granites are rarely cut by LPD, whereasthe alkali granites have no any LPD (Fig. 1). Most of thesedykes are dissected by two perpendicular sets of joints. Thesedykes are relatively resistant to weathering, mostly giving riseto pronounced ridges which cut across the country rocks. LPDcomprise calc-alkaline lamprophyres (CAL), which includekersantite and spessartite and alkaline lamprophyres (AL).

LPD are straight or curved, vertical or inclined. They occurin the form of dyke swarms cutting the syeno-monzogranite(Fig. 2a).

Spessartite dyke swarms preferentially trend in N32-41 Edirection with 5 to 25 m thickness. In the field, it is not easy todiscriminate between spessartite and DBD. Kersantite dykesare relatively rare and occur either as swarms or as straightdykes associated with spessartites (Fig. 2c).

Camptonite dykes are fine-grained with dark gray to blackcolor. Compared with other types of dykes, they are the richestin vesicles. They occur in swarms composed of about fivedykes with 2–4 m in width. They are trend preferentially inN12-32W direction. Camptonite dykes are post-date most ofthe diabase dykes; meaning that, they are probably the youn-gest dykes in the area. There is no direct field relation betweenspessartite and camptonite dykes.

DBD forms long straight dykes with width of up to 10 m.They are very numerous and cut through most of plutons inthe area. They are trending preferentially in N 30–40 E direc-tion. Their color varies from green to black according to theirdegree of alteration. Some of DBD show a remarkable paral-lelism with each other forming dyke swarms (Fig. 2b).Weathered DBD usually exhibit a well-developed onion struc-ture (Fig. 2d). No absolute age dating has yet been determinedfor any of these dykes and their age can be inferred from

Fig. 1 Simplified geological mapof W. Umm Adawi-W. Mandararea

223 Page 2 of 21 Arab J Geosci (2018) 11: 223

geological relationships. The field observations, distributions,trends, and cross cutting relationships of the studied dykessuggest that the emplacement of CAL preceded that of theDBD, while camptonite appears to be later than the DBD.

Petrography

The lamprophyre dykes (LPD) are mostly fine- to medium-grained porphyritic dykes. Based on the modal mineralogyclassification (Streckeisen 1978), the plagioclase in LPD ismuch more than alkali-feldspar. LPD are free from any Na-foids or leucite. Micas are dominating than amphiboles inSpessartite and camptonite, while in kersantite, the oppositeholds true. The olivine minerals are recorded only incamptonite. Opaque minerals are common, including magne-tite, titanomagnetite, ilmenite, and sulfides.

Camptonites are fine-grained porphyritic dykes. They arecomposed mainly of plagioclase, K-feldspar, amphibole, py-roxene (Ti-augite), olivine, and mica. Olivine pseudomorphsoccur as phenocrysts and they are partially or totally replaced

by serpentine and chlorite along fractures. Some olivine crys-tals are altered along their edges to iddingsite. The plagioclaseand olivine are settled in fine groundmass forming porphyritictexture. Amphibole occurs as long euhedral prismatic orrhombic megacrysts. Two types of ocelli are recoded, the firstwhere calcite and secondary silica filled either casts of alteredolivine crystals, interstitial spaces or fractures. This type isreferring to a large CO2 content of parental magma. The sec-ond ocelli type is filled by calcite, sericite, chlorite, secondaryquartz, and zoisite (Fig. 3a). The presence of chlorite, calcite,secondary quartz, and zeolite is indicative of their inductionthrough hydrothermal alterations during post-magmatic stage.This type is a typical type characterizses the alkalinelamprophyre.

Kersantites are commonly non-porphyritic and they con-tain the lowest mafics compared with other lamprophyretypes. They are composed mainly of plagioclase, K-feldspar,mica, pyroxene, and rare olivine. Biotite occurs as euhedral tosubhedral microphenocrysts or flakes, which are partiallyaltered to chlorite (Fig. 3b). Vesicles are common, and theyare filled with calcite and chlorite. Fe-Ti oxides are repre-sented by magnetite and titanomagnetite. Ti-magnetite-magnetite intergrowths are very common. Sulfides occuras pyrite, chalcopyrite, and pyrrhotite.

Spessartites are composed mainly of plagioclase, K-feldspar, amphibole, and clinopyroxene (i.e., augite). Theamphibole (i.e., oxyhornblende) occurs as long prismatic, smallneedles, or rhombic phenocrysts (Fig. 3c). Amphibole crystalsare rimmed by iron-oxides. Clinopyroxene occurs asmegacrysts or as fine-grained groundmass. Porphyritic textureis common in these dykes (Fig. 3c). Uralitization processproceeded in two stages: the augite changed to actinolite, whichin turn changed to basaltic hornblende. Alteration in thespessartite samples includes sericitization, saussuritization,chloritization, and uralitization. Most of these alterationprocesses are responsible for the formation of carbonates.

Fe-Ti oxides are represented by magnetite andtitanomagnetite. Both of Ti-magnetite-ilmenite and Ti-magnetite-magnetite (Fig. 3d) intergrowths are very common.The sulfides are represented by pyrite, chalcopyrite, andpyrrhotite.

DBD are fine- to medium-grained dykes with dark green toblack color. They are composed mainly of plagioclase, pyrox-ene, olivine, and actinolite with minor amounts of secondaryepidote, chlorite, and calcite. They show porphyritic,glomeropophyritic, diabasic, ophitic, and subophitic textures(Fig. 3e). Pyroxene is highly altered to actinolite and/or chlo-rite. Olivine occurs as subhedral to anhedral phenocrysts andsometimes is elongated in the direction of C-axis (Fig. 3e).Ilmenite occurs as subhedral grain, which intergrown eitherwith hematite or Ti-magnetite (Fig. 3f). In ilmenite-Ti-magnetite intergrowth, the lamellae of Ti-magnetite enclosedroplets of silicate minerals, which refer to an early

Fig. 2 a Swarms of parallel LPD traversing the syeno-monzogranite(SMG) at W. Mandar. b Swarms of DBD cut syeno-monzogranites(SMG) in different directions at W. Um Adawi. c Spessartite (Sp.) andKersantite (Ker.) vertical dykes cutting through syeno-monzogranites(SMG) at W. Mandar. d DBD cutting syno-monzogranite (SMG) andshows onion structure at W. Mandar

Arab J Geosci (2018) 11: 223 Page 3 of 21 223

crystallization of these Fe-Ti oxides. Coarse trellis intergrowthbetween Ti-magnetite and magnetite is also recoded.Magnetite-hematite intergrowth is very common. The sulfidesare sporadically scattered in the groundmass.

Analytical methods

A total of 99 spots (19 pyroxenes, 10 amphiboles, 7 micas,14 chlorites, 19 feldspars, 8 ilmenites, 8 magnetites, and 14sulfides) were analyzed using microprobe analyses(Tables 1, 2, 3, 4, and 5). These analyses were carried outby using energy dispersive X-ray (EDX) at the Institute ofMineralogy and Crystallography, University of Vienna,Austria. During the analyses, an acceleration voltage of20 keV was applied, with channel width 20 eV and usingZAF corrections. The analytical precision was accurate to± 2%. A total of 14 representative samples (4 from CAL, 3

from AL, and 7 from DBD; Tables 6 and 7) were analyzedfor major and trace element analyses. The analyses werecarried out by X-ray fluorescence (XRF) technique using aPhilips PW 2400 series spectrometer at Earth ScienceInstitute, Vienna University, Austria. The analytical preci-sion is better than 1% for major elements and 2–5% fortrace elements.

Results

Mineral chemistry

Pyroxenes

The clinopyroxene analyses in these mafic dykes show a widerange of compositional variation. TiO2 contents decrease fromAL through DBD to CAL.

Fig. 3 a Photomicrographshowing an ocelli filled by calcite(Cal), secondary quartz (Qz), andchlorite surrounded by finegroundmass in camptonite dyke,CN. b Photomicrograph showingsubhedral flakes of brown biotite(Bt) associated withpanidiomorphic plagioclase andopaques exhibiting radial texturein kersantite dyke, CN. cPhotomicrograph showing longprismatic phenocrysts of basaltichornblende (Hb) with porphyritic-panidiomorphic textures in spes-sartite dyke, CN. dPhotomicrograph showing the in-tergrowth between Ti-magnetite-magnetite in camptonite dyke,RL. e Photomicrograph showingphenocrysts of clinopyroxene(Cpx), plagioclase (Pl), andopaques, forming porphyritic andophitic-subophitic textures inDBD, CN. f Photomicrographshowing ilmenite-Ti-magnetitetrellis intergrowth with inclusionsof chalcopyrite (Cpy) andgoethite(Gth) in DBD, RL

223 Page 4 of 21 Arab J Geosci (2018) 11: 223

Table1

Microprobeanalyses

(wt%

)andstructuralform

ulae

(apfu)

ofpyroxenesin

lamprophyre

anddiabasedykes

Rock

CAL

CAL

CAL

AL

Diabase

Diabase

Diabase

Diabase

Sample

L14

L16

L28

L3

21D

XQ13

S25

Spots

12

31

12

12

34

12

31

21

21

2

SiO

248.45

51.47

52.96

53.13

50.82

52.23

50.34

50.07

48.01

49.83

50.99

50.21

49.37

50.09

50.17

50.29

51.66

51.06

51.15

TiO

20.24

0.78

0.12

0.21

0.64

0.21

1.35

1.23

1.82

1.15

0.96

0.9

1.35

0.79

0.1

0.28

0.55

0.78

0.82

Al 2O3

4.44

1.97

0.24

0.11

3.62

1.14

2.8

2.65

5.03

2.89

3.31

2.89

4.01

4.15

5.21

3.28

4.04

1.98

1.74

Cr 2O3

0.3

0.02

0.02

0.02

0.21

0.23

0.05

0.02

0.12

0.2

0.13

0.15

0.19

0.19

0.17

0.16

0.16

0.25

0.23

FeO

12.49

11.12

13.58

13.15

12.64

8.63

11.35

11.79

11.09

11.34

9.89

11.24

11.91

11.38

11.6

11.5

11.56

10.92

10.78

MnO

0.31

0.01

0.05

0.47

0.4

0.48

0.05

0.04

0.21

0.4

0.2

0.38

0.21

0.2

0.32

0.4

0.19

0.4

0.4

MgO

15.62

16.01

14.54

13.83

18.92

16.47

14.65

15.95

14.19

15.95

16.51

16.56

16.38

16.91

16.02

16.32

15.44

17.2

18.14

CaO

17.3

18.08

18.18

19.07

11.77

20.02

18.3

17.78

19.1

16.8

17.39

16.94

16.09

15.21

15.08

16.92

15.91

15.88

15.38

Na 2O

0.02

0.01

00

00

0.81

00.01

00.02

00

00

00

00

K2O

0.02

00

00

00

00

00

00

00

00

00

Sum.

99.2

99.46

99.69

100.01

99.01

99.41

99.7

99.54

99.58

98.56

99.4

99.27

99.5

98.92

98.66

99.15

99.5

98.46

98.64

Structuralform

ulabasedon

6oxygen

Si1.82

1.92

22.01

1.89

1.94

1.88

1.87

1.8

1.88

1.9

1.88

1.84

1.87

1.88

1.88

1.93

1.92

1.91

Ti

0.01

0.02

00.01

0.02

0.01

0.04

0.03

0.05

0.03

0.03

0.03

0.04

0.02

00.01

0.02

0.02

0.02

Aliv

0.11

0.12

0.07

0.00

0.00

0.16

0.19

0.11

0.11

0.05

0.10

0.11

0.14

0.15

0.12

0.12

0.11

0.08

0.08

Alvi

0.02

0.00

0.02

0.01

0.00

0.04

0.04

0.02

0.05

0.00

0.04

0.02

0.06

0.03

0.06

0.11

0.04

0.10

0.01

Cr

0.01

00

00.01

0.01

00

00.01

00

0.01

0.01

00

00.01

0.01

Fe3+

0.15

0.02

00

0.02

0.05

0.1

0.06

0.07

0.03

00.06

0.05

0.02

00.07

00.02

0.04

Fe2+

0.24

0.33

0.45

0.45

0.38

0.22

0.25

0.3

0.28

0.32

0.31

0.29

0.32

0.34

0.37

0.29

0.44

0.33

0.3

Mn

0.01

00

0.01

0.01

0.02

00

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

Mg

0.87

0.89

0.82

0.78

1.05

0.91

0.81

0.89

0.79

0.9

0.92

0.92

0.91

0.94

0.9

0.91

0.86

0.96

1.01

Ca

0.69

0.72

0.74

0.77

0.47

0.8

0.73

0.71

0.77

0.68

0.69

0.68

0.64

0.61

0.61

0.68

0.64

0.64

0.62

Na

00

00

00

0.06

00

00

00

00

00

00

Mg#

0.78

0.73

0.65

0.64

0.74

0.8

0.77

0.75

0.74

0.74

0.75

0.76

0.74

0.74

0.71

0.76

0.66

0.75

0.77

Fe#

0.61

0.94

1.04

1.08

0.96

0.83

0.71

0.82

0.81

0.9

10.82

0.86

0.95

1.02

0.8

1.23

0.95

0.88

En

0.48

0.46

0.41

0.39

0.55

0.47

0.45

0.47

0.43

0.47

0.48

0.49

0.49

0.5

0.48

0.49

0.44

0.5

0.53

Fs0.13

0.17

0.22

0.22

0.2

0.11

0.14

0.16

0.15

0.17

0.16

0.15

0.17

0.18

0.2

0.15

0.23

0.17

0.15

Wo

0.38

0.37

0.37

0.39

0.25

0.41

0.41

0.37

0.42

0.36

0.36

0.36

0.34

0.32

0.32

0.36

0.33

0.33

0.32

XPT

34.88

37.26

38.93

38.99

35.54

37.75

35.9

36.56

34.44

35.83

36.02

36.16

35.31

35.15

34.38

35.93

35.7

36.61

36.82

YPT

−24.45

−25.24

−23.99

−23.79

−25.48

−26.79

−24.19

−24.43

−23.68

−24.37

−25.9

−25

−24.42

−25.31

−25.46

−25.27

−25.24

−25.32

−25.7

Arab J Geosci (2018) 11: 223 Page 5 of 21 223

Table2

Microprobeanalyses

(wt%

)andstructuralform

ulae

(apfu)

ofam

phiboles

andmicas

inlamprophyre

anddiabasedykes

Amphibole

Micas

AL

AL

CAL

CAL

CAL

CAL

CAL

MineralRockSample

L3

L2

L14

L16

L28

Sample

L16

L28

Spots

12

12

34

12

11

Spots

12

34

56

1

SiO

247.77

44.79

45.45

44.13

54.35

44.65

45.4

49.84

50.97

51.28

SiO2

35.78

35.51

36.6

35.42

34.82

36.02

36.11

TiO

20.67

0.81

0.36

0.71

0.01

0.47

0.29

0.59

0.52

0.38

TiO

22.88

2.43

2.55

2.91

2.56

2.6

1.34

Al 2O3

8.57

9.83

8.47

8.58

2.62

8.37

11.86

7.76

8.01

5.13

Al 2O3

14.82

14.53

14.88

15.83

15.91

15.09

18

FeO

14.08

12.59

14.29

18.22

9.14

16.2

10.31

12.33

10.1

10.35

FeO

20.02

20.41

19.19

20.4

19.87

18.75

18.05

MnO

0.4

0.53

0.34

0.32

0.5

0.45

0.41

0.4

0.45

0.51

MnO

0.1

0.12

0.12

0.22

0.21

0.02

0.59

MgO

15.11

16.49

14.98

12.36

16.24

13.95

15.91

14.71

14.17

15.42

MgO

13.91

13.6

13.46

12.56

14.62

13.2

12.4

CaO

10.2

10.63

11.38

11.54

1311.55

10.92

11.17

12.31

13.3

CaO

0.1

0.2

0.05

0.06

0.17

0.74

0.54

Na 2O

0.4

0.55

2.86

1.75

0.92

1.45

1.75

0.32

0.54

0.4

Na 2O

0.3

0.2

0.3

0.45

0.59

0.97

0.75

K2O

0.82

0.97

0.44

0.94

0.34

0.81

0.33

0.68

0.78

0.37

K2O

9.58

9.89

8.84

9.68

8.65

8.52

9.19

Sum.

9897.19

98.77

98.52

97.12

97.89

97.18

97.79

97.85

97.14

Sum.

97.5

96.88

96.01

97.52

97.41

95.9

96.98

Structuralform

ulabasedon

23oxygens

Structuralform

ulabasedon

22oxygens

Si

7.04

6.7

6.47

6.48

6.55

7.78

6.41

7.28

6.38

Si

5.33

5.36

5.46

5.3

5.2

5.4

5.33

Aliv

1.3

1.62

1.44

1.48

0.22

1.43

1.59

0.96

0.72

0.59

Aliv

2.6

2.58

2.54

2.7

2.8

2.6

2.67

Alv

i0.11

0.03

00

0.22

00.39

0.33

0.63

0.28

Alv

i0

00.08

0.09

00.07

0.47

Ti

0.07

0.09

0.04

0.08

00.05

0.03

0.06

0.06

0.04

Altotal

2.6

2.58

2.62

2.79

2.8

2.67

3.13

Fe3+

1.65

1.5

11.13

01.36

1.22

0.91

00

Ti

0.32

0.28

0.29

0.33

0.29

0.29

0.15

Fe2+

00

0.72

1.1

1.09

0.61

00.55

1.21

1.25

Fe

2.5

2.58

2.39

2.55

2.48

2.35

2.23

Mn

0.05

0.06

0.04

0.04

0.06

0.05

0.05

0.05

0.05

0.06

Mn

0.01

0.02

0.02

0.03

0.03

00.07

Mg

3.16

3.5

3.22

2.7

3.47

3.02

3.35

3.1

3.02

3.32

Mg

3.09

3.06

2.99

2.8

3.25

2.95

2.73

Ca

1.53

1.62

1.76

1.81

1.99

1.8

1.65

1.69

1.88

2.06

Ca

0.02

0.03

0.01

0.01

0.03

0.12

0.09

Na

0.11

0.15

0.8

0.5

0.25

0.41

0.48

0.09

0.15

0.11

Na

0.09

0.06

0.09

0.13

0.17

0.28

0.22

K0.15

0.18

0.08

0.18

0.06

0.15

0.06

0.12

0.14

0.07

K1.82

1.9

1.68

1.85

1.65

1.63

1.73

(Ca+Na)B

1.64

1.77

22

22

1.96

1.78

22.06

Mg/Mg+Fe

0.55

0.54

0.56

0.52

0.57

0.56

0.55

Na(B)

0.11

0.15

0.24

0.19

0.01

0.2

0.31

0.09

0.12

0Fe/Fe

+Mg

0.45

0.46

0.44

0.48

0.43

0.44

0.45

(Na+K)A

0.15

0.18

0.64

0.48

0.31

0.35

0.23

0.12

0.17

0.18

223 Page 6 of 21 Arab J Geosci (2018) 11: 223

According to En-Wo-Fs ternary diagram (Morimoto et al.1988), the pyroxenes were classified as augite (Fig. 4a). OnMgO/FeOt-SiO2/TiO2 diagram (Rock 1987), the pyroxenesin LPD fall in the field of pyroxene, which characterizescalc-alkaline and alkaline lamprophyres (Fig. 4b). To de-tect the nature of magma, the pyroxene analyses plotted onAl2O3-SiO2 diagram (Le Bas 1962). The pyroxenes inCAL, DBD, and AL were crystallized from transitionalsubalkaline to alkaline magma (Fig. 4c). Ca-Ti + Cr dia-gram (Letterrier et al. 1982) indicates that the pyroxeneswere crystallized in non-orogenic tectonic environment(Fig. 4d). Soesoo (1997) calculated XPT and YPT valuesfrom pyroxene chemistry to determine the pyroxenegeothermobarometric conditions. The analyzed pyroxeneswere crystallized under temperature between 1100 and1150 °C (Fig. 4e). The pyroxenes in CAL and DBD werecrystallized under pressure 2–5 kbars, while those in ALwere crystallized under 2 kbars (Fig. 4f). Plots of pyroxenes

on 2Ti + Aliv + Cr–Alvi + Na diagram (Schweitzer et al. 1979)confirm the high oxygen fugacity (fO2) conditions underwhich pyroxenes were crystallized (Fig. 5a).

Amphiboles

The analyzed amphiboles in LPD are Mg-rich amphibolesand contain moderate amount of Al2O3 (Table 2). Asshown in SiO2-TiO2 diagram (Rock et al. 1991), the am-phiboles are primary magmatic (Fig. 5b). Using plots ofamphiboles on (Ca + Na)B-Na(B) diagram (Leake et al.1997), classify them as calcic-amphiboles (Fig. 5c).According to Si-(Na + K)(A) diagram (Leak et al. op cit),the amphiboles were classified into manegsio-hornblendeand tschermarkite except two samples from CAL and AL,which were classified as tremolite and pargasite, respec-tively (Fig. 5d). Aliv-Fe2+/Fe2+ + Mg diagram (Andersonand Smith 1995) confirms the high fO2 conditions under

Table 3 Microprobe analyses (wt%) and structural formulae (apfu) of chlorites in lamprophyre and diabase dykes

Rock AL AL CAL CAL Diabase Diabase Diabase

Sample L1 L2 L12 L28 21D Mg6 Q13

Spots 1 2 1 2 1 2 3 1 1 2 1 1 2 3

SiO2 28.38 28.76 29.2 29.96 30.69 30.73 27.53 30.67 29.64 29.98 28.46 29.62 29.31 28.8

TiO2 0.01 0.02 0.01 0.02 0.25 0.14 0.51 0.04 0.88 0.23 0.12 0.18 0.91 0.28

Al2O3 18.81 20.1 16.75 16.5 15.13 14.25 17.18 15.46 16.78 15.46 18.24 12.96 15.1 15.7

FeO 27.63 28.65 25.15 27.28 23.57 25.32 24.49 27.16 26.84 27.63 28.73 27.97 28.13 26.24

MnO 0.03 0.02 0.03 0.04 0.02 0.02 0.01 0.03 0.04 0.02 0.37 0.19 0.19 0.17

MgO 16.33 16.65 18.85 17.64 20.49 19.44 19.45 18.45 15.88 18.14 15.52 16.38 16.64 17.89

CaO 0.02 0.02 0.02 0.1 0.02 0.12 0.33 0.02 0.28 0.04 0.12 0.19 0.13 0.12

Na2O 0 0 0 0 0.03 0.14 0 0.01 0.85 0.05 0.02 0.13 0.17 0.03

K2O 0 0.02 0 0.02 0.12 0 0 0 0.27 0.02 0 0.02 0.11 0.04

H2O 11.78 12.16 11.75 11.85 11.9 11.76 11.65 11.91 11.8 11.81 11.74 11.2 11.61 11.54

Sum. 102.99 106.4 101.76 103.41 102.22 101.92 101.15 103.75 103.25 103.4 103.32 98.84 102.3 100.8

Structural formula based on 28 oxygen

Si 5.78 5.67 5.95 6.06 6.18 6.25 5.63 6.18 5.98 6.07 5.81 6.33 6.04 5.97

Al iv 2.22 2.33 2.05 1.94 1.82 1.75 2.37 1.82 2.02 1.93 2.19 1.67 1.96 2.03

Al vi 2.29 2.35 1.98 1.99 1.78 1.68 1.8 1.85 2 1.77 2.21 1.6 1.72 1.82

Ti 0 0 0 0 0.04 0.02 0.08 0.01 0.13 0.04 0.02 0.03 0.14 0.04

Fe3+ 0.04 0.01 0 0.03 0 0 0 0.02 0 0 0.03 0 0 0

Fe2+ 4.66 4.71 4.31 4.58 3.97 4.34 4.36 4.55 4.56 4.72 4.88 5.02 4.86 4.61

Mn 0.01 0 0.01 0.01 0 0 0 0.01 0.01 0 0.06 0.03 0.03 0.03

Mg 4.95 4.9 5.73 5.32 6.15 5.9 5.93 5.54 4.77 5.48 4.73 5.22 5.11 5.53

Ca 0 0 0 0.02 0 0.03 0.07 0 0.06 0.01 0.03 0.04 0.03 0.03

Na 0 0 0 0 0.02 0.11 0 0.01 0.66 0.04 0.02 0.11 0.13 0.02

K 0 0.01 0 0.01 0.06 0 0 0 0.14 0.01 0 0.01 0.06 0.02

Fe/Fe +Mg 0.49 0.49 0.43 0.46 0.39 0.42 0.42 0.45 0.49 0.46 0.51 0.49 0.49 0.45

*T °C 405.71 454.77 390.78 523.02 431.3 491.03 514.49 405.71 448.37 429.17 484.63 373.71 435.57 450.5

*T °C: temperature chlorite formation is calculated according to Cathelineu and Nieva (1985)

Arab J Geosci (2018) 11: 223 Page 7 of 21 223

Table4

Microprobeanalyses

(wt%

)andstructuralform

ulae

(apfu)

offeldsparsin

lamprophyre

anddiabasedykes

RockALALCALCAL

Diabase

Diabase

Diabase

Sample

L1

L13

L12

L28

21D

Q13

Mg6

spots

12

12

12

34

12

34

12

31

21

2

SiO

252.76

60.4

62.04

62.88

63.04

57.85

53.69

49.83

58.8

62.83

60.48

60.4

62.29

57.37

60.38

53.86

60.10

61.12

62.18

TiO

224.56

21.14

22.66

20.82

19.72

25.34

31.03

29.33

24.64

21.48

21.1

20.33

20.62

22.87

23.03

26.24

20.17

21.39

20.57

Al 2O3

0.01

0.01

0.01

0.01

0.02

0.03

0.01

00.13

0.12

0.04

0.11

0.01

0.03

0.01

0.14

0.11

0.01

0.14

FeO

0.03

0.03

0.03

0.03

0.05

0.09

0.08

0.04

0.05

0.03

0.05

0.12

0.00

0.10

0.02

0.15

0.36

0.35

0.32

MnO

0.02

0.02

0.03

0.01

0.05

0.01

0.03

0.03

0.03

0.09

0.05

0.04

0.05

0.02

0.04

0.25

0.14

0.12

0.03

MgO

0.02

0.03

0.01

0.02

0.08

0.04

0.03

0.04

0.03

0.04

0.09

0.07

0.12

0.05

0.05

0.45

0.23

0.25

0.14

CaO

5.28

0.9

1.63

00

3.09

0.69

14.67

3.88

0.81

1.52

2.47

4.29

3.92

3.14

7.95

0.00

2.27

0.90

Na 2O

5.19

17.14

12.99

0.75

6.59

8.52

5.49

4.21

10.54

13.79

4.45

15.52

10.99

11.77

11.65

8.84

7.72

14.20

14.80

K2O

11.79

00.43

14.99

9.56

4.18

8.62

1.39

1.54

0.5

11.83

0.7

1.23

3.68

0.78

1.62

10.97

0.00

0.00

Sum.

99.66

99.67

99.83

99.51

99.11

99.15

99.67

99.54

99.64

99.69

99.61

99.76

99.59

99.82

99.09

99.50

99.80

99.71

99.08

Structuralform

ulabasedon

6oxygen

Si

2.63

2.84

2.87

32.99

2.75

2.59

2.42

2.76

2.91

2.91

2.84

2.90

2.74

2.83

2.59

2.90

2.85

2.90

Al

00

00

00

00

0.01

0.01

00.01

0.00

0.00

0.00

0.01

0.01

0.00

0.01

Ti

0.92

0.75

0.79

0.75

0.7

0.91

1.13

1.07

0.87

0.75

0.76

0.72

0.72

0.82

0.81

0.95

0.73

0.75

0.72

Mg

00

00

0.01

00

00

00.01

0.01

0.00

0.00

0.00

0.01

0.01

0.01

0.01

Ca

0.28

0.05

0.08

00

0.16

0.04

0.76

0.2

0.04

0.08

0.12

0.00

0.00

0.00

0.01

0.01

0.00

0.00

Na

0.5

1.56

1.17

0.07

0.61

0.79

0.51

0.4

0.96

1.24

0.41

1.42

0.01

0.00

0.00

0.03

0.02

0.02

0.01

K0.75

00.03

0.91

0.58

0.25

0.53

0.09

0.09

0.03

0.73

0.04

0.21

0.20

0.16

0.41

0.00

0.11

0.04

Or

48.89

0.01

2.01

92.92

48.84

21.18

49.1

6.9

7.38

2.26

59.55

2.64

5.7

14.81

3.71

7.46

48.31

0.1

0.01

Ab

32.7

97.18

91.64

7.07

51.15

65.65

47.58

31.83

76.96

94.68

34.03

89.48

77.57

71.95

83.81

61.81

51.68

91.8

96.76

An

18.41

2.81

6.35

0.01

0.01

13.17

3.32

61.27

15.66

3.07

6.42

7.88

16.73

13.24

12.47

30.73

0.01

8.1

3.23

223 Page 8 of 21 Arab J Geosci (2018) 11: 223

Table5

Microprobeanalyses

ofFe-Tio

xidesandsulfides

(wt%

)in

lamprophyre

anddiabasedykes

Rock

CAL

AL

AL

CAL

Diabase

Diabase

Diabase

Diabase

Diabase

Diabase

Sample

L16

L2

L2

L28

Q13

21D

Mg6

21D

Q13

Mg6

Spots

12

31

Spots

12

31

12

11

11

21

SiO

20.36

0.09

0.54

0.40

SiO2

0.37

0.10

0.55

0.12

0.11

0.01

0.09

0.05

SiO2

0.52

0.05

0.01

0.19

TiO

243.99

44.51

44.48

46.01

TiO

20.34

13.52

29.42

0.24

43.35

45.29

47.17

45.20

TiO

212.78

11.67

11.14

10.28

Al 2O3

0.05

0.08

0.00

0.02

Al 2O3

0.35

0.11

0.25

0.46

0.02

0.04

0.01

0.00

Al 2O3

0.22

0.03

0.03

0.06

Cr 2O3

0.31

0.36

0.31

0.22

Cr 2O3

0.29

0.49

0.3

0.22

0.25

0.21

0.21

0.19

Cr 2O3

0.27

0.31

0.30

0.31

V2O3

1.13

0.75

1.16

0.45

V2O3

0.44

0.91

0.87

0.26

0.68

0.46

0.81

0.55

V2O3

0.39

0.74

0.46

0.59

Fe 2O3

15.83

14.86

14.24

12.07

Fe2O3

66.36

41.34

9.56

68.37

50.26

50.03

48.00

48.87

Fe2O3

79.59

80.51

81.54

82.11

FeO

36.21

35.97

36.62

37.39

FeO

30.24

41.34

56.69

28.96

0.02

0.16

0.07

0.07

FeO

0.41

0.38

0.40

0.41

CaO

0.30

0.02

0.05

0.02

NiO

0.49

0.34

0.39

1.11

2.68

1.50

2.51

3.28

NiO

0.85

1.16

0.74

0.80

MnO

2.19

2.93

2.57

3.71

MnO

0.37

1.44

1.35

0.22

0.19

0.58

0.05

0.14

MnO

0.28

0.26

0.25

0.25

MgO

0.02

0.02

0.02

0.03

MgO

0.38

0.42

0.26

0.91

0.26

0.25

0.05

0.12

MgO

0.15

0.18

0.05

0.26

ZnO

0.00

0.01

0.00

0.01

ZnO

0.22

0.03

0.4

0.18

0.81

0.05

0.01

0.12

ZnO

95.45

95.30

94.92

95.26

Sum.

100.38

99.60

99.98

100.34

Sum.

99.84

100.03

100.06

101.04

97.57

98.33

98.94

98.47

Sum.

0.52

0.05

0.01

0.19

Rock

AL

AL

CAL

Diabase

Diabase

Pyrite

pyrrhotite

Chalcopyrite

Pyrite

Pyrrhotite

sample

L13

L2

L16

21D

21D

spots

12

31

23

12

31

23

12

As

0.18

0.18

0.15

0.66

0.59

0.63

0.11

0.11

0.11

0.14

0.11

0.09

0.61

0.61

Fe45.98

45.7

46.07

59.24

59.31

58.99

30.36

30.55

30.38

46.01

46.47

46.23

59.54

58.74

Cu

0.04

0.04

0.04

0.10

0.10

0.10

34.33

34.27

34.32

0.00

0.00

0.00

0.00

0.00

Zn

0.00

0.00

0.00

0.00

0.00

0.00

0.11

0.08

0.06

0.05

0.05

0.04

0.10

0.10

Co

0.25

0.24

0.20

0.13

0.12

0.13

0.04

0.04

0.04

0.20

0.17

0.16

0.13

0.13

Ni

0.04

0.05

0.14

0.59

0.61

0.61

0.09

0.09

0.08

0.15

0.21

0.24

0.63

0.62

S53.04

53.33

53.09

38.96

38.99

39.25

34.77

34.62

34.76

53.18

52.77

53.01

38.68

39.53

Sum.

99.83

99.54

99.68

99.68

99.73

99.71

99.82

99.75

99.75

99.72

99.77

99.77

99.68

99.74

Arab J Geosci (2018) 11: 223 Page 9 of 21 223

which amphiboles were crystallized (Fig. 5e). To determinethe geobarometry of amphiboles, the data were plotted on Alt-Fet/(Fet +Mg) diagram, which prove that the amphiboles were

crystallized under pressure 3–5 kbars (Fig. 5f). According toAl2O3-TiO2 diagram (Jiang and An 1984), the amphiboleswere crystallized from mixed crustal-mantle source (Fig. 6a).

Table 6 Representative major (wt%) and trace elements (ppm) in lamprophyre dykes

Rock AL AL CAL AL CAL CAL CAL

Sample L2Camptonite

L3Camptonite

L12Spessartite

L13Camptonite

L14Spessartite

L16Kersantite

L28Kersantite

SiO2 46.73 47.48 47.04 47.31 44.79 54.02 52.22

TiO2 2.76 2.14 2.01 2.7 1.88 1.73 1.59

Al2O3 13.92 15.84 15.55 15.16 15.28 15.76 15.82

Fe2O3 14.53 12.78 12.41 13.45 12.41 9.39 9.92

MnO 0.23 0.17 0.16 0.16 0.15 0.13 0.13

MgO 5.07 6.22 6.89 5.2 6.26 4.12 4.43

CaO 9.1 8.21 9.24 7.01 8.27 5.14 6.25

Na2O 2.73 3.54 2.73 3.84 2.18 3.87 4.25

K2O 1.56 1.22 0.79 1.19 0.54 1.14 2.25

P2O5 0.57 0.28 0.26 0.5 0.24 0.63 0.73

LOI 2.84 2.23 2.27 2.67 7.48 3.79 1.44

Sum 100.05 100.11 99.34 99.18 99.48 99.73 99.02

Mg# 40.88 49.10 52.39 43.38 49.99 46.51 46.95

Q 0.00 0.00 0.00 0.00 1.54 10.01 0.00

or 9.59 7.44 4.85 7.36 3.50 7.07 13.72

ab 24.02 30.89 24.02 33.99 20.25 34.36 37.11

an 21.96 24.47 28.95 21.57 33.28 22.44 18.00

di 17.29 12.72 13.73 9.27 8.17 0.00 7.38

hy 12.69 1.51 13.97 9.09 23.35 15.90 14.20

ol 1.21 12.68 4.60 5.79 0.00 0.00 0.11

mt 6.42 5.44 5.29 6.37 5.38 4.91 4.62

il 5.45 4.19 3.97 5.36 3.92 3.45 3.12

ap 1.37 0.67 0.63 1.21 0.61 1.53 1.75

As 1 2 2 1 3 1 2

Ba 905 290 342 558 316 223 978

Co 50 41 58 50 55 33 35

Cr 47 27 43 42 50 79 94

Cu 88 46 43 53 17 29 43

Ga 24 18 23 23 21 25 22

Mo 2 3 1 2 1 2 2

Nb 21 12 14 26 12 19 18

Nd 49 25 32 51 28 62 55

Ni 77 85 126 80 104 45 55

Rb 51 23 26 37 21 62 52

Sc 28 19 24 22 26 20 26

Th 4 3 4 4 3 9 7

U 5 3 4 4 2 5 6

V 362 251 274 350 261 235 279

Y 40 21 26 36 26 28 36

Zr 248 130 158 261 154 370 291

Ti 16,546.2 12,829.3 16,186.5 12,049.95 11,270.6 10,371.35 9532.05

K 12,951.12 10,128.44 9879.38 6558.58 4483.08 9464.28 18,679.5

P 2487.59 1221.98 2182.1 1134.69 1047.41 2749.45 3185.87

Fe 101,627.2 89,387.15 94,073.34 86,799.26 86,799.26 65,676.48 69,383.46

ΔNb − 0.06 − 0.02 − 0.03 − 0.05 − 0.08 − 0.58 − 0.30

223 Page 10 of 21 Arab J Geosci (2018) 11: 223

Micas

The analyzedmicas in CAL have highMgO and FeO contents(Table 2). The micas classified asMg-rich biotites (Fig. 6b) byusing Fet/Fet +Mg-Si diagram (Föster 1960). On FeO-10 +TiO2-MgO diagram (Föster 1960), the biotites fall in primarymagmatic field (Fig. 6c). To detect the nature of magma, thebiotite data plotted on (Fet + Mg)/Al-Si/Al diagram(Maracuchiev and Tararin 1966). The biotite analyses fromCAL fall in subalkaline magma field (Fig. 6d).

Chlorites

The analyzed chlorites from CAL, AL, and DBD are enrichedin FeO and MgO and depleted in K2O (Table 3). The plots ofchlorite on Si-Fe3+ + Fe2+ diagram (Hey 1954) classify thechlorites into pycnochlorite except two samples from CALand diabase, which fall in diabantite field (Fig. 6e).Cathelineu and Nieva (1985) used the following equation todetermine the geothermometry of chlorite: T (°C) =213.3Aliv + 17.5.

The average temperatures calculated for the chlorite forma-tion are 439.59, 465, and 436.99 °C for the chlorite fromCAL,AL, and DBD, respectively (Table 3).

Feldspars

The feldspars in LPD and DBD have wide range of variationin their composition (Table 4). According to Ab-An-Or terna-ry diagram (Deer et al. 1966), the plagioclases in CAL rangein composition from albite, oligoclase to labradorite. The pla-gioclases in DBD range in composition from albite, oligoclaseto andesine, while those in AL have albite composition. K-feldspars in CAL, DBD, and AL have sanidine composition(Fig. 6f).

Fe-Ti oxides

Fe-Ti oxides in the mafic dykes are represented by ilmeniteand Ti-magnetite (Table 5). Ti-magnetite have high TiO2 con-tents in AL (up to 29.42 wt%) and moderate contents in DBD(up to 12.87 wt%). To distinguish between the Fe-Ti oxidephases, the Fe-Ti oxide analyses were plotted on FeO-TiO2-Fe2O3 diagram (Buddington and Lindsley 1964). As shown inFig. 7a, there is no pure magnetite or ilmenite in the studieddykes. Fe-Ti oxide phases in CAL and AL are represented byTi-magnetite-magnetite, Ti-magnetite-ilmenite, magnetite-he-matite, and ilmenite-hematite phases (Fig. 7a). Fe-Ti oxidephases in DBD are represented by ilmenite-Ti-magnetite, il-menite-hematite, and magnetite-hematite phases. This simul-taneous growth between magnetite and Ti-magnetite may re-fer to oxidizing conditions and increase in fO2 (Frost andLindsley 1992).

MnO increases gradually from magnetite through Ti-magnetite to ilmenite, while Cr2O3 and V2O3 remain constantthrough all the studied dykes (Fig. 7b). The ilmenite in CALand AL is correlated with ilmenite in the lamprophyres typesafter Rock (1987) they fall in the field of ilmenite from CALand AL (Fig. 7c).

Sulfides

The sulfide minerals are represented by pyrite and pyrrhotitein DBD and by pyrite, pyrrhotite, and chalcopyrite in LPD(Table 5). Both of As and Co (wt%) increase gradually withdecreasing Ni (wt%) in pyrite from DBD and CAL (Fig. 7d).The chalcopyrite hosted in DBD and AL exhibit nearly con-stant As, Co, and Ni (wt%).

As, Cu, Ni, and Fe (wt%) are almost constant in pyrrhotitefrom CAL and AL and in chalcopyrite from AL (Fig. 7e, f).According to Co/Ni ratio, the sulfides hosted in DBD andLPD were classified into two types. The first with Co/Ni(wt%) ratio ˃ 1 and the second with Co/Ni (wt%) ˂ 1(Table 5). The second type is the most common between sul-fides, which suggests a magmatic-hydrothermal origin forthese sulfides (Mazdab and Force 1998).

Geochemistry

Generally, the mafic dykes of Wadi Mandar-Um Adawihave relatively high SiO2, moderate alkalis (Na2O andK2O), and low MgO (Tables 6 and 7). In contrary toDBD, LPD contain a wider range of silica content(46.73–54.28 wt%). CAL are enriched in SiO2 more thanAL. As shown in Table 6, only kersantite contains a con-siderable amount of free normative quartz (up to 10.01).TiO2 contents are high in DBD and AL compared withCAL, which is consistent with their alkaline character.These dykes have low contents of Cr and Ni (Tables 6and 7). Mg# values in these dykes are moderately low.

According to TAS classification diagram (Le Maitre et al.1989), CAL were classified into basaltic andesite, basaltictrachyandesite, and basalt, while DBD and AL were classifiedas basalt (Fig. 8a). Rock et al. (1991) distinguished betweenlamprophyre, kimberlite, and lamproite using MgO-K2O-Al2O3 diagram. LPD analyses fall within lamprophyre field(Fig. 8b). By using Rock (1987) classification scheme, LPDwere differentiated into calc-alkaline and alkalinelamprophyres (Fig. 8c). Al/(Na + K + Ca)-Al (Na + K) dia-gram (Maniar and Piccoli 1989) confirms the metaluminousnature of these dykes (Fig. 8d). According to SiO2-Na2O +K2O diagram (Middlemost 1997), CAL and DBD exhibittransitional characters from calc-alkaline to mildly alkaline,while AL show mildly alkaline characters (Fig. 8e).

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Discussion

The mafic dykes in Wadi Mandar-Wadi Um Adawi area arerepresented CAL, DBD, and AL (Fig. 4b, Fig. 8c). CAL rangein composition from basaltic andesite, basaltic trachyandesiteto basalt, while DBD and AL are basaltic in composition (Fig.8a). The mafic dykes have metaluminous nature. CAL andDBD show transitional characters from calc-alkaline to alka-line, while AL exhibit alkaline character (Fig. 4d, Fig. 8d, e).

These dykes were crystallized under temperature between1100 and 1150 °C and under pressure from 2 to 5 kbars inhigh oxygen fugacity conditions (Fig. 4e, f, Fig. 5a, e, f).

K2O-TiO2-P2O5 ternary diagram (Pearce et al. 1975)shows that the investigated dykes were emplaced in acontinental rather than in oceanic setting (Fig. 8f). Thesimilarity of both shapes and slopes of the trace elementspider patterns of the studied dykes is a common featurein many dyke swarms in Sinai (Eyal et al. 2010). Trace

Table 7 Representative major(wt%) and trace elements (ppm)in diabase dykes Sample

21D MG6 Q13 R1 X S25 K21

SiO2 47.99 48.43 48.32 47.23 46.78 47 50.56TiO2 2.69 3.26 2.73 2.22 3.01 0.15 1.09Al2O3 14.62 13.53 14.41 16.09 15.39 21.9 18.16Fe2O3 14.19 15.11 13.94 12.63 13.46 5.18 8.23MnO 0.18 0.21 0.18 0.2 0.17 0.1 0.2MgO 5.23 4.33 5.03 5.25 5.16 7.28 5.6CaO 7.12 7.2 7.39 7.25 7.59 13.53 8.27Na2O 3.37 3.38 3.23 2.31 3.26 1.49 3.14K2O 1.48 1.61 1.48 2.53 1.39 0.74 1.54P2O5 0.56 1.01 0.59 0.57 0.66 0.02 0.3LOI 1.82 1.78 1.82 3.64 2.79 2.07 2.1Sum 99.24 99.86 99.11 99.94 99.67 99.8 99.18Mg# 42.21 36.22 41.69 45.17 43.17 31.33 57.42Q 0.00 2.55 1.09 0.00 0.00 0.00 0.33or 9.07 9.81 9.08 15.67 8.56 4.51 9.43ab 29.57 29.48 28.38 20.49 28.74 12.99 27.53an 21.15 17.51 21.23 27.32 24.23 52.44 32.02di 9.55 10.25 10.48 5.29 8.51 13.22 6.81hy 16.62 14.51 16.58 19.46 14.68 6.78 17.13ol 1.10 0.00 0.00 0.31 0.92 7.27 0.00mt 6.30 7.11 6.37 5.65 6.81 2.47 3.89il 5.30 6.38 5.38 4.42 5.96 0.29 2.14ap 1.35 2.41 1.42 1.38 1.59 0.05 0.72As 3 3 1 2 2 4 6Ba 649 994 567 736 646 569 503Co 54 42 52 41 47 45 20Cr 36 42 28 35 31 70 179Cu 53 32 73 129 29 29 185Ga 24 22 23 21 23 20 18Mo 1 2 2 1 1 1 2Nb 20 24 21 20 29 17 5Nd 50 62 49 43 54 77 28Ni 85 40 83 46 56 42 73Rb 44 32 34 87 39 21 76Sc 25 28 25 24 23 30 23Th 4 5 4 4 5 3 3U 5 3 4 3 5 3 5V 365 324 350 292 318 363 207Y 37 49 39 31 36 55 22Zr 246 297 258 197 268 264 145Ti 16,126.55 6534.55 19,543.7 16,366.35 13,308.9 899.25 18,044.95K 12,286.96 12,785.08 13,366.22 12,286.96 21,004.06 6143.48 11,539.78P 2443.95 1309.26 4407.84 2574.88 2487.59 87.28 2880.37Fe 99,249.12 57,563.09 105,683.9 97,500.54 88,338.01 36,230.47 94,143.28ΔNb − 0.11 − 0.07 − 0.10 0.01 − 0.03 − 0.01 − 0.30

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element spider diagram (Wood et al. 1979b) shows en-richment in LILE and prominent negative Nb, P, and Cranomalies (Fig. 9a). Nb and P negative anomalies are acharacteristic feature of arc signature (Gill 2010). Pearceand Gale (1977) used SiO2–Nb diagram to differentiatebetween lava that has been formed in within-plate (Nb-

rich) and volcanic-arc (Nb-poor) settings. CAL, DBD, andAL analyses fall within a transitional tectonic setting be-tween volcanic-arc and within-plate (Fig. 9b). Therefore,the studied dykes do not display a typical arc-type signature,but actually, they have aspects of a within-plate character. Thesubduction signature of the studied dykes may be due to the

Fig. 4 a En-Wo-Fs ternary diagram (Morimoto et al. 1988) to classify thepyroxene in LPD and DBD. bMgO/FeOt-SiO2/TiO2 discrimination dia-gram (Rock 1987) of the pyroxene in LPD and DBD, CAL: calc-alkalinelamprophyres, AL: alkaline lamprophyres, UML: ultramaficlamprophyres and LL: lamproites. c Al2O3-SiO2 diagram (Le Bas 1962)of the pyroxene in LPD and DBD. d Ca-Ti + Cr diagram (Letterrier et al.

1982) of the pyroxenes in LPD and DBD solid field represent 81% ofclinopyroxene from non-orogenic basalt. e XPT-YPT diagram (Soesoo1997) to determine the geothermometry of the pyroxenes in LPD andDBD. fXPT-YPT diagram (Soesoo op cit) to determine the geobarometryof pyroxenes in LPD and DBD

Arab J Geosci (2018) 11: 223 Page 13 of 21 223

partial melting of a lithospheric mantle enriched during a pre-vious subduction event in the ANS. Thus, the chemistry ofsubduction-related melt exceeding by far the lifetime of thetectonic events they result from (Eyal et al. 2010). The studieddykes were emplaced in Banorogenic^ environment and cer-tainly not in compressional arc-type (Fig. 4d). Furthermore,Y/Nb-Rb diagram (Pearce et al. 1984) clearly indicates thatthe studied dykes were emplaced in post-collisional tectonicenvironment (Fig. 9c).

Geodynamic implications of post-collisional stage

The post-collisional stage (630–550 Ma) in ANS began afterperiod of collision between ANS crust and the SaharanMetacraton (Abdelsalam et al. 2002), explained by the exten-sional collapse of the thickened lithosphere, leading to exten-sion and thinning of the ANS crust, which continued untilapproximately 550 Ma (Greiling et al. 1994; Eyal et al.2010. The extensional collapse was controlled by slab break

Fig. 5 a 2Ti + Aliv + Cr–Alvi + Na diagram (Schweitzer et al. 1979) of thepyroxene in LPD. b SiO2-TiO2 diagram (Rock et al. 1991) to differentiatebetween primary and secondary amphiboles in LPD. c (Ca + Na)(B)-Na(B) diagram (Leake et al. 1997) to classify the amphiboles in LPD. d Si–(Na + K)(A) diagram (Leake et al. 1997) for classification of the

amphiboles in LPD. e Aliv-Fe2+/Fe2+ + Mg diagram (Anderson andSmith 1995) to determine oxygen fugacity of the amphiboles in LPD. fAlt-Fet/(Fet + Mg) diagram (Anderson and Smith op cit) to determinegeobarometry of the amphiboles in LPD. Symbols as in Fig. 4

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off combined with delamination of the continental lithosphere(El-Bialy 2010; Moghazi et al. 2011; Moufti et al. 2013). Thecrustal thinning was accompanied by the development ofdeep-seated strike-slip faults and shear zones that favored lith-ospheric delamination. These structures could have facilitatedthe decompression melting processes within lithosphere. Bothcalc-alkaline (∼ 630–590 Ma) and alkaline (610–580)

magmatism were formed coevally (Liégeois 1998; Bonin2004). This contemporaneous calc-alkaline and alkalinemagmatism should involve extensive heat and material trans-fer from the asthenosphere into the lithospheric mantle andlower crust. Underplating and/or interplating of ascendingmafic magma to different juvenile crustal levels could havecaused melting, magma mixing, and differentiation.

Fig. 6 a Al2O3-TiO2 diagram (Jiang and An 1984) for the amphiboles. bFe/Fe +Mg-Si diagram (Föster 1960) for classification of the mica inCAL. c FeO-10*TiO2-MgO ternary diagram (Föster op cit, neoformedbiotite field after Nachit et al. 2005) of micas in CAL. d alkalinity-aluminosity or M = (Fet + Mg)/Al-S = (Si/Al) diagram (Maracuchiev

and Tararin 1966) for micas in CAL. e Si-Fe2+ + Fe3+ diagram of thechlorites in LDP and DBD (Hey 1954). f Ab-An-Or ternary diagram(Deer et al. 1966) for classification of the feldspars in LPD and DBD.Symbols as in Fig. 4

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Petrogenesis

Derivation of AL and DBD from CAL

As the CAL emplaced earlier than DBD and AL, so in thissection, the availability of derivation of DBD and AL fromCAL either by partial melting or by fractionation crystalliza-tion will be discussed. The behavior of high field strengthelements (HFSE) and large ion lithophile elements (LILE)could be helpful in testing the derivation of DBD by small

degree of partial melting of from CAL. Partial melting shouldbe accompanied by enrichment in HFSE such as Nb, P, Ti, Y,and LILE such as Rb, K, and Ba. Nb and Rb are slightlyincreased in DBD, while Ba has an opposite behavior (i.e.,503–994 ppm in DBD and 223–978 ppm in CAL).Furthermore, the partial melting causes depletion in the com-patible elements such as Fe, Cr, and Ni. In the fact, Cr and Niare slightly low in DBD compared with CAL, while Fe isenriched in DBD and depleted in CAL (Table 6). This behav-ior of HFSE and LILE in CAL and BDB does not favor the

Fig. 7 a, f FeO-TiO2-Fe2O3 solid solution system (Buddington andLindsley 1964) for Fe-Ti oxides in LPD and DBD. b V2O3-MnO-Cr2O3 ternary diagram of Fe-Ti oxides in LPD and DBD. c Molar(Fe2+-Fe3+-Mg) ternary diagram (Rock 1987, kimberlite field after

Mitchell 1986). d Ni-As-Co ternary diagram of studied sulfides in LPDand DBD. eCu-As-Ni ternary diagram of sulfides in LPD and DBD. f Fe-S-Cu ternary diagram for the studied sulfides LPD. Symbols as in Fig. 4

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derivation of BDB from CAL by partial melting. From theother side, DBD are less differentiated than the CAL, whichevidenced by Mg# values (i.e., 46.51–52.39; 31.33–57.42 inCAL and diabase, respectively). DBD have slightly highercontents of Rb, Nb, and Y more than CAL (i.e., 32–87, 21–62; 20–29, 12–19; 22–55, 26–29 ppm in DBD and CAL,respectively). Those chemical differences between CAL andDBD exclude the generation of DBD from CAL by fractionalcrystallization.

To examine the derivation of AL from CAL either bypartial melting or by fractional crystallization, the behaviorof some trace elements and Mg# should be followedthrough CAL and AL. Mg#, Rb, P, Cr are depleted in ALcompared with CAL, while Ni, Ti, Nb, Ba, K, Fe, Y areslightly higher in AL than CAL. This behavior of both Nband Y and Ni, P, Fe in CAL and AL are not in concordancewith both fractional crystallization and partial melting process,respectively.

Fig. 8 a Total-alkali and silica (TAS) diagram (Le Maitre et al. 1989) forthe studied LPD and DBD. b MgO-K2O-Al2O3 ternary diagram (Rock1987) for the studied LPD. c CaO-SiO2/10–4* TiO2 ternary diagram(Rock op cit), CAL: calc-alkaline lamprophyre and AL: alkaline

lamprophyre. d Al/(Na + K + Ca)-Al (Na + K) diagram (Maniar andPiccoli 1989). e SiO2-Na2O + K2O diagram, fields after Middlemost(1997). f K2O–TiO2-P2O5 ternary diagram (Pearce et al. 1975).Symbols as in Fig. 4

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Role of crustal contamination/assimilation

The Cr, Ni (ppm), and Mg# values in DBD, CAL, and AL arevery low compared with primary mantle melts (> 250 ppmNi,> 1000 ppm Cr, > 0.65 Mg#; Perfit et al. 1980; Wilson 1989),suggesting fractional crystallization of crustal source.Furthermore, Y/Nb ratios for the studied dykes > 1.2 whichsuggests the derivation of these dykes from crustal rather thanmantle-derived source (Eby 1990). On Rb/Y-Nb/Y diagram,the studied dykes plot close to lower crustal values (Rudnick

and Gao 2003) and none of these dykes have primary primi-tive mantle melt (Fig. 9d).

Both of MgO-Rb/Zr and MgO-Ba/Nb diagrams (Fig. 9e, f)reveal that the main trend of most of the studied dykes followsfractional crystallization. AL and DBD samples show a sub-trend following assimilation. This sub-trend is more promi-nent in DBD samples (Fig. 9f). The studied dykes were de-rived in continental settings (Fig. 8f). The fact that DBD andAL are mostly porphyritic (Fig. 3e) and glomeroporphyriticrocks (i.e., subvolcanic), implying that they may have resided

Fig. 9 a Rock/chondrite normalized values (Wood et al. 1979b) for traceelements in LPD and DBD. b SiO2–Nb diagram (Pearce and Gale 1977)to differentiate between within-plate and volcanic-arc lavas. c Y/Nb-Rbdiagram (Pearce et al. 1984 and post-collisional field after Pearce 1996). dRb/Y-Nb/Y. diagram (Chazot and Bertrand 1995), upper and lower

crustal values are from Rudnick and Gao (2003) and upper mantle valuefrom Sun and McDonough (1989). eMgO-Rb/Zr binary diagram. fMgOBa/Nb binary diagram, FC: fractional crystallization, AFC: assimilation-fractional crystallization and BA: bulk assimilation. Symbols as in Fig. 4

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in crustal magma chambers prior to extrusion/shallow intru-sion and would have had sufficient residence period to interactwith continental crust. Accordingly, the role of assimilationand/or contamination should be considered in the magmaticevolution of DBD and AL.

By using ΔNb value of Fitton (2007) whereas, ΔNb =1.74+ log (Nb/Y)-1.92 Log (Zr/Y) for the studied dykes.ΔNb values for all the studied dykes are negative (Tables 6and 7), suggesting their derivation from an enriched mantlesources through partial melting (Fitton 2007). Ni and Crdepletion especially in DBD and to some extent in CALand AL could be explained by small degree of partial melt-ing of heterogeneous mantle source followed by fractionalcrystallization (Fitton and Upton 1985).

The evidences from mineral chemistry, major and traceelements, and geochemical ratios mentioned before favor themodel of mixed crustal-mantle source (Fig. 6a). Thus, theparental magmas of the investigated dykes were generatedmost likely from lower crustal sources (Fig. 9d), with contri-bution from mantle-derived melt. Therefore, the mafic dykesin Wadi Mandar-Wadi Um Adawi area were generated fromdifferent magmatic sources by partial melting followed byfractional crystallization (Fig. 9e, f). Furthermore, the crustalcontamination/assimilation has a considerable role in themagmatic evolution of AL and DBD (Fig. 9f).

Conclusion

(1) The mafic dykes in Wadi Mandar-Wadi Um Adawi areaare represented by lamprophyre and diabase dykes. Thefield observations, distributions, trends, and cross cuttingrelationships suggest that the emplacement of calc-alkaline lamprophyres preceded that of the diabasedykes, while alkaline lamprophyres emplaced later thanthe diabase dykes.

(2) The dykes in Wadi Mandar-Wadi Um Adawi area repre-sent three episodes of dyke swarms in Precambrian rock inSinai, which are calc-alkaline lamprophyres, diabase, andalkaline lamprophyres. These dykes have metaluminousnature. Calc-alkaline lamprophyres and diabase dykesshow transitional characters from calc-alkaline to alkaline,while alkaline lamprophyres exhibit alkaline character

(3) The dykes were crystallized under crystallization temper-atures between 1100 and 1150 °C and under pressureranges from 3 to 5 kbars. They were crystallized underhigh oxygen fugacity conditions.

(4) Calc-alkaline lamprophyres, diabase dykes, and alkalinelamprophyres have different magmatic sources and thepartial melting and or fractional crystallization could notbe considered for the generation of diabase dykes oralkaline lamprophyres lamprophyre from calc-alkalinelamprophyres.

(5) The dykes emplaced during the post-collisional stage,i.e., Bnon-orogenic^ environment and certainly not incompressional arc-type one.

(6) The parental magmatic sources of the studied dykeswere originated from crustal material with addition ofmantle-derived melt. During post-collisional stage,the mantle-derived melt underplate and intraplate thecrust, which generate coeval calc-alkaline and alka-line magmatic sources. Partial melting and subsequentfractional crystallization were the responsible processin the magmatic evolution of the studied dykes. Inaddition to partial melting and fractional crystalliza-tion, the crustal contamination/assimilation is consid-ered in generation of diabase dykes and alkalinelamprophyres.

Acknowledgments The authors are very grateful to Prof. Dr. K.Petrakakis, Mr. P. Nagl, and Mr. F. Kiraly, Faculty of Erath Sciences,University of Vienna for their help in carrying out X-ray fluorescenceand microprobe analyses.

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