On the Pan-African transition of the Arabian–Nubian Shield from ...

On the Pan-African transition of the Arabian–Nubian Shield from compression to 

extension: The post-collision Dokhan volcanic suite of Kid-Malhak region, 

Sinai, Egypt 

Mohammed Z. El-Bialy 

Geology Department, Faculty of Science, Suez Canal University, Port Said, Egypt 

article info 

Article history: 

Received 19 March 2009 

Received in revised form 18 May 2009 

Accepted 12 June 2009 

Available online 21 June 2009 

Keywords: 

Pan-African 

Arabian–Nubian Shield 

Volcanic suite 

Petrography 

Geochemistry 

Tectonic setting 

1. Introduction 

abstract 

The Egyptian basement complex of the Eastern Desert and Sinai 

consist of Neoproterozoic juvenile crust developed in the northeastern 

part of the Arabian–Nubian Shield (Stern, 1994, 2002). The most 

prominent feature of this crust is the presence of dismembered 

ophiolites, metamorphosed volcano-sedimentary successions and 

calc-alkaline I-type intrusive complexes. Current idea on the tectonic 

evolution of these orogenic terrains points to an essential role of 

convergent processes, through the formation of intra-oceanic island arc 

system, subsequent ocean closure, amalgamation of the arc complexes 

and accretion to continental crust, followed by crustal thickening 

(Bentor, 1985; Abdel-Rahman and Martin, 1987; Kröner et al., 1988; 

Stern, 1994, 2002).These tectonic events took place during the Pan- 

African orogenic event between 900 and 614 Ma (Stern and Hedge, 

E-mail address: mzbialy@yahoo.com. 

Gondwana Research 17 (2010) 26–43 

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Gondwana Research 

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The Pan-African Kid-Malhak Dokhan volcanic suite (609 ±12 Ma) is exposed in the northernmost part of the 

Arabian–Nubian Shield. The suite consists of non-metamorphosed varicolored alternating succession of 

porphyritic lava flows of commonly felsic composition (rhyolite–dacite) interlayered with compositionally 

equivalent pyroclastic beds (dominantly ignimbrites). These Dokhan volcanics are quite evolved (SiO2≈ 65– 

77 wt.%), with strong high-K calc-alkaline affinity and are characterized by relative enrichment in total 

alkalis, Ba, Y, Zr and total REEs, depletion in Sr, and a LREE-enriched REE patterns with significant negative Eu 

anomalies. The Kid-Malhak Dokhan lavas display geochemical characteristics of both orogenic arc-type and 

anorogenic within-plate environments, suggesting eruption in a transitional “post-collisional tectonic 

setting. The ages of emplacement of the Dokhan volcanics in Egypt including that of Kid-Malhak region (580– 

620 Ma) coincide with end of the documented collision between the juvenile Arabian–Nubian crust and 

Saharan Metacraton and the subsequent extensional collapse event. This post-collision transition from 

compression to extension is explained by the extensional collapse following continental collision, which was 

controlled mainly by lithospheric delamination and slab breakoff (passive rifting). Various trace element 

characteristics discussed herein have indicated that the studied Dokhan magma was highly likely generated 

from crustal sources and that assimilation–fractional crystallization (AFC) and crustal contamination have 

played a major role and are most probably superimposed on fractional crystallization during the magmatic 

evolution of Kid-Malhak Dokhan volcanic suite. The eruption of the high-K calc-alkaline post-collisional 

Dokhan volcanics in Egypt defines a tectono-magmatic transition between the older calc-alkaline arc-related 

and the subsequent alkaline magmatism in the northern part of the Arabian–Nubian Shield. 

© 2009 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. 

1342-937X/$ – see front matter © 2009 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. 

doi:10.1016/j.gr.2009.06.004 

1985; Kröner et al., 1992; Beyth et al., 1994; Stern, 1994). The final stage 

(between 614 and 550 Ma) in the Pan-African crustal evolution in Egypt 

was characterized by the eruption of K-rich volcanic rocks (Dokhan 

volcanics) and emplacement of shallow level felsic intrusions (Egyptian 

Younger Granites). The term “Dokhan volcanics” refers to varicolored 

thick sequence of lava flows and pyroclastics of predominantly andesitic 

to rhyolitic composition in association with ignimbritic rhyolites (Basta 

et al., 1980; Heikal et al., 1980; Stern and Gottfried, 1986). The Dokhan 

volcanic sequences are widely distributed and extensively studied in the 

Eastern Desert of Egypt, whereas they are much less known in Sinai 

(Fig. 1). However, some workers consider some comparable nonmetamorphosed 

volcanic sequences in Sinai (e.g. G. Khashabi, G. Fierani, 

W. Kid, W. Meknas and others) as representatives and equivalent to the 

Dokhan volcanics of the Eastern Desert (e.g. Bentor, 1985; Hassan and 

Hashad, 1990; El Metwally et al., 1999; Azzaz et al., 2000; Hassan et al., 

2001; El-Bialy and El Omlla, 2007).The various studies carried out on the 

geochemistry of the Dokhan volcanics in the Egyptian Eastern Desert 

revealed that they have medium- to high-K calc-alkaline affinities. There 

is general agreement that fractional crystallization of basaltic magma

Fig. 1. Distribution of the Dokhan volcanics in Eastern Desert and Sinai (modified after 

Abdel-Rahman (1996), and location of the study area. 

coupled with minor crustal contamination controlled their magmatic 

evolution (Stern and Gottfried,1986; El Gaby et al.,1989; Abdel-Rahman, 

1996; Mohamed et al., 2000; Saleh, 2003; Moghazi, 2003; El Sayed et al., 

2004; Eliwa et al., 2006). However, there is considerable discussion and 

no consensus has been achieved concerning the tectonic setting for the 

genesis of these magmas. The controversy is centered around whether 

Dokhan volcanics have been formed (1) in a subduction environment 

(Hassan and Hashad, 1990; El Gaby et al., 1990; Abdel-Rahman, 1996; 

Hassan et al., 2001; Saleh, 2003), (2) in association with extension after 

crustal thickening (Stern et al., 1984, 1988; Stern and Gottfried, 1986; 

Mohamed et al., 2000), or (3) during transition between subduction and 

extension (Ressetar and Monard, 1983; Moghazi, 2003; El Sayed et al., 

2004; Eliwa et al., 2006). Much of the available reliable ages on Dokhan 

volcanics (580–620 Ma), were obtained from the Eastern Desert rather 

than from Sinai (El Shazly et al., 1973; Stern, 1979; Ries et al., 1983; 

Ressetar and Monard,1983; Gillespie and Dixon, 1983; Stern and Hedge, 

1985; Abdel-Rahman and Doig, 1987; Wilde and Youssef, 2000; 

Breitkreuz et al., 2008). In Sinai, Bentor (1985) concluded that a 

comparable period to the Dokhan volcanism of intense and apparently 

continuous volcanism occurred between 620 and 580 Ma ago. Also, 

similar Rb–Sr ages were obtained on orogenic calc-alkaline andesite– 

rhyolite rocks from Sinai, such as 587±9 Ma for Wadi Rutig andesite– 

rhyolite and 609±12 Ma for rhyolites–dacites from Wadi Madsus and 

Wadi Qabila (the investigated volcanics) by Bielski (1982). 

The volcanics, under investigation, are usually included within 

the other surrounding metavolcano–sedimentary complex, known 

as Kid Group of Shimron (1980), in many research works (i.e. 

Shimron, 1980, 1983; Reymer, 1983; Reymer and Yogev, 1983; Furnes 

et al., 1985; Hassanen, 1992). This paper presents new geologic and 

geochemical data on the Dokhan volcanic rocks of Kid-Malhak 

region, South Sinai, Egypt. The aim is to integrate field, petrographic 

and geochemical data to correlate them with the Dokhan volcanics of 

the Eastern Desert and to contribute to the understanding of their 

origin and tectonic setting. 

M.Z. El-Bialy / Gondwana Research 17 (2010) 26–43 

2. Geological setting 

2.1. Regional geology 

The basement rocks exposed in the Kid-Malhak region (Fig. 2) can 

be categorized into the following major units (from the oldest to 

youngest): gneisses, metasediments, metavolcanics (basalts and 

andesites), metagabbro–diorite complex, old granites (tonalities– 

quartz diorites), Dokhan volcanics (rhyolites and dacites) and younger 

granites (monzo-syenogranites). The investigated Dokhan volcanics 

are believed to be extruded between the emplacement of the 

preceding old and post-dating younger granites. 

Gneissic rocks consist of foliated and lineated diorites and tonalites 

with occasional mafic-rich xenoliths. Development of augen structure 

is obvious in some outcrops. These gneisses were referred to as Qenaia 

Formation by Bentor and Eyal (1987) and are considered of plutonic 

origin (Brooijmans et al., 2003; Be'eri-Shlevin et al., 2009b). 

Metasediments are the major exposed rock unit, covering about half 

of the basement in the mapped area. El Metwally et al. (1999) 

distinguished them as meta-calcpelites and meta-psammopelites. 

Meta-calcpelites comprise banded para-amphibolites, and hornblende 

and chlorite schists, while meta-psammopelites include garnetiferous 

biotite schist and phyllite. The aforementioned metasediments 

make up the Umm Zariq Formation (Furnes et al., 1985), Heib 

Formation and most of Malhak Formations (Shimron, 1980). The 

metasediments crop out around the downstream of Wadi Kid (southern 

part of the mapped area; Fig. 2) are quite different from the above 

mentioned one. They are dominantly a metasedimentary sequence 

consisting of low-grade schists, metaconglomerates, metamudstones 

and metasandstones. The conglomerates contain granitic, andesitic, 

and pelitic pebbles, whereas psammitic and pelitic sequences display 

occasionally sedimentary structures, such as graded bedding and low 

angle structures (Blasband et al., 1997, 2000; Brooijmans et al., 2003). 

This sedimentary sequence was referred to as Tarr Formation 

(Shimron, 1980, 1983). The metavolcanics are greenschist to amphibolite 

facies metamorphosed lava flows, ranging in composition from 

basalts to andesites (Furnes et al., 1985). In hand specimen, they are 

either aphyric or fairly porphyritic with scattered plagioclase phenocrysts 

(andesites). The lavas may be massive, structureless flows N5 m 

in thickness, or in some cases with pillow structures. The lower lava 

flow sheets in this unit are interbedded with and overlying the 

abovementioned thick metasedimentary succession. The grade of 

metamorphism decrease upward in these metavolcanics, and the 

rocks of the upper horizons are relatively fresh or weakly 

metamorphosed to the lower greenschist facies (Hassanen, 1992). 

The metagabbro-diorite complex occurs as a single large intrusive 

body in the northern part of the Kid-Malhak region. It was called as 

“Sharira gabbro and diorite complex” by Furnes et al. (1985) who 

described it as a layered gabbroic and dioritic layered intrusive 

massif of at least 2000 m thick and was dated at 570 ± 4 Ma by 

Moghazi et al. (1998). Old granites are found as several isolated 

bodies in the most southwestern corner of the mapped area along 

the northern bank of W. Yahmid. Old granites are quite heterogeneous, 

and several varieties of different composition and/or 

texture are recognized. These rocks are grey colored, ranging in 

composition from quartz diorite to tonalite, and in texture from 

granular to porphyritic. They often host rounded to sub-rounded 

microgranular mafic enclaves of mela-quartz diorite composition. 

Younger granites represent the last magmatic activity in the region, 

bordering it from the north, west and south and expanding laterally 

outside the mapped area. They are cross-cut by numerous dykes of 

variable composition and directions. Aplitic dykes and quartz veins 

traversing these rocks are rather common. They have a dominant 

granite to granodiorite composition and biotite as the main mafic 

mineral. Moreover, they vary in texture from fine to coarse-grained 

granular to porphyritic with pink alkali feldspar megacrysts. 

27

28 M.Z. El-Bialy / Gondwana Research 17 (2010) 26–43 

2.2. Field observations 

Fig. 2. Simplified geological map of Wadi Kid-Wadi Malhak region, Sinai (modified after Shimron (1980) and El Metwally et al. (1999)). 

The investigated Dokhan volcanics in Kid-Malhak region form 

brown to dark purple landscape of moderate relief, covering an area 

of approximately 110 km 2 of the entire mapped area (495 km 2 ). The 

studied Dokhan volcanics are exposed along Wadi Kid, Wadi Malhak, 

and Wadi Qabila (Fig. 2). They extrude and overlie other older 

metamorphosed basement units including the gneisses, metasediments 

and metavolcanics, and are intruded by the younger granites 

at Wadi Qabila with sharp contacts. A younger to contemporaneous 

rocks to these volcanics are thick interbedded epiclastic conglomerate 

beds (100–150 m), separating these volcanics into upper and 

lower stratigraphic sequences, and enclose frequent pebbles of them 

along with those of other older basement. These interbedded 

epiclastic conglomerates are most probably stratigraphically equivalent 

to the Hammamat Group (Akaad and Noweir, 1980) clastic 

sediments of the Egyptian Eastern Desert. The Dokhan volcanics in 

the study area consist of non-metamorphosed varicolored alternating 

succession of dominantly porphyritic flows of commonly felsic 

composition interlayered with compositionally equivalent pyroclastic 

beds. The later is dominated by welded ash tuffs (ignimbrites) 

and less commonly crystal-lithic ash tuffs. Individual flows in this 

area average less than 10 m thick. The very lowermost part of the 

succession is characterized by minor andesitic flows, while the rest 

of the succession upward is dominated by felsic lava flows and 

pyroclastics of the rhyolite–rhyodacite–dacite compositional range. 

Mafic cognate volcanic xenoliths are occasionally encountered in the 

rhyolite–dacite lava flows. 

3. Petrography 

Based on mineralogical composition, textural and field characteristics 

and geochemical data (see below), the investigated volcanics 

can be divided into two units, namely: lava flows and ignimbrites. 

Twenty eight volcanic samples were studied in the present work, 

twenty three of them are lava flows, and the remainders are welded 

tuffs (ignimbrites). 

3.1. Lava flows 

Lava flows predominate in this volcanic suite, comprising chiefly 

rhyolites with subordinate dacites and trachydacites (Fig. 3). Lava 

flows are strongly porphyritic, with up to 41% phenocrysts set in an 

originally partly glassy, now devitrified groundmass. Groundmass of 

almost all lavas is fine-grained anhedral granular displaying flow 

banding or trachytic textures. Rhyolites contain quartz, sodic plagioclase 

and K-feldspar phenocrysts with occasional biotite and/or 

hornblende microphenocrysts (b0.5 mm). Quartz phenocrysts occur 

as highly corroded and embayed crystals 1–3 mm across. Furthermore, 

coarse secondary quartz forming veins and nests is widespread. Such 

nests are up to 7 mm in size and are composed of anhedral interlocking 

grains, 0.1–2 mm across. Plagioclase phenocrysts (An10–19) are lath- or

Fig. 3. Geochemical classification of the studied volcanics using total alkalis vs. silica 

(TAS) diagram (Le Bas et al., 1986), with the discriminating boundary between alkaline 

and subalkaline fields after Irvine and Baragar (1971). For comparison, a field is shown 

for Dokhan volcanics (DV) from other areas (Basta et al., 1980; Ressetar and Monard, 

1983; Stern and Gottfried, 1986; Bentor and Eyal, 1987; Abdel-Rahman, 1996; Azzaz 

et al., 2000; Hassan et al., 2001; Moghazi, 2003; Eliwa, 2006). 

tabular-shaped, euhedral to subhedral, and range up to 1 cm in size, 

tending sometimes to cluster in glomerocrysts. Interiors of some of the 

phenocrysts are highly sericitized with relatively coarse secondary 

muscovite scales. Moreover, some plagioclase phenocrysts frequently 

contain irregular patches of K-feldspar within them. The textural 

relation of these patches with the plagioclase host indicates intergrowth 

rather than exsolution. Some rhyolite samples lack plagioclase 

as a phenocryst phase. Alkali feldspar phenocrysts are common in 

most rhyolites, represented by subhedral to resorbed perthitic 

sanidine and occasional fine-cross-hatch twinned anorthoclase. Biotite 

and hornblende microphenocrysts (b1 mm) are present in some 

rhyolite samples. The groundmass consists of quartz, K-feldspar and 


plagioclase with intergranular biotite, opaques, chlorite, sericite and 

accessory apatite and zircon. Devitrification textures are quite 

common in the groundmass, including granophric intergrowths, 

micro-poikilitic quartz and bow-tie spherulites. Dacites consist of 

abundant plagioclase and quartz and mafic phenocrysts that are set in 

a felty textured microcrystalline groundmass of quartz, feldspars, 

biotite and opaques. Plagioclase phenocrysts have albite–oligoclase 

composition (An8–22) and are found either independent or as 

glomerocrysts. They are frequently altered to sericite, particularly in 

their cores. In contrast to rhyolites, quartz is rare and alkali feldspars 

are absent as phenocryst phases. Alkali feldspars and plagioclase are 

found in sub-equal amounts in the groundmass. Trachydacites are less 

porphyritic compared with rhyolites and dacites. They consist of sparse 

sodic plagioclase and alkali feldspar phenocrysts and pyroxene 

microphenocrysts enclosed in a pilotaxitic fine-grained groundmass 

of sanidine, quartz and plagioclase microlites impregnated with tiny 

chlorite flakes and fine opaque dust. 

3.2. Ignimbrites 

Ignimbrites are welded vitric tuffs, with few and smaller crystals 

and lithic fragments (b10%). They are characterized by the predominance 

of glass shards and pumaceous fragments and displaying 

features indicative of pyroclastic flow origin. The degree of welding 

and nature of the principle juvenile materials (Pumice and glass 

shards) can readily distinguish them into eutaxitic textured and thinlaminated 

vitric tuffs. Eutaxitic-textured vitric tuffs are highly welded, 

consisting of flattened and stretched pumaceous fragments of 

lenticular shape, sometimes with crenulated ends (fiamme) that lie 

parallel and beside one another, showing a well defined lineation. 

Fiammes can be clearly distinguished from the enclosing matrix by 

their lenticular form and higher degree of devitrification. Crystals and 

lithic fragments may occasionally cause divergence and bending of the 

fiamme around them. The linear fabric resulted from stretching and 

welding of the fiamme indicates secondary mass flowage of the tuff 

during welding (Cas and Wright, 1987). Relics of glassy shards are 

Table 1 

Major elements composition (wt.%), calculated CIPW normative minerals and some elemental ratios of Kid-Malhak area Dokhan volcanics. 

Sample no. M2 M7 Q1 M6 Q10 Q7 Q11 Q6 Q8 K6 Q5 K5 K1 K2 K11 K12 Average 

Normalized major elements (wt.%) 

SiO2 76.61 75.39 72.02 64.87 75.84 72.21 70.63 71.15 74.03 64.66 68.9 69.34 74.43 70.12 75.46 66.95 71.41 

TiO2 0.19 0.17 0.33 1.11 0.32 0.37 0.45 0.4 0.32 1.1 1.02 1.01 0.3 0.65 0.25 1.05 0.57 

Al2O3 11.7 13.83 15.61 16.01 13.28 15.23 15.31 15.33 13.77 16.23 14.44 14.13 13.54 14.59 13.15 15.22 14.46 

FeO* 1.8 0.72 1.38 5.14 1.53 1.66 2.27 2.16 1.93 5.06 5.5 5.13 1.83 3.34 1.5 5.21 2.89 

MnO 0.06 0.06 0.05 0.09 0.08 0.03 0.05 0.05 0.09 0.09 0.11 0.13 0.06 0.08 0.07 0.11 0.07 

MgO 0.69 0.15 0.26 1.48 0.27 0.17 0.45 0.54 0.44 1.47 1.02 1.01 0.5 1.1 0.39 1.21 0.7 

CaO 1 0.63 0.94 2.28 1.03 0.64 2.44 1.63 0.62 2.37 2.1 2.26 1.22 1.85 0.82 2.26 1.51 

Na2O 2.09 4.56 5.94 4.83 4.78 6.07 4.68 4.37 2.26 4.86 3.67 3.71 3.75 4.21 3.42 4.29 4.22 

K2O 5.84 4.45 3.43 3.8 2.83 3.56 3.58 4.25 6.52 3.78 2.93 3.01 4.31 3.88 4.91 3.38 4.03 

P2O5 0.02 0.03 0.04 0.4 0.04 0.06 0.14 0.12 0.02 0.4 0.29 0.27 0.06 0.18 0.03 0.32 0.15 

Total 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 

Na2O+K2O 7.92 9.01 9.37 8.63 7.61 9.63 8.25 8.62 8.78 8.63 6.6 6.72 8.06 8.09 8.33 7.67 8.25 

Na2O/K2O 0.36 1.03 1.73 1.27 1.69 1.71 1.31 1.03 0.35 1.28 1.25 1.23 0.87 1.09 0.7 1.27 1.13 

FeO /MgO 2.6 4.74 5.26 3.48 5.7 9.8 5.07 3.96 4.42 3.44 5.4 5.07 3.66 3.04 3.85 4.31 4.61 

A/CNK 1.01 1.03 1.03 0.99 1.04 1.02 0.96 1.04 1.16 0.99 1.11 1.05 1.04 1.01 1.06 1.03 1.04 

CIPW norm 

Quartz 37.63 29.84 21.16 13.02 33.65 20.74 22.94 24.08 32.64 12.58 27.52 27.3 31.65 23.49 33.45 19.94 25.73 

Anorthite 4.83 2.93 4.4 8.7 4.85 2.78 10.19 7.3 2.95 9.14 8.52 9.45 5.66 8 3.87 9.12 6.42 

Diopside 0 0 0 0 0 0 0.85 0 0 0 0 0 0 0 0 0 0.05 

Hypersthene 4.57 1.44 2.54 10.74 2.86 2.7 3.89 4.44 4 10.61 10.41 9.79 3.97 7.48 3.25 10.34 5.82 

Albite 17.69 38.59 50.26 40.87 40.45 51.36 39.6 36.98 19.12 41.12 31.05 31.39 31.73 35.62 28.94 36.3 35.69 

Orthoclase 34.51 26.3 20.27 22.46 16.72 21.04 21.16 25.12 38.53 22.34 17.32 17.79 25.47 22.93 29.02 19.98 23.81 

Apatite 0.05 0.07 0.09 0.93 0.09 0.14 0.32 0.28 0.05 0.93 0.67 0.63 0.14 0.42 0.07 0.74 0.35 

Ilmenite 0.36 0.32 0.63 2.11 0.61 0.7 0.85 0.76 0.61 2.09 1.94 1.92 0.57 1.23 0.47 1.99 1.07 

Corundum 0.17 0.44 0.51 0.76 0.58 0.37 0 0.86 1.92 0.79 2.11 1.31 0.63 0.53 0.79 1.16 0.81 

Magnetite 0.15 0.06 0.12 0.42 0.13 0.13 0.19 0.17 0.16 0.41 0.45 0.42 0.15 0.28 0.12 0.42 0.23 

Zircon 0.09 0.03 0.06 0.06 0.09 0.07 0.03 0.03 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 0.06 

Diff. index 89.83 94.73 91.69 76.34 90.82 93.14 83.69 86.17 90.29 76.04 75.88 76.48 88.85 82.04 91.4 76.22 85.23 

29


devitrified into axiolites and fan spherulites, while some other glassy 

shards are devitrified into an assemblage of spherulites, granophyres 

and very fine aggregates of recrystallized quartz. Crystals and crystal 

fragments consist mostly of juvenile interatelluric quartz, sanidine 

and plagioclase, while lithic fragments are predominated by cognate 

volcanic rocks. Thin-laminated vitric tuffs are composed of alternations 

of thin devitrified microcrystalline laminae, which are mostly 

large stretched fiamme, and thicker opaque-rich cryptocrystalline 

laminae contain scattered crystal and lithic fragments. Both are 

usually parallel and even, but the former laminae may diverge and 

warp-round different crystals and lithic fragments included in them. 

The striking difference between the studied Dokhan volcanics and 

others in Sinai (El Metwally et al., 1999; Azzaz et al., 2000, Hassan 

et al., 2001) and those of the Eastern Desert of Egypt, is their felsic 

compositional range in comparison with the “bimodal” or continuous 

spectral composition of the Dokhan volcanics in the Eastern Desert 

(e.g. Basta et al., 1980; Ressetar and Monard, 1983; Stern and Gottfried, 

1986; Abdel-Rahman, 1996; Mohamed et al., 2000; Saleh, 2003; 

Moghazi, 2003; El Sayed et al., 2004; Eliwa, 2006). 

4. Geochemistry 

4.1. Analytical techniques 

Concentrations of major and most trace elements (XRF) for 16 

representative lava flows samples and of REEs plus Cs, Hf and Ta (ICP- 

MS) for 5 selected samples of them were determined at the 

GeoAnalytical Laboratory, Washington State University, Pullman, 

WA, USA. Major elements and the trace elements Cr, Sc, V, Ba, Sr, Rb, 

Zr, Y, Nb, Ga, Cu, Zn, Pb, Th and U were determined on fused beads 

(3.5 g sample + 7 g dilithium tetraborate flux) by (ThermoARL 

Advant'XP+) X-ray fluorescence spectrometer using a rhodium (Rh) 

target operated at 50 kV/50 mA with full vacuum and a 25 mm mask 

for all the previous elements. The trace element concentrations (ppm) 

Table 2 

Trace and REE elements contents (ppm), calculated crystallization temperatures and some elemental ratios of Kid-Malhak area Dokhan volcanics. 

Sample no. M2 M7 Q1 M6 Q10 Q7 Q11 Q6 Q8 K6 Q5 K5 K1 K2 K11 K12 Average 

Ni 1 0 0 4 0 0 1 0 0 0 16 14 1 13 0 9 3.7 

Cr 2 2 1 2 4 1 4 3 4 1 18 10 4 21 3 8 5.55 

Sc 5 3 6 11 8 6 4 3 8 9 11 8 6 8 6 11 7.08 

V 3 2 11 51 10 10 32 28 13 47 91 82 15 44 7 68 32.09 

Cs 0.77 0.74 2.21 0.98 2.26 1.39 

Ba 1390 716 1076 744 913 1301 1039 914 992 693 706 641 1028 926 1003 712 924.66 

Rb 89 103 90 72 64 81 86 112 137 68 80 77 88 87 99 75 88.01 

Sr 129 100 151 321 149 160 528 380 133 297 311 298 221 282 127 308 243.47 

Hf 11.11 9.65 4.92 8.57 7.71 8.39 

Zr 415 121 301 293 413 337 181 164 282 272 283 304 331 280 309 291 286.09 

Y 49 18 33 36 39 29 16 14 32 33 35 29 35 32 35 34 31.04 

Ta 1.95 0.84 0.71 1.23 1.09 1.16 

Nb 21.9 11.3 13.2 13 12.3 11.1 7.9 7.7 11.9 12.3 22.4 19 13.98 14.1 14.4 16.7 13.95 

Ga 17 15 16 20 17 17 18 19 21 17 20 17 18 19 18 18 17.91 

Cu 1 1 0 5 0 2 2 0 0 6 41 43 0 11 1 25 8.65 

Zn 19 19 18 85 6 21 35 35 38 79 92 88 21 49 21 86 44.38 

Pb 8 20 8 9 6 11 13 12 10 7 12 11 9 10 11 10 10.48 

Th 12 15 17 11 15 17 12 12 14 7 8 8 11 12 14 9 12.04 

U 4 4 5 3 5 5 3 3 4 3 2 2 4 4 4 2 3.46 

Rb/Sr 0.69 1.03 0.6 0.22 0.43 0.51 0.16 0.3 1.03 0.23 0.26 0.26 0.4 0.31 0.78 0.24 0.46 

Ba/Sr 10.75 7.15 7.1 2.32 6.15 8.15 1.97 2.4 7.44 2.33 2.27 2.15 4.65 3.28 7.9 2.31 4.9 

K/Rb 547 357 316 439 368 366 344 314 395 465 303 325 407 370 412 374 381 

Ba/Rb 15.69 6.93 11.92 10.35 14.29 16.13 12.06 8.13 7.23 10.26 8.8 8.32 11.68 10.64 10.13 9.49 10.75 

Y/Nb 2.21 1.58 2.46 2.76 3.15 2.57 1.99 1.82 2.66 2.71 1.56 1.53 2.5 2.27 2.44 2.03 2.27 

Zr/Nb 18.95 10.71 22.77 22.56 33.59 30.35 22.92 21.31 23.71 22.15 12.63 16 23.68 19.86 21.52 17.41 21.26 

Zr/Hf 37.34 42.81 33.35 38.62 36.32 

Nb/Ta 11.23 14.64 10.85 11.37 12.94 

T(C) 882 766 841 821 881 850 785 786 854 814 841 843 857 830 854 831 833.5 

La 47.29 31 60 35 48.85 54 29 30.3 33 34 27 30 42.44 38.25 40 32 38.5 

Ce 100.65 59 114 77 100.65 107 55 59.37 76 73 65 69 86.92 79.45 84 71 79.79 

Pr 12.16 12.25 6.59 10.39 10.28 0 10.34 

Nd 46.2 24 44 39 46.95 44 22 22.85 36 38 35 36 38.55 39.24 38 38 36.7 

Sm 9.63 9.48 3.96 7.6 7.92 7.72 

Eu 1.14 2.02 0.84 1.39 1.54 1.38 

Gd 8.2 7.86 2.91 6.34 6.53 6.37 

Tb 1.41 1.26 0.45 1.02 1.04 1.04 

Dy 8.85 7.37 2.56 6.25 6.19 6.24 

Ho 1.86 1.51 0.51 1.31 1.27 1.29 

Er 5.2 3.81 1.42 3.48 2.89 3.36 

Tm 0.79 0.58 0.23 0.57 0.52 0.54 

Yb 5.05 3.56 1.49 3.39 3.16 3.33 

Lu 0.79 0.56 0.25 0.55 0.52 0.54 

REE 249.23 246.72 133.76 210.2 198.8 207.74 

Eu/Eu* 0.39 0.71 0.75 0.61 0.65 0.62 

Ce/Yb 19.95 28.27 39.76 25.64 25.14 27.75 

La/Yb 9.37 13.72 20.29 12.52 12.1 13.6 

Sm/Nd 0.21 0.2 0.17 0.2 0.2 0.2 

Eu/Sm 0.12 0.21 0.21 0.18 0.19 0.18 

(La/Yb)N 6.37 9.32 13.78 8.5 8.22 9.24 

(La/Sm)N 3.07 3.22 4.78 3.49 3.02 3.51 

(Gd/Yb)N 1.31 1.79 1.58 1.51 1.67 1.57 

(La/Lu)N 6.21 8.98 12.35 8.01 7.64 8.64 

Cs, Hf, Ta and REE concentrations of the underlined samples are determined by ICP-MS, otherwise by XRF.

are un-normalized, where original major element concentrations 

determined are normalized to 100% on a volatile-free basis, with total 

iron expressed as FeO. REE, Cs, Hf and Ta elements were analyzed by a 

(Sciex Elan-250) ICP-Mass Spectrometer. Samples were first subjected 

to complex combined fusion-dissolution procedure to ensure the 

complete dissolution of zircons and other refractory phases. Dissolved/diluted 

samples (60 ml final volume; 1:240 final dilution) are 

introduced into the argon plasma at 1.0 ml/min using a peristaltic 

pump and an automatic sampler. Plasma power is 1500 W. The 

instrument is run in “multi-element” mode averaging 10 repeats of 

0.5 s/element for a total integrated count time of 5 s/element. Full 

details on sample preparation, analytical procedures, precision and 

accuracy are given by Johnson et al. (1999) and Knaack et al. (1994), 

also available on WSU Department of Geology website at (http:// 

www.wsu.edu/~geolab/note.html). 

4.2. Results 

Major, trace and REE data of the investigated Dokhan volcanics are 

listed in Tables 1 and 2 in addition to calculated normative minerals, 

different geochemical ratios and parameters as well as crystallization 

temperature estimates. Table 3 shows a comparison between data of 

the studied Dokhan volcanics average with other averages of Dokhan 

volcanics from different occurrences in the Egyptian Eastern Desert 

and Sinai. 

4.2.1. Whole-rock geochemical characteristics 

Geochemical classification using total alkalis versus silica (TAS) 

diagram (Le Bas et al., 1986) shows that the studied volcanics 

(SiO2≈65–77 wt.%) are classified predominantly as rhyolites and 

much less as dacites and trachydacites (Fig. 3). Further, they plot 

within the field constructed on the TAS diagram for the Dokhan 

volcanics using some published data. All the lava samples plot in the 


subalkaline field of Irvine and Baragar (1971) on the TAS diagram 

(Fig. 3). Moreover, all the samples have clear calc-alkaline affinity, as 

shown in the AFM diagram (Fig. 4A). K2O contents of the studied 

volcanics are plotted vs. SiO 2 in the diagram of Le Maitre (1989) 

shown in Fig. 4B. In this diagram, most of the samples exhibit apparent 

strong high-K affinity, with few medium-K samples. This is consistent 

with the prevalent high potassic nature of Dokhan volcanics from 

other areas, particularly in the more evolved dacite to rhyolite lavas 

(e.g. Mohamed et al., 2000; Moghazi, 2003; El Sayed et al., 2004; 

Eliwa, et al., 2006). With the exception of one diopside–normative 

sample (Q7), all samples are corundum–normative, and most of them 

have molar A/CNK ratios greater than one, indicating a dominant 

peraluminous character of these volcanics (Table 1). Likewise, felsic 

members of the Dokhan volcanic suites in the Eastern Desert have 

been demonstrated to be peraluminous (Ressetar and Monard, 1983). 

The Dokhan volcanics of the Eastern Desert occurrences form a 

compositionally continuous suite from basalt to rhyolite (Basta et al., 

1980; Abdel-Rahman, 1996; Mohamed et al., 2000; Saleh, 2003; 

Moghazi, 2003; El Sayed et al., 2004; Eliwa, et al., 2006) and 

occasionally a bimodal suite with silica gap between mafic and felsic 

rocks at the southernmost Dokhan localities (Ressetar and Monard, 

1983; Stern and Gottfried, 1986; Stern et al., 1988). In contrast, the 

investigated Dokhan volcanics and others in Sinai (see Table 3) have 

narrow evolved compositional range (rhyolite–dacite). Further, the 

Dokhan volcanics from Eastern Desert have average dacitic composition 

with average silica (63–68%) and total alkalis (6.7–7.5 wt.%) while 

those from Sinai, including the studied volcanics, have an average 

rhyolitic composition (see Table 3). 

The studied Dokhan volcanics are relatively evolved with their SiO 2 

contents ranging from 64.66 to 76.61 wt.% and the differentiation 

index (DI, sum of normative Q+Or+Ab: Thornton and Tuttle, 1960) 

ranging from 94.73 to 76.03 (Table 1). Also, they are marked by high 

contents of total alkalis (6.6–9.63 wt.%; average–8.25 wt.%) and a 

Table 3 

Comparison of average major and trace element concentrations of Kid-Malhak Dokhan volcanics with other Dokhan volcanics from Sinai and Eastern Desert of Egypt: 1 and 2 — Gabal 

Khashabi (Bentor and Eyal, 1987; Azzaz et al., 2000 respectively); 3 — Wadi Meknas (Hassan et al., 2001); 4 — Mount El-Kharaza (Abdel-Rahman, 1996); 5 — Wadi Um Sidra-Um 

Asmer (Eliwa et al, 2006); 6 — South Safaga area (Moghazi, 2003); 7 — Wadi Fatira and Qena-Safaga road (Ressetar and Monard, 1983); 8 — Fatira area (Mohamed et al., 2000). 

Location Sinai Eastern Desert Continental crust 

Reference This study 1 2 3 4 5 6 7 8 9 

No. of samples 16 5 7 18 24 35 26 59 34 – 

SiO2 71.41 71.64 73.46 68.43 66.21 65.31 64.68 63.46 67.98 59.1 

TiO2 0.57 0.54 0.42 0.52 0.65 0.87 0.86 1.14 0.66 0.7 

Al2O3 14.46 15.47 14.33 15.11 16.01 15.55 15.61 15.6 14.99 15.8 

FeO* 2.89 2.11 2 3.66 4.82 5.31 4.92 6.16 4.29 6.6 

MnO 0.07 0.6 0.48 0.11 1.45 0.08 0.11 2.82 0.08 0.11 

MgO 0.7 0.06 0.07 1.65 0.1 1.83 2.38 0.1 2.01 4.4 

CaO 1.51 1.02 0.88 1.78 3.07 3.41 3.64 4.02 3.04 6.4 

Na2O 4.22 4.65 3.77 4.43 4.36 4.3 4.42 4.14 3.64 3.2 

K2O 4.03 3.78 4.48 4.1 3.16 3.12 3.21 2.57 3.16 1.9 

P2O5 0.15 0.12 0.11 0.21 0.17 0.22 0.18 0.16 0.2 

Total 100 100 100 100 100 100 100 100 100 98.41 

Na2O+K2O 8.25 8.43 8.25 8.53 7.52 7.42 7.63 6.71 6.8 5.1 

Ni 3.7 21.72 31 44.5 55 24.68 51 

Cr 5.55 103 38.33 69 90.13 67 75.74 91 

V 32.09 30 33.83 112 112.88 203 60.68 131 

Ba 924.66 883 801 532 888.57 630 705.83 660 582 390 

Rb 88.01 108 112 121.22 72.78 84 85.67 57.8 59.43 58 

Sr 243.47 359 266 191 330.58 524 433.33 723 404 325 

Hf 8.39 4.76 5.21 3.7 

Zr 286.09 112 279 236 202.13 239 232.71 258 155 123 

Y 31.04 21 31.83 20.98 24 30.29 27.6 16.68 20 

Nb 13.95 15 16.43 11.43 15.63 10.58 14.7 10.21 12 

Zn 44.38 39 64.78 37.21 73 

Pb 10.48 15.72 12.6 17.21 12.6 

Th 12.04 6.89 8.2 7.5 16.61 5.6 

U 3.46 8.52 2.4 4.14 2.43 1.42 

∑REE 207 155 160 104 103.05 

Average composition of the continental crust (reference 9) is after Rudnick and Fountain (1995). 

31


Fig. 4. (A) AFM diagram for the studied volcanics showing distinction between tholeiitic 

and calc-alkaline suites (Irvine and Baragar, 1971). (B) SiO 2 vs. K 2O diagram (Le Maitre, 

1989). Field for Dokhan volcanics (DV) as in Fig. 3. 

wide range of Na2O/K2O ratios (0.35–1.73). Overall, they are 

characterized by rather wide range of the major oxides; TiO 2, (0.19– 

1.11%), Al2O3 (11.7–16.23%), FeO* (0.72–5.5%), MgO (0.15–1.48%), MnO 

(0.03–0.13%) and CaO (0.62–2.44%) with the higher contents in 

dacites and the lower in the more evolved rhyolites. Major elements 

Harker diagrams (Fig. 5), show a tight compositional gap between 

64.87 and 66.95 wt.% SiO2 values. The studied volcanics, exhibit a 

general negative correlation between silica and Al 2O 3, FeO*, MgO, 

P2O5, CaO and TiO2. These negative trends vary between fairly linear 

(MgO, CaO and P 2O 5), and inflected or segmented trends (Al 2O 3, TiO 2 

and FeO*). The depicted similar inflections in TiO2 and FeO* occur 

around silica value of 70%, CaO and MgO display much broader scatter 

towards the SiO2-rich end of the diagrams, which is attributed most 

likely to mixing processes. Al 2O 3 shows an exclusive zigzag pattern 

with intermediary period of alumina augmentation with silica rise, 

which can be attributed to a transitory dominant role of feldspar 

fractionation. 

4.2.2. Trace elements 

The trace element compositions of 16 representative samples 

from the Kid-Malhak Dokhan volcanics are given in Table 2. The 

investigated volcanics are relatively enriched in Ba (706–1390, 

average; 925 ppm), Y (14–49, average; 31 ppm), Zr (121–415, 

average; 286 ppm), and total REEs (134–249, average; 207 ppm) 

compared to other Dokhan volcanics, and also to average continental 

crustal rocks (Table 3). In contrast, they are fairly depleted in Sr 

(100–528, average; 243 ppm). The most striking feature of the 

studied volcanics is their serious depletion in the transition metals 

Cr (1–21 ppm) and Ni (0–16 ppm), even regarded as incompatible 

elements in felsic magmas. Silica variation diagrams of trace elements 

are illustrated in Fig. 6. Rb, Zr and Y show scattered linear to 

curvilinear trends, typified by slight enrichment with increasing of 

silica. The HFS pair; Zr and Y show exceedingly coherent convex 

trends, in which both remain slightly varying through differentiation 

(SiO 2 rise), then begin to increase gradually at about 75% silica value. 

This coherence may be explained in terms of the typical concentration 

of Y in accessory minerals, commonly zircon, as it replaces Zr. 

Nb, as alumina does, exhibit a zigzag-shaped plot, with a midway 

segment of rapid Nb declination with increasing silica. Ba show a 

wavy pattern, in which it reaches a climax of concentration around 

72 wt.% silica, then start to fall again with increasing silica. This 

behavior of Ba, also observed in other fractionating calc-alkaline 

Dokhan volcanics in the Eastern Desert, has been documented by 

several authors (Mohamed et al., 2000; Moghazi, 2003; Eliwa et al., 

2006). Sr concentrations are almost steady in dacites (bSiO 2 70 wt.%) 

but in contrary decrease over the entire rhyolite compositional range. 

The combination of linear, curvilinear and scattered trends on the 

variation diagrams indicates that several processes influenced the 

compositions of the rocks. 

Table 2 reveals that the studied rocks display a quite wide range of 

Rb/Sr ratios (0.22–1.03) with an average of 0.46. Many of the 

calculated Rb/Sr values are quite higher than lower and middle 

continental crust which have Rb/Sr ratios of 0.12 and 0.22 respectively 

(Rudnick and Fountain, 1995; Wedepohl,1995), indicating a role of the 

upper continental crust in their genesis, as the crust can be regarded 

as being vertically zoned with Rb/Sr increasing upward (Blevin and 

Chappell, 1995). Y/Nb ratios of the studied volcanics vary between a 

minimum of 1.53 and a maximum of 2.76 (Table 2). Zr/Hf and Nb/Ta 

ratios for five samples are given in Table 2. With the exception of 

sample Q10, the rest of the samples have Zr/Hf ratios within the 

narrow range of 33 to 40 typifying most igneous rocks including the 

values of chondrites (36) (Jochum et al., 1986; Dostal and Chatterjee, 

2000). Such deviation from chondritic value is rare and in this sample 

may be attributed to crystal fractionation involving accessory phases 

(Wolff, 1984). 

Incompatible trace-element spider diagram for the Kid-Malhak 

Dokhan volcanics, normalized to primitive sources (MORB of Taylor and 

McLennan (1985) is shown in Fig. 7. In this diagram, the pattern have 

rather steep slope, with obvious tilting of the trace element patterns up 

to left due to selective enrichment of the incompatible elements at the 

left-hand side (LIL, Th, U and LREE) over the more compatible one to the 

right (Y and HREE). HRRE are the most depleted, reaching levels 

comparable or even lower than those of MORB. Also, the pattern is 

characterized by serious negative Nb, Sr and Ti anomalies. The negative 

Nb anomaly is most characteristic of subduction zone volcanic rocks or 

typical continental crust. The negative anomalies for Sr and Ti may be 

attributed to fractionation of plagioclase and ilmenite and/or rutile 

respectively during petrogenesis. Marked positive spikes occur at Ba, U, 

La and Zr. Such spiked pattern may be a characteristic of subductionrelated 

magmas (Wilson, 1989). The more mobile Ba, U and La elements 

relative enrichment attests to the involvement of subduction zone fluids 

rich in them (Wilson, 1989; Rollinson, 1993). The less mobile Zr 

enrichment is largely controlled by the chemistry of the source, 

suggesting derivation from a crustal source.

4.2.3. Rare earth elements 

The concentrations of rare earth elements (REE) of five Dokhan 

volcanic samples in ppm are given in Table 2. The analyzed samples 

have comparatively high abundances of total REEs (average; 

207 ppm) (Tables 2 and 3). They are characterized by moderate 

degree of REE fractionation, {(La/Yb) N=13.78–6.37}. La concentrations 

(31–60 ppm) vary between about 130 and 257 times chondrite 

value, while Lu (0.25–0.79 ppm) ranges between 10 and 32 times 

chondrite value. The degree of LREE fractionation is rather high with 

reasonably steep slope pattern {(La/Sm) N=3.07–4.78}, while the 

heavy REE are weakly fractionated with approximately flat pattern 

{(Gd/Yb) N=1.31–1.79}. The REE patterns have reasonable concordance, 

with some difference in attitude due to variation in absolute 

abundances (Fig. 8). All the REE patterns have negative Eu anomalies 

and display concave upward shapes of quite negative slopes (Ce/ 

Yb=19.95–39.76 and La/Yb=9.37–20.29) due to light REE enrich- 


Fig. 5. Harker variation diagrams of some major oxides against SiO 2 (wt.%) for the Kid-Malhak Dokhan volcanics. 

ment relative to middle and heavy REE. The heavy REE are not highly 

depleted, but in turn are comparable or even sometimes slightly 

enriched relative to middle REE (i.e. sample Q6), suggesting absence 

of garnet in the source, since heavy REE are highly compatible in 

garnet (Wilson, 1989). The REE patterns of the studied samples 

display negative Eu anomalies of notably variable sizes (Eu/ 

Eu*=0.39–0.75). These negative Eu anomalies are ascribed to the 

removal of feldspar from the melt by crystal fractionation or the 

partial melting of a rock in which feldspar is retained in the source 

(Wilson, 1989; Rollinson, 1993). Explanation of Eu anomalies solely on 

the basis of feldspars is an oversimplification, because other minerals 

have a role, although minor relative to feldspars, in producing Eu 

anomalies (Rollinson, 1993). Hornblende fractionation may contributes 

in part for reduction of the negative Eu anomaly sizes, because 

although REE are compatible in hornblende in felsic and intermediate 

liquids, Eu has a considerably lower partition coefficient relative to 

33


most middle and heavy REE. The REE diagram in Fig. 8 shows that the 

five REE patterns are nearly parallel LREE-enriched with negative Eu 

anomalies of variable sizes. The heaviest MREE and the HREE show 

steady decrease with increasing atomic number, giving rise to fairly 

flat segments of the patterns. Compared to other Dokhan volcanics 

from various localities in the Eastern Desert and Sinai, the REE 

patterns of the investigated Dokhan volcanics are very similar to those 

of the other Dokhan volcanics in the Eastern Desert and Sinai (Fig. 8). 

5. Discussion 

5.1. Zircon saturation thermometry 

Fig. 6. Harker variation diagrams of some trace elements against SiO 2 (wt.%) for the Kid-Malhak Dokhan volcanics. 

Experimental studies have demonstrated that zircon, when 

crystalline, has low solubility in crustal melts and fluids (e.g., Watson, 

1979; Waston and Harrison, 1983; Ayers and Watson, 1991). 

Zirconium (Zr) commonly forms a separate phase, the mineral zircon 

(ZrSiO4). In felsic rocks, Zr and Hf are usually incompatible and are 

typically concentrated in residual silicate liquids until zircon saturation 

occurs (Watson, 1979; Waston and Harrison, 1983). Melt 

temperature estimates of the studied Dokhan volcanics are calculated 

and listed in Table 2 according to the experimental works of Waston 

and Harrison (1983) on Zr saturation in hydrous, low-temperature, 

intermediate and felsic magmas. They investigated the relation 

between zircon crystallization and melt composition which is given 

by the solubility model: 

ln Dzr Zircon=melt = f−3:80−½0:85ðM−1ÞŠg +12; 900 = T 

where: DzrZircon/melt is the concentration ratio of Zr in the stoichiometric 

zircon to Zr in the melt, T is the absolute temperature and M is 

the cation ratio (Na+K+2Ca)/(Al*Si). This geothermometer is based

on the fact that, in felsic rocks, Zr is an essential structural component 

in the accessory mineral zircon and its concentration depends on the 

solubility of zircon the magma, which is a function of temperature, 

given a certain melt composition. Thus, assuming magma saturation 

in Zr, magma temperature can be calculated from a chemical analysis 

(Barrie, 1995; Rosa et al., 2006). Temperature values inferred range 

between a minimum of 766 °C and a maximum of 882 °C, with 

average temperature of 833 °C for the whole samples. However, recent 

sensitive high-resolution ion microprobe (SHRIMP) U–Pb dating of 

zircons from the Dokhan volcanic suite at the type locality of Gabal 

Dokhan and at Gabal Urf, Wadi Qaa and Gabal Kharaza, Eastern Desert 

of Egypt (Wilde and Youssef, 2000; Breitkreuz et al., 2008 respectively) 

revealed a significant inherited zircon component. Therefore, 

and since some of the Zr in the studied lavas may have been in 

inherited zircon, the calculated temperatures are to be considered 

maximum temperatures of crustal fusion. 

5.2. Petrogenesis 

5.2.1. Fractional crystallization vs. crustal contamination 

It has been previously argued that the evolved Dokhan volcanic 

rocks (andesites, dacites and rhyolites), at many areas in the Eastern 

Desert of Egypt, were generated from more primitive basaltic 

precursors by crystal fractionation (Stern and Gottfried, 1986; 

Abdel-Rahman, 1996; Mohamed et al., 2000; Saleh, 2003; Moghazi, 

2003; El Sayed et al, 2004). Moreover, it is highly likely that crystal 

fractionation was coupled with assimilation of crustal materials (Stern 

and Gottfried, 1986, Moghazi, 2003). 

The systematic variation of the major and trace element contents 

of the investigated Dokhan lavas can reasonably be interpreted 

qualitatively in terms of fractional crystallization. This is indicated 

by the curvilinear trends of some elements in Harker diagrams, 

especially Zr and Y, and by the common turnover or change of slopes 

of the trends of many elements including; Al2O3 TiO2, FeO*, Ba, Sr, and 

Nb versus SiO 2 (Figs. 5 and 6). Also, major and trace element 

abundances vary along general trends of decreasing Al2O3, CaO, MgO, 

FeO*, P 2O 5, TiO 2 and Sr and increasing Rb, Y, and Zr (Figs. 5 and 6) with 

increasing SiO2. However, much of the broad scatter readily 

recognized in most of these diagrams, is presumably attributed to 

crustal contamination processes. Additionally, the comparable and 

parallel configuration of the normalized REE patterns (Fig. 8) coupled 

with increasing total REE contents with increasing SiO2 (Tables 1 and 

2), imply a major role of crystal fractionation during the evolution of 

these rocks. Petrographically, the general absence of textural and 

compositional evidence for disequilibrium, mixing, or contamination 

supports derivation through fractional crystallization. The abovementioned 

characteristics support previous suggestions that the 

Fig. 7. MORB-normalized multi-element patterns for Kid-Malhak Dokhan volcanics. 

Normalization values are from Taylor and McLennan (1985). 


Fig. 8. Chondrite normalized REE diagram for Kid-Malhak Dokhan volcanics. C1chondrite 

normalization values are from McDonough and Sun (1995). For comparison, a 

compiled pattern is shown for Dokhan volcanics (DV) from other areas (Abdel-Rahman, 

1996; Mohamed et al, 2000; Moghazi, 2003; Eliwa, 2006). 

Dokhan volcanics evolved predominantly through fractional crystallization 

of the petrographically observed phenocryst assemblage, 

which is plagioclase+K-feldspar+biotite+hornblende+magnetite. 

On the other hand, it is significant to evaluate whether or not the 

studied Dokhan volcanics have undergone crustal contamination. This 

is because mafic rocks are absent and all of these felsic lavas are 

porphyritic indicating that they might have resided in crustal magma 

chambers prior to eruption and would thus have had adequate 

opportunity to interact with continental crust. For this intention, 

evidences from trace element ratios for the examined volcanics are 

considered. During closed system fractionation, the ratio of strongly to 

moderately incompatible elements will remain constant or slightly 

increase, whereas during partial melting process, this ratio dramatically 

increases with decreasing degree of melting. Davidson et al. 

(1988) argued that ratios, such as K/Rb, Ba/Nb and Rb/Zr, do not 

significantly change by simple fractional crystallization, whereas 

variations in these ratios are preferably related to crustal contamination 

by assimilation–fractional crystallization (ACF; De Paolo, 1981) 

processes. Examination of the investigated rocks (Fig. 9) shows that 

there is a substantial variation between the samples in these ratios, 

which may reach five orders of magnitude (i.e. Rb/Zr and Ba/Nb). This 

implies that crustal contamination did play a major role in the 

evolution of the studied Dokhan volcanics. Additionally, these rocks 

feature distinct negative Nb anomalies which suggest involvement of 

crustal materials and crustal contamination. Moreover, a useful index 

to differentiate between crystal fractionation and crustal contamination 

is given in Fig. 10 using trace element ratios such as Nb/Y vs. Rb/Y 

(Chazot and Bertrand, 1995). In such diagram, crustal compositions 

and crustal melts are distinguished by high Rb/Nb ratios (N1) (Chazot 

and Bertrand, 1995). In the Nb/Y vs. Rb/Y diagram, all the Kid-Malhak 

lavas have exceedingly high Rb/Nb ratios (N3) and plot relatively close 

to lower and upper crustal values (Rudnick and Fountain, 1995). 

Therefore, crustal contamination is most probably superimposed on 

crystal fractionation in the evolution of Kid-Malhak Dokhan volcanics. 

Furthermore, this possible contributions from the crust to magma 

compositions (e.g. assimilation–fractional crystallization (AFC) process 

(De Paolo,1981), as well as crustal contamination phenomena are 

further investigated using the Th/Nb elemental ratios plotted vs. Zr 

(Fig. 11). In this diagram a LILE/HFSE ratio (Th/Nb), which should not 

be significantly affected by fractional crystallization, are plotted 

against an incompatible trace element (Zr) whose abundance 

increases as fractionation increases. Such a diagram allows the 

distinction between magmatic evolutions controlled by simple 

fractional crystallization in closed systems, that will produce an 

almost horizontal trend with increasing fractionation, and those 

influenced by additional processes. Kid-Malhak Dokhan volcanics 

35


Fig. 9. SiO 2 vs. Ba/Nb, Rb/Zr and K/Rb for the Kid-Malhak Dokhan volcanics showing the 

variation of Ba/Nb, Rb/Zr and K/Rb values with increasing SiO 2. 

define trends characterized by fairly elevated Th/Nb elemental ratios 

(Fig. 11), implying that assimilation–fractional crystallization (AFC) 

and crustal contamination have played a major role during magmatic 

evolution of Kid-Malhak Dokhan volcanics. After all, the recognition of 

680 Ma xenocrysts in andesite samples of the Dokhan Volcanics at the 

type locality area at Gabal Dokhan (Wilde and Youssef, 2000) 

additionally supports the idea of crustal contamination during 

evolution of these rocks. 

5.2.2. Source material: crustal- vs. mantle-derived components 

Source materials from which the studied Dokhan magma were 

generated are highly likely crustal sources, with little contribution 

from mantle, which might acted mainly as a source of heat required 

for fusion of the crustal precursor. This conclusion is supported by 

their prevalent peraluminous nature, enrichment in alkalis, Ba and Th, 

Fig. 10. Nb/Y vs. Rb/Y diagram for the Kid-Malhak Dokhan volcanic rocks (modified after 

Chazot and Bertrand, 1995). The upper and lower crustal compositions are from 

Rudnick and Fountain (1995). 

and depletion in Nb and HREE. Further, MORB normalized trace 

element patterns (Fig. 7) show significant negative Sr, Nb and Ti. The 

negative Nb and Ti anomalies might suggest a derivation from a 

crustal source or crustal contamination coupled with advanced 

degrees of differentiation. Table 2 reveals that the studied rocks 

display a quite wide range of Rb/Sr ratios (0.22–1.03) with an average 

of 0.46. Taking into account that mantle materials have very low Rb/Sr 

ratios, 0.1–0.01, (Taylor and McLennan, 1985; Hofmann, 1988) while 

lower and middle continental crust have Rb/Sr ratios of 0.12 and 0.22 

respectively (Rudnick and Fountain, 1995; Wedepohl, 1995), the Rb/Sr 

ratios of the studied Dokhan volcanics negate mantle material 

contribution and imply genuine crustal components on their genesis. 

Y/Nb ratios of the studied volcanics vary between a minimum of 1.53 

and a maximum of 2.76 (Table 2). This provides unambiguous 

evidence of their exclusive derivation from crustal material, in view 

of the fact that mantle sources have Y/Nb ratios less than 1.2, while Y/ 

Nb ratios greater than 1.2 characterizes materials of crustal origin 

(Eby, 1990, 1992). A typical primitive mantle value for Nb/Ta ratio is 

accepted to be 17.5±2.0 (Hofmann, 1988; Green, 1995). However, 

there is a controversy whether a typical continental crust value is 

within the range of the mantle-derived melts (Hofmann et al., 1986; 

Jochum et al., 1986) or is significantly lower (~11–12; Taylor and 

Fig. 11. Zr vs. Th/Nb plot for Kid-Malhak Dokhan volcanic rocks. Schematic trends 

reflecting increasing fractional crystallization (FC), assimilation–fractional crystallization 

(AFC), and bulk assimilation (BA) are from Nicolae and Saccani (2003).

McLennan, 1985; Green, 1995; Barth et al., 2000). The author favors 

the second opinion, typical continental crust Na/Ta ratio approximates 

11, which implies that these two elements in the studied 

samples (Nb/Ta; 10.85–14.64) were fractionated from each other in 

the continental crust. I suggest that, earlier accreted arc sequences of 

the juvenile Arabian–Nubian Shield crust probably melted to give rise 

to this calc-alkaline suite, a view supported by the presence of 

inherited zircons and older xenocrysts (680 Ma) in the Dokhan 

volcanics from the Eastern Desert (Wilde and Youssef, 2000; 

Breitkreuz et al., 2008). 

5.3. Tectonic setting 

The Kid-Malhak Dokhan volcanics display many of the chemical 

characteristics of the magmas formed at subduction-related settings. 

This includes their; calc-alkaline nature, strong enrichment of LIL 

elements (Cs, Rb Ba, Th and U) and depletion in HFS elements (Zr, Hf, 

Nb, Y, Ti) relative to typical MORB values, negative Nb anomalies, light 

REE-enriched patterns and weak fractionation of MREE and HREE. 

Also, the high-K calc-alkaline affinity strongly points to their eruption 

at continental (active continental margin), rather than oceanic setting 

(Pearce et al., 1984). However, they have slightly higher contents of 

alkalis, Nb, Zr and Y than typical island arc or continental margins 

volcanic suites. The studied Dokhan volcanic samples are plotted on a 

series of tectonic discrimination diagrams (Fig. 12), which are 

appropriate for magmas of felsic composition. Nb is one of the most 

effective elements to identify whether an acid igneous rock has a 

within-plate (high Nb) or volcanic arc (low Nb) character. The studied 

Dokhan lavas are sub-equally plotted in both volcanic arc field and the 

overlap zone between the volcanic arc and within plate settings on the 

binary SiO 2–Nb diagram of Pearce and Gale (1977) (Fig. 12A), 

suggesting a transitional tectonic setting. Pearce (1982) suggested 

the use of a simple bivariant plot of Ti against Zr in intermediate and 

acid volcanic rocks for recognition volcanic arc and within plate 

settings. He also stated that the volcanic arc lavas never reach the 

higher Ti contents of the within plate lavas for any given Zr 

concentration, due to the early crystallization of magnetite. Fig. 12B 

shows the relationship between these two immobile elements, where 

the studied volcanics are dually plotted in the within-plate and 

volcanic arc lava fields. The Dokhan samples plot in the “volcanic arc 

granite” field on the binary Y+Nb–Rb diagram of Pearce et al. (1984) 

(Fig. 12C), except for two samples, which fall in the “within-plate” 

field. Accordingly, the Kid-Malhak Dokhan lavas have geochemical 

characteristics of both subduction-related and within-plate settings, a 

phenomenon previously noted by many authors and has led to a 

dispute on the convergent margin versus within-plate geotectonic 

setting for the Dokhan volcanics. Since determination of the tectonic 

environment for the Dokhan volcanic rocks is one of the main 

objectives of this work, previous tectonic models will be debated in 

order to explain their implication and relationship to the emplacement 

of the Dokhan volcanics in Egypt. 

5.3.1. Arc-related model 

In accordance with their geochemical characteristics, several 

workers (Basta et al., 1980; Hassan and Hashad, 1990; El Gaby et al., 

1990; Abdel-Rahman, 1996; Blasy, 2000; Hassan et al., 2001; Saleh, 

2003) show that the Dokhan volcanics are calc-alkaline in nature and 

their trace element and REE contents resemble those of arc-related 

orogenic suites and thus they were erupted during the final stages of 

active subduction beneath the Eastern Desert of Egypt. Nevertheless, 

there is some regional evidence that supports the termination of 

subduction processes before their eruption: 

1- The Younger and the alkaline granites intrusions in Egypt are 

massive and un-deformed post-orogenic to anorogenic granites 

with many of the former and exclusively all of the later having 


typical A-type characteristics (Stern and Gottfried, 1986; Abdel- 

Rahman and Martin, 1990; Hassan and Hashad, 1990; Moghazi, 

1999; El-Bialy and El Omlla, 2007; El-Bialy and Streck, 2009; 

Farahat et al, 2007; Katzir et al., 2007; Moussa et al., 2008). The 

reported ages for these post-orogenic to anorogenic granitoid 

assemblages range between 610 and 475 Ma. (Hashad, 1980; 

Fig. 12. Discrimination diagrams illustrating tectonic setting of the studied volcanics: 

(A) SiO 2 vs. Nb diagram (Pearce and Gale,1977); (B) Zr vs. TiO 2 (Pearce,1980); (C) Yb+Nb 

vs. Rb (Pearce et al., 1984). The A-type granites field in (C) is after Whalen et al. (1987). 

37


Bielski, 1982; Bentor, 1985; Stern and Hedge, 1985; Abdel-Rahman 

and Martin, 1990; Beyth et al., 1994; Moghazi, 1999; Katzir et al. 

2007; Moussa et al., 2008; Ali et al., 2009; Be'eri-Shlevin et al., 

2009b). The range of emplacement ages of the spatially associated 

Dokhan volcanics (620–580 Ma) matches and falls within that of 

those granitoids. Assumption of the eruption of the Dokhan 

volcanics in orogenic arc-related setting implies two different 

tectonic environments for a single province during the same time 

period, which is impossible. 

2- Geological and geochronological studies carried out at different 

parts in the Egyptian basement complex have documented two 

tectono-magmatic episodes in the Neoproterozoic evolution of 

Egypt. The first tectono-magmatic episode (between 700 and 

720 Ma) represents the age of ophiolite obduction and island arc 

terrain accretion (Kröner et al., 1992; Stern, 1994; Kröner et al., 

1994; Harms et al., 1994; Stern, 2002; Kusky et al., 2003), while the 

accreted terrane collided with the East Saharan Metacraton during 

the second episode (between 650 and 620 Ma) (Kröner et al.,1994; 

Sultan et al., 1994; Stern, 1994; Stern, 2002; Abdelsalam and Stern, 

1996). Greiling et al. (1994) suggested that collision ceased at 615– 

600 Ma and the extensional collapse commenced sometime 

between the 600 and 575 Ma time period, followed by a stage of 

transpressional tectonism along major shear zones until 530 Ma. 

The un-deformed character of the Dokhan volcanics along with 

their emplacement ages (580–620 Ma; see Section 1), which 

synchronize to post-date the end of the collisional stage, suggest 

that their eruption had taken place at the transition between 

collision and extension (post-collisional). 

3- Plotting of the Dokhan lava samples on the Y+Nb–Rb diagram of 

Pearce et al. (1984), shows that the majority of the samples fall in 

the field of A-type granite of Whalen et al. (1987) on the same 

diagram (Fig. 12C). Moreover, plots of the samples on the on Zr+ 

Nb+Ce+Y versus (K2O+Na 2O)/CaO and FeO*/MgO diagrams 

(Whalen et al., 1987) reveal that the majority of the studied 

samples fall in the A-type granite field (not shown here). The same 

phenomenon is also reported for Dokhan volcanics from different 

parts of the Eastern Desert (e.g. Mohamed et al., 2000; Eliwa et al., 

2006). The prevalent A-type character of the Dokhan volcanics 

indicate that they were emplaced in “non-orogenic” environment, 

either post-collision or true anorogenic within-plate setting (Eby, 

1992), and positively not in compressional arc-related one. 

4- The emplacement of the Dokhan volcanics in the Eastern Desert 

and Sinai (580–620 Ma) were almost contemporaneous with the 

predominance of dyke swarms (Stern et al., 1983; Stern and Hedge, 

1985; Stern and Gottfried, 1986; Stern and Manton, 1987; Stern 

et al., 1988; Friz-Töpfer, 1991; El-Sayed, 2006), the major postaccerationary 

(640–540) Najd strike-slip fault system and shear 

zones in the Arabian–Nubian Shield (Stacey and Agar, 1985; Stern, 

1985; Sultan et al. 1993; Abdelsalam and Stern, 1996, Fritz et al., 

1996; Kusky and Matsah, 2003), and exhumation of metamorphic 

core complexes at about 600–580 Ma (Fritz et al., 1996; Fritz et al., 

2002; Blasband et al., 1997; Blasband et al., 2000; Brooijmans et al, 

2003) preclude the prevalence of compression tectonic regime and 

indicate that extensional tectonics were active during the Dokhan 

volcanics formation. 

5.3.2. Continental rifting model 

Several workers considered the A-type character of the felsic 

members of Dokhan volcanics, linked with the synchronous emplacement 

of the Dokhan volcanics with the high level A-type granite 

intrusions, together with the bimodal nature of some Dokhan volcanic 

suites in the Eastern Desert as evidences of strong crustal extension in 

an anorogenic within-plate rifting environment, analogous to that of 

the Neoproterozoic Oslo Rift of Norway (Stern et al., 1984; Stern et al., 

1988; Stern and Gottfried, 1986; Willis et al, 1988; Mohamed et al., 

2000). Nevertheless, there are various oppositions to the emplace- 

ment of the Dokhan volcanics in authentic anorogenic rift-related 

settings. 

1- The bimodal nature of Dokhan lava suites, which is used as a criteria 

to substantiate the anorogenic rifting model for the genesis of this 

rock unit is not the norm, but only restricted to the southernmost 

Dokhan localities(i.e. Safaga-Qena and S. Safaga areas) (Eliwa et al., 

2006). In most of the localities in the Eastern Desert, Dokhan 

volcanics form a compositionally continuous suite (Basta et al., 

1980; Abdel-Rahman, 1996; Blasy, 2000; Eliwa et al., 2006; Saleh, 

2003; Moghazi, 2003; El Sayed et al., 2004). From other side, this 

bimodality, if accepted as a typical nature of Dokhan volcanics, 

cannot be applied as an explicit evidence of anorogenic rifting, since 

it is now evident that many arc magmatism is bimodal in 

composition, and lacks andesitic magmas (Tamura and Tatsumi, 

2002; Leat et al., 2003; Smith et al., 2003). 

2- The A-type character of the felsic members of the Dokhan volcanic 

suites does not crucially imply anorogenic rift-related setting. It is 

now widely accepted that the A-type magmas can be generated in 

post-orogenic and anorogenic settings (Whalen et al., 1987; Eby, 

1990, 1992; Whalen et al., 1996). According to Eby (1990, 1992), Atype 

magmas are divided into A1 and A2 groups. The A1 group (true 

anorogenic) refers to differentiates of magmas derived from sources 

like those of oceanic–island basalts (OIB) but emplaced in continental 

rifts or during intra-plate magmatism. The A2 group (post-orogenic 

or post-collisional), on the other hand, represents magmas derived 

from continental crust or underplated crust that has been through a 

cycle of continent–continent collision or island–arc magmatism. 

3- Correspondence between the tectonic setting of the Dokhan 

volcanics and Oslo Rift is an oversimplification. Basaltic lavas of 

Oslo rift, and other continental rift systems, have major and trace 

element concentrations comparable to ocean island basalts (OIB), 

indicating the participation of asthenospheric mantle in their 

genesis (Neumann, 1994; Neumann et al., 2002). Conversely and 

for example, the studied Dokhan lavas have major and trace 

element abundances and characteristics, which are very similar to 

subduction-related magmas and imply greater contribution from 

crustal sources rather than asthenospheric mantle. 

5.3.3. Post-collision extensional collapse (the suggested model) 

From the previous discussion, it is obvious, that the Kid-Malhak 

Dokhan lavas have geochemical characteristics of both orogenic arctype 

and anorogenic within-plate environments, suggesting eruption 

in a transitional tectonic setting. Fig. 12C reveals that all samples were 

emplaced in a “post-collisional” regime rather than volcanic arc or 

within-plate settings. The same conclusion can also be achieved 

through their prevalent A-type character combined with their Nb/Y 

ratios (N1.2), which characterize the post-orogenic (post-collision) A2 

subtype magmas (Eby, 1990, 1992). Post-collision magmatism is 

linked to rapid post-closure uplift, which may take place some time 

after the collision itself, and which is also linked to the subsequent 

collapse of the orogenic belt (Pearce, 1996). For clarification of the 

post-collision stage of the Arabian–Nubian Shield (ANS) evolution, 

during which the Dokhan volcanics had been emplaced, a summary of 

the Shield's tectonic evolution is given below: 

1- Rifting of Rodinia super-continent led to the formation of the 

Mozambique Ocean. Intra-oceanic subduction gave rise to the 

development of island-arcs, back-arc basins and ophiolitic sequences 

(Fig. 13A) (El Gaby et al., 1984; Bentor, 1985; Pallister et al., 1988; 

Stern, 1994) at approximately 900–750 Ma in the Mozambique 

ocean (Stern, 1994; Abdelsalam and Stern, 1996; Abdelsalam et al., 

2008; Rino et al., 2008; Vaughan and Pankhurst, 2008). 

2- Subduction at continental margins led to accretion of island-arcs 

and ophiolite remnants in the Mozambique Ocean and the 

amalgamation of accreted terrains onto east Gondwana continental 

block. Terrane accretion in the ANS took place along north to east

trending arc–arc sutures developed between 700 and 800 Ma. The 

arc accretion marked the closure of Mozambique Ocean, and was 

responsible for fast continental crustal growth and lithosphere 

thickening of the juvenile ANS crust. (Pallister et al., 1988; Kröner 


Fig. 13. Cartoons displaying the major stages of the evolution of the Arabian Nubian Shield (A and B), with special emphasis on the generation of the Dokhan volcanics during the 

post-collisional stage (C and D) (modified after Blasband et al., 2000 and Davies and von Blanckenburg, 1995). The oceanic phase is shown in [A], with island-arcs developing in the 

Mozambique ocean. Oceanic crust was formed at the MOR, in fore-arcs and back-arcs. At stage [B], “off-shore amalgamation” or arc-accretion and subduction at the continental 

margins took place and accretion of the island-arcs and superterranes started. In [C]; the start of extensional collapse and slab breakoff of the oceanic lithosphere as a consequence of 

the collision between the accreted juvenile Arabian–Nubian Shield crust with the Pre-Neoproterozoic Saharan Metacraton to the west after the closure of Mozambique Ocean. 

Following subduction, rifting of the oceanic lithosphere allows asthenosphere to rise and fill the rift; slab weakening follows with underplating of continental crust. In [D]; slab 

detaches and sinks away. High temperatures maintained at the base of lithosphere by deep return flow causing partial melting of the underplate to form Dokhan magmas, which 

ascend to the surface through the crust. 

et al., 1992, 1994; Stern, 1994, 2002; Abdelsalam and Stern, 1996; 

Rino et al., 2008; Condie et al., 2009). 

3- The juvenile accreted ANS crust collided with pre-Neoproterozoic 

continental blocks of west Gondwana (Saharan Metacraton; 

39


Abdelsalam et al., 2002) at 750–650 Ma along arc–continental 

sutures (Fig. 13b) (Kröner et al., 1994; Sultan et al., 1994; Stern, 

1994, 2002; Abdelsalam and Stern, 1996; Stoeser and Frost, 2006; 

Stern, 2008). 

4- Collision ceased at ca. 615–600 Ma and the extensional collapse of 

the thickened lithosphere took place at ca. 600–560 Ma. Extensional 

or gravitational collapse led to extension and thinning of the 

Arabian–Nubian Shield crust, which continued until approximately 

530 Ma. (Greiling et al.,1994; Blasband et al.,1997, 2000; Brooijmans 

et al., 2003). 

The ages of emplacement of the Dokhan volcanics in Egypt 

including that of Kid-Malhak region (609±12 Ma; Bielski, 1982) 

coincide with end of collision and the extensional collapse event. The 

post-collision transition from a compressional arc-accretion setting to 

an extensional regime is best explained by the extensional collapse 

model (Dewey, 1988). Extensional collapse follows continental 

collision and is controlled mainly by lithospheric delamination and 

slab breakoff (passive rifting) and not by rifting controlled by the 

ascent of the asthenospheric mantle material (active rifting) as in the 

Oslo rift in Norway (see Fig. 13C, D). The extensional collapse model 

has been argued and documented in several parts of the world (e.g. 

Dewey, 1988; Davies and von Blanckenburg, 1995; Cosca et al, 1999; 

Atherton and Ghani, 2002; Clift et al., 2004; Abdelsalam et al., 2008; 

Casini and Oggiano, 2008; Sun et al, 2008; Jöns et al., 2009) and also in 

the northern part of the Arabian–Nubian Shield (e.g. Blasband et al., 

1997, 2000; Brooijmans et al., 2003; Moghazi, 2003). 

“Slab breakoff” is the buoyancy-driven detachment of subducted 

dense oceanic lithosphere from the light continental lithosphere that 

follows it during continental collision (Davies and von Blanckenburg, 

1995). This situation of opposing buoyancy forces leads to extensional 

deformation (narrow rifting) in the subducted slab. As a result 

of the rifting during breakoff, the asthenosphere upwells into the 

narrow rift, and following breakoff it impinges on the mechanical 

lithosphere of the overriding plate (Davies and von Blanckenburg, 

1995; Sperner et al., 2001; Coulon et al., 2002; Heidbach et al 2008; 

Regard et al, 2008). The generation of the Dokhan Volcanic magma 

can thus be regarded as a consequence of continental collision 

between the juvenile arc-accreted crust of the Arabian–Nubian 

Shield and the pre-Neoproterozoic Saharan Metacraton to the west 

(Fig. 13C). As the oceanic slab falls away (Fig. 13D), more of the 

enriched mantle would be exposed, in a manner similar to a plume 

impinging on lithosphere, and may lead to limited thermal erosion of 

the lithosphere (Monnereau et al., 1993). The overlying continental 

lithosphere is heated by conduction as the asthenosphere impinges 

on its base leading to melting of the metasomatised, veined and 

hydrated layers (Atherton and Ghani, 2002). This part of lithosphere 

may have obtained unique trace element characteristics owing to its 

interaction with fluids and melts driven off from the subducting slab 

during previous long subduction events (i.e. between 900 and 

620 Ma; Stern, 1994) in the Arabian–Nubian Shield (Moghazi, 2003). 

Expected melts, according to Davies and von Blanckenburg (1995), 

could be alkaline to ultrapotassic from small degree melts or calcalkaline 

from slightly higher degree melting of more fertile or 

hydrated peridotite layers. These magmas will rise into the crust, 

pass through and induce crustal melting to produce granitic magma. 

Crustal melting will be enhanced by thermotectonic processes, e.g. 

heat conduction after shallow breakoff, or heating and decompression 

on rapid unroofing (Davies and von Blanckenburg, 1995). In 

agreement with Moghazi (2003), the calc-alkaline nature of the 

Dokhan volcanics can be explained by high degree partial melting of 

the juvenile Arabian–Nubian Shield crust. Even though this model 

needs to be evaluated geodynamically, it seems to be the most 

conceivable for the stratigraphic position and geochemical characteristics 

of the Dokhan volcanics in Egypt and other comparable 

magmatic rocks formed at the post-collisional transitional stage 

between arc-accretion and crustal extension in the Arabian–Nubian 

Shield. 

5.4. Dokhan volcanics: a transition between calc-alkaline and alkaline 

magmatism? 

The gradual transition from an “orogenic” calc-alkaline magmatism 

to a continental intra-plate alkaline suite has been described in several 

regions worldwide (e.g. North Africa; El Bakkali et al., 1998; Coulon 

et al., 2002; Turkey and Anatolia; Wilson et al., 1997; Aldanmaz et al., 

2000; Agostini et al., 2007; Southern India; Rajesh, 2004; Sardinia: 

Lustrino et al., 2007; Carpathian Pannonian Region; Harangi, 2001; 

Konecny et al., 2002; Seghedi et al., 2005; Central Africa Belt; 

Tetsopgang et al., 2008). This transition may follow either a continental 

collision (e.g. Turkey, Iran), or the cessation of subduction at a 

previously convergent margin, for instance, as a result of a ridge– 

trench collision (e.g. California; Cole and Basu, 1992). In the northernmost 

part of the Arabian–Nubian Shield, in Sinai, Jordan and 

southern Israel, such transition is also recorded (Beyth et al., 1994; 

Jarar et al., 2003; Stern, 2008; Ali et al., 2009; Be'eri-Shlevin et al., 

2009a,b). The late evolutionary stages of the northern Arabian–Nubian 

Shield (650–545 Ma) document the growth and maturation of the 

continental crust from an orogen to a craton. During this period 

magmatism changed from calc-alkaline to alkaline and the tectonic 

setting in which these magmas emplaced, have changed from collision 

to post-collision, to within-plate extension and finally to a stable 

platform setting. The nature of transition from calc-alkaline to alkaline 

magmatism, whether abrupt or gradual, and its correlation to field 

evidence for initiation of extension in the northern Arabian–Nubian 

Shield are poorly resolved. Beyth et al. (1994) and Ali et al. (2009) 

referred to the transition between calc-alkaline and within-plate 

alkaline magmatism in southern Israel and Sinai respectively, and 

suggested that it occurred at c. 610 Ma, which is concordant with the 

emplacement ages of the Dokhan volcanics in Egypt. 

The northernmost Arabian–Nubian shield comprising the Eastern 

Desert of Egypt, Sinai, southern Jordan and Israel is characterized by 

vast and prolonged (~820–570 Ma) intrusive and extrusive magmatism. 

Magmatic rocks were divided to (1) syn- to late-orogenic I-type 

and (2) anorogenic, A-type, the transition between the two types 

occurring at ~610–600 Ma (Bentor, 1985; Beyth et al., 1994; Stern, 

1994; Jarar et al., 2003; Moussa et al., 2008; Ali et al., 2009; Be'eri- 

Shlevin et al., 2009a,b). The recognition of a widespread high-K calcalkaline 

suite, formed at about the time of this transition, and partially 

overlapping the beginning of alkaline A-type magmatism (Be'eri- 

Shlevin et al., 2009a,b), redefines different stages of calc-alkaline 

magma production in this region. The magmatic calc-alkaline pulses 

thus include (a) early medium-K calc-alkaline plutons (now gneisses) 

associated with metavolcanics and metasediments, and older synorogenic 

I-type granitoids, all of arc-type affinity that formed at ~820– 

740 Ma, (b) a late syn-collisional medium-K to high-K calc alkaline 

suite (many of the younger granites of Egypt) formed during late 

stages of accretion (~670 Ma to 635–625 Ma) and (c) post-collisional 

mainly high-K calc-alkaline suite of 620–580 Ma (the Dokhan 

volcanics and latest phases of the Egyptian younger granites) that 

overlaps the alkaline suite of ~600–470 Ma (post-collisional and 

anorogenic A-type granites) for ~20 m.y. The temporal transition from 

medium-K through high-K calc-alkaline to alkaline magmatism is 

correlated with the change in tectonic regime (Bentor, 1985; Stern and 

Hedge, 1985; Beyth et al., 1994; Jarar et al., 2003; Moussa et al., 2008, 

Ali et al., 2009; Be'eri-Shlevin et al., 2009a,b) and implies either a 

change in magma sources or a change in the processes that formed 

magmas during 820–580 Ma. Therefore, the eruption of the high-K 

calc-alkaline post-collisional Dokhan volcanics defines a tectonomagmatic 

transition between the older calc-alkaline arc-related 

magmatism and the subsequent alkaline magmatism in the northern 

part of the Arabian–Nubian Shield.

6. Conclusions 

The concluding remarks, based on the field, petrographic and 

geochemical investigations presented here, are as follows: 

1- The Pan-African Dokhan volcanic suite in Kid-Malhak region (609± 

12 Ma; Bielski, 1982), extrudes and overlies other older metamorphosed 

basement units including the gneisses, metasediments and 

metavolcanics, and conversely intruded by the younger granites. A 

younger to contemporaneous thick interbedded epiclastic conglomerate 

beds (100–150 m), separate their succession into upper and 

lower stratigraphic sequences, and are most probably stratigraphically 

equivalent to the Hammamat Group (Akaad and Noweir, 1980) 

clastic sediments of the Egyptian Eastern Desert. 

2- The Dokhan volcanics in the study area consist of non-metamorphosed 

varicolored alternating succession of porphyritic lava flows 

of commonly felsic composition interlayered with compositionally 

equivalent pyroclastic beds (dominantly ignimbrites). Lava flows 

predominate in this volcanic suite, comprising chiefly rhyolites 

with subordinate dacites and trachydacites. 

3- The studied Dokhan volcanics are quite evolved (SiO 2≈65–77 wt. 

%), with strong high-K calc-alkaline affinity and are characterized 

by relative enrichment in total alkalis, Ba, Y, Zr and total REEs, and 

fair depletion in Sr. Also, they are characterized by a LREE-enriched 

REE patterns with significant negative Eu anomalies. 

4- The striking difference between the studied Dokhan volcanics and 

others in Sinai (El Metwally et al., 1999; Azzaz et al., 2000; Hassan 

et al., 2001) and those of the Eastern Desert of Egypt, is their 

evolved felsic compositional range (rhyolite-dacite) in comparison 

with the “bimodal” or continuous spectral composition of the 

Dokhan volcanics in the Eastern Desert. 

5- The Kid-Malhak Dokhan lavas have geochemical characteristics of 

both orogenic arc-type and anorogenic within-plate environments, 

suggesting eruption in a transitional “post-collisional tectonic setting. 

The ages of emplacement of the Dokhan volcanics in Egypt including 

that of Kid-Malhak region (580–620 Ma) coincide with end of the 

documented collision between the juvenile Arabian–Nubian crust and 

Saharan Metacraton and the subsequent extensional collapse event. 

The post-collision transition from a compressional arc-accretion 

setting to an extensional regime is explained by the extensional 

collapse following continental collision and is controlled mainly by 

lithospheric delamination and slab breakoff (passive rifting). 

6- Trace element characteristics (Nb depletion and the variation of 

the K/Rb, Ba/Nb, Rb/Nb, Th/Nb and Rb/Zr ratios), strongly indicate 

that assimilation–fractional crystallization (AFC) and crustal 

contamination have played a major role and are most probably 

superimposed on fractional crystallization during the magmatic 

evolution of Kid-Malhak Dokhan volcanics. 

7- Source materials from which the studied Dokhan magmas were 

generated are highly likely crustal sources. This conclusion is 

supported by their prevalent peraluminous nature, enrichment in 

alkalis Ba and Th, depletion in Nb, Ti and HREE, high Rb/Sr and Y/ 

Nb and low Nb/Ta ratios comparable to crustal rock, and finally the 

presence of inherited zircons and older xenocrysts in other Dokhan 

volcanics in the Eastern Desert. 

8- Application of zircon saturation thermometry revealed temperatures 

ranging between a minimum of 766 °C and a maximum of 

882 °C. These calculated temperatures cannot simply regarded as 

crystallization temperatures, but are to be considered maximum 

temperatures of crustal fusion, since inherited zircon components 

are reported in other Dokhan volcanic suites from Eastern Desert. 

9- The eruption of the high-K calc-alkaline post-collisional Dokhan 

volcanics defines a tectono-magmatic transition between the older 

calc-alkaline arc-related magmatism and the subsequent alkaline 

anorogenic magmatism in the northern part of the Arabian–Nubian 

Shield. 


Acknowledgments 

Sincere thanks are extended to Dr. I. H. Khalifa (Geology Department, 

Suez Canal University, Ismailia, Egypt) for assistance during field work. I 

greatly appreciate the comments and suggestions of Professor M. Santosh 

(Editor-in-Chief; Gondwana research). Also, I gratefully acknowledge the 

thorough and constructive comments of Dr. H.M. Rajesh and of an 

anonymous reviewer that seriously improved the manuscript. 

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