ORIGINAL PAPER

Dokhan volcanics of Gabal Monqul area, North EasternDesert, Egypt: geochemistry and petrogenesis

Adel A. A. Abdel Wahed & Khaled G. Ali &Magdy M. A. Khalil & Ahmed E. Abdel Gawad

Received: 1 December 2009 /Accepted: 9 March 2010# Saudi Society for Geosciences 2010

Abstract The Dokhan volcanics are represented by a thickstratified lava flows succession of basalt, andesite, imperialporphyry, dacite, rhyodacite, rhyolite, ignimbrites, and tuffs.These lavas are interbanded with their pyroclastics in someplaces including banded ash flow tuffs, lithic tuffs, crystallapilli tuffs, and agglomerates. They are typical calc–alkalineand developed within volcanic arc environment. All rocksshow moderate enrichment of most large ion lithophileelements relative to high field strength elements (HFSE).The incompatible trace elements increase from basalt throughandesite to rhyolite. The felsic volcanics are characterized bymoderate total rare earth elements (REE) contents (162to 392 ppm), less fractionated patterns {(Ce/Yb)N=(1.24 to10.93)}, and large negative Eu anomaly {(Eu/Eu*)=(0.15 to0.92)}. The mafic volcanics have the lowest REE contents(61 to 192 ppm) and are relatively steep {(Ce/Yb)N=(3.2 to8.5)}, with no negative Eu anomalies {(Eu/Eu*)=(0.88 to1)}. The rhyolite displays larger negative Eu anomaly(Eu/Eu*=0.28) than those of other varieties, indicating thatthe plagioclase was an early major fractionating phase. Themineralogical and chemical variations within volcanics areconsistent with their evolution by fractional crystallizationof plagioclase and clinopyroxene.

Keywords Dokhan volcanics . HFSE .

Arabian–Nubian Shield

Introduction

The Eastern Desert (ED) of Egypt is a part of the Arabian–Nubian Shield, which is made up of arc-inter-arc rockassociations, which are represented by dismembered ophio-litic slabs thrusted over the deformed arc terrane. These arccomplexes are believed to have evolved and cratonizedbetween 900 and 550 Ma (Stern 1979; Kröner et al. 1987;Stoeser and Camp 1985). The arc associations includevolcano-sedimentary rocks with rare sedimentary ironformations and carbonate beds of possible back-arc setting(Sims and James 1985). They are intruded by syn- to latetectonic dioritic–granodioritic plutonites. This tectonomag-matic cycle ended with cratonization through thrusting, lowangle shearing, and associated folding (Sturchio et al. 1983;Abdel-Meguid 1992) and culminated by the intrusion ofgranodiorites at ∼612 Ma as in the Meatiq area (Sturchio etal. 1983). After cratonization, the Neoproterozoic crust wascharacterized by the eruption of K-rich volcanic rocks(Dokhan volcanics) and emplacement of shallow levelfelsic intrusions (Egyptian Younger Granites) (El Shazlyet al. 1980). The term “Dokhan volcanics” refers tovaricolored thick sequence of lava flows and their pyro-clastics of predominantly andesitic to rhyolitic compositionin association with ignimbritic rhyolites (Basta et al. 1980;Stern and Gottfried 1986). Breitkreuz et al. (2010) havepublished SHRIMP U–Pb zircon ages of 615±4 and 616±5.4 Ma (Ediacaran age) for two lithic- and crystal-poorignimbrites. Associated subaerial molasse sediments (Ham-mamat), mainly derived from the Dokhan volcanics, andwere deposited laterally, in intracratonic basins (Grothaus etal. 1979; Abdel-Meguid 1986, 1998). Hammamat sedi-ments occur interfingered with the upper member of theDokhan volcanics (Khalaf et al. 2000; Stopora andZimmermann 2007). The deposition of the Hammamat

A. A. A. Abdel Wahed :K. G. Ali (*) :A. E. Abdel GawadNuclear Materials Authority,P.O. Box 530, Maadi, Cairo, Egypte-mail: khaled_ali66@yahoo.com

M. M. A. KhalilFaculty of Science, Damietta Branch, Mansoura University,Mansoura, Egypt

Arab J GeosciDOI 10.1007/s12517-010-0136-z

Sediments took place in several environments, includingalluvial fan, braided river and lacustrine (both deep lakeand delta), which was synchronous in many cases with theformation of Dokhan volcanics and structurally controlledintra-montane basin system during the Early Ediacaran(Eliwa et al. 2010).

The Dokhan volcanics are widely distributed in SouthernSinai, Northern, and Central ED. They are representing thesecond major volcanic episode recognized in the Precam-brian crust of the Arabian–Nubian Shield. The Dokhanvolcanics differ from the younger metavolcanics in theirgreater abundance of acidic volcanics (dacite and rhyolite),higher potassic nature, and common presence of ignimbritesand welded tuffs (El-Gaby et al. 1991).

Many studies show the high-K calc–alkaline nature ofthe Dokhan volcanic and provide evidence for theoperation of fractional crystallization and crustal contam-ination in the evolution of these rocks. However, thegeotectonic interpretation of the Dokhan volcanic hasbeen highly debated with models, which can be groupedin three main settings:

– Anorogenic settings: intra-continental rift model similarto Oslo rift system in Norway (Stern et al. 1984; Sternand Gottfried 1986)

– Orogenic setting: active continental margin (Basta et al.1980; Ragab 1987; El-Gaby et al. 1989; Abdel Rahman1996; El-Bayoumi et al. 1997; El-Sheshtawi et al.1995).

– Transitional setting: transition between compressionaland extensional settings (Ressetar and Monard 1983;Mohamed et al. 2000; Eliwa et al. 2006).

The studied area is located in the northern part of theED, between longitudes 33° 02′ 30″ and 33° 06′ 30″E andlatitudes 27° 48′ 30″ and 27° 53′ 30″N. The area wasinvestigated by many authors (e.g., Francis 1972; Botros1995; Botros and Wetait 1997; Wetait and Botros 1997;Abdel-Magid et al. 1998; Abdel Gawad 2008). The presentpaper reports field aspects, petrography, and geochemistrywith special emphasis on rare earth content of the Dokhanvolcanic rocks in consideration.

Field aspects

The examined area is dominated by older granitoids,Dokhan volcanics, Hammamat sediments and youngergranitoids (Fig. 1). The Dokhan volcanics extrude the oldergranitoids and intruded by younger granitoids with sharpcontact (Fig. 2a). The various rock units of the study areaare dissected by numerous dikes and veins includingfelsites, andesite, basalt, and dolerite dikes in addition toquartz and barite veins. The Dokhan volcanic constitute a

thick sequence of stratified lava flows of basalt, andesite,dacite, rhyodacite, and rhyolite together with subordinatesheets of ignimbrite. These lavas are interbanded with theirpyroclastics. These volcanics are mostly porphyritic andamygdaloidal of different shades of gray that frequentlygrades into reddish to deep purple color of imperialporphyry. Brecciated basalt (Fig. 2b) occupies the northernpart of the area with black to dark gray color, fine-grained,massive, and form low to moderate relief. Andesite ischaracterized by green to dark green colors, mediumgrained. It is located in the central western part of the area.The acidic lava, including dacite, rhyodacite, and rhyolitevolcanics, crop out in the north-western part of the mappedarea. These rocks are fine-grained, hard, massive, andwhitish to reddish pink, buff, pale red, to red in colors.Some rhyolite rocks show flow structure (Fig. 2c).

These lavas are interbanded with their pyroclastics insome places including banded ash flow tuffs (Fig. 2d), lithictuffs, crystal lapilli tuffs, and agglomerates. The agglomer-ate beds contain surrounded volcanic porphyry as clasts,some of them showing reaction rims. Intercalation ofvolcanic agglomerates and lapilli tuffs contain bombs upto 20 cm in diameter. Locally, the sequence intercalatedwith welded ignimbrite sheets, which are typically poorlysorted, non-bedded, and have a wider range of particle size,are recorded. Dark brown to brownish black flattened,lenticular clots, embedded in a tuffaceous matrix ofrhyolitic composition are recorded. The fiamme structureis observed in the field much better on naturally exposedsurfaces, where the black lenses stand out clearly againstthe brownish matrix (Fig. 2e). The linear fabric that resultedfrom stretching and welding of the fiamme indicatessecondary mass flowage of the tuff during welding (Casand Wright 1987).

The Dokhan volcanics are unconformably followed bythick sequences of Hammamat sediments formed ofconglomerate, sandstone greywacke, and siltstone. Thecontact between the Dokhan volcanics and Hammamatsediments is controlled along normal fault strikes 90° anddip 64° to the south at wadi Monqul (Fig. 2f).

Petrography

The Dokhan volcanics are represented by basalt, andesite,imperial porphyry, dacite, rhyodacite, rhyolite, and theirpyroclastics. Microscopically, these rocks can be identifiedbelow.

Basalt rocks are fine grained; some varieties areamygdaloidal (Fig. 3a). They are holocrystalline and consistof plagioclase (An55-60, labradorite), laths pyroxene, andolivine. Accessories are apatite and opaque minerals.Pyroxenes occur as pale greenish aggregates and subhedral

Arab J Geosci

prismatic crystals and are usually transformed into fibrousactinolite (Fig. 3b), tremolite, and chlorite.

Andesite rocks are the most common intermediatevolcanics in the area. They are fine to medium grainedand range from aphanitic to typical porphyritic varieties.Microscopically, they consist of plagioclase (An25–40,andesine), hornblende, biotite, and quartz. Accessories areapatite and opaque minerals, while secondary minerals arechlorite, calcite, and sericite. Plagioclase crystals showglomeroporphyritic texture (Fig. 3c), while the other

crystals are porphyritic enclosing opaque minerals. Horn-blende crystals show pale green color with brownishpleochrism. Subhedral to euhedral prismatic poikilitichornblende phenocrysts contain inclusions of apatite,quartz, and opaques (Fig. 3d).

Imperial porphyry rocks are composed of crystal lithic ofandesite and dacite fragments surrounded by trachyticgroundmass (Fig. 3e). Plagioclase, k-feldspar, quartz, andopaque minerals are the main constituents of these frag-ments. Plagioclase occurs as euhedral to subhedral crystals

Fig. 1 Geologic map of GabalMonqul area, North EasternDesert, Egypt

Arab J Geosci

surrounded by tuffaceous matrix composed of shreds ofquartz, amorphous silica, k-feldspar, and opaque minerals.Quartz fragments are angular to subangular crystalsenclosed in plagioclase and tuffaceous matrix. Flowtextures are the main characteristic features.

Dacite rocks are mainly composed of plagioclase (An10–25,oligoclase), quartz, k-feldspar, and biotite set in fine-grainedgroundmass composed of k-feldspar, quartz, and biotite.Accessories are mainly represented by opaque minerals andapatite. Sericite and epidote are secondary minerals. Plagio-clase crystals show glomeroporphyritic texture and exhibitlamellar twinning, while some contain oscillatory zoning.Oscillatory zoning in plagioclase (Fig. 3f) involving alter-nating calcic and sodic zones with small compositionaldifferences has been explained by diffusion-controlled,recurrent supersaturation of the melt in anorthite and then

albite components adjacent to the growing crystal (Haase etal. 1980).

Rhyodacite are fine grained, commonly displaying spher-ulitic and porphyritic texture. They consist of phenocrysts ofk-feldspar, plagioclase, biotite, and quartz embedded in a fine-grained groundmass. Accessory minerals are apatite andopaques, while sericite, chlorite, and kaolinite occur assecondary minerals. Plagioclase occurs as euhedral tosubhedral crystals showing simple twinning (Fig. 4a). Plagio-clase encloses apatite and corroded by quartz showingpoikilitic and glomeroporphyritic textures.

Rhyolite rocks consist of quartz, k-feldspars, andplagioclase phenocrysts embedded in fine groundmassthat is entirely glassy and has been vitrified. These rocksshow porphyritic texture (Fig. 4b). Zircon, fluorite,apatite, and opaques are accessories, whereas sericite,

Fig. 2 a General view showingthe older granitoids extruded byDokhan volcanics with a sharpcontact. b Bracciated lava ofbasaltic composition in thenorthern part of east Monqul. cFlow structure in rhyolite fromGabal Monqul area. d Finebanded ash tuffs from GabalMonqul area. e Fiaminestructure of ignimbrite rocks. fStructure contact betweenDokhan volcanics andHammamat sediments at wadiMonqul along E–W normal fault

Arab J Geosci

epidote, kaolin, and muscovite occur as secondaryminerals (Fig. 4c).

Ignimbrite rocks are hard, massive with streaks ofvitrified, collapsed, and aligned pumice fragments formingeutaxitic structure. They are mainly composed of angularcrystals of quartz, plagioclase, k-feldspar, and crystalfragments embedded in a laminated tuffaceous matrix.The matrix consists of perthite, biotite, quartz, and ironoxides. They are rhyolite to rhyodacite in composition,occasionally showing spherulitic texture (Fig. 4d). Thewelded groundmass in ignimbrite (Fig. 4e) encloses rareidiomorphic crystals and crystal fragments of feldspars,quartz, and scarce biotite together with lithic rock fragmentsand fiamme shreds. The fiamme is distinguished from theenclosing matrix by their sinuously curved lenticular formand devitrified nature.

Ash tuffs are fine grained, laminated, and composed ofcrystal fragments of quartz, feldspars, sericite, opaqueminerals, and epidote set in a fine-grained matrix of quartz

and k-feldspar. Iron oxides are the main accessoriespresented as a matrix of minute crystals and/or devitrificationproducts in glassy volcanic rocks. Laminated ash tuffs consistmainly of medium glassy rhyolite band followed by finek-feldspar band of ash tuffs (Fig. 4f).

Petrochemistry

Analytical techniques The geochemical characterization ofDokhan volcanic rocks encountered in the Gabal Monqularea is carried out through the study of the chemicalcomposition of 13 selected samples representing thedifferent varieties of Dokhan volcanic rocks. Major elementcompositions and Sc, Ba, and Ni abundances weredetermined by inductively coupled plasma–atomic emissionspectrometry. The remainder of trace elements and the rareearth elements (REE) were determined by inductivelycoupled plasma–mass spectrometry. All the analyses were

Fig. 3 a Amygdales filled byfine laths of plagioclase showingflow structure in basalt. C.N.,X=60. b Actinolite showingfibrous structure in basalt. C.N.,X=120. c Euhedral crystals ofplagioclase showing glomero-porphyritic texture in porphyriticandesite. C.N., X=120. d Inclu-sions of apatite in hornblende inandesite. C.N., X=240. e Lithicfragment of dacite surroundedby trachytic groundmass inimperial porphyry. C.N., X=60.f Sericitized plagioclase show-ing oscillatory zoning in dacite.C.N., X=60

Arab J Geosci

carried out at the ACME Analytical Laboratories Ltd,Canada. Analytical precision, as calculated from replicateanalyses, is 0.5% for major elements and varies from 2% to5% for trace elements of >80 ppm, 2–10% for traceelements of 10 to 80 ppm, and 5–20% for trace elements of<10 ppm. The results of chemical analysis are given inTables 1 and 2 (Fig. 5).

Major and trace elements

The compositions of Dokhan volcanics do not exhibit acompositional gap from basalt to rhyolite (50 to 77 wt.%SiO2). Variation diagrams display the chemical variationsand trend among related rock varieties. Figures 6 and 7show some major and trace elements variation diagrams forthe Dokhan volcanics using differentiation index (DI) and

basic index (B) as a differentiation index. The variationdiagrams display a continuous magmatic trend with otherrock varieties, suggesting a single-stage magmatic processof volcanicity.

Using a discrimination diagram based on the relationbetween differentiation index (Zr/TiO2) and the indicator ofalkalinity (Bb/Y), it showed that the studied volcanics rangein composition from andesite/basalt, andesite, rhyodacite,dacite, to rhyolite (Fig. 7a). The total alkalis versus silicadiagram demonstrates the subalkaline affinity of theDokhan volcanics (Fig. 7b). Furthermore, the rocks showcalc–alkaline trend on the ternary diagram (Y+Zr)−(TiO2*100)−Cr (Fig. 7c).

On the Nb (ppm) versus (SiO2 wt.%) binary diagram andTiO2–K2O–P2O5 ternary diagram shown in Fig. 7d, e, it isclear that most of the samples plot in the volcanic arcmagma and continental field. Ternary diagrams utilized byWood (1980) based upon the immobile high field strength

Fig. 4 a Phenocrysts of plagio-clase showing simple twinningin rhyodacite. C.N., X=60. bRhyolite showing porphyritictexture. C.N., X=60. c Musco-vite flakes in rhyolite. C.N.,X=240. d Spherulitic rhyolitefragment in ignimbrite. C.N.,X=60. f K-feldspar and quartzfragments band with glassyrhyolite band in laminated ashtuffs. C.N., X=60

Arab J Geosci

Table 1 Chemical analysis of major oxides and trace elements of the studied Dokhan volcanics

Rock type Basalt Andesite Imperial porphyry Rhyodacite Rhyolite Ignimberite

Major oxides (wt.%)

S. No. M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13

SiO2 50.68 51.27 59.08 68.04 69.77 68.14 69.75 70.97 74.8 75.87 77.29 70.38 76.36

TiO2 2.45 0.88 1.3 0.83 0.52 0.46 0.34 0.14 0.18 0.15 0.13 0.48 0.17

Al2O3 15.78 16.91 16.17 15.56 15.08 15.4 15.09 15.92 13.23 12.61 10 15 11.78

Fe2O3a 14.41 9.28 7.45 4.49 3.69 2.85 2.38 2.52 1.75 2.04 2.48 3.83 1.97

MnO 0.22 0.16 0.13 0.07 0.17 0.1 0.05 0.02 0.02 0.02 0.06 0.05 0.05

MgO 2.99 5.15 2.59 0.22 0.04 1.94 0.43 1.2 0.06 0.08 0.22 0.12 0.98

CaO 6.67 10.23 3.9 0.69 0.29 1.19 1.19 0.18 1.11 0.55 2 0.34 1.1

Na2O 3.59 3.47 3.54 5.65 6.56 5.29 4.31 0.98 7.31 4.32 1.04 6.04 4.07

K2O 1.68 0.9 3.44 3.66 2.97 2.74 5.4 5.59 0.29 3.41 5.53 3.13 2.61

P2O5 0.67 0.29 0.49 0.16 0.13 0.15 0.07 0.02 0.02 0.02 0.02 0.1 0.03

LOI 0.6 0.5 1.5 0.2 0.4 1.5 0.4 2.2 1.1 0.7 0.9 0.2 0.7

Total 99.78 99.9 99.63 99.63 99.69 99.81 99.47 99.78 99.93 99.81 99.76 99.74 99.87

DI 48.57 38.55 65.87 89.78 93.7 84.23 90.29 85.18 94.68 94.03 89.32 92.72 89.6

Trace elements (ppm)

Ba 758.6 519.3 1,382 1,519.5 1,189.1 759 1,519.1 349.2 63.8 687.3 544.5 814.2 370.8

Cr 205.3 328.4 246.3 390 451.6 287.4 431.1 246.3 431.1 314.7 595.3 478.9 390

Be 2 1 3 4 12 2 4 11 3 6 4 3 5

Co 30.4 27.1 12.1 2.6 3.1 7.4 2.5 1.4 1.1 1.4 2.4 2.1 2.9

Cs 0.7 1.7 3.6 1.9 0.7 0.6 1.1 7.3 0.4 1 2.9 1.5 2.8

Ga 21.6 19.4 20.2 21.9 23.6 16.6 19.8 28.3 27.7 23.8 14.6 25.5 17.5

Hf 7.2 1.6 6.4 11.7 14.5 5.5 8.4 10.4 16.5 9.9 9.1 15.3 9.3

Nb 13 2.4 9.9 16.6 20.7 9.4 13.5 22.7 23.7 17.8 17.2 19.9 16.3

Rb 15.5 13.8 87.3 46.9 32.9 50.1 85.8 179.1 6.1 50.4 87 45.2 66.2

Sn 2 <1 3 3 4 2 1 7 4 4 3 4 4

Sr 489.8 356.8 908.1 256.5 121.8 285.3 258.6 33.2 52 54.9 110.2 176.8 111.5

Ta 0.8 0.1 0.6 1.1 1.5 0.6 1.3 1.6 1.4 1.1 0.9 1.4 1

Th 2.9 1.5 6.2 6.4 7.8 7.9 17.4 13.4 11.6 10.8 9.1 8.3 10.2

U 0.8 0.6 2.2 1.7 1.9 2.8 7 1.8 3.2 2.1 2.5 2.6 4.4

V 235 271 134 17 8 28 12 <5 6 5 10 21 5

W 0.5 0.5 0.7 1.5 8.2 2.9 0.9 1.3 1 1.2 0.9 3.3 1.3

Zr 263.2 54.3 254.9 423.1 578.3 187 294.9 277.9 554.7 262 243.3 580 262.6

Y 49.1 17.5 25.9 53.4 58.3 25.9 20.5 85.9 112.8 57.5 77 66.6 67.1

Mo 10.9 17.7 6.4 13.4 16.8 7 15.9 9.5 13.4 8.2 13.4 10.9 10.4

Cu 16.9 13.3 19.5 6 6.4 10.5 4.7 2.7 5.6 4.6 5.4 3.5 4.8

Pb 2.2 2.4 3.5 3 10 2.4 20.2 1.5 3 4.1 4 13.9 3.4

Zn 104 41 69 23 23 30 41 40 4 9 15 15 91

Ni 12.9 14.9 7.3 7.6 8.3 7.8 10.8 4.8 9.1 7.8 10.7 8.2 7.2

As 1.6 2.6 4.9 20.3 119.9 1.4 1.8 1.4 1.7 1.1 2.5 89 7.7

Au 1.4 0.9 4.3 1.9 0.5 1.1 4.8 2.2 <0.5 1.7 1.8 1.1 0.9

Nb/Y 0.26 0.14 0.38 0.31 0.36 0.36 0.66 0.26 0.21 0.31 0.22 0.30 0.24

Zr/TiO2 107 62 196 510 1,112 407 867 1,985 3,082 1,747 1,872 1,208 1,545

Hf/Th 2.48 1.07 1.03 1.83 1.86 0.70 0.48 0.78 1.42 0.92 1 1.84 0.91

LOI loss of ignition, DI differentiation indexa Fe2O3 (as a total iron oxide)

Arab J Geosci

elements (high field strength elements (HFSE), e.g., Hf, Th,Nb, Ta, and Zr) are used to distinguish between differenttectonic environments. It is observed that all samples plot inthe volcanic arc basalt field (where the studied sampleshave Hf/Th<3) (Fig. 8).

The studied volcanics are plotted in a linear pattern onthe diagram of Sun and Nesbitt (1978) and Sun andMcDonough (1989) (Fig. 9a). This may suggest that theyresult from a continuity of magmatism with high TiO2

being the least fractionated andesite.On the AFM diagram (Petro et al. 1979), the studied

volcanics plot was formed in compressional environment(orogenic) in volcanic arc setting (Fig. 9b). Based on theinter-element ratios and fractionation vectors of Arth(1976), it is evident that the Dokhan volcanics are stronglyaffected by fractionation of plagioclase and clinopyroxene(Fig. 9c–e).

The relation between the SiO2 and Ba/Nb ratio after(Hubbard et al. 1987) shows a decrease of the Ba/Nb ratioas a function of differentiation in the studied Dokhanvolcanics. This indicates that the high Ba/Nb in the mostprimitive rocks is a characteristic feature inherited fromtheir source (Fig. 9f).

The relative concentrations of trace elements are shownin the form of a primitive mantle-normalized diagram(Fig. 8a–d) based on the normalization factors of Sun andMcDonough (1989). In general, all rocks show moderateconcentrations of most large ion lithophile elements (LILE)

and HFSE. The depletion of Sr and Ti of rhyolite,rhyodacite, ignimbrite, and imperial porphyry suggest thatthe extensive fractional crystallization of plagioclase,apatite, and Fe–Ti oxides occurred during evolution of themagma, while the less-evolved basalt and andesite volcanicsexhibit Nb-negative anomalies, which is a characteristicfeature of the subduction-related rocks or continental crust(Tarney and Weaver 1987) and may be related to ilmenitefractionation, which explains the negative anomaly of Ti(Green 1994).

Rare earth elements

Many studies have used REE data to interpret themagmatic origin and evolution of volcanic rocks.Harrman (1974) has shown that the study of the REE inrocks from ancient terrains is in particular useful, as theyare usually stable or only slightly affected by alterationand metamorphism.

The chondrite-normalized patterns after Haskin and Frey(1966) are shown in Fig. 8e–h. The REE diagrams forrhyolite, rhyodacite, ignimbrite, and imperial porphyryshow moderate total REE contents (162 to 392 ppm) withan average 232 ppm of rhyolite rocks and 259 ppm ofrhyodacite rocks, less fractionated patterns [(Ce/Yb)N=(1.24 to 10.93)], which are steeply sloping from La to Smand gently sloping from Gd to Yb (Gd/Yb)N=(0.58 to

Table 2 Chemical analysis of REE of the studied Dokhan volcanics

Rock type Basalt Andesite Imperial porphyry Rhyodacite Rhyolite Ignimberite

S. No. M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13

La 31 9.1 40.6 46.8 52.9 34.6 48.7 75.7 24.7 48.2 47.6 57.1 48.5

Ce 69.7 21 86.4 105.6 120.9 67.1 99.9 181.8 59.7 106.2 94.5 131.1 102.8

Pr 9.2 2.9 10.49 13.45 14.88 7.81 11.27 16.88 7.34 12.4 12.09 15.9 12.1

Nd 40.1 13.2 41.5 54 58.6 29.5 41.3 58.7 29.2 45.1 45.2 61.9 44.5

Sm 9.1 3.3 7.7 11.2 12 5.7 7 11.1 7 9.3 10 12.7 9.8

Eu 2.53 1.06 2.09 3.08 2.4 1.49 1.27 0.46 0.97 0.58 0.85 2.31 0.73

Gd 8.59 3.19 5.27 9.42 9.63 4.29 4.25 8.19 9.25 7.17 9.68 10.53 8.96

Tb 1.44 0.5 0.88 1.7 1.74 0.74 0.64 1.82 2.18 1.38 1.9 1.9 1.76

Dy 8.39 2.78 4.33 9.24 9.63 3.78 3.04 12.06 15.37 8.22 10.99 11.2 10.17

Ho 1.71 0.59 0.85 1.87 1.94 0.85 0.61 2.84 3.71 1.97 2.46 2.26 2.17

Er 4.75 1.68 2.41 5.25 5.84 2.54 1.89 9.31 11.84 6.43 7.59 6.56 6.66

Tm 0.73 0.26 0.37 0.84 0.88 0.42 0.33 1.61 1.93 1.09 1.25 1.07 1.1

Yb 4.47 1.54 2.39 4.97 5.49 2.64 2.16 10.21 11.38 6.97 7.37 6.34 6.88

Lu 0.66 0.23 0.33 0.72 0.81 0.43 0.34 1.61 1.73 1.07 1.11 0.97 0.98

∑REE 192.4 61.3 205.6 268.1 297.6 161.9 222.7 392.3 186.3 256.1 252.6 321.8 257.1

(Ce/Yb)N 3.69 3.22 8.54 5.02 5.2 6.01 10.93 4.21 1.24 3.6 3.03 4.89 3.53

(La/Sm)N 1.97 1.59 3.05 2.42 2.55 3.51 4.02 3.94 2.04 3 2.75 2.6 2.86

(Gd/Yb)N 1.4 1.51 1.6 1.38 1.27 1.18 1.43 0.58 0.59 0.75 0.95 1.21 0.95

Eu/Eu* 0.88 1 1 0.92 0.68 0.92 0.71 0.15 0.37 0.22 0.26 0.47 0.24

Arab J Geosci

1.43). However, basalt is depleted in the total REE content(61 to 192 ppm) and relatively steep, (Ce/Yb)N=(3.2 to8.5). The andesite rocks have relatively moderate REEcontents (206 ppm).

The fractionation of the LREE with an average ofrhyodacite [(La/Sm)n=3.82] is higher than the othervarieties. The HREE with an average of basalts arerelatively less fractionated [(Gd/Yb)N=1.46] relatively

Fig. 5 Variation diagramsbetween some major oxides anddifferentiation index DI (Q+BAb+Or) after Thoronton andTuttle (1960). Symbols as emptycircles basalt, filled circlesandesite, inverted trianglesimperial porphyry, multiplicationsymbols rhyodacite, plus signsrhyolite, and filled trianglesignimbrite

Arab J Geosci

similar to an average of imperial porphyry (1.33), ignimbrite(1.08), rhyodacite (1.06), and rhyolite (0.76).

The rhyolite displays larger negative Eu anomaly (Eu*/Eu=0.28) than those of other types. The basalt (Eu/Eu*=0.94) and andesite (Eu/Eu*=1) are characterized by no Euanomalies and may require few as no residual plagioclase in

the source. However, the imperial porphyry, ignimbrite, andrhyodacite rocks have small −ve Eu anomalies except fortwo samples (M4 and M6), which show large –ve Euanomalies (Eu/Eu*=0.92).

The large negative Eu anomalies in the rhyolite rockssuggest that plagioclase was an early major fractionating

Fig. 6 Variation diagramsbetween the trace elements andB (basic index) after Debonand Le Fort (1983). Symbols asseen in Fig. 5

Arab J Geosci

Fig. 7 a Zr/TiO2–Nb/Ydiagrams (after Winchester andFloyd 1977); b alkali–silicadiagram (after Irvine andBaragar 1971; MacDonald andKatsura 1964); c (Y+Zr)−(TiO2*100)−Cr diagram (Daviset al. 1979); d Nb–SiO2 diagram(Pearce and Gale 1977); e K2O–TiO2–P2O5 (Pearce et al. 1975);f–h ternary diagrams (afterWood 1980), A—N-typeMORB, B—E-type MORB andwithin plate tholeiites, C—calc–alkaline eithin plate basalts, andD—volcanics arc basalts.Symbols as seen in Fig. 5

Arab J Geosci

phase and indicate formation under condition of relativelylow temperature and pressure and/or low water content inthe melt (Gill 1981). Also, higher oxidation conditions inmore-evolved melts could also cause negative Eu anomalies(Green and Roberts 1998).

Discussion and conclusions

The present study revealed the following characteristics:

1. Dokhan volcanics at Gabal Monqul area consist of athick succession stratified lava flows of basalt,andesite, imperial porphyry, dacite, rhyodacite, rhyo-lite, ignimbrite, and tuffs. These lavas are interbandedwith their pyroclastics in some places includingbanded ash flow tuffs, lithic tuffs, crystal lapilli tuffs,and agglomerates. They are overlying the oldergranitoid rocks and were intruded by younger granit-oid ones with sharp contacts.

2. Field relations indicate that they are unconformablyfollowed by thick sequences of Hammamat sedimentsformed of conglomerate, sandstone, greywacke, andsiltstone along normal fault strikes 90° and dip 64° tothe south at wadi Monqul. This is consistent withAkaad (1996) who stated that the Dokhan volcanics arepredate the Hammamat sediments, while the Dokhanvolcanics are divided into lower and upper volcanicrock sequences separated by the classic Hammamatsediments (El-Gaby et al. 1989; Takla et al. 1991). Onthe other hand, Beyth et al. (1994), and Moghazi et al.(1998) stated that the field and geochronological dataindicate that the Dokhan volcanics and Hammamatsediments are broadly penecontemporaneous where Rb/Sr ages of 610–560 and 600–585 Ma have beendetermined for the Dokhan volcanics and Hammamatsediments.

3. Petrographically, the studied Dokhan volcanics haverevealed (a) the decrease in the anorthite content of

Fig. 8 Petrogenesis diagrams ofthe studied Dikhan volcanics: a(Al2O3/TiO2)–TiO2 diagram(after Sun and Nesbitt 1978); bAFM diagram (after Irvine andBaragar 1971), compressionaland tensional trends (after Petroet al. 1979); c–e Ba versus Rb,Ba versus Sr, and Cr versus Ni(after Arth 1976), and f Ba/Nb-SiO2 diagram after Hubbard etal. (1987) for the studiedDokhan Symbols as seen inFig. 5

Arab J Geosci

Fig. 9 a–d Normalized multi-elements patterns for the studiedDokhan volcanics using theprimitive mantle values afterSun and McDonough (1989).e–h Normalized rare earthelements patterns for the studiedDokhan volcanics using thechondritic values after Haskinand Frey (1966)

Arab J Geosci

plagioclase as passing from basalt (labradorite, An55–60),through andesite (An25–40), to rhyolite (An10–25,oligoclase). (b) Amphiboles have mainly hornblendecomposition. (c) Presence of pyroxene illustrates thesubalkaline nature for the host volcanics.

4. They are typical calc–alkaline, as mentioned by Garcia(1978), the identification of a thick sequence of calc–alkaline record strongly suggesting the presence of aformer volcanic arc. Accordingly, the calc –alkalinetrend of the studied Dokhan volcanics may indicatetheir evolution in volcanic arc environment. The calc–alkaline magmas are generated by many models; thesemodels include:

(a) Fractional crystallization of tholeiitic magma.(b) Partial melting of hydrous peridotite.(c) Melting of subducted oceanic crust.(d) Partial melting of the lower crust caused by

mantle diapirism arising from the subductionzone (Condie 1976).

Model (a) is the most compatible with the origin of thestudied volcanics.5. They show geochemical features of rocks developed

within volcanic arc tectonic setting. This is consistentwith Gabal El Kharaza (Abdel Rahman 1996), SouthSafaga (Moghazi 2003), and Gabal El Urf (El-Gameel2010) who stated that the Dokhan volcanics of theseareas are related to continental and volcanic arc settingwhere their pyroclastics are related to continental arcfield. Eliwa et al. (2006) considered that Dokhanvolcanics appears to have formed in the transition stagebetween subduction tectonics and post-collision tecton-ics induced mainly by the subducted ridge heat sourcethat previously existed in oceanic environment. On theother hand, Ressetar and Monard (1983) quoted byStern and Gottfried (1986) considered the mafic rocksof the Dokhan type overlap between arc and intra-cratonic magma types, while Heikal and Ahmed (1984)and Ragab (1987) considered the Dokhan volcanics torepresent immature island arcs.

6. The Dokhan volcanics are enriched in LILE relative to theHFSE. Also, the low pressure fractionation is indicated byincrease of incompatible elements (Nb, U, Th, Y, Ta, andHf) as passing from basalt through andesite to rhyodaciteand rhyolite, whereas this is consistent with Singh et al.(2006) who stated that the acidic volcanic rocks arestrongly enriched in highly incompatible trace elements.Ta and Nb are present in anomalously low concen-trations in the studied volcanics, indicating that theiremplacement was in subduction-related setting. Thedepletion of Sr and Ti of rhyolite, rhyodacite, ignimbrite,and imperial porphyry suggest that the extensivefractional crystallization of plagioclase, apatite, and Fe–

Ti oxides occurred during evolution of the magma. Thisis characteristic of calc–alkaline tectonic setting.

7. The observed enrichment in the REE of the studiedvolcanics is mainly due to increasing LREE abundances.The studied volcanics have steep LREE and nearly flatHREE. The felsic volcanics are characterized bymoderatetotal REE contents (162 to 392 ppm), less fractionatedpatterns (LREE/HREE ratio {(Ce/Yb)N=1.24 to 10.93}.The less-evolved basaltic rocks have the lowest REEcontents with an average (61 to 192 ppm) and LREE/HREE ratio (Ce/Yb)N=3.2 to 3.7). The fractionation ofthe LREE of rhyodacite [(La/Sm)n=3.82] is higher thanthe other varieties. The HREE of basalts [(Gd/Yb)N=1.46] are relatively less fractionated similar to othervarieties. The felsic volcanics display a range of –ve Euanomalies, while the mafic volcanics have no Euanomalies. The large negative Eu anomalies in therhyolite rocks (Eu/Eu*=0.28) than those of othervarieties suggest that plagioclase was an early majorfractionating phase and indicate formation undercondition of relatively low temperature and pressureand/or low water content in the melt (Gill 1981).Also, higher oxidation conditions in more-evolvedmelts could also cause negative Eu anomalies (Greenand Roberts 1998).

8. The studied Dokhan volcanic rocks show normalfractional crystallization (AFC) of coherent source andthe dominant role of clinopyroxene and plagioclaseremoval in controlling the behavior of these elements.

9. The eruption of the high-K calc–alkaline post-collisionalDokhan volcanics defines a tectonomagmatic transitionbetween the older calc–alkaline arc-related magmatismand the subsequent alkaline anorogenic magmatism in thenorthern part of the Arabian–Nubian Shield.

References

Abdel Gawad AE (2008) Geology and Radioelements distribution inGabal Monqul area, North Eastern Desert, Egypt. Unpublished M.Sc. Thesis, Faculty of science (Damietta), Mansoura Univ., 161

Abdel Rahman AM (1996) Pan-African volcanism: petrology andgeochemistry of the Dokhan volcanic suite in the northernNubian shield. Geol Mag 133/1:17–31

Abdel-Meguid AA (1986) Geologic and radiometric studies ofuraniferous granites in Um Ara-Um Shilman area South EasternDesert, Egypt. Ph.D. Thesis, Suez Canal Univ., Ismailiya, Egyptp 233

Abdel-Meguid AA (1992) Late Proterozoic Pan African tectonicevolution of the Egyptian part of the Arabian-Nubian Shield.Middle East Research Center (M. E. R. C.) Ain Shams Univ.,Cairo, Egypt. Earth Sc Ser 6:13–28

Abdel-Meguid AA (1998) Structural analysis of ElNasb-ElAzrak areaand its implication on the tectonic evolution of the CentralEastern Desert. Egypt J Geol 42/1:155–181

Arab J Geosci

Abdel-Magid EA, Khyamy AA, Mostafa MO, Mohamed HA, AbdelGawad GM, Ibrahim GA (1998) Geology of Gabal Monqul andGabal Dara area, North Eastern Desert, Egypt, Egyptian Mineral.Resource Authority (EMRA), Internal Report 91

Akaad MK (1996) Rock succession of the basement: an autobiographyand assessment. Geol Surv Egypt, Spec 71:1–87

Arth JG (1976) Behaviour of trace elements, during magmaticprocesses a summary of theoretical models and their application.J Res US Geol Surv 4:41–72

Basta EZ, Kotb H, Awadallah MF (1980) Petrochemical andgeochemical characteristics of the Dokhan Formation at the typelocality, Gabal Dokhan, Eastern Desert, Egypt. Bull. Inst.Applied Geol., King Abdel Aziz Univ., Jeddah, 4/3, 121–140

Beyth M, Stern RJ, Altherr R, Kroner A (1994) The Late PrecambrianTimna igneous complex, southern occupied Palestine: evidencefor comagmatic-type sanukitiod monzodiorite and alkalinegranite magma. Lithos 31:103–124

Botros NS (1995) Genesis of gold mineralization in the North EasternDesert. Egypt Ann Geol Surv Egypt 25:381–409

Botros NS, Wetait MA (1997) A possible porphyry coppermineralization in South Monqul, Eastern Desert, Egypt. EgyptJ Geol 41/1:175–196

Breitkreuz C, Eliwa H, Khalaf I, El Gameel K, Sergeev S, Larionov A(2010) Neoproterozoic SHRIMP U–Pb zircon ages of DokhanVolcanics in the northern part of the Eastern Desert, Egypt. 33rdInternational Geological Congress Oslo 2008 August 6–14th.Abstract

Cas RAF, Wright JV (1987) Volcanic successions, modern andancient. Allen and Unwin, London, p 528

Condie C (1976) Trace element geochemistry of Archean greenstonebelts. Earth-Sci Rev 12:393–417

Davis JF, Grant RWE, Whitehead RES (1979) Immobile traceelements and Archean volcanic stratigraphy in the TimminsMining area. Ontario Can J Earth Sci 16:305–311

Debon F, Le Fort P (1983) Chemical-mineralogical classification ofplutonic rocks and associations—example from southern Asiabelts. In: Xu Keqin and Tu Guangchi (eds) Geology of granitesand their metallogenetic relations. Sc. Press, Beijing, 293–311(Equally in Chinese)

El Shazly EM, Dixon TH, Engel AEJ, Abdel-Meguid AA, Stern RJ(1980) Late Precambrian crustal evolution of Afro-Arabia fromoceanic arc to craton. Egypt J Geol 24/1–2:101–121

El-Bayoumi RM, Abu Zeid HT, Khalaf EA (1997) UpperProterozoic calc–alkaline and tholeiitic volcanic and theirassociates in the Gulf of Suez region. Egypt Ann Geol SurvEgypt 20:125–142

El-Gaby S, Khudier AA, El Taky M (1989) The Dokhan volcanics ofwadi Queh area, Central Eastern Desert, Egypt. 1st Cnf. OnGeochemistry, Alexandria, Egypt, 42–62

El-Gaby S, Khudeir AA, Abdel Tawab M, Atalla RF (1991) Themetamorphosed volcanosedimentary succession of Wadi Kid,Southeastern Sinai, Egypt. Ann Geol Surv Egypt 17:19–35

El-Gameel KG (2010) Geology of the area around Gabal El Urf, withspecial emphasis on the Late Neoproterozoic volcanosedimentarysuccession, north Eastern Desert, Egypt. Unpublished Ph.D.Thesis, Faculty of science, Minufiya Univ., Egypt, p 146

El-Sheshtawi YA, El Tokhi MM, Ahmed AM (1995) Petrogenisis of theDokhan volcanics of wadi Dib and wadi Abu Had, Esh El Mellaha,North Eastern Desert. Egypt Ann Geol Surv Egypt 25:163–184

Eliwa HA, Kimura J-I, Itaya T (2006) Late Neoproterozoic DokhanVolcanics, North Eastern Desert, Egypt: geochemistry andpetrogenesis. Precambrian Res 151:31–52

Eliwa H, Breitkreuz C, Khalaf I, El Gameel K (2010) Depositional stylesof Early Ediacaran terrestrial volcanosedimentary succession inGebel El Urf area, North Eastern Desert, Egypt. J Afr Earth Sci(in press). doi:10.1016/j.jafrearsci.2009.11.002

Francis M (1972) Geology of the basement complex in the NorthEastern Desert between Latitudes 27 30 and 28 00 N. Ann GeolSurv Egypt 2:161–180

Garcia MO (1978) Criteria for the identification of ancient volcanicareas. Earth-Sci Rev 14:147–165

Gill JB (1981) Orogenic andesites and plate tectonics. Springer, BerlinGreen TH (1994) Experimental studies of trace element partitioning

applicable to igneous petrogenesis at Sedona 16 years. LaterChem Geol 117:1–36

Green T, Roberts D (1998) The Holonda porphyrite, NorwegianCaledonides: geochemistry and tectonic setting of Early–Mid.Ordovician shoshonitic volcanism. J Geol, Soc, London 155:131–142

Grothaus B, Eppler D, Ehrlich R (1979) Depositional environmentand structural implications of the Hammamat formation. EgyptAnn Geol Surv 9:564–590

Haase CS, Chandam J, Feinn D, Ortoleva P (1980) Oscillatory zoningin plagioclase feldspar. Science 209:272–274

Harrman AG (1974) Yttrium and lanthanides. In: Wedephol KH (ed)Handbook of geochemistry. Springer, New York, pp 39–57

Haskin MA, Frey FA (1966) Dispersed and not-so-rare earths. Science152:299–314

Heikal MA, Ahmed AM (1984) Late Precambrian volcanism in GabalAbu Had, Eastern Desert, Egypt: evidence for an island-arcenvironment. Acta Miner Petr Szeged 26(2):221–233

Hubbard HB, Wood LF, Rogers JJ (1987) Possible hydration anomalyin the upper mantle prior to Red Sea rifting: evidence frompetrologic modelling of the W. Natash alkali basalt sequence ofeastern Egypt. Geol Soc Amer Bull 92–98

Irvine TN, Baragar WRA (1971) A guide to the chemicalclassification of the common volcanic rocks. Can J Earth Sci8:523–548

Khalaf IM, Shalaby IM, Razek KA (2000) Geology of the area aroundGabal el-Kharaza, Northern Eastern Desert, Egypt with specialemphasis on the Dokhan volcanics. 5th International Conferenceon the Geology of the Arabic world, Cairo Univ., Egypt

Kröner A, Greiling R, Reischamann T, Hussein IRM, Stern RJ, DurrS, Kruger I, Zimmer M (1987) Pan African crustal evolution inthe Nubian segment of northeast Africa. In: Kröner A (ed)Proterozoic lithosphere evolution, American Geophysical UnionGeodynamics Series, Washington 17:235–257

MacDonald GA, Katsura T (1964) Chemical composition of Hawaiianlavas. J Petrology 5:82–133

Moghazi AM (2003) Geochemistry and petrogenesis of a high-Kcalc–alkaline Dokhan volcanic suite, South Safaga area, Egypt:the role of Late Neoproterozoic crustal extension. PrecambrianRes 423:161–178

Moghazi AM, Andersen T, Oweiss GA, El-Bouseily AM (1998)Geochemical and Sr–Nd–Pb isotopic data bearing on the originof Pan-African granitoids in the Kid area, southeast Sinai, Egypt.J Geol Soc, London 155:697–710

Mohamed FH, Moghazi AM, Hassanen MA (2000) Geochemistry,petrogenesis and tectonic setting of late Neoproterozoic Dokhan-type volcanic rocks in the Fatira area, eastern Egypt. Int J EarthSci 88:764–777

Pearce JA, Gale GH (1977) Identification of ore-deposition environmentfrom trace element geochemistry of associated igneous host rocks.Geol Soc Spec Publ 7:14–24

Pearce JA, Gorman BE, Birkett TC (1975) The TiO2–K2O–P2O5diagram: a method of discriminating between oceanic and non-oceanic basalts. Earth Planet Sci Lett 24:419–426

Petro WL, Vogel TA, Wilband JT (1979) Major element chemistry ofplutonic rock suites from compressional and extensional plate-boundaries. Chem Geol 26:217–235

Ragab AI (1987) On the petrogenesis of the Dokhan volcanics of theNorthern Eastern Desert of Egypt. MERC Ain Shams Univ,Egypt. Earth Sci Ser 1:151–158

Arab J Geosci

Ressetar R, Monard JR (1983) Chemical composition and tectonicsetting of the Dokhan volcanic formation, Eastern Desert, Egypt.J Afr Earth Sci 1:103–112

Sims RJ, James HL (1985) Banded iron-formations of Late Proterozoicage in the Central Eastern Desert, Egypt: Geology and tectonicsetting. Econ Geol Bull 79:1777–1784

Singh AK, Singh RKB, Vallinayagan G (2006) Anorogenic acidvolcanic rocks in the Kundal area of the Malani igneous suite,Northwestern India: geochemical and petrogenetic studies. JAsian Earth Sci 27:1–14

Stern RJ (1979) Late Precambrian crustal environments as reconstructedfrom relict igneous minerals, Central Eastern Desert of Egypt. AnnGeol Surv Egypt 9:9–13

Stern RJ, Gottfried D (1986) Petrogenesis of Late Precambrian (575–600 Ma) bimodal suite in northeast Africa. Contrib MineralPetrol 92:492–501

Stern RJ, Gottfried D, Hedge CE (1984) Late Precambrian rifting andcrustal evolution in the North Eastern Desert of Egypt. Geology12:168–172

Stoeser DB, Camp VE (1985) Pan-African micro plate accretion of theArabian Shield. Geol Soc Am Bull 96:817–826

Stopora K, Zimmermann J (2007) Final report —sedimentologicaland volcanological investigations in Gabal el-Urf, Gabal el-Kharaza, and Wadi Bali area, Eastern Desert, Egypt (KP III—unpublished)

Sturchio N, SultanM, Sylvester P, Batiza R, Hedge C, Abdel-Meguid AA(1983) Geology, age and origin of Meatiq Dome: implications forthe Precambrian stratigraphy and tectonic evolution of the Eastern

Desert of Egypt, Jeddah, Saudi Arabia, King Abdul Aziz Univ. FacSc Bull 6:127–143

Sun SS, McDonough WF (1989) Chemical and isotopic systematics ofoceanic basalts: implications for mantle composition and processes.In: Saunders AD, Norry MJ (eds) Magmatism in the ocean basins.Geol Soc London Spec Publ 42:313–345

Sun SS, Nesbitt RW (1978) Petrogenesis of the Archaean ultrabasicand basic volcanics: evidence from rare earth elements. ContribMinr Petrol 65:301–328

Takla MA, Basta FF, Abdel Tawab MM, Khalid AM (1991) ThePrecambrian rocks of Wadi Watir area, south eastern Sinai. AnnGeol Surv Egypt 17:37–52

Tarney J, Weaver BI (1987) Geochemistry of Scourian complex:Petrogenesis and tectonic model. In: Park PG, Tarney J (eds)Evolution of the Lewisian and Comparable terrains. Geol SocLondon, Spec Publ 27:45–56

Thoronton CP, Tuttle OF (1960) Chemistry of igneous rocks, part 1,differentiation index. Am J Sc 258/9:664–684

Wetait MA, Botros NS (1997) Barite mineralization in south UmMonqul area, North Eastern Desert, Egypt. J African Earth Sci 25(3):485–489

Winchester JA, Floyd PA (1977) Geochemical discrimination ofdifferent magma series and their differentiation products usingimmobile elements. Chem Geol 20:325–343

Wood DA (1980) The application of a Th–Hf–Ta diagram to problemof tectonomagmatic classification and to establishing the natureof crustal contamination of basaltic lavas of the British Tertiaryvolcanic province. Earth Planet Sci Lett 50:11–30

Arab J Geosci