Annals Geol. Surv. Egypt. V. XXIX (2007), pp 135-157

SOURCE AND TECTONIC SETTING OF SHARM EL-SHIEKH ALKALINE A-TYPE GRANITOIDS, SINAI, EGYPT El-Bialy, M. Z. and EI-Omla, M. M. Geology Department, Faculty of Science, Suez Canal University Ismailia, Egypt

ABSTRACT The Sharm El-Shiekh alkaline granite is a typical Late Pan-African A -type granitoid pluton in Sinai segment of the Arabian-Nubian Shield. Such granitoids represent in general the last major · magmatic activity, and in specific the termlnal granitic plutonism in Sinai massive. They are hypersolvous textured, ranging in composition from alkali feldspar perthitic granite to quartz alkali · feldspar syenite. The most striking compositional feature of the studied granites is their extreme enrichment in Kz(J and total alkalis that led to formation of normative acmite and sodium metasilicate, and consequently a strong alkaline and peralkaline nature. The present granitoids exhibit typical features of A -type granitoids, characterized by low CaO content (averaging 0. 71 wt.%), high FeO.jMgO ratios (9.28-115.5) and NKJA ratios (1.01-1.36), with exceptionaUy high concentrations

of the trace elements Y, Nb, Zr, , Zn and Ga and low Sr and Ba contents. K20 The use of different petrogenetic discrimination criJeria and diagrams reveal that they are anorogenic A-type granites, evolved in within-plate (rift-related) setting. However, the Yb/Nb ratio has given rise to a contrasting dual source material derivation and tectonic setting of these A-type granitoids. The studied samples are discriminated between granitoids derived from sources like those of oceanic-island basalts but emplaced in continental rifts or during intraplate magmatism (Anorogenic), and granitoids derived from continental crust or underplated crust through a cycle of · continent-continent collision or island-arc magmatism (Post-orogenic). INTRODUCTION Alkaline granite plutons occur without any recognizable alignment, all over the Arabian Shield with estimated combined area of about 5000 Km2 (Harris & Marriner, 1980). In Sinai, these granites seem to be more widespread than in any other part of the Arabian-Nubian . Shield, accounting for some 20% of all granites and covering more than 1000 Km2 (Bentor 1985). The worldwide distribution of A-type granites has been recognized more than 25 years ! ago (Loiselle and Wones 1979; White and Chappell 1983). The composition of A-type ~granites is diverse; they comprise syenogranite, peralkaline and alkali-feldspar granite and f syenite, rapakivi granite, monzogranite and F-rich topaz granite (e.g.; Whalen et al. 1987; Eby . 1992; Whalen et al. 1996). In the vast crustal provinces of Central Asia and the Arabian-Nubian Shield three rock types are dominant among the A-type granites (Bentor 1985; Litvinovsky et al. 2002): metaluminous syenogranite (e.g. G. Firani; El-Masry 1998), . peralkaline granite, (e.g. G. Gharib; Abdel-Rahman & Martin 1990) ) and alkali-feldspar · (mostly perthitic) granite (e.g. the investigated A-type granite). The intrusion of anorogenic (A-type) granitic magma into the upper crust commonly, follows a cycle of compressive tectonic activity and orogenic magmatism (Boullier et al. El-Bialy, M.Z. & El Omla, M.M.

1986; Liegeois and Black 1987). Anorogenic alkaline magmas are believed to be emplaced into the Arabian-Nubian Shield crust between the waning stages of the Pan-African orogeny and the opening of the Red Sea 23 Ma ago (l-Iashad 1980; Harris 1982; Vail 1985; El-Ramly and Hussein 1985). They were identified in Egypt by Hussein et al. (1982) as ; 03-granites ; intraplate, anorogenic granites, related to hot spots and incipient rifting, El Gaby et al. (1990) as Phanerozoic alkaline A-type granites and Ragab & El Alfy (1996) as late collision granites. Further, In Sinai, Agron & Bentor (1981) and (Bentor 1985) grouped these alkaline granites as intrusive partner of late alkaline batholithic phase, the so called "Katharina Superprovince ". The A-type alkaline granites under consideration were reported in previous works and interpreted in various connotatjons (e.g. Ghoniem et al. 1991; Higazy et al. 1992 a& b; Khalaf ct al. 1994; Abdel Maksoud et al. 1994; Abu El-Leil et al. 1995 ; El-Nashar 2000). The published absolute ages of Sinai alkaline granites range from 600±24 to 560±10 Ma (Baubron et al. 1976; Stoeser & Elliott 1980; Halpern 1980; Bielski 1982). On the other side, the Mt. Gharib A-type granite (nmth Eastern Desert of Egypt) yielded a much younger ages of 476±2 Ma(Abdel-Rahman & Martin 1990) and 483 Ma (Hashad 1980). Recently, Katzir et al. (2006) gave a Rb-Sr isochron age of Kathelina pluton A-type granite, S. Sinai, of 593±16 Ma.

METHODOLOGY & ANALYTICAL TECHNIQUES

Mapping The construction of the geological map (Fig. 1) was based on a TM satellite image at scale of 1:100,000 (JPEG format) and a base topographic map (1:250,000), aided by the available former geologic maps (e.g. Abdel Maksoud et al. 1994 Khalaf et al. 1994 and Azzaz et al. 2000). Tracing, drawing, hashering and other processmgs were produced using CORELDRA W version 5.0 software.

Petrography A total of 27 representative thin sections were prepared and studied using a polarizing microscope. Modal analysis was carried out for some selected 18 thin sections, using a Swift automatic point counter and a mechanical stage. Reliable modal analysis was accomplished at 1300-1500 counts for each sample. Such reliable modal counts are achieved either by ·following the method recommended by Nisbett (1964) or by counting multiple thin sections of the same rock sample to reduce the modal variation (error) within each sample by about 50% and 15.38% respectively (Emerson 1964). Ternary plots on the QAP diagram were produced using Triplot version 4.01 software. Anorthite content (An%) of the plagioclase feldspar was determined optically by measuring the extinction angle of the twinned plagioclase using the appropriate charts and methods described in Shelly (1975) and Kerr (1977). The grain size of different grains or crystals was measured microscopically using an eyepiece micrometer.

136 Source & Tectonic Setting of Sharm El-Shiek.h Alkaline A-type Granitoids

21" ~. ;-· r r (A} Gulfof - ~· } Aqaba c.

rf47' Lf(;ENb 0 Phanerozoic sediments 0 1.25 2.5 3]5 5 0 Alkali granites Km 0 Younger granites t<~·:·:')Dokhan-~ vokarlies f mfl Meta volcaniC$ Fig. (1): Geological map of Sharm El-Shickh area showing the alkaline A-type granitoids and their country rocks outcrops (modified after Abdel Maksoud et al. 1994; Khalaf at al. 1994 and Azzaz et al. 2000). Geochemistry Based on the petrographic studies, 15 bulk rock samples were analyzed for major and some trace elements by the XRF analysis techniques in Suez Cement Company laboratories. The total volatiles were determined gravimetrically as weight percentage using the method of loss of ignition (LOI). Iron is reported initially as total ferric oxide (Fe20 3T), and is later resolved into FeO and Fe20 3 using the following iron oxidation ratio equation adopted by Le Maitre (1976):

FeO/ (FeO + Fe20 3) = 0.93 - 0.0042 (Si02)- 0.022 (Na20 + K20).

Data processing involved computation of several geochemical parameters, ratios, and calculations and construction of numerous different variation diagrams. Software used in data processing includes; Microsoft excel, NewPet, Corel Draw 5 & 9, Adobe PhotoShop 6, Triplot 3.1, chemcast 4.1 and others

137 EI·Bialy, M.Z. & El Omla, M.M.

GEOLOGIC SETTING The Shatm El-Shiekh alkaline granite is a typical Late Pan-African A-type granitoid pluton in the Arabian-Nubian Shield. A_long with numerous A-type granite plutons found northward, it was formed in the last stage of the Shield evolution, when a fundamental transition in tectonic style, from compressional to extensional, occutTed some 620-600 Ma ago (Gass 1982; Bentor 1985; Kroner et al. 1987; Stem 1994; Meert 2003). The investigated A-type granites crop out among the rocks of the southernmost tip of Sinai basement complex (Fig. 1). 2 The area encompassing them covers about 165 Km , and is bounded between longitudes 33°3' and 34° 24'E and latitudes 27° 47' and 28° ·s, N. Occurre111ces And Morphology Alkaline granites account for more than one-third of the exposed basement rocks in the mapped area. The outcrop area of Sharm El-Shiekh alkaline granite (Fig. 1) is bordered exclusively by younger granites, except in small sections where it touches the metavolcanic rocks at Wadi Esahi and Wadi Negebat. To the north and south, Sharm alkaline granite is intrusive into younger granites. The pluton was strongly affected by younger faulting. Its eastern and western parts are down-thrown by the border faults of the Suez and Aqaba Rifts respectively, and buried beneath the Rift Valleys sedimentary fill. A serjes of NNE-trending faults also cut through the exposed part of the Sharm alkaline granites and older basement. The high density of faults in this area is a consequence of the position near the southern tip of the Sinai Peninsula, where the NNE fault trend of the Aqaba rift system meets the northwest-trending Suez Rift System (Bentor & Eyal 1987). The alkaline granites are more resistant to erosion than the other types of younger granitoids, and they form many of the highest and steepest peaks of the mapped area. The dark brown landscape of Sharm Granite is steep and its skyline is strongly sen·ated. However, in most of its outcrops the rock is fairly wyathered.

Outcrop Characteristics In the field, Sharm alkaline granites vary considerably and can readily be distinguished into several varieties on bases of color, absolute granularity and mineralogy. Fresh rocks vary in color from light and dark grey to pink and red. On weathering, the color changes to brown or greenish-brown. They are granular, modulating between medium and coarse-grained verities. The dominant mineralogical type is alkali-feldspar granite, and less commonly quartz alkali-feldspar syenite. Mafic content is another matter of variability as these rocks vary from leucocratic with sparse inegular amphiboles and biotite to relatively mafic with sharp p1ismatic amphibole crystals. The contact between the varieties of Sharrn Granite is not evident, it is obvious that the different rock varieties grade into each other over a distance of several tens of meters; nowhere can one observe a sharp intrusive contact between them. Some exposures exhibit small mafic xenoliths and/or microgranular encl aves, showing various stages of assimilation. They measure several centimeters on the average, but some ol them attain a size of half a meter. Further, in many places Sharrn alkaline granite show! intense limonitic staining along two perpenili cular systems of tectonic joints.

138 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids

Country Rocks

1. Younger Granites Younger granites are volumetrically the major rock type exposed in the mapped area. The landscape of these granites is much Hghter than Shann alkaline granite; yellow to light brown. They often form moderately elevated mounts and hills with gentle slopes covered by their debris and that of their intruding dykes. Weathering features such as spheroidal weathering, exfoliation, and quadrangle detached blocks are not uncommon. Unlike Sharm alkaline granites, they are traversed by numerous dykes of different composition and directions. In hand specimen, they can range in composition from granites (Monzo- /syeno) to granodiorites. Mafics are represented only by biotite flakes, which in tum can discriminate them into leucocratic and biotite granitoids. Moreover, they vary in texture from granular to porphyritic.

2. Metavolcanics Metavolcanics are exposed basically as two mappable bodies at Wadi Esahi and Wadi Negebat, in addition to some preserved relics measuring few square meters found throughout the intrusive Shann alkaline pluton. These metavolcanics are occasionally interbedded with volcanogenic metasediments. The metavolcanics comprise lava flows units and interlayered pyroclastics of tuffs and coarse agglomerate. They are dominated by meta-andesites, meta­ basaltic andesites and meta-dolerites, but meta-rhyodacites and meta-rhyolites do occur (Azzaz et al. 2000).

3. Dokhan-type Volcanics They are a sequence of volcanic rocks covering a triangular area around the lower course of Wadi Khashabi and south of it , at the extreme southern part of the mapped area. These volcanics fmm a brown-violet landscape of moderate relief, culminating at Gabal Khashabi (326 m). The contact with the spatially neighboring younger granites can not be detected in the field, but in most places it is a tectonic one. .The volcanics are strongly sheared and jointed, and traversed by numerous dykes of variable composition. The volcanics are successive acidic to intetmediate lava flows of commonly porphyritic textures and different shades of grey, brown and pink colors. Vitrous quartz phenocrysts can be identified in the more acidic varities. Field Relations With Country Rocks Relics of metavolcanics occur throughout the Sharm alkaline granite. They range in size from xenoliths, a few centimetres across, to relics measuring tens or hundreds of metres., The contacts between Sharm alkaline granite and these metavolcanics are sharp, and numerous offshots, dikes and small inegular bodies of Sharm alkaline granite dissect these rocks. On the contrary, no field relationship do occur between Sharm alkaline granite and the Dokhan-type volcanics of Gabal Khashabi. The contact between Sharm granite and younger granites extends for a distance of several kilometers, much of which is well exposed. The contact,

139 El-Bialy, M.Z. & El Omla, M.M.

which is marked in the field by a strong colour contrast between the darker Sharm alkaline granite and the much lighter younger granites, is always sharp. At some contacts, a fine-grained, chilled margine of Sharm alkaline granite, 10-30cm wide, is well developed. Further, small apophyses of Sharm alkaline granite, 5-10 em in width, can be followed into younger granites for a distance of several tens of meters. Although, these rocks may be regarded generally as the youngest magmatic ones, they are infrequently dissected by later (Tertiary ?) basaltic dykes. PETROGRAPHY These rocks exhibit a granular, allotriomorphic coarse to medium-grained texture. They are commonly of hypersolvous texture, although subordinate separate plagioclase do occasionally exist. Microcline perthite is the dominant mineral constituent accounting sometimes for more than three quarters of the bulk composition. It is mostly subhedral and measures 3-7 mm, rarely exceeding 10 mm. The major perthite textures are viened and patchy, and rod, braided and flame textures being infrequent. These primary exsolution perthite fotms are sometimes interrupted by a secondary generation of replacement albite veinlets. The albitic fraction of some coarse perthites show polysynthetic twining. The microcline component of the perthite is always slightly to moderately altered, while the albitic fraction is generally fresh. Simple and grid twinings may sporadically coexist indicating incomplete inversion to triclinic symmetry from an orthoclase precursor (Smith 1974). Inclusions in perthite comprise other early-formed minerals such as amphiboles, biotite, plagioclase and opaques as well as early crystallized smaller perthite grains. Boundaries between adjacent perthite crystals are frequently marked by exsolved swapped tims of albite. Quartz varies in amount from 14.6% to 19.1% in quartz alkali feldspar syenites, and from 21.42% to 41.13% in alkali feldspar granites. It occurs essentially either as large interlocked grains, up to 5 mm, with sutured mutual boundaries or as smaller interstitial grains corroding and replacing perthites and mafics. Quartz may enclose tiny inclusions of the former minerals, along with opaques. This quartz commonly shows undulatory extinction and sometimes features deformation lamellae and incipient granulation. Further, quartz may occur in graphic intergrowths within some perthite crystals. Plagioclase if present, occurs as independent subhedarl crystals, rarely exceeding 1 mm, and as resorbed and myrmikitized inclusions in perthites. Independent

plagioclase was found to be an oligoclase (An 13_18). The investigated granitoids are quite variable in their ferromagnesian minerals content and species. Some are almost leucocratic, while others contain higher proportions of mafics (7 .32% ). Amphiboles are the dominant ferromagnesians, despite few rocks contain only biotite. Further, amphiboles may exist exclusively or coexist with subordinate biotite. Amphiboles are normally hornblende, but exceptional samples were found to contain only riebekite. Amphibole crystals are subhedral , measuting 2-6 mm and tend to assemble in cumulophyric aggregates together with Fe-Ti opaques Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type granitoids altered and replaced by opaques. Biotite, occurs as sma11 resorbed and corroded flakes that are occasinally partly chloritized and/or decomposed into opaques. Accessory minerals are Fe-Ti

140 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids opaques and relatively frequent zircon, while apatite is very rare.

MODAL COMPOSITION The modal compositions of 18 samples of the investigated granitoids are listed (Table 1), and their representative modal plots are shown in figure (2-A & -B) on the QAP classification diagram (Streckeisen 1976). On this diagram, it is obvious that nearly all of the samples are classified principally as alkali feldspar granites and much less as quartz alkali feldspar syenites. Syenogranite composition is represented by one sample. Use of the discriminating tectonic and genetic boundaries adopted by Lameyre and Bowden (1982) and Maniar and Piccoli (1989) on the QAP diagram (Fig. 2-A & -B), revealed that these granitoids are rift-related A-type granitoids. Table (1 ): The Modal analysis (volume%) of some A-type granites from Sharm El- Sheikh area.

Sample no. Quartz -Perthite Plagioclase Amphiboles Biotite Opaques Zirc~m Alkali feldspar granite A4 21.42 69.81 4.65 1.63 1.95 0.37 0.22 A7 32.29 62.22 0.99 3.72 0.6 0.07 A9 37.06 49.06 6.13 7.32 0.2 . 0.12 A to 29.24 63.44 4.28 1.7 0.21 0.96 0.14 Q4 41.13 56.19 0.8 0.53 1.2 0.06 Q5 30.2 59.73 6.66 2.6 0.8 Ql3 34.93 62.93 0.18 0.49 1.37 0.06 Ml 38.56 56.33 2 2.46 0.34 M5 24.81 70.12 4.37 0.56 0.12 M7 25.49 70.51 1.15 1.96 0.35 0.54 N 29.1 63.64 3. 1 1 2.66 0.52 0.69 0.14 M9 26.36 67.15 5.06 1.02 .12 .28 M3 26.52 64.28 3.4 5.24 0.52 0.14

Quartz alkali feldspar sye11ite

A6 15.6 79.87 .J.., ."'3J 0.4 0.4 0.33 M2 14.6 78.86 0.66 4.86 0.6 0.4 A13 19.1 73.17 3.6 3.21 0.28 0.52 0. 12 MJI 18.79 72.12 6.63 2.21 0.25 Syenogranite Al 28.1 55.15 11.1 2.05 0.5 0.9 0.2

141 El-Bialy, M.Z. & El Omla, M.M.

Q Q

ll(Xj ~ PoSI·l'lf'Qgtnk: !fi'Mitoids CCG "'· C.ontim•ntlll collision amr1imids OP '"' Occ1Ulic plagio~:'11Jnit~ CI\G "' Continental an:: granhf~kl~ lAG .,, bland arc: granitt•ids RR(.1 .. RifHclikd granitoids CEUG -.. ConriM'IKal cpirogcnic UJlliflP"anitoids

(A) (B) C AC:

Fig. (2): Modal composition plots of some Sharm alkaline granitoid samples on the QAP diagram of Streckeisen ( 1976): (A) Discrimination boundaries of A-, 1- and S-type granites are adapted by Lameyre and Bowden (1982); (B) Zones of tectonic environments are after Maniar and Piccoli (1989). GEOCHEMISTRY The whole-rock major composition of the selected analyzed granitoids, are listed in Table (2). The average compositions of there major elements are listed and compared with those of comparable Egyptian and world granites (Table 3). In an overall comparison with the average major elements composition of the different granites cited in Table (3), the most striking features of the studied granites are their extreme enrichment in total alkalis in general and

K20 in particular and on the other hand, their comparably lower Si02 average and contents. Petrocbemical Classification Thtal alkalis-silica (TAS) diagrams are some of the most commonly used schemes m chemical classification and nomenclature of igneous rocks. On Middlemost (1985) TAS classification diagram for felsic plutonic rocks, most of the studied granitoids plot in the field of alkali feldspar granite (Fig. 3-A), while few samples are shifted away in no-field area due to their enrichment in total alkalis. Similarly, plots of the samples on Wilson (1989) adapted T AS classification diagram of plutonic rocks, reveals that the majm;ty of the samples are classified as alkali granites and more less as syenites (Fig. 3-B), Therefore, both TAS diagrams designate exactly the studied samples their proper names. Normative Composition Table (2) lists the CIPW norm values for the studied granitoids. They were calculated using both Newpet and Chemcast 4.1 computer programs to insure accuracy of the results. An apparent non-con·espondence does exist between the norm and the mode. Normative quartz values are fairly different from modal values for all samples, being either significantly higher or lower. The same is true regarding normative sum of albite and orthoclase versus modal perthites. No normative anorthite occurs in all samples. Ca is being allocated to apatite and wollastonite. Rationally, the modal OH-bearing ferromagnesian minerals, hornblende and

142 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids

biotite, are offset by acmite, hypersthene and diopside or wollastonite. The presence of normative quartz and hypersthene in all samples indicates their silica-oversaturation. Further the absence of normative corundum and formation of normative acmite and sodium metasilicates indicate their strong alkaline and peralkaline nature. Table (2): Chemical composition of granites from Sharm El -Shiekh area

Sample A4 A6 A7 A9 AlO Qll Q4 Ml QS N All MH M3 M7 M9 Avenge Major tlttllfllts (Wl %) Si01 70.66 70.23 72.03 7023 69.69 73.02 70.69 71.38 72.94 71.21 75.43 7S 75.3 74.8 75.9 72.6 TiOz 0.38 0.40 0.33 0.39 0.43 0.26 0.38 0.42 0.24 0.36 0.0) OAI 0.2 0.22 0.14 0.35 AhOJ !380 12.86 11.94 11.68 ll.87 1248 12.64 11.48 12.80 12.39 11.)8 10.8 10.9 11.3 IIJ 12 F~O; 0.70 1.40 1.31 l.29 179 0.88 1.01 1.92 0.51 1.20 1.27 1.39 1.03 1.32 1.03 1.2 FtO l.lO 2 19 1.98 2.05 2.84 Ln 1.57 2.84 0.75 1.85 0.39 0.92 0.8 0.6 158 1.52 MuO 0.05 0.05 0.05 0.00 0.06 0.05 0.01 0.04 o.ca 0.05 0.04 0.05 0.03 0.()2 0.04 0.04 MgO 0.11 1).19 0.20 0.36 . 0.41 o.w 0.11 0.17 010 0.19 0.10 0.00 0.00 0.04 0.05 0.15 CaO 0.79 037 0.39 2.56 110 0.37 1.28 0.70 1.03 0.9S 012 0.28 0.29 0.24 0.25 0.71 I Na20 4.76 4.93 4.69 4.67 4.61 4.22 3.94 4.38 349 4.41 417 4.16 . 5.69 5.76 4.49 4.56 K20 6.03 6.03 5.45 5.35 5.81 5.67 6.56 5.83 6.66 5.93 561 5J2 5.4 5.38 4 51 5.7 PtO~ 0.02 003 001 0.02 0.05 0.03 tlo:l 0.03 0.04 om 0.02 0.02 0.05 0.05 0.03 O.Ql ~ W l 0.39 0.42 0.40 0.54 0.61 0.26 0.18 0.28 0.48 071 0.39 0.38 0.22 0.27 0.31 0.43 Total 98.79 99.10 9S.78 99.21 99.28 98.65 99.01 99.47 99.07 99.28 9941 98.70 99.98 99.94 99.60 99.2 Trace elements (ppm) Rb 100 228 219 192 201 210 219 201 llO !87 95 150 124 140 141 168 Sr 7? 17 43 23 19 25 45 93 61 45 59 57 86 75 72 53.1 Ba 305 161 170 515 362 ISS 40~ 285 345 301 381 141 370 241 230 291 Nb 27 62 39 54 52 64 70 56 45 52 95 81 76 81 54 60.5 Zr 562 1036 1036 ggg 1184 333 31R %1 452 752 650 852 762 448 478 7t4 y 38 110 94 95 126 118 110 121i 16 93 43 61 53 45 37 78.1 Ga 44 52 31 59 37 44 37 32 44 42 26 29 28 23 20 36.5 Cu 18 16 21 13 15 18 12 11 18 16 12 li 12 15 16 14.9 Za 64 158 145 145 22.5 72 139 175 434 173 124 105 154 120 i09 156 Su !58 118 142 134 126 150 118 291 165 i56 152 142 148 139 151 153 CIPW Norm Q 193!! 20.13 25.6 22 21 265 22.2 24.6 26 23.1 339 34.1 32.5 30.7 33.1 26.3 Ah 37.98 33.05 31.6 30.7 29.1 331 29 268 29.1 31.1 26.6 264 25.8 28.2 33.1 30.1 Or 36.23 36.11 32.7 32 3~ .8 34 39.5 34.8 40 35.6 33.5 32 32 31.9 268 3~ .1 Di 3.35 1.51 1.~ 8.81 4.48 149 5.49 2.93 2.62 3.1.1 0.4 1.12 0.98 0.76 0. 93 2.7 I Ily 0.26 J.ro 3.28 0 3.91 !.88 0.02 4.18 0 169 0.94 1.7 1.66 1.68 2.73 1.84 Wo () 0 0 1.07 0 G 0 0 0.7& 0 0 0 0 0 0 0.1 2 ! Ac U i 3.33 3.1 3.15 4.34 Wl 2.43 4.46 0.73 2.S6 1.5 2.14 !.58 1.74 2.43 252 Na:SIOl 0.24 126 1.22 1.33 1.28 0.17 0.5 1.28 0 0.8 1.71 163 4.19 4.36 0.57 1.41 II 0.74 {J _']lj 0.65 0.76 0.84 0.49 0.74 0.8 0.46 0.7 133 0.8 038 0.42 0.27 0.68 Ma 0 0 0 0 0 0 0 0 0.23 0 0 0 0 0 0 002 Ap 0.05 0,07 0.02 0.05 0.14 0.07 O.fJi 0.07 0.09 O.D7 0.05 0.05 0.12 0.12 0.07 0.07 'l:t 0.12 0.21 0.21 0.18 0.24 0.06 0.00 0.19 o.ro 0.15 01 3 0.1 8 ()!.) 0.0'1 0.09 0.14 Total 100 100 100 100 100 100 100 100 100 100 100 100 100 ICO 100 100 . Some !"'tios & Temptrature estimates FeO*!Mgo 16.4 18.9 16.5 9.28 1!3 2t6 23.5 28 12.6 16i 16.6 11 6 20.3 48 52.2 28.6

Log(X10 /Mgo) 1.64 1.50 1.44 1.17 1.15 1.80 1.78 1.54 l.82 1.49 175 2.42 1.78 2.13 1.96 1.69 Alk. Rdio 6.. 68 10.66 10.26 5.75 9.i7 7. ~ i . l~ 11.37 6.52 789 IJ.87 12.97. 370.0 59.63 8.17 3!!.7 N'KJA. 1.04 1.14 I.H l.IS 1.17 ! OS 1.07 1.18 1.01 1.01 1.16 1.17 1.4 1.36 1.09 !.14 Rh/Sr 1.3 13.4 5.1'-1 8.35 10.6 8.4 4.&7 2.16 1.8 4.16 1.16 2.63 1.44 1.87 1.96 4.61 YINb 1.41 1.77 2.41 1.76 2.42 1.84 1.57 2.25 0.36 1.79 0.45 0.83 0.70 0.56 0.69 1.39 T(c} 881 940 944 874 933 g«) 813 921 863 901 'Xl3 928 882 lJ35 R17 889 I ·-·--

143 El-Bialy, M.Z. & El Omla, M.M.

Table (3):Comaparison of the average composition ofShann granites with other comparable granitoids:

Reference 1 2 3 4 s 6 7 8 9 1- The present ShaJlll Esbcikh A-type grJnites Si02 72.57 74.27 73.8 1 74.01 73.86 74.04 74.&8 74.49 76.21 2- Low-Ca granite (Turc kian & Wcdepohl, 1%1 ). Ti02 0.35 0.2 0.26 0.23 0.19 0.2S 0.16 0.21 0.12 3-A-type granites (Whalen et al., 19987) Al203 11.95 13.61 12.4 11.59 j 1.71 11.4 11.87 12.97 12.62 4- Peralka1ine granites (Clarke, 1992) Fe203 1.2 1.24 1.75 3.48 0.75 0.79 5-JX-'rdlkalinc granites of Nigeria, (Bowden and FeO 1.52 2.03* 1.58 3.08• 1.47 0.5 1.03 0.86 1.54* Tumer, 1974). MnO 0.04 0.05 0.06 0.1 0.06 0.1 0.05 0.04 (l.05 6- Alkaline gra nites of Arabian SIJield (Jackson et MgO 0.1 5 0.27 0.2 0.55 0.17 0.02 0.05 0.26 0.1 al., 1984). CaO 0.71 0.71 0.75 0.48 0.42 0.43 0.43 0.6\1 0.46 7- Mount Gharib A-type granites (Abde1-Rah man Na20 4.56 3.48 4.07 4.33 5.16 4.1 I 4.38 3.82 3.71\ & Ma1tin, 19911) KlO 5.7 5.06 4.65 5.09 4.61 4.54 4.74 5.03 4.6 8- Phase Ill of Katherine f.'T'dnitcs (Hassan, 1997! l: Aib lis 10.26 8.54 8.72 9.42 9.77 8.65 9.12 8.85 8.38 9- A-type granites ofK atharina plutone (Katzir et P205 0.03 0.1 4 0.04 0.06 0.03 0.05 0.02 0.05 0.09 al., 2006)

Chemical Classifications

1. Magma Series The investigated granitoids are definitely belonging to the alkaline series as they a11 contain excessive alkalis to form normative acmite and sodium metasilicate. The alkalinity ratio was proposed by Wright (1969) as an indicator of the nature of sialic or upper crustal magmas . (peralkaline to calc-alkaline). Wright's alkalinity ratios of the investigated granitoid samples were calculated and plotted against silica (Fig. 4-A). Plots of the investigated granitoids on the Wright's alkalinity ratio diagram show that a11 samples fall in the strong alkaline to peralk.aline fields. Rogers and Greenberg (1981) constructed a diagram to permit the maximum separation of the two common granitic rock suites (alkaline and calc-alkaline) by

plotting Si02 versus Log (K20 I MgO). Figure (4-B) shows the relation between Si02 and Log

(K20 I MgO) for the investigated granitoids. From this diagram, it can be noticed that the studied samples fall entirely within the Alkali granite field. Further, plots of the investigated granitoids on TAS diagram (Fig. 3-B ) expose their affiliation to the alkaline magma series

(M}yashiro 1978). Moreover, On the K20-Si02 plot (Rickwood 1989) the studied granitoids duster wholly in the shoshonitic (High potassic rocks) field (Fig. 4-C).

~· 20 (A) . Alknl.ina ma.gma !W:.; lt (B) 3-.Alluoli fcltlspao· (>ranitc 6- Gn~oit e J6 14

~u l a10 + I I f. 4 2 0 .,, 10 10 u 40 ... !$ 16 6S 10 10 ., • am {Wt"l

Fig. (3): Cl a s.~ i tication of the studied granitoids using total alkalis-silica diagrams. (A) Middlcmost (1985). (B) Wilson ( 1989), the dashed dividing line between alkaline and sub-alkaline magma series is after Miyashiro ( 1978).

144 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids

------~·-,.·~.-~ .. - .-. _ __..,., ...... _ , ...-.-~...... 80 r- , ____ -, 80 (A) .. i (R) ;.... --· ~ 0 0 1s r' i ,- " ~;- o / o OCt 0 o a o ! 70 l / _:/ .g "'r 4_,0· ,-.. i CaJo.J.JiiaJk ~ Peralkaline BarlloiiiiJ """ . -·· :..: ...- i ('ktro.ngly aJkAline) ""! 65 If -60 /( /~ i r '~- - - -- ~ · "\. 8... ~ I AlbJ1 {/) I r /'•' Crnila ...- so 5S r

4S I._____. ._ ___.___~--'----~--~-' ..0 10 ., -2 2 J Alk. ratio ·1 0 los (t201Ma0)

8 --- T - ...... , ...... ,------y---- ··-.--,-...... ----- ,· ---- , l 3 f ·------···------1-- ~- I (C) - 1 l (D) . I

6 o' 0 '0 t ~ i l 0 I : ~""' -~------I l' Shoshonitic .--~ --~- " I ~ 2 l I 1 .--- _____.~----~-I . ~ __ ••. ----··· . ~~'(,'r'-e ~---· ! _.. c-a\c/e> ----.- I. / _,/ -r;'4n-'f-- . ______--· l l I ! /' .--" \ 2 r Calc-alkaline _...... i 1 ! I f ~ .. --· ,. . ------I Il .....----·· - -··-- I I l_~_::~: :· ~~-'-- ·------~ole~it~- , _ .... ,______I ______,_1______.,, ~------~~- - -· ·- 0 --·- . 50 55 60 85 70 7 5 60 1 AICNK • 5102 ~IIYt%)

Fig. (4): Plots of the investigated granitoids on: (A) alkalinity ratio diagram of Wright ( 1969); (B) Si01 versus log

(K20 /Mg0) diagram (Rogers & Greenberg, 1981 ) (C) K 2 0 vs Si02 diagram with fields aflcr Rickwood ( 1989) ; (D) Shand's index using A/NR vs A/CNK plots (after Maniar and Picc,oli, 1989). 2. Alumina Saturation Since "Granitoids", quartz-bearing plutonic felsic rocks, can vary from corundum-normative (Al20 3 oversaturated) to acmite-normative (Al20 3 critically undersaturated), alumina saturation appears to be the most important criterion in classification of these rocks. Table (2) reveals that all of the examined samples are alumina undersaturated, as they contain both normative acmite and sodium metasilicate. In terms of the molar NK/A ratio (Shand 1947), all of the samples are considered as peralkaline since their NK/A ratios are exceeding unity (Table 2). Maniar and Piccoli (1989) employ Shandfs index in discrimination between different tectonic settings of granitoid rocks using a plot of NCNK versus NNK . Herein, their diagram is only employed as an effective alumina saturation index (Fig. 4-D). This diagram evidently discloses the prevalence of the peralkaline nature among the studied granitoid samples.

Magmatic Trends Figure (5) shows Harker type plots of major and some trace elements of the investigated granitoids against Si02. On the diagrams, poor-defined lin.ear to slightly scattered trends are apparent for all the trace and major elements diagrams. However, the overall trend of all major elements without exception show negative cmrelation with silica. On the other hand,

145 El-Bialy, M.Z. & El Omla, M.M.

--::-1 ,, .-----~-----.,.------, aoj. ,. .ww i 11

11

ll i •• ______.___ ~ ------J • .s 11 1'$ ..

".,..• ,.._.,._ ..... M~,... - ~ ...... , ._.., ...._ ...... _ 1 I - ·:l 1111110 100 I I

.J . ~. , I • L---~ --l------"------·· - ' ,_,_.; ...... ' '""'"·- ·"-·""-·" ··~ ·--'" ....,. ..,.,.,,...... --- ~--...... a ~ " • M ~ 1'J ..

..... ·~ _,,, ~----,.. ,._ ~-~- ·-~.... - tMI r-·- --··--·.,., ------·----~------... - -· .. -- ...... ---·- ....1 ' ... --- ...... _ -...... Tin ... f \ ltl . I .. ' , !u • '"< i -~ . \ ' I I 4.;S

f • -1 '\: "·-•.. "' lt • •

'

Fig. (5): Harker-type variation diagrams of major and some trace elements of the studied granitoids

146 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids only Sr and Nb roughly increase with silica rise, while Zr, Rb, Ba, Ga andY exhibit relatively apparent transgression. Thorough verification of the roughly scattered trends on Harker diagrams reveal two or more coherent sub-trends in most plots. The overall scatter on Harker diagrams may be interpreted as due to interpluton variations, with individual intrusions typically defining relatively coherent trends. Estimated Crystallization Temperatures And Depth Of Intrusion Melt temperature estimates of the studied granitoids are calculated and listed in Table (2) according to the experimental works of Watson (1979) and of Watson and Harrison (1983) on Zr saturation in hydrous, low-temperature, intetmecliate and felsic magmas. In 1983, Watson and Harrison described the saturation behavior of Zr in crustal anatectic melts by the following equation: lnDzr Zircon/melt={ -3.80-[0.85(M-1)]}+12900/T where, Dzr Zircon/melt is the concentration ratio of zirconium in the stoichiometric zircon to that in the melt, T is the absolute temperature and M is the cation ratio (Na+K+2Ca)/ (Al*Si). Anderson and Morrison (1992) indicated that zircon is a near-liquidus phase in many granites, and therefore the estimation of its temperature of initial crystallization enables not only assessment of liquidus conditions but also minimum temperatures achieved during magma formation. Temperature values infe1Ted range between a minimum of 813°C and a maximum of 944 °C, with average temperature of 889oC for the whole samples (Table 2). However, the highest temperatures obtained can be considered estimates of the temperature of emplacement while the lowest temperatures probably represent the last magmatic activity (Ramirez & Grundvig 2000). The Rb/Sr ratio is very sensitive to depth of intrusion (Condie 1973), as the crust can be regarded as being vertically zoned with Rb/Sr increasing upward (B ievin & Chappell 1995). The relation between Rb and Sr is used to determine the depth at which the crystallization of magma had taken place (Condie 1973). Figure (6-A) shows that all of the investigated granitoids have been emplaced at depth ranging between 20- 30 Km, indicating emplacement at lower crust I upper mantle regimes. Such depth of intrusion is concurrent with that of alkaline and shoshonitic rock series on intermediate to thick (~ 25 km) crust (Condie, op. cit.). Petrogenesis And Tectonic Setting The present granitoids display characteristics of A-type granitoids as defined by Whalen et al. (1987), Eby (1990) and Creaser et al. (1991), exhibiting anhydrous, hypersolvus mineralogy, quartz syenite to peralkaline granite composition, relatively high content of alkalis (9-11.14 wt%) and an alkaline chemical affinity with low CaO content (0.12-1.28, averaging 0.7lwt.%), high FeO-/MgO ratios (9.28-115.5) and NK/A ratios (1.01-1.36), with exceptionally high concentrations of the trace elements Y, Nb, Zr,, Zn and Ga and low Sr and Ba contents (Table 2 ). On the AFM diagram (Fig. 6-B), the studied granitoids spread very close and parallel to the AF side, clustering entirely in the field of A-type granites defined by

147 El-Bialy, M.Z. & El Omla, M.M.

Kilpatrick and Ellis (1992) and following the trend of rocks evolved in extensional environments (Petro et al. 1979). The peralkaline nature of the studied granitoids is consistant with their affiliation to extensional environments (Petro et al. op.cit). The FeOT /MgO ratio versus Si02 is a more effective discriminant criterion, as most A-type granitoids have higher ratios than the I-type and S-type granitoids (Eby 1990). On this diagram (Fig. 6-C ) , all the data points are plotted in the A-type field due to their higher FeOT /MgO ratios relative to l­ and S-types. Good discrimination can be obtained between A-type (alkaline or anorogenic) granitoids and most orogenic granitoids(M-, I- and S-types) on plots employing Ga/Al ratio versus major element ratios and Y, Nb, Ce, and Zr (Whalen et al. 1987). Of these, the studied granitoid samples are plotted on Ga/Al versus Nb and Zr diagrams (Fig.7 A& B), in which they are all classified as A-type granites. However, highly fractionated I- and S-type granites have GalAl ratios and some major and trace elements values which overlap those of typical A-type granites (Whalen et al. op. cit.). Therefore, The A-type identity of these granites was confitmed by plotting them on Zr+Nb+ Y versus (~O+Na20)/Ca0 and FeO*/MgO diagrams

>301cm 'S -·----..- ··- ·-- ~-- - 0 CD 6 ...... ~ ... I o ' 100 t- (A) 20-30km \ .\ \ 'l .> l' M ...... _ ...... _ __ ·--· •·· - ·~ -"'- ·- -....- - .. - ....

... ,.,~ <15 lcm ' '\ .• ' 1 1 . •. 10 100 1000 Na10 + 100 Sr (ppm)

149 2$00 r-1:~=-T---r-- ·- T·- -~ ---,-,Ji 0 100 2000 ,... .3- ~UpJIA 0 ~ 1 4 -~ 1 0 + 5-~ \ ~ .. 0 A~ 0 0 i 900 0 0 10 0 ~ (C) 0 (D)

~0· 6 lv - -05 0 ..30--:0-:--..,-.,-=--7· ' 1 0 1000 1500 2000 2SOO 3000 3250 50 6'0Sl02 10 0 k1 • -451 • U(Na+ I()-2(F~ + ll)

Figure (6): (A) .R.b-Sr diagram sho>ving distribution of the studied granitoids. Numbers in kilometers refers to crustal thickness as interred from Rb-Sr crustal thickness index (Condie 1973); (B) AFM diagram for Sharnn granitoids with fields of the !-type and A-type granites and igneous charnockites after Kilpatrick and Ellis (1992). The trend of extensional suites is adopted by Petro et al. (1979); (C) Si02 vs. FeO/MgO diagram (aflcr Eby 1990); ([h R1 -R1 multicationic variation diagram. Fields of tectonic setting are after Batchelor and Bowden ( 1985)_

148 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids

(Whalen et al. op.cit.), which distinguish them from highly fractionated I- and S-type granites (Fig.7 C& D). In spite of absence of Ce in the former two diagrams, all samples plot within the A-type field due to their high contents in Zr, Nb and Y, a typical characteristic of A-type granitoids. Whalen et al. (1987), plotted many granitoid data of different tectonic settings on the Rb­ (Y+Nb) and Y-Nb diagrams of Pearce et al. (1984) and showed that most A-type granites plot in within plate (WPG) granite field whereas average M-, 1-, and S-type granites are differentiated as volcanic arc granites (VAG). Plots of the studied granitoids on Pearce et al. (op cit.) diagrams show that all samples are classified as within plate granites (Fig. 8). This ,

300 I 3000

1000 ..- :.,. 0 0 .. 0 1110 "': ., "

.10 ~ "': ~~ I, SAM 10 I,SatM

I 1 1 l l~Al ton 1 to u

1.99 r-r-rTT~

100 0 . 0 0 110 1:- -:: 0 0 0 0 A-tJpe 0 ! ~ ~... A..type ~ 0 0 GtaiiJta ~ IG 0 0 0 0 00 I 0 0 :- 0 f 0 + 10 to- 0 -:: Q " " FG B 0 OOT OGT .J l 1 e 106 tOOl ttl .... Zr+Nb+ Cc(.. )+Y (pp•) 1-t'+MI+C.(_.)+Y 0..) Fig. (7): Plots of the studied granitoids on diagrams discriminating A-type granites from the other types of granites (after Whalen et al. 1987).

1000 1999 ,---.--,...... ,"T"Tr.,--,-,.,.-rrn.,..--r--r;rr-rrr.,.---, 1000

100 -•oo I ~ 10 10

1 ~--~~~--..~~_.~~~~ l ~~~~~~~~ll-~~~=-_J l 10 100 1000 ., I 10 100 1000 1999 y Y+Nb (ppD)

Fig. (8): Plots of the studied gmnites on the (M: Nb-Y and (b): Rb-(Y + Nb) tectonic discrimination diagrams of Pearce el al. (1984).

149 EI-Bialy, M.Z. & El Omla, M.M. consequently, confirms that the present granitoids are genuine anorogenic (A-type) granites. Further , the multicationic Rl-R2 tectonic discrimination diagram of Batchelor and Bowden (1985) is used to examine the tectonic setting of the studied granitoids (Fig. 6-D). Herein, most of the granitoid samples plot in the "Anorogenic" field. In recent years, there has been a tendency to divide A-type granites into those formed in post-orogenic and anorogenic settings (Whalen et at. 1987, 1996; Eby 1990, 1992). However, it is not easy to distinguish these two settings of A-type granites since they do not have distinctive petrological, mineralogical or geochemical features. Eby (1992) subdivided A-type granites into Al and A2 groups. The Al group refers to differentiates of magmas derived from sources like those of oceanic-island basalts but emplaced in continental rifts or during intraplate magmatism. The A2 group, 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. Eby (1992) recommended the use of Al and A2 discrimination diagrams only for granitoids that plot in the field of within-plate granite of Pearce et al. (1984) and in the A-type granitoid field of the Ga/Al plots of Whalen et al. (1987). Therefore, the investigated A-type samples are plotted on the (Nb-Y -Zr/4) and (Nb-Y -3Ga) A-type granites discrimination diagrams, (Fig. 9), introduced by Eby ( op. cit.). The examined A-type granitoid samples straddle the border between anorogenic ,rift-related, (Al) and postorogenic (A2) A-type granites. The c1i tical c1iteria that affect Lhis subdivision is the Y/Nh ratio at 1.2 value (Eby, 1990). Samples have Y/Nb ratios less than 1.2 fall in the anorogenic (Al) field (6 samples), while the other nine samples have Y/Nb ratios greater than 1.2 and are classified as post-orogenic (A2) granitoids (Table 2).

Nb Nb

...'

y 'b/4 y 3Ga

Fig. (9): The A I and A2 subgroup discriminations of the studied A-type granitoids (Eby 1992}.

150 Source & Tectonic Setting of Sharm El-Shiekh Alkaline A-type Granitoids

El Masry (1998) using Eby (1992) discrimination diagrams differeniated the A-type syenogranites of Gabal Fierani area into biotite-hornblende Algranite and fluorite-bearing, biotite A2 granites. Recently, Katzir et al. (2006) criticized the use of Eby (1992) discrimination diagrams on their A-type granites of Katharina pluton due to the same petrogenetic inconsistency. Calculation of their Y/Nb ratios (Eby 1990) and plotting their data on Eby (1992) diagrams revealed a binomial distribution of their 15 samples between AI granites (7 samples) and A2 granites (8 samples). CONCLUSIONS All mineralogical and geochemical characteristics of the investigated A-type granitoids confirm that that they are anorogenic granites emplaced in continental rifts or during intraplate magmatism (Al of Eby 1992). Of these their anhydrous hypersolvous textures, strong alkaline (alkalis-silica balance) and peralkaline (alumina undersaturation) characters, their trend on the AFM diagram (Petro et al. 1979). Moreover, the application of other petrogenetic and tectonic discrimination diagrams (e.g. Pearce et al. 1984; Batchelor & Bowden 1985); Whalen et al. 1987; Eby 1990 and Kilpatrick & Ellis 1992) have confirmed these conclusions. The rely on a single ctiterion (Y/Nb ratio) in the four A-type granite subdivision diagrams of Eby (1992) is not sufficient. Therefore, the authors favor leaving the miginal definition and petrogenetic character of A-type granites to the studied grantoids. ACKNOLEDGMENT The authors wish to express their deep gratitude to Dr. Nasser Moustafa, Chemistry Department, Suez Canal University, who gratefully helped in XRF chemical analysis of the samples in Suez Cement Company laboratories through personal communications. Sincere thanks are extended to Dr. Nabil N. El Masry ,Geology Depat1ment, Suez Canal University, for valuable discussion. REFERENCES

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