geochemical and petrological evidence of calc-alkaline and ...rjstern/egypt/pdfs/ce...

Pergamon Journal of African Earth Sciences, Vol. 29, No. 3, pp. 535-549, 1999

© 1999 Elsevier Science Ltd PI1:S0899-5362(99)00114-1 A, rights reserved. Printed in Great Britain

0899-5362199 $* see front matter

Geochemical and petrological evidence of calc-alkaline and A-type magmatism in the Homrit Waggat and

EI-Yatima areas of eastern Egypt

A.M. MOGHAZP.* , F.H. M O H A M E D 1 and S. KANISAWA 2 1Geology Department, Faculty of Science, Alexandria University, Egypt

2Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Japan

ABSTRACT--The Neoproterozoic plutonic complex in the Homrit Waggat and EI-Yatima areas, central Eastern Desert of Egypt, comprises a deformed calc-alkaline I-type metagabbro-diorite complex and tonalite-granodiorite suite invaded by felsic high level intrusions of A-type characteristics. The metagabbro-diorite complex exhibits petrological and geochemical characteristics of mantle-derived island-arc basalts, and its magma was derived possibly from partial melting of a mantle wedge above an early Pan-African subduction zone. The rocks of the tonalite-granodiorite suite have a wide range of SiO 2 (62-71%), and K, Rb and Ba enrichment relative to Nb and Y. Their chemical variations suggest that they are not related to the gabbro-diorite complex, but most probably derived by partial melting of the amphibolitic lower crust in a subduction zone. The A-type granites are mainly syeno- and alkali-feldspar granites characterised by sub- and hyper-solvus textures, late magmatic interstitial biotite and interstitial or vein-fluorite. They are geochemically evolved (SiO 2 = 74-78%), metaluminous to mildly peraluminous, enriched in Fe, Y, Nb, Rb, Zr and F, and depleted in CaO, MgO, Ba and Sr. Although they can be classified as A- type and within-plate granites, the least differentiated samples have F, Nb, Y and Rb contents similar to those in the surrounding I-type tonalite-granodiorite suite. This similarity suggests that high concentrations of these elements in the A-type granite are mostly related to unusual fractionation processes rather than to source rock (A-type source). This simply indicates that these granites are I-type and their classification as A-type reflects the process of evolution. A petrogenetic model of dehydration partial melting of an early Pan-African lower crust along major shear zones in a post- collisional environment to produce granodioritic melt seems likely. Fractional crystallisation of this granodioritic melt gave silicic granites, during which a F-rich fluid phase was evolved. Late magmatic F-rich fluid-rock interaction and F complexing played an important role in the evolution and chemical characterisation of the A-type granites. © 1999 Elsevier Science Limited. All rights reserved.

RI~SUMIr:--Le complexe plutonique fini-prot6rozo'l'que dans les r6gions de Homrit Waggat et EI- Yatima, dans le d~sert oriental central ~gyptien, comprend un complexe d6form~ calco-alcalin de type I de m6tagabbro-diorite et une suite tonalite-granodiorite envahis par des intrusions felsiques de haut-niveau de type A. Le complexe de gabbro-diorite possede des caract6ristiques p6trologiques et g6ochimiques de basaltes d'arc insulaire d'origine mantellique; ce magma pourrait avoir d6riv~ de la fusion partielle d'un coin mantellique situ6 au-dessus d'une zone de subduction pan-africaine. Les roches de la suite tonalite-granodiorite montrent une large gamme de compositions (dont SiO 2, 62-71%), et un enrichissement en K, Rb et Ba par rapport ~ Nb et Y. Ces variations chimiques sugg~rent que cette suite ne soit pas li~e au complexe gabbro-dioritique, mais qu'elle d6rive plus probablement de la fusion partielle d'une cro0te inf6rieure amphibolitique dans le cadre d'une zone de subduction. Les granites de type A sont principalement des granites ~ feldspath alcalin caract6ris6s par des textures sub- et hypersolvus, de la biotite interstitielle tardi-magmatique et de la fluorite interstitielle ou en veine. IIs sont g6ochimiquement 6volu6s (SiO 2 = 74-78%),

*Corresponding author [email protected]

Journal of African Earth Sciences 535

A.M. MOGHAZl et al.

m6talumineux =~ I~g6rement hyperalumineux, enrichis en Fe, Y, Nb, Rb, Zr et F et appauvris en CaO, MgO, Ba et Sr. Quoiqu'ils puissent 6tre classes comme granites de type A et intraplaques, les ~chantillons les moins diff6renci6s ont des concentrations en F, Nb, Ye t Rb semblables celles de la suite tonalite-granodiorite de type I qui les environne. Cette similarit6 sugg~re que les hautes concentrations de certains 61~ments dans les granites de type A soient plutSt li~es ~ des processus inhabituels de fractionnement qu'~ une source particuli~re (source de type A). Ceci indique simplement que ces granites sont de type Iet que leur classification de type A refl~te le processus d'6volution. Un mod61e p6trog~n6tique de fusion partielle par d6shydratation d'une cro0te inf6rieure pan-africaine le long d'accidents transcurrents dans un environnement post- collisionnel pour produire le magma granodioritique est probable. La cristallisation fractionn6e de ce magma granodioritique aurait engnedr~ des granites siliceux pendant laquelle une phase fluide riche en F a 6t6 produite. L'interaction entre les fluides tardi-magmatiques riches en F et les roches ainsi que la complexation de la F a jou~ un grand rSle dans I'~volution et la caract6risation chimique des granites de type A. © 1999 Elsevier Science Limited. All rights reserved.

(Received 19/8/97: revised version received 14/10/98: accepted 31/12/98)

INTRODUCTION

It has been widely accepted that the Neoproterozoic crustal evolution of the Arabian-Nubian Shield was dominated by subduction-related processes. The evolution of the shield, as summarised by Stern (1993) and KrOner (1993), began some 950 Ma ago with rifting fol lowed by sea-floor spreading and the initiation of subduction where a group of juvenile island arcs terranes were formed between 900-650 Ma ago. The various arc terranes were welded together along ophiolite-bearing suture zones (microplate accretion, Stoesser and Camp, 1985) fol lowed by large-scale calc-alkaline magmatism, continental collision and accretion to the East Saharan Craton (Schandelmeier etal., 1987). Granitic rocks const i tute a significant proportion of the continental crust of the Nubian Shield. They are classified into two groups: older and younger granites (EI-Gaby, 1975; Akaad and Noweir, 1980). The older group comprises calc-alkaline syntectonic (700-850 Ma) gabbro-diorite, tonalite, trondhjemite, and granodiorite intrusions, which was followed by late-to post-tectonic (650-520 Ma) younger group of granodiorites, granites, and alkali feldspar granites (EI-Gaby, 1975; Rogers and Greenberg, 1981 ; Hussein etal., 1982; Stern and Hedge, 1985; Bentor, 1985; Stem and Gottfried, 1986). Some of the younger granite plutons show an A-type geochemical signature such as low CaO and MgO and high SiO 2, Na20 + K20, Nb, Y, and REE (Greenberg, 1981 ; Abdel Rahman and Martin, 1990; Mohamed, 1993; Mohamed etal., 1994).

A-type granites have attracted a great deal of attention in the last decade because of their unusual mineralogy and chemistry, and because their origin and tectonic sett ing is somewhat controversial. Although the idea of linking A-type granite complexes to rifting processes in intracontinental sett ings has become conventional, they can also arise in various other tectonic contexts, including active subduction

zones (Whalen etal., 1987; Sylvester, 1989; Lumbers eta/., 1991 ; Eby, 1 992). Regarding the origin of A- type granites in the Nubian Shield, one of the major unsolved problems is the diff iculty of assessing the tectonic environment and the protolith of these granites. Many authors (viz. Stern etaL, 1984; Abdel Rahman and Martin, 1990; Beyth etal., 1994) thought that these granitoids appear clearly related to extensional tectonics (i.e. rift-related A-type granites) and specifically compared them with granitic intrusions in the Oslo Rift. Their deductions were based on the distinctive enrichment of these granitoids in REE and HFS elements, which are comparable with the A-type granite. Sylvester (1989) considers that these granites are post-collisional highly fractionated granites emplaced in association with strike-slip movements that follow the collisional event by about 25-75 Ma.

In the Homrit Waggat and EI-Yatima areas, rocks belonging to an island-arc association (metagabbro- diorite complex), older granitoids (tonalite-granodiorite association) and younger granitoids (leucogranite) are represented..The emplacement ages of the three rock units are not clear and only the leucogranites are dated at 535 Ma (EI-Manharawy, 1977). In this paper, major and trace element data for the three rock units are presented. The authors also have added useful infor- mation about their tectonic environment and the petrogenetic processes involved during their formation. The leucogranites are characterised by a shallow level of emplacement and provide a useful case study of A-type granite in the Eastern Desert of Egypt. The most important question regarding the genelJc nature of these A-type granites is whether their chemical characteristics are inherited from the source (A-type source) or result from subsequent magmatic processes. This paper also attempts to answer these questions based on a discussion of the geochemistry.

536 Journal of A fffcan Earth Sciences

Geochemical and petrological evidence o f calc-alkaline and A-type magmatism

GEOLOGICAL SETrlNG General The Pan-African terrane in the central Eastern Desert at latitude 25°N (Fig. 1 ), which comprises the Homrit Waggat and El-Yatima area, consists of four major tectonic units:

i) a metamorphosed island-arc assemblage of calc- alkaline metagabbro-diorite, metavolcanics and volcaniclastics, which was overthrusted by

i) an ophiolitic and volcaniclastic sequence (EI-Ramly etaL, 1984). The former unit was deformed pre-680 Ma, whereas the latter was deformed at ca 580 Ma (Stern and Hedge, 1985). They are overlain by

i/) molasse-type Hammamat Group of sediments, which are intimately associated with intermediate Dokhan Volcanics and felsites (Rice etal., 1993) and intruded by

iv) late- to post-orogenic granites (Hussein etaL, 1982). Structurally, the central Eastern Desert of Egypt is characterised by north-northwest steeply dipping ductile-brittle shear zones (Bennett and Mosley, 1987) and east-northeast deep seated faults (Garson and Krs, 1976). The studied plutons lie along one of the east-northeast trending deep tectonic faults (Fig. 1 ).

Homr'~ Waggat area The rocks of the Homrit Waggat area (Fig. 2a) comprise a volcano-sedimentary association and a metagabbro-diorite complex intruded by a tonalite- granodiorite suite, which is in turn intruded by leucogranites. The volcano-sedimentary association is the oldest rock unit and occupies a large surface area to the east of the leucogranite pluton. It consists of a metamorphosed thick succession of pelitic rocks with intercalation of lava flows and volcaniclastic sandstone and siltstone. The metagabbro-diorite complex intrudes the volcano-sedimentary association with sharp contacts, although diffuse contacts occasionally occur. Both the volcano-sedimentary association and the metagabbro-diorite complex display lineation, mostly trending north-northwest. The tonalite-granodiorite suite shows a poorly defined contact with the leucogranite due to advanced weathering and development of a wide erosional valley. In places, the tonalite-granodiorite is sheared and a foliation is defined by the alignment of feldspar crystals and biotite clots which are locally segregated into small-scale compositional layers parallel to the foliation, giving the rock a gneissic appearance.

The leucogranite pluton is one of the major younger granite intrusions in the region. It forms an elliptical structure (5x8 km) enclosing a hollow occupied by sandy plains with poor granite outcrops. The pluton

intrudes the metamorphosed volcano-sedimentary association and the metagabbro-diorite complex to the north and east and tonalite-granodiorite suite to the northwest and northeast (Fig. 2a). It is cut by a few pegmatitic veins, which locally contain cassiterite and dark patches of Fe-Mn oxides, and by north- northwest to northwest trending fluorite veins (up to 2 m wide and 30 m long) located close to the granite- granodiorite contact. The pluton consists of three granite types:

i) a coarse-grained massive and homogeneous pink biotite-granite, which occupies the core of the pluton. Rocks of this type contain biotite and granodioritic xenoliths a few centimetres long;

i ) a main phase of medium-grained mylonitised pink granite which is distinctly lineated, and locally foliated in the northwest and west-northwest directions. The foliation occurs along the southern, eastern and northern peripheries of the pluton and results from the alignment of the constituent minerals particularly quartz and feldspars. This foliation has been interpreted as a tectonic fabric (Stanek et al., 1993) due to the presence of two northwest strike-slip faults bordering the pluton (Fig. 2a); and

i i ) a coarse-grained red granite that forms irregular dyke-like bodies up to 500 m thick, which occupy the upper part of the mylonitised granite phase.

EI-Yatima area In the Gebel EI-Yatima area (Fig. 2b), the leucogranites occur as an isolated irregular mass with moderate relief which covers an area of about 6 km 2. They intrude the low-lying tonalite-granodiorite suite, but the contact between them is poorly defined due to weathering and the development of wide erosional areas around the leucogranite pluton. The EI-Yatima leucogranite pluton contains rounded granodioritic xenoliths up to 25 cm across and is dissected by a set of northwest and north-northwest faults (Fig. 2b) along which the granite is sheared and foliated. Two main granite types in this pluton are recognised based on their textural appearance:

i) a main phase of porphyritic K-feldspar megacrystic pink granite; and

ii) a fine- to medium-grained biotite monzogranite to syenogranite. The contact between the two types is gradational implying a comagmatic relation.

PETROGRAPHY Metagabbro-diorite complex Typical gabbroic rocks contain 45-55% euhedral to subhedral zoned plagioclase which is variably altered to sericite and epidote. Optical determinations indicate that it ranges from labradorite to andesine

Journal of A fdcen Earth Sciences 537

A.M. MOGHAZI et al.

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538 Journal of African Earth Sciences

Geochemical and petrological evidence of calc-alkaline and A-type magmatism

but the latter is the dominant. Hornblende is the main mafic mineral in the gabbroic rocks with modal content of about 25-40%. It occurs as medium-grained subhedral twinned crystals as well as poikilitic patchy grains with inclusions of plagioclase, magnetite and apatite. Augite (-5%) is present in some varieties as small subhedral to anhedral grains and also as cores in hornblende. Diorite is composed predominantly of andesine and hornblende, with minor amounts of quartz, biotite and K-feldspar.

Tonalite-granodiorite The bulk of the tonalite-granodiorite suite is medium- to coarse-grained, grey, equigranular, foliated to massive and biotite-rich. Felsic minerals include oligoclase, quartz, microcline and orthoclase. The quartz is in most cases undulatory. Dark reddish-brown biotite, magnetite and minor hornblende form mafic clots that define the foliation in the sheared variety. Accessory minerals include abundant apatite, sphene and zircon forming pleochroic haloes in biotite.

Homrit Waggat leucogranite The massive pink biotite-granite is typically equigranular containing subequal amounts of quartz, plagioclase and K-feldspar. K-feldspar is mostly perthitic subhedral to anhedral with albite stringers and coarse patches. Plagioclase is mainly subhedral to anhedral oligoclase with thin albitic rims. Quartz grains are occasionally strained, anhedral to subhedral and locally form granophyric intergrowths. Biotite and lesser amount of hornblende generally constitute less than 10% of the rock mode. Accessory minerals include apatite, zircon and fluorite. The mylonitised granite variety is the most abundant in the Homrit Waggat Pluton. It is medium-grained and consists essentially of K-feldspar, quartz and plagioclase in addition to minor amounts of biotite and hornblende. Accessory phases include fluorite, zircon, allanite, apatite and ilmenite. Based on the degree of deformation, the rocks can be classified texturally as protomylonite (towards the core of the pluton) where large porphyritic crystals of quartz and feldspar are surrounded by a mylonitic matrix. The protomylonite grades outwards into typical mylonitic granite with foliated matrix. The red granite variety consists mainly of alkali feldspar, quartz, sodic amphibole, rare plagioclase and green biotite. Accessory phases include zircon, apatite, ilmenite, allanite and fluorite. The alkali feldspar is usually vein- or patch-mesoperthites. Granophyric and graphic intergrowths are common in some samples. Quartz is present as large anhedral to subhedral crystals containing inclusions of perthites and zircon. The sodic amphibole is euhedral to subhedral and occurs as

interstitial clusters or as small euhedral inclusions in feldspars. It is commonly twinned and the large crystals often carry inclusions of ilmenite, zircon and apatite.

EI-Yatima leucogranite The megacrystic facies of Fig. 2b is a medium- to coarse-grained foliated to massive biotite-bearing granite with megacrysts of K-feldspar set in a groundmass of medium-grained plagioclase, quartz, microcline and perthite. Biotite and minor hornblende, which are sometimes altered to chlorite, form the mafic clots that define the foliation in the sheared varieties. Dark reddish-brown sphene, apatite, zircon and ilrnenite are the main accessory phases. The massive fine- to medium-grained biotite granite facies (Fig. 2b), is similar in composition to the porphyritic variety but it is typically equigranular.

GEOCHEMISTRY A total of 54 representative samples from the rnetagabbro-diorite complex, tonalite-granodiorite suite and the leucogranite were chemically analysed for major and trace elements. Results of 15 representative samples of the various rock types are listed in Table 1. Major oxides and trace elements were determined by X-ray fluoresence spectroscopy (XRF), using a Rigaku 3080EZ instrument, at the Institute of Geology, University of Tohoku, Japan. Calibration was done with international rock standards some of which were also used as unknowns. Analytical Precision is better than _ 3% for major elements and :1:5 to :1: 10% for trace elements. Fluorine was determined using an Orion model 94-09 fluoride-ion electrode and 90-01 reference electrode in conjunction with an Orion model 401A ion meter.

Metagabbro-diorite complex Figure 3 shows the metagabbro-diorite complex plotted on Harker diagrams. The metagabbros together with the diorites show relatively well-defined trends with increasing SiO 2, particularly with respect to AI203, CaO, MgO, total Fe, Na20, K20, Cr, Ni, Ba and Zr. Colinear trends of decreasing MgO, Cr and Ni, and increasing Na20 and K20 with increasing SiO 2 indicate that the evolution of these rocks is probably controlled by fractional crystallisation of pyroxene, calcic-plagioclase and hornblende. Plagioclase cumulates may account for the high AI203 ( > 18%) and CaO in some samples. The abundances of selected elements are shown diagramatically on MORB-normalised diagram (Fig. 4a). The most striking feature of the metagabbro-diorite rocks is that all analyses show LILE enrichment and Nb depletion: a


A.M. MOGHAZl et al.

feature often taken as indicative of subduction-related processes (Pearce, 1983). The positive Sr anomaly in some samples may be attributed to plagioclase cumulates. The patterns are mostly similar to the Neoproterozoic island-arc metagabbro-diorite complex reported by Fumes et al. (1996) for the Wadi EI-Ernra in the central Eastern Desert of Egypt (Fig. 4a). This is also confirmed by the tectonic discrimination diagram of Fig. 4b (Pearce and Norry, 1979), which indicates that the gabbroic rocks have remarkable similarities to island-arc basalts.

The granitoid rocks On the Q'-ANOR diagram (Fig. 5a) of Streckeisen and le Maitre (1979), the granodiorites are tonalitic to granodioritic in composition whereas the leucogranites of the Homrit Waggat and El-Yatima areas lie either within, or close to, the alkali feldspar granite and syenogranite fields. The alumina saturation (Shand, 1927) of the studied granitoids, measured by the molecular ratio AI2OJCaO + Na20 + K20 (A/CNK), as a function of SiO 2 is shown in Fig. 5b. Samples of the granodiorite-tonalite and leucogranites are metaluminous to weakly peraluminous; their A/CNK ratios show a narrow range (0.97-1.03) throughout the entire range of SiO 2 compositions. The alkalinity of the studied granitoids is shown by lO0(MgO + FeO t -t- TiO2/SiO 2) versus AI203 + CaO/FeO t + Na20 + K20 diagram (Fig. 5c). The tonalite-granodiorite samples fall in the calc- alkaline field, whereas the leucogranite samples lie in the field of highly fractionated calc-alkaline granites. The Fe enrichment of the leucogranite relative to the granodiorite-tonalite is shown in Fig. 5d. The degree of Fe enrichment is typical of A-type granites of all ages and is similar to other Proterozoic A-type granites reported by Anderson (1983) and Lumbers et al. (1991 ) for the Wolf River and Mulock A-type granites.

Figure 3 shows all the granitoid rocks plotted in Harker diagrams. AI203, MgO, CaO, total Fe, Cr, Ni, Sr and Ba show a continuous decrease with increasing SiO 2, whereas Na20 shows no variation with increasing SiO 2. Trends of K20, Rb, Nb, Zr and Y are poorly developed in all the granitoid rocks. They form two separate groups: the tonalite-granodiorite suite and the leucogranites. The former show little variation in the content of these elements but the latter exhibit a wide variation over a restricted range of SiO 2. In the multi-element, chondrite normalised diagrams (Fig. 6a), the granodiorite-tonalite suite is characterised by high abundances of LILE (K, Rb and Ba) relative to HFSE (Zr, Ti and Y). Compared to the granodiorite- tonalite suite, the Homrit Waggat and EI-Yatima leucogranites are enriched in Zr, Nb and Y, and depleted in Ba, Sr and Ti. Such depletions are consistent with early fractionation of K-feldspar, a

mineral which readily accepts both Ba and Sr (mineral/ melt distribution coefficients are 6.1-12.9 and 3.6- 3.9, respectively; Arth and Hanson, 1975; Mittlefehldt and Miller, 1983).

Discrimination between granitoid rocks of various affinities has been proposed by Pearce et al. (1984). On this widely used diagram (Fig. 6b), the data points of the tonalite-granodiorite suite plot within the field of volcanic-arc granite (VAG); and, thus, have dist inct ive subduction-related signature. The leucogranites plot in the within-plate granite (WPG) field and are of comparable composition with the A- type granites of Whalen etaL (1987). However, the least fractionated samples of the Homrit Waggat leucogranite plot in and near the VAG field and define a distinct trend from VAG to WPG. This simply reflects that these granites are I-type and the trend to A-type granite reflects the process of evolution. It is, thus, the process which correlates with the tectonic environment in this case and these granites are an extremely fractionated I-type as delineated on the binary variation diagram Y/Nb versus Rb/Nb (Fig. 6c) of Eby (1992). On this diagram, the studied leucogranites fall in the field of orogenically-related A2-subtype granite.

PETROGENESIS The metagabbro-diorite complex The metagabbro-diorite complex shows geochemical characteristic features of having been generated in an island-arc setting. They are characterised by enrichment of the LILE such as K, Rb, Ba and Sr relative to the HFSE and by K and Rb enrichment with increasing SiO 2. Such features are consistent with modern calc-alkaline island-arc suites. The parental magma of the rnetagabbro-diorite complex are, thus, believed to be generated by partial melting of mantle wedge above subduction zones that have been previously metasomatised by slab-derived fluids (Saunders et al., 1980). The presence of cumulate features and the steep fall in Ni, Cr and MgO abundances are consistent with significant clinopyroxene (olivine), and plagioclase fractionation so that crystal/melt fractional crystallisation may explain the geochemical variations within the metagabbro-diorite pluton.

The tonalite-granodiorite suite The syntectonic metagabbro-diorite complex and tonalite-granodiorite suite show chemical characteristics of calc-alkaline subduction-related magma and they are to be regarded as I-type products. However, geochemical data show marked discontinuities in major and trace element abundances versus SiO 2 (Fig, 3) suggesting that the two suites are genetically

540 Journal o f African Earth Sciences


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lO

/ / / / W P B /

i i i ~ ~ 1 i I L i i i

lOO Zr

, I , , /

I (b) ,

I

] I

lOOO

Figure 4. Tecton ic d i sc r im ina t i on d iagrams for the metagabbro-diori te complex. (a) MORB-normalised trace e lement abundances compa red w i t h an is land-arc metagabbro-diorite complex (stippled pattern) from Wadi EI- Imra, Eastern Desert, Egypt (Fumes et al.. 1996). Normalising values are after Pearce (1980). (b) Zr versus Zr/Y (Pearce and Norry, 1979). lAB: island arc basalt; MORB: mid-oceanic ridge basalt; WPB: within-plate basalt.

unrelated. If the metagabbro-diorite complex and the granodiorite-tonalite suite were related to each other by fractional crystallisation processes, colinear trends should exist between Ba versus Sr and Rb versus K/ Rb, but are absent, (see Fig. 7). Although plagioclase feldspar is a major fractionating phase in the evolution of the gabbroic rocks, there is no change in the Sr content from gabbro to granodiorite-tonalite (Fig. 7a), which means that they are not evolved from the same source by fractional crystallisation. In the Rb versus K/Rb diagram (Fig. 7b), each rock type shows a distinct separate trend.

Crustal contamination of the gabbroic magma with silicic material can also give rocks of granodioritic composition. In such cases, there should be a positive trend of Ba and other LILE with increasing SiO 2 from gabbro to granodiorite. The absence of such positive correlations (Figs 3 and 7) imply that crustal contamination processes did not play a major role in the evolution of the tonalite-granodiorite suite.

From a number of experimental studies (e.g. Beard, 1995; Brandon and Lambert, 1993; Beard and Lofgren, 1989, 1991 ), there is growing evidence that the melting of amphibolites in oceanic and continental arcs can yield acidic magmas. For example, dehydration melting of amphibolites at 900- 1000°C and high pressure (> 1 kbar, < 10 kbar) has been shown to produce 6-60% of a tonalitic melt with low SiO 2 contents (52-55%) and a resi- duum dominated by plagioclase, pyroxene and Fe-Ti oxides (Wolf and Wyllie, 1994; Beard and Lofgren, 1991; Rushmer, 1991; Rapp etaL, 1991). The authors, therefore, favour a model of dehy-dration partial melting of a lower crust as a plausible mechanism to generate the investigated tonalite- granodiorite suite. This idea is consistent with the field observation of amphibolite xenoliths and veins in most of the Egyptian older granitoids and, in particular, in the granodiorites of Homrit Waggat and EI-Yatima areas. Also, geophysical studies show that the crust in the Arabian-Nubian Shield is composed of a lower mafic layer of modified oceanic crust and mafic cumulates, which are overlain by an intermediate calc-alkaline amphibolitic juvenile crust of about 700-900 Ma age (Healy etaL, 1980; Jackson etaL, 1984; Gettings etaL, 1986).These amphibolites must represent basalts, gabbros or volcanics of an island-arc system that were transported to the level of the island arc crust during continental growth where the P-T conditions are suitable for partial fusion.

The A-type granites In the normative Qz-Ab-Or system (Fig. 8), the Homrit Waggat and EI-Yatima A-type granites plot along the polybaric granitic minima line at low pressure (Tuttle and Bowen, 1958). This distribution suggests that all the points are related by fractional crystallisation. Other geochemical data cited above also suggest that the Homrit Waggat and EI-Yatima A-type granites are extremely fractionated and their present composition is compatible with partitioning of elements between a silicic melt and minerals crystallising from that melt (alkali feldspar, sodic amphibole, titanomagnetite and apatite). This is true for the elements Ba, Sr, AI203, MgO and Ti which show strong negative anomalies on the spider diagram (Fig. 6a) or negative correlation with SiO 2 (Fig. 3). However, the lack of correlations seen among the elements Nb, Y, and Zr (Fig. 3) and the wide variations in Rb/Sr, K/Ba, K/Rb and Rb/Ba (Fig. 9) in rocks with similar SiO 2 contents suggest that the trace element relations in the studied A-type granites are a typical result of a combination of more than one process.

Journal of A frfcan Earth Sciences 543

A.M. MOGHAZl et al.

a t

50

40

3O

2O

10

0

10

2O

F'

2.2 o

2 + 0 ~" 1.e

Z .i- ~ 1.6 ®

1.4

1.2 o

~ ~ ~ ~ 1.3

, . ,

. . . . []

_ I

o /Nom~tive Fields: Symbols: A N O R | o.g I-(2) alkali granite B Granodionte-tonalite -I |(3a) syenogranite • Homrit Waggat leucograniteJ 0.8 ~-(3b) monzogranite 0 El YaUma leucogranite -I |(4) granoaiorite I /(5) tonalite / 07

55

[ ] [ ]

[ ] [ ]

Highly [] fractionated calcalkaline E

I ~ ~ ~ Calcalkaline & trongly peraluminous

..-'" Alkaline

(c)

80

70

60

50

i

A/CNK

Strongly Peraluminous

Mildly P e r a l u m i n o u s ,

Metaluminous

I l

60 65

I

(b)

Mulock A-type granite

SiO2 (wt %)

70 75 80

SiO2 ( % ) / ,~ d

" .,'i ulock A-typ ,It1 i ~ , , ~ granite ,/

" i [] [] ? ."7

[ ] " ,,' Wo l f R iver A/type

0 . 8 I

0 2 4 6 8 10 12 0.5 1 O0*(MgO+FeO,+TiO,/SiO,)

[ ] / , ,, granite

" i \ / ' J r /

Mg-rich /'avera~' Fe-rich

• " (d) / /

1" I i I J I

0.6 0 .7 0 .8 0 .9 1.0

Fe203*/FeiO3*+MgO

Figure 5. Chemical classification diagrams for the granodiorite-tonalite and leucogranites. (a) Q'-ANOR diagram after Streckeisen and le Maitre (1979); Q" and ANOR are calculated using the norm values as follows: Q '=(Q/ [Q+Or+Ab+An] )x lO0, and ANOR=An/(Or+An)xlO0• (b) Molecular ratio AI~O3/CaO+Na20+K20 (A/CNK) versus SiO 2 (wt%) binary diagram after Chappell and White (1974)• (c) (41203 + CaO)/(FeOt + Na20 + K~O) versus l O0(MgO + FeO , + TiO~/SiO 2 diagram after Sylvester (1989)• (d) Fe number versus SiO 2 diagram after Aleinikoff et al• (1993)• Reference fields for the Mulock A-type granite (Lumbers et al•, 1991) and Wolf River A-type granite (Anderson, 1983) are shown for comparison.

The effects of F in granites is wel l -known and it is suggested that the F-rich fluid could produce HREE and HFSE enrichment in the late stages of evolution of granitic melt due to F complexing (Webb et al., 1985; Dingwell, 1988; Ponader and Brown, 1989; Rogers and Satterfield, 1994). The addition of F into the melt promotes the formation of SiO3F complexes of HREE and HFSE, result ing in depolymerisat ion (Dingwell, 1988), and a reduction in the availability of SiO 4 tetrahedra to form HREE- and HFSE-bearing phases. The development of F-bearing fluids and their interaction wi th the silicic melt at the late magmatic stage enhances element fract ionation since the addition of F decreases silicate melt viscosity (Mysen and Virgo, 1985) and expands the primary phase field of quartz (Manning, 1981 ; Manning and Pichavant, 1983), thus extending the duration of crystallisation. In the studied A-type granites, there is abundant field

and geochemical evidence of the presence of a late magmatic fluid phase. Field evidence includes the presence of pegmatitic and quartz veins associated with cassiterite mineralisation and fluorite, which occurs as common minor interstitial phases or as green fluorite veins. Geochemical evidence indicating that late stage subsolidus fluid-rock interaction and F-complexing are dominant processes include the positive correlation of enriched trace elements such as Nb, Y, and Rb with F (Fig. 10), which indicates that the granites are the products of a closed-system fractionation and even the fluids are internally derived. In addition, the F, Nb, Y and Rb contents in the least evolved samples of the A-type granites is similar to those of the surrounding normal I-type tonalite- granodiorite suite (Fig. 1 O). This similarity suggests that high concentrations of these elements are related to unusual fractionation processes rather than to an

544 Joumal of African Earth Sciences


I

0,1'-

(a) Granodiorite-tonalite

~ ~ Waggat leucogranite Homrit o El Yatima leucogranite

• Rb K.._Nbb Ce~Nd ' Ta, S,m, Y b

Ba Th Ta La Sr Hf Zr Ti Y

1000

~ 100

10

I . . . . . . I . . . . . . ] ' /~ " ' . . . . -]

(b) / : WPG " " symCOLG .~"/ . . . . . . .

VAG , .- ORG I . . / I

w Granodiodte-tonalite I | • Homrit Waggat leucogranite~ c El Yatima leucogranite |

, , , , , , , , I L L L I I ' ' ' ' , , , , , , , , I

10 100 1000 Y + Nb (ppm)

~ , u )

,° I t . . .

0.1 ~ , L , , ~ , 01 1

Y/Nb 10

Figure 6. Tectonic discrimination diagrams for the granitoid rocks. (a) Chondrite-normalised trace element abundances. Normalising values are after Sun (1982). (b) Y +Nb versus Rb diagram after Pearce et al. (1984). VAG: volcanic arc granitoids; synCOLG: collision zone granitoids; ORG: ocean ridge granitoids; WPG: within-plate granitoids. The dashed field is for A-type granites using data from Whalen et al. (1987). (c) Y/Nb versus Rb/Nb binary diagram. Fields A~ and A 2 represent the anorogenic- and orogenic-related A- type granites, respectively (Eby, 1992).

500

100

10

1000

100

5O

(a) X "@r t

10

, ' ) <~ . ,

"',X

©

o

0 0 O o

0 •

Ba (pprni I I i i i I I i I ~

1 O0 700 , , . . . . , - i r -

(bi'"

,.~<

Symbol=: × Metagabbro-dionte complex r2 Gra nodiorite-to nalite I • Homrit Waggat leucogranite~ o El Yatima leucogranite i

I I I I I [ 11

10 100 Rb (ppm)

I i , , = J L ~ l j

500

Figure 7. Variation of (a) Ba versus Sr and (b) Rb versus K/ Rb in the metagabbro-diodte complex, tonafite-granodiorite association and leucogranites.

Q

\ / ~ a I~c°gran i t t ~

Ab Or Rgura 8. Normative composition of the Homrit Waggat and E/-Yatima leucogranites plotted in the hap/ogranite system Q-Ab-Or+H20 (Turtle and Bowen, 1958). The dotted line shows the locations of minima mel t composit ions at saturated water pressures ranging from 0.5 kbar to 10 kbar (Winkler et al., 1975).


A.M. M O G H A Z I et al.

1000

100

50

10

K/Rb i

Symf~ols: - ] [ ] Granodiori te-to nalite

: o H o m d t Waggat leucogranite I I 0 El Yatima leucogranite j

[] [ ] F~ F~

[ ]

++ %

Rb/Ba

3000 - -

K/Ba 1000

0.1

0.01 - - ' ' , - - - 0.01 • 60 65 70 75 60

SiO2 (wt %) 8O

lOO f 50 ~ [] [ ]

[] [ ]

~[]

' I ; 500 ', 7 :Rb/Sr 1100

~ e ! 1 0 '

[][]~I [] • , ~ 1 I

[] ~ ~ I- ~ [ ] ;a 0.1 [ ] [ ] r~

co%

,I. 4 '

I

,,'C)

,e.~'

6s ;o 80

SiO2 (wt %)

Figure 9. SiO 2 versus K/Rb, K/Ba, Rb/Ba and Rb/Sr for the tonalite-granodiorite association and the leucogranites.

unusual source rock (A-type source) for the studied A-type granite.

Although previous studies of the Homrit Waggat leucogranite (Hassanen, 1997) concluded that it was derived from the surrounding granodiorite by fractional crystallisation, the chemical data presented here indicate that the A-type granites are genetically unrelated to any of the surrounding rocks. The main lines of evidence may be summarised as follows:

i) the compositional gaps on variation diagrams (Fig. 3);

ii) the markedly different trends on the Ba versus Sr and Rb versus K/Rb diagrams (Fig. 7);

iii) the age difference in their emplacement where the Homrit Waggat and EI-Yatima leucogranite plutons are post-orogenic and have been dated at 535 and 533 Ma, respectively (EI-Manharawy, 1977; Hashad, 1980), and the granodiorite (syntectonic) in the nearby areas have been dated at older than 650 Ma (Hashed, 1980; Stern and Hedge, 1985); and

/v) the absence of surface exposures of mafic rocks of the same age as the A-type granites in the Homrit Waggat and EI-Yatima areas.

It is possible that the studied A-type granites could have been derived from granodioritic magma from which the highly silicic granites evolved by fractional

crystallisation, during which the HFSE preferentially partitioned into a F-rich fluid phase. Calc-alkaline basaltic rocks of volcanic arc setting are considered as attractive sources that can generate granodioritic magma by dehydration melting. These rocks as a protolith (metagabbro-diorite complex) host the studied A-type granite, but their subsurface extent in the Nubian Shield is unknown. However, taking into consideration the fact that the crust in the Arabian- Nubian Shield is juvenile Pan-African crust, with the early formed rocks (i.e. 850-700 Ma) being of island- arc assemblage, it is possible that rocks of basaltic composition similar to those of the metagabbro-diorite complex are present at lower crustal levels. It is difficult to establish the heat source which was responsible for partial melting. However, it is now well-established that the emplacement of many granite plutons is controlled by major crustal lineaments, usually faults and shear zones (Leake, 1978, 1990; Hutton, 1996). Post-collision granites, in particular, are more usually allied with broad zones of diffuse extension, transcurrent faulting and translational shear zones (Gaudemer et aL, 1988; Sylvester, 1989). Although not syntectonic with respect to the main orogenic event, emplacement of the studied A-type granites seems to have been

546 Journal of Afdcen Earth Sciences

Geochemical and petrological evidence of ca/c-alkaline and A-type magmatism

90

70

Z 30

10

..... 150 E i

~1oo >..

I I I

- • Homrit Waggat leucogranite

Symbols: [] Granodiorite-tonalite

I ~. o El Yatirna leucogranite

o

o

~il [] []

I

I ° 50 #

[ ] [ ] [ ]

. . . . I - - - 4 - - - - -

~ _ 4 0 0

~ 300

200 [ 100 i •

0

I

@

£>

©

@ @

© ©

[] [] []

500 1000 1500

@ @

O

F (ppm)

©@ @@

.1

I I

2000 2500 3000

Figure 10. Variation diagrams of F versus Nb, Y and Rb for the tonalite-granodiorite association and the leucogranites.

contemporaneous with an important tectonic episode that involved movement along major shear zones. For example, most of the A-type granites, including the studied ones, occur at the intersection of major reactivated Precambrian east-northeast transform faults and north-northwest deep-seated tectonic zones (Garson and Krs, 1976; Schandelmeier etaL, 1987; Schandelmeier and Pudlo, 1990). This is demonstrated by the synchronous timing of these granites with the major ca 655-540 Ma Najd strike- slip fault system (Moore, 1979; Sultan etaL, 1988). The results of strike-slip motion may generate pull- apart structures moving segments of the lower crust

against each other and the mantle (Leake, 1990). The fault planes in the mantle would be preferred sites of partial melting, producing mantle-derived magma. Underplating by this magma, in addition to the heat from shearing, provoked partial melting of the lower crust.

CONCLUSIONS

Petrological and geochemical studies of the plutonic rocks in the Homrit Waggat and EI-Yatima areas of eastern Egypt reveal the presence of two genetically unrelated types of magmatism:

i) a syntectonic I-type magmatism represented by metagabbro-diorite complex and tonalite-granodiorite suite; and

~7) a post-tectonic A-type magmatism represented by leucogranites.

The metagabbro-diorite complex and the tonalite- granodiorite suite (I-type magmatism) are calc-alkaline and meta- to mildly peralurninous. Although they are syntectonic, major and trace element chemistry indicates that they are genetically unrelated. It is suggested that the metagabbro-diorite complex was probably formed by fractional crystallisation of a basaltic magma derived by partial melting of a metasomatised upper mantle in an island-arc setting. The tonalite-granodiorite suite, on the other hand, is believed to has been originated from partial melting of an amphibolitic lower crust in a volcanic arc environment.

The leucogranites (A-type magmatism) are geochemically evolved and enriched in Rb, Y, Nb and F, thus leading to their classification as A-type granite. However, the contents of these elements in the least evolved samples of A-type granites are more or less similar to those of the surrounding normal I-type tonalite-granodiorite suite. This suggests a normal I-type source for these granites and the high concentrations of these elements are related to unusual fractionation processes rather than to an unusual source rock (A-type source). The previously determined ages (535 Ma) for the Homrit Waggat and EI-Yatima leucogranites (EI-Manharawy, 1977), their geological sett ing and chemical characteristics led to the original conclusion that they represent a post-collision A-type magmatism in the Nubian Shield. It is suggested that they could have been derived by fractional crystallisation of a granodioritic magma, during which the HFSE may preferentially partitioned into a F-rich fluid phase. The granodior i t ic melt could be formed by dehydration partial melting of earlier Pan-African I- type calc-alkaline basaltic rocks along major shear zones.

Journal of A ftfcen Earth Sciences 547

A.M. M O G H A Z l et al.

ACKNOWLEDGEMENTS

The authors express their thanks to Prof. A. M. EI- Bouseily, Alexandria University, for his numerous helpful discussions. Thanks are also due to Prof. Fujimaki and Dr Ishikawa for kindly giving the opportunity to use the XRF spectroscopy in chemical analyses. The authors are indebted to Dr D. K0ster and another anonymous referee for their critical reviews and suggestions, which have substantially improved the manuscript. Editorial handling - D. Turner

RB=ERENCES Abdel Rahman, A.M., Martin, R.F., 1990. The Mount Gharib

A-type granite, Nubian Shield: petrogenesis and role of metasomatism at the source. Contributions to Mineralogy and Petrology 104, 173-183.

Akaad, M.K., Noweir , A.M., 1980. Geology and lithostratigraphy of the Arabian Desert orogenic belt of Egypt between latitudes 25 ° 35' and 26 ° 30' N. Institute of Applied Geology, Jeddah, Bulletin 3, 127-135.

Aleinikoff, J.N., Reed, J.C., DeWitt, E., 1993. The Mount Evans batholith in the Colorado Front Range: revision of its age and reinterpretation of its structure. Geological Society of America Bulletin 105, 791-806.

Anderson, J.L., 1983. Proterozoic anorogenic granite plutonism of North America. Geological Society of America Memoir 161, 133-154.

Arth, J.G., Hanson, G.N., 1975. Geochemistry and origin of the early Precambrian crust of northeastern Minnesotta. Geochimica et Cosmochimica Acta 39, 325-362.

Beard, J.S., 1995. Experimental, geological and geochemical constraints on the origin of Iow-K silicic magmas in oceanic arcs. Journal of Geophysical Research 100, 15,593-15,600.

Beard, J.S., Lofgren, G.E., 1989. Effect of water on the composi t ion of part ial melts of greenstone and amphibolites. Science 244, 195-197.

Beard, J.S., Lofgren, G.E., 1991. Dehydration melting and water-saturated melt ing of basalt ic and andesit ic greenstones and amphibolites at 1, 3 and 6.9 kbar. Journal of Petrology 32, 365-402.

Bennett, J., Mosley, P., 1987. Tiered-tectonics and evolution, Eastern Desert and Sinai, Egypt. In: Matheis, G., Schandelmeier, H. (Eds.), Current Research in African Earth Science. Balkema, Rotterdam, pp. 79-82.

Bentor, Y.K., 1985. The crustal evolution of the Arabo-Nubian massif with special reference to the Sinai Peninsula. Precambrian Research 28, 1-74.

Beyth, M., Stern, R.J., Altherr, R., KrSner, A., 1994. The late Precambrian Timna igneous complex, southern Israel: evidence for comagmatic-type sanukitoid monzodiorite and alkali granite magma. Lithos 31, 103-124.

Brandon, A.D., Lambert, R., 1993. Crustal melting in the Cordilleran interior: the mid-Cretaceous White Creek Batholith in the southern Canadian Cordillera. Journal of Petrology 34, 239-269.

Chappell, B.A., White, A.J.R., 1974. Two contrasting granite types. Pacific Geology 8, 173-174.

Dingwell, D.B., 1988. The structures and properties of fluorine-rich magmas: a review of experimental studies. In: Taylor, R.P., Strong, D.F. (Eds.), Recent Advances in the Study of Granite-Related Mineral Deposits. Canadian Institute of Mineralogy and Metallogenesis, Montreal, Quebec, pp. 1 - 12.

Eby, G.N., 1992. Chemical subdivisions of the A-type

granitoids: petrogenesis and tectonic implications. Geology 20, 641-644.

EI-Gaby S., 1975. Petrochemistry and geochemistry of some granites from Egypt. Neues Jahrbuch Mineralogie Abhandlungen, 125, 147-189.

EI-Manharawy, M.S., 1977. Geochronological investigation of some basement rocks in central Eastern Desert, Egypt, between Lat. 25 ° and 26°N. Ph.D. thesis (unpubl.), Cairo University, Egypt.

EI-Ramly, M.F., Greiling, R.O., KrSner, A., Rashwan, A., 1984. On the tectonic evolution of Wadi Hafafit area and environs, Eastern Desert of Egypt. Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Bulletin 6, 113-126.

Fumes, H., EI-Sayed, M.M., Khalil, S.O., Hassanen, M.A., 1996. Pan-African magmatism in the Wadi El-lmra district, Central Eastern Desert, Egypt: geochemistry and tectonic environment. Journal of the Geological Society of London 153, 705-718.

Garson, M.S., Krs, M., 1976. Geophysical and geological evidence of the relationship of Red Sea transverse tectonics to ancient fractures. Geological Society of America Bulletin 87, 169-181.

Gaudemer, Y., Jaupart, C., Tapponnier, P., 1988. Thermal control on post-orogenic extension in collision belts. Earth Planetary Science Letters 89, 48-62.

Gettings, M.E., Blank, H.R., Mooney, W.D., Healey, J.H., 1986. Crustal structure of southwestern Saudi Arabia. Journal of Geophysical Research 91, 6491-6512.

Greenberg, J.K., 1981. Characteristics and origin of Egyptian Younger Granites. Summary. Geological Society of America Bulletin, Part I 92, 224-232.

Hashad, A.H., 1980. Present status of geochronological data on the Egyptian basement complex. Institute of Applied Geology of Jeddah, Bulletin 3, 31-46.

Hassanen, M.A., 1997. Post-collision, A-type granites of Homrit Waggat complex, Egypt: petrological and geochemical constraints on its origin. Precambrian Research 82, 211-236.

Healy, J.H., Money, W.D., Blank, H.R., Gettings, E., 1980. Deep structure of the Arabian Shield from the 1979 USGS/ DGMR seismic refraction profile. Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Research Series 13, 136-137.

Hussein, A.A., All, M.M., EI-Ramly, M.F., 1982. A proposed new classification of the granites of Egypt. Journal of Volcanology and Geothermal Research 14, 187-198

Hutton, D.H.W., 1996. The space problem in the emplacement of granite. Episodes 19, 114-119.

Jackson, N.J., Walsh, J.N., Pegram, E., 1984. Geology, geochemistry and petrogenesis of late Precambrian granitoids in the central Hijaz region of the Arabian Shield. Contributions to Mineralogy and Petrology 87, 205-219.

KrOner, A., 1993. The Pan-African Belt of Northeastern and Eastern Africa, Madagascar, Southern India, Sri Lanka and East Antractica: terrane amalgamation during formation of the Gondwana Super continent. In: Thorweihe, U., Schandelmeier, H. (Eds.), Geoscientif ic Research in Northeast Africa. Balkema, Rotterdam, pp. 3-9.

Leake, B.E., 1978. Granite emplacement: the granites of Ireland and their origin. In: 8owes, D.R., Leake, B.E. (Eds.), Crustal Evolution in Northwest Britain and Adjacent Regions. Seel House Press, Liverpool, pp. 221-248.

Leake, B.E., 1990. Granite magmas: their sources, initiation and consequences of emplacement. Journal of the Geological Society of London 147, 579-589.

Lumbers, S.B., Wu, T.-W., Heaman, L.M., Vertolli, V.M., and MacRae, N.D., 1991. Petrology and age of the A- type Mulock granite batholith, northern Grenville Province, Ontario. Precambrian Research 53, 199-231.

548 Journal o f African Earth Sciences


Manning, D.A.C., 1981. The effect of fluorine on liquidus phase relationships in the system Qz-Ab-Or with excess water. Contributions to Mineralogy and Petrology 76, 206- 215.

Manning, D.A.C., Pachavant, M., 1983. The role of fluorine and boron in the generation of granitic rocks. In: Atherton, M.P., Gribble, C.D. (Eds.), Migmatites, Melting and Metamorphism. Shiva, Nantwich, pp. 94-110.

Mittlefehldt, D.W., Miller, C.F., 1983. Geochemistry of the sweetwater wash pluton, California: implication for anomalous trace element behaviour during differentiation of felsic magmas. Geochimica et Cosmochimica Acta 47, 109-124.

Mohamed, F.H., 1993. Rare metal-bearing and barren granites, Eastern Desert of Egypt: geochemical characterisation and metallogenic aspects. Journal of African Earth Sciences 17, 525-539.

Mohamed, F.H., Hassanen, M.A., Matheis, G., Shalaby, M.H., 1994. Geochemistry of the Wadi Hawashia granite complex, northern Egyptian Shield. Journal of African Earth Sciences 19, 61-74.

Moore, J.M., 1979. Tectonics of the Najd transcurrent fault system. Journal of the Geological Society of London 136, 441-454.

Mysen, B.O., Virgo, D., 1985. Structure and properties of fluorine-bearing alumosilicate melts: the system Na20- AI203-SiO2-F at 1 atm. Contributions to Mineralogy and Petrology 91, 205-220.

Pearce, J.A., 1980. Geochemical evidence for the genesis and eruptive setting of lavas from Tethyan ophiolites. In: Ophiolites, Proceeding of the International Ophiolite Symposium, Cyprus 1979, pp. 261-272.

Pearce, J.A., 1983. The role of subcontinental lithosphere in magma genesis at destructive plate margins. In: Hawkesworth C.J., Norry, H.J. (Eds.), Continental Basalt and Mantle Xenoliths. Nantwich, Shiva, pp. 230-249.

Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element d iscr iminat ion diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25, 956-983.

Pearce, J.A., Norry, H.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variation in volcanic rocks. Contributions to Mineralogy and Petrology 69, 33-47.

Ponader, C.W,, Brown, G.E., 1989. Rare earth elements in silicate glass/melt systems, II. Interaction of La, Gd and Yb with halogens. Geochimica et Cosmochimica Acta 53, 2905-2914.

Rapp, R.P., Waston, E.B., Miller, C.F., 1991. Partial melting of amphibolite/eclogite and the origin of Archean trondhjemites and tonalites. Precambrian Research 51, 1-25.

Rice, A,H.N., Osman, A.F., Abdeen, M.M., Sadek, M.F., Ragab, A.I. 1993. Preliminary comparison of six late- to post-Pan- African molasse basins, E. Desert, Egypt. In: Thorweihe, U., Schandelmeier, H. (Eds.)., Geoscientific Research in Northeast Africa. Balkema, Rotterdam, pp. 41-45.

Rogers, J.J.W., Greenberg, J.K., 1981. Trace elements in continental margin magmatism; part III. Alkali granites and their relationship to cratonization. Geological Society of America Bulletin 92, Part I, 6-9; Part II, 57-93.

Rogers, J.J.W., Satterfield, M.E., 1994. Fluids of anorogenic granites: a preliminary assessment. Mineralogy and Petrology 50, 157-171.

Rushmer, T., 1991. Partial melting of two amphibolites: contrasting experimental results under fluid abscent conditions. Contributions to Mineralogy and Petrology 107, 41-59.

Saunders, A.D., Tarney, J., Weaver, D., 1980. Transverse geochemical variations across the Antractic Peninsula:

implications for the genesis of calc-alkaline magmas. Earth Planetary Science Letters 46, 344-360.

Schandelmeier, H., Pudlo, D., 1990. The Central-African Fault zone in Sudan - a possible continental transform fault. Berliner Geowissenshaften Abhandlungen 120-A, 31-44.

Schandelmeier, H., Richter, A., Harms, U., 1987. Proterozoic deformation of the East Saharan Craton in southeast Libya, south Egypt and north Sudan. Tectonophysics 140, 233- 246.

Shand, S.J., 1927. The eruptive rocks, 1st edition. John Wiley, New York, 488p.

Stanek, K.P., Pohl, T., Li, Z., Shedit, G., 1993. Rare-metal province central Eastern Desert, Egypt; I, Tectonic setting of magmatism. In: Thorweihe, U., Schandelmeier, H. (Eds.), Current Research in Africa Earth Science. Balkema, Rotterdam, pp. 477-482.

Stern, R.J., 1993. Tectonic evolution of the late Proterozoic East African Orogen: constraints from crustal evolution in the Arabian Nubian Shield and the Mozambique Belt. In: Thorweihe, U., Schandelmeier, H. (Eds.), Geoscientific Research in Northeast Africa. Balkema, Rotterdam, pp. 73-74.

Stern, R.J., Gottfried, D., 1986. Petrogenesis of late Precambrian (575-600 Ma) bimodal suite in northeast Africa. Contributions to Mineralogy and Petrology 92,492- 501.

Stern, R.J., Gott fr ied, D., Hedge, C.E., 1984. Late Precambrian rifting and crustal evolution in the northeast Desert of Egypt. Geology 12, 168-172.

Stern, R.J., Hedge, C.E., 1985. Geochronologic and isotopic constraints on late Precambrian crustal evolution in the Eastern Desert of Egypt. American Journal of Science 285, 97-1 27.

Stoeser, D.B., Camp, V.E., 1985. Pan-African micro plate accretion of the Arabian Shield. Geological Society of America Bulletin 96, 817-826.

Streckeisen, A., Le Maitre, R.W., 1979. A chemical approximation to the modal QAPF classification of the igneous rocks. Neues Jahrbuch Mineralogie Abh. 136, 169-206.

Sultan, M., Arvidson, R.E., Duncan, I.J., Stern, R.J., EI- Kaliouby, B.E., 1988. Extension of the Najd shear system from Saudi Arabia to the central Eastern Desert of Egypt based on int6grated field and Landsat observations. Tectonics 7, 1291-1306.

Sun, S.-S., 1982. Chemical composition and origin of the Earth's primitive mantle. Geochimica Cosmochimica Acta 46, 179-192.

Sylvester, P.J., 1989. Post-collisional alkaline granites. Journal of Geology 97, 261-280.

Tuttle, D.F., Bowen, N.L., 1958. Origin of granites on the light of experimental studies in the system NaAISi~O 8 - KAISi30 s- SiO2H20. Geological Society of America Memior 74, 130-142.

Webb, P.C., Tindle, A.G., Barritt, S.D., Brown, G.C., Miller, J.F., 1985. Radiothermal granites of the United Kingdom: comparison of fractionation patterns and variation of heat production for selected granites. In: High Heat Production (HHP) Granites, Hydrothermal Circulation and Ore Genesis. Institute Mineralogy Metallogeny London, pp. 409-424.

Whalen, J.B., Currie, K.L., Chappel, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology 95, 407-419.

Winkler, H.G.F., Boese, M., Marcopoulos, T., 1975. Low temperature granitic melts. Neues Jahrbuch Mineralogie Monatshefte 6, 245-268.

Wolf, M.B., Wyllie, P.J., 1994. Dehydration-melting of amphibolites at 10 kbar: the effects of temperature and time. Contributions to Mineralogy and Petrology 115, 369-383.


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