structural and tectonic evolution of the neoproterozoic feiran ...logic units, the sequence of main...

Precambrian Research 123 (2003) 269–293

Structural and tectonic evolution of the NeoproterozoicFeiran–Solaf metamorphic belt, Sinai Peninsula:

implications for the closure of the Mozambique Ocean

M.K. El-Shafeia,b, T.M. Kuskya,∗a Department of Earth and Atmospheric Sciences, St. Louis University, St. Louis, MO 63103, USA

b Department of Geology, Suez Canal University, Ismailia, Egypt

Received 1 April 2001; received in revised form 20 January 2002; accepted 12 April 2002

Abstract

The Feiran–Solaf metamorphic belt of the southern Sinai Peninsula consists predominantly of amphibolite facies metapelitic,arenaceous, and minor calcareous rocks deformed during Neoproterozoic (850–550 Ma) orogenesis and intruded by dioritic–tonalitic–granitic plutons. The belt is divided into the Solaf Zone in the southeast and the Feiran Zone in the northwest. Twenty-fivedetailed structural cross-strike transects reveal that intense polyphase deformation resulted in complex fold geometries and fabricrelationships. On outcrop scale, the progressive D1 deformation is recognized as early, NW-striking, intrafolial isoclinal folds(F1), an associated steeply dipping gneissic (S1) fabric, and the development of calc-mylonite zones along the NE margin of thebelt. Tight, NW-striking, recumbent similar folds (F2) characterize the late D1 deformation, whereas NE-striking open (F3) foldsrepresent D2. Macro-scale folds of the F1 and F2 account for the map-scale structural pattern shown by the lithologic units. F3

is represented mostly by meso-scale folds. The early SE- and NW-plunging F1 and F2 fold axes may be related to accretion ofintraoceanic sediments deposited between arcs and/or microcontinents, whereas the late NE-trending upright F3 folds may berelated to post-accretionary tectonic events. In particular, the F3 folds and associated mineral stretching lineations, which trendNW–SE, may be related to the Najd fault system.© 2003 Elsevier Science B.V. All rights reserved.

Keywords: Arabian–Nubian Shield; Sinai Peninsula; Feiran–Solaf metamorphic belt; Deformational phases; Mesoscopic folds; Structuralevolution

1. Introduction

1.1. Geologic setting and tectonic significanceof the southern Sinai Peninsula

The Arabian–Nubian Shield is part of the EastAfrican Orogen formed in the late Proterozoic

∗ Corresponding author. Tel.:+1-314-977-3132;fax: +1-314-977-3117.

E-mail address: [email protected] (T.M. Kusky).

(900–550 Ma; Bentor, 1985; Kröner, 1985; Stern,1994; Loizenbauer et al., 2001) by the accretion andamalgamation of oceanic and continental magmaticarcs and accretionary prisms during subduction andobduction of oceanic crust, and the closure of theMozambique Ocean, suturing East and West Gond-wana (e.g.Kröner et al., 1987). Late stages of thisorogenic cycle are marked by abundant intraplatemagmatism, intraplate rifting, and transcurrent fault-ing associated with the Najd fault system amongothers (Bentor, 1985; Sultan et al., 1992; Johnson,

0301-9268/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0301-9268(03)00072-X

270 M.K. El-Shafei, T.M. Kusky / Precambrian Research 123 (2003) 269–293

2003; Kusky and Matsah, 1999, 2003; Blasband et al.,2000). The rugged mountains of the southern SinaiPeninsula form a critical link between the Arabianand Nubian Shields in the northern part of the EastAfrican Orogen. However, little is known about thestructural sequence and chronology of events in thisregion, nor of the tectonic setting or correlation ofmajor rock belts with other regions. Most structuresrelated to accretionary events during closure of theMozambique Ocean are oriented roughly NE to ENEin southern Sinai (Shimron, 1984; El-Shafei et al.,1992), with the exception of the Feiran–Solaf meta-morphic belt, which is dominated by NW strikes.

The Arabian–Nubian Shield is divided into a num-ber of arc, microcontinent and other terranes, withsouthern Sinai sitting near the northern exposed limitof Neoproterozoic crust. The Midyan terrane to theeast in Saudi Arabia has affinities to oceanic arc ter-ranes, as do rocks of the Gerf terrane (also knownas the Aswan and SE Desert terrane; see Abdelsalamet al., in press;Johnson, 2000; Kusky and Ramadan,2002). The Feiran–Solaf belt, and its possible correl-atives in the Kid and Sa’al-Zaghra belts of southernSinai, form a relatively thin elongate belt of highly de-formed metasedimentary and metavolcanic rocks thatseparate the parts of the Midyan terrane from parts ofthe Gerf terrane. As such, the studies reported herehave implications about correlations between the Gerfand Midyan terranes, and whether these represent sep-arate or similar terranes.

The entire Egyptian part of the Arabian–NubianShield was subdivided byEl-Gaby et al. (1988, 1990)into an older gneissic unit considered to be basement,upon which an upper structural level (including ophi-olitic melange ofShackleton et al., 1980) was ob-ducted during the late Pan-African orogeny.Stern andHedge (1985)andKröner et al. (1990, 1994)suggestedthat basement domes formed during the Pan-Africanmagmatic evolution of island-arcs without the involve-ment of older continental crust. This interpretation isbased on isotopic ages and geochemical constraints.

The Feiran–Solaf metamorphic belt forms a NWstriking, 35-km long belt of migmatites, gneisses,and schists in the southern Sinai Peninsula (Fig. 1).Rock types include several varieties of quartzofelds-pathic and hornblende-biotite gneiss, migmatites,and calc-silicate schists, intruded and surrounded byplutonic rocks, including non-deformed meladiorite,

a pre- to syn-tectonic granodiorite–tonalite–quartzdiorite association, and late-, syn-, and post-tectonicgranites and dikes. The rocks are disposed in a re-gional dome, with higher-grade migmatites formingthe core of the dome in the more deeply eroded FeiranZone, and a rim of amphibolite-grade metapelitesand metapsammites in the Feiran and Solaf Zones.Metacarbonates are rare except for in a narrow stripalong the east side of the belt. A Phanerozoic coversequence unconformably overlies the western part ofthe belt.

U–Pb zircon ages of some of the paragneissic unitsinclude an age of 632± 3 Ma (Stern and Manton,1987), and a granodiorite east of the belt have yieldedU–Pb ages as old as 782± 7 Ma (Jarrar et al., 1983).Post-tectonic dikes have yielded Rb–Sr whole-rockages of 591± 9 Ma (Ayalon et al., 1987). We re-port preliminary U–Pb results that indicate a gran-odiorite that intrudes the eastern side of the belt is804.8 ± 4.7-Ma-old.

During this study about 25 cross-strike transectswere made throughout the belt, along which severalthousand planar and linear structural elements weremeasured. Penetrative planar and linear fabrics dis-play a close geometric relationship with outcrop- andmap-scale folds in the Feiran–Solaf belt. In this con-tribution, we describe the major rock units and meta-morphism of the Feiran–Solaf belt, present a detailedanalysis of the structural geometry and evolution ofthe belt, and offer a preliminary tectonic model thatexplains our observations.

2. Description of major rock units

The Feiran–Solaf belt is a medium- to high-gradegneiss terrane. We subdivide the belt into two zoneswith different metamorphic characteristics: (1) the So-laf Zone to the southeast; and (2) the Feiran Zone tothe northwest. A meladiorite intrusion roughly sepa-rates the two zones (Fig. 1). The Solaf Zone comprisespredominantly amphibolite-grade metasediments(pelitic, semi-pelitic, quartzofeldspathic, calc-silicaterocks, quartzite and marble), whereas a migmatizedparagneiss complex is the most abundant outcrop unitin the Feiran Zone.

The belt was mapped at a scale of 1:10,000 sothat complex relationships and data from small-scale

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Fig. 1. Location and simplified geologic map of the Feiran–Solaf metamorphic belt, modified afterAhmed (1981).


structures could be shown in adequate detail. Out-crop maps rather than contact maps were made sothat all structural interpretations shown on the mapscould be objectively evaluated. Lithologic units anddistinctive lithologies (marker beds) rather than strati-graphic units (cf.El-Gaby and Ahmed, 1980; Hegazi,1988) were mapped because they delineate map-scalestructures best. For mapping, the Feiran–Solaf beltwas subdivided into broad lithological units, someof which are biotite-, hornblende- and biotite-, orquartz-rich.

The present study reveals that the Feiran–Solaf beltcontains at least three-fold generations of alternatingand superimposed antiforms and synforms, which playa great role in the spatial distributions of the differentrock units. Based on the spatial distribution, contactrelationships, and the structural pattern of the litho-logic units, the sequence of main rock units exposed inthe belt is arranged from oldest to youngest inFig. 1,and discussed in that order here.

2.1. Gneissic and migmatitic units

2.1.1. AmphiboliteAmphibolite of the Feiran–Solaf belt occurs as in-

clusions, bands, linear bodies of variable thickness,and irregular lenses in paragneisses (too small to beshown inFig. 1). Previous investigators (e.g.El-Tokhi,1992) suggested an igneous origin for the amphibo-lites, based on chemical evidence. They suggested thatthe amphibolites were derived from tholeiitic mag-mas, transitional in character between continental andisland arc chemistry. Ortho-amphibolite enclaves arefound in different metamorphic rock units and alsoin the syntectonic granitoids; some of them are mas-sive, whereas others are foliated. They are fine- tomedium-grained, grayish green to black in color. Min-eralogically, the amphibolites consist of hornblende,plagioclase, biotite, iron oxides, and quartz. High con-tents of opaque minerals, titanite, and apatite indicatethe basic nature of their parent rocks and support anigneous origin for the amphibolites (El-Tokhi, 1992).

2.1.2. Migmatized gneissic complexA migmatized gneiss complex forms the core of

the Feiran antiform outcropping along Wadi Feiran(Fig. 1). This complex is about 10 km long and 2 kmwide, and includes dioritic, tonalitic, granodioritic,

and granitic orthogneiss, intercalated with bandedhornblende-biotite gneiss of probable metapelitic ori-gin. The migmatitic paragneisses show compositionalbanding on the millimeter to centimeter scale, de-fined by alternation of coarse-grained leucosomes andmedium- to fine-grained mesosomes (both in the senseof Ashworth, 1985). The gneiss belt is intruded alongthe eastern and the southern parts of the mapped area(Fig. 1) by granitoid rocks that contain xenoliths ofthe migmatites, amphibolites, and gneisses (Fig. 2a).

The migmatites can be easily differentiated in thefield and separated into two separate rock units, includ-ing granitic and trondhjemitic migmatites, and con-stitute the area between Wadi Aleiyat and Wadi Tarr(Fig. 4). Further west, the migmatites occur at the ex-posed base of the metamorphic sequence. No migma-tized rocks are recorded in the Solaf Zone.

The megascopic appearance of the migmatites inthe study area is strongly variable. Stromatic, ag-matic, ptygmatic, and folded migmatitic structuresare present (sensuSederholm, 1907, 1934; Mehnert,1968; Ashworth, 1985; Johannes et al., 1995). Themost common migmatitic structures are the stro-matic type with leucosomes parallel to the foliationof the gneisses. Light color, coarse-grain size, andthe absence of gneissosity and common fold interfer-ence patterns characterize the migmatite leucosomes,which typically consists of quartz and plagioclaseas dominant components. Melanosomes, which oc-cur adjacent to leucosomes, are present as layersof variable thickness (up to 2 cm), but typically arethinner than the leucosomes. The leucosomes andthe melanosomes are mostly concordant with sharpcontacts between them. Ptygmatic structures in themigmatites reflect the effect of partial melting (i.e.the deformation occurred while the leucosome wasmostly liquid and the melanosome was recrystallized)(e.g.Mehnert and Bush, 1982).

Two generations of leucosomes occur in the Feiranmigmatite: granitic and tonalitic. The granitic leu-cosomes exist mostly as equigranular coarse- tomedium-grained layers dissected by the tonalitic leu-cosomes. They range in color from pinkish white toreddish and are composed mainly of quartz, plagio-clase, K-feldspar and biotite. Accessory minerals in-clude titanite, epidote, zircon and iron oxides. Quartz,plagioclase, biotite, and/or hornblende dominate thetonalitic leucosomes, which are generally white to

M.K. El-Shafei, T.M. Kusky / Precambrian Research 123 (2003) 269–293 273

Fig. 2. Outcrop field photographs: (a) different relics of migmatitic structures engulfed in the pre- to syn-tectonic granite, Feiran Zone; (b)pinch-and-swell boudinage structures, Feiran Zone; (c) fold flattened by ductile shearing, Feiran Zone; (d) F1 isoclinal folds in hornblendebiotite gneiss of Feiran Zone;(e) Parasitic folds in pegmatite veins in hornblende-biotite gneiss showing systematic change in symmetrybetween limbs of larger fold; (f) Z-shaped fold in calc-silicate rocks of Solaf Zone. Note the intensive development of the smallestwavelength at the hinge of the larger fold; (g) type-3 interference pattern: F1 isoclinal fold refolded by F2 dextral fold, migmatized gneissof Feiran Zone; (h) F3 open fold superimposed on both F1 and F2 structures, Solaf Zone calc-silicate rocks; (i) dextral simple-shear senseshown by rotated porphyroclast, Solaf Zone.

light-gray in color, and coarse- to medium-grained.Mesosomes are medium-grained, equigranular tosub-equigranular, and show variable mineral com-position from one mesosome layer to another. Thedominant minerals are quartz, plagioclase, biotite, andhornblende. Melanosomes are fine-grained, stronglyfoliated, and display a granoblastic texture com-posed essentially of quartz, plagioclase, biotite, andhornblende; biotite is generally more abundant thanhornblende.

2.1.3. Hornblende-biotite gneissHornblende-biotite gneissic rocks are widely dis-

tributed in the area. They are interlayered with the

biotite and quartzofeldspathic gneisses and also occuras xenoliths in the quartzofeldspathic gneiss. Theydominate the outcrop pattern of the western part ofthe belt (Feiran Zone,Fig. 1), and field relation-ships suggest that they represent the oldest exposedgneissic rock unit in the Solaf Zone. The boundaryshown on the map is based on the relative abun-dance of these rocks with regard to other units. Thehornblende-biotite gneiss is fine- to medium-grained,strongly foliated, and dark-colored. It shows band-ing, and recumbent folds in Feiran Zone and similarfolds in Solaf Zone. The hornblende-biotite gneissesconsist of hornblende, plagioclase, biotite, and quartzwith subordinate amounts of sillimanite, chlorite, and


epidote (clinozoisite) (El-Shafei, 1998). Iron oxides,zircon, apatite and titanite are accessory minerals.The presence of titanite and apatite, suggests thatthese rocks could be metamorphosed mafic rocks, asopposed to metapelitic rocks (El-Tokhi, 1992). How-ever, their intricate intercalation with other metasedi-mentary gneisses suggests that they may have had asedimentary protolith.

2.1.4. Biotite gneissBiotite gneisses are brownish gray in color, fine- to

medium-grained, exhibit a pronounced foliation, andpredominantly crop out in the Solaf Zone, where theyare intercalated with hornblende-biotite gneiss and in-terlayered with quartzofeldspathic gneiss. These rocksare strongly foliated and altered, and display similarfold styles and common boudinage structures. Nearthe contact with the syntectonic granitoids, these rocksbecome rich in garnet, cordierite and spinel, while thehornblende-biotite gneisses become rich in diopside(El-Shafei, 1998).

2.1.5. Biotite, hornblende-biotite, and localquartzofeldspathic gneiss

Biotite, hornblende-biotite, and local quartzofelds-pathic gneisses crop out at the eastern part of the So-laf Zone in contact with the granitoid rocks. Theserocks form the uppermost unit in the succession anddefine the closure of a large antiform (Fig. 1). Theyare fine-grained and of a medium amphibolite facies.They have experienced thermal and dynamic meta-morphism, giving rise to granoblastic textures, whichare more massive than in the lower-grade varieties.

2.1.6. Quartzofeldspathic gneissQuartzofeldspathic gneisses are characterized by

light-whitish red and grayish to reddish color withvariable grain size. On the meso-scale, they alsoshow clear banding, faults and open folds. A foliationand overturned meso-scale open folds are observedin the Feiran Zone. In the southeast of the belt, thequartzofeldspathic gneisses are interlayered with thehornblende-biotite gneisses and biotite gneisses, andare generally cut by numerous pegmatite veins. Thefine-grained quartzofeldspathic gneisses are charac-terized by granoblastic textures, with rare scatteredbiotite flakes oriented within the quartzofeldspathicmosaic.

2.1.7. Calc-silicatesCalc-silicate rocks form a relatively minor compo-

nent of the Feiran–Solaf belt. However, the exposuresare remarkable in the field, displaying a wide varietyof mesoscopic structures and containing garnet crys-tals of relatively large size. They occur in the SolafZone as a relatively narrow, discontinuous, highly de-formed belt (70 m wide), running parallel to and incontact with the granitoid rocks in the eastern partof the study area. Northwards, these rocks becomepure marble 500 m before the junction of Wadi Feiran,Wadi El-Sheikh, and Wadi Solaf (Fig. 3), and showa slight difference in the attitude of the foliation andbanding. Calc-silicate rocks are fine-grained, massive,light-green in color, and show distinctive banded struc-tures defined by the alternation of white and dark greenbands.

2.1.8. QuartziteQuartzite forms small exposures in the Solaf Zone.

It is composed essentially of quartz, K-feldspars, andopaque minerals, and shows fine-grain size and gra-noblastic textures.

2.1.9. Metavolcanic rocksMetavolcanic rocks were recorded at only two lo-

calities in the Solaf Zone. The first is located to theSE in contact with the granitoid rocks and is charac-terized by a fine-grain size, light green color, and lowmetamorphic grade. The second location is close to thejunction of Wadi Solaf and Wadi Rim (Fig. 3), wherethe rocks are leucocratic, fine-grained, hard, banded,and have a high specific gravity.

2.2. Plutonic rocks

2.2.1. Pre- to syn-tectonic granitoidsPre- to syn-tectonic granitoid rocks include a

gray granodiorite–tonalite–quartz diorite associa-tion that intrude along the south and east bordersof the Solaf Zone (Fig. 1). They extend furthereast forming numerous low-relief hills characterizedby intense shearing and they contain many xeno-liths of amphibolite and hornblende-biotite gneiss,particularly near the southern and eastern contactswith the metamorphic belt. Kusky et al. (in prepara-tion) report a U–Pb zircon age for this pre- to syn-tectonic granodiorite of 804.8 ± 4.7 Ma, providing


Fig. 3. Structural map showing the main planar and linear structural elements of the Solaf Zone; inset is equal-area projection of the linearelements throughout the entire belt.

a minimum age for the Feiran–Solaf metamorphicunits.

2.2.2. MeladioriteA large non-deformed meladiorite body forms an

elongated, NE-striking intrusion that contains inclu-sions of darker diorite, gabbro, and amphibolite. Theelongation of the intrusion suggests that it may haveintruded along a pre-existing crustal weakness located

roughly to the north between the Solaf and FeiranZones.

2.2.3. Um Takha white graniteUm Takha white granite crops out along the upper

part of Wadi Um-Takha (Solaf Zone). Red alkali gran-ites of Gabel Serbal intrude it (Fig. 1). Small outcropsalso occur in contact with calc-silicate rocks caus-ing local contact metamorphism. They show gneissic


textures and contain xenoliths of hornblende-biotitegneiss and different metamorphic enclaves.

2.2.4. Late syn- and post-tectonic granitesLate syn- and post-tectonic granites form large

mountainous outcrops bordering the belt and the syn-tectonic granitoids. Reddish color and the absence ofdike swarms that are recorded within the early plu-tonic phases characterize late syn- and post-tectonicgranites (e.g.Ahmed, 1981).

2.2.5. DikesThe belt and surrounding plutonic rocks are cross-

cut by a great number of Mesozoic–Cenozoic and,less-common, Precambrian dikes of variable grain sizeand composition. The dikes trend mostly NE, but alsoNW, parallel to the Gulf of Aqaba and the Gulf ofSuez. The Mesozoic–Cenozoic dikes are related to theopening of the Red Sea (e.g.Ahmed and Youssef,1976). Most of the dikes cut the rocks along frac-tures whereas some of them run parallel to foliationplanes.

3. Metamorphism and protoliths ofmetamorphic rocks

According to a detailed petrographic study(El-Shafei, 1998) and results of previous investiga-tors (e.g.Akaad, 1959; Ahmed, 1970; El-Gaby andAhmed, 1980; Hegazi, 1988; Belasy, 1991; El-Tokhi,1992), it is concluded that the parent rocks of thegneisses and migmatites were sedimentary with minorvolcanic intercalations. We suggest that the primaryrock types included, in order of abundance, pelite,graywacke, sandstone, volcanic intercalations, andcalcareous sandstone. This interpretation is based onthe following observations: (1) preserved relict bed-ding revealing intercalated pelitic, semi-pelitic, andmarly layers; (2) presence of well-rounded zircongrains marked by corroded outlines; and (3) abundanceof biotite and the occurrence of cordierite and silliman-ite, defining the argillaceous parent sedimentary rocks.The quartzofeldspathic gneiss, calc-silicate rocks, bi-otite gneiss, hornblende-biotite gneiss, and amphibo-lite are derived from arenaceous, arenaceous–limey,pelitic, calcareous–pelitic or marly, and limey sedi-ments, respectively. The higher quartz contents in the

quartzofeldspathic gneiss and calc-silicate rocks indi-cate their arenaceous nature. The argillaceous nature ofthe biotite gneiss is evidenced from the higher volumepercentage of biotite and K-feldspar. The occurrenceof iron oxides surrounded by thick clusters of titanitein some amphibolites suggests an igneous origin (e.g.Williams et al., 1982). Alternatively, these oxides maybe simple reaction products as seen in many meta-morphosed pelites. Also, it is concluded that the areaexperienced regional amphibolite facies metamor-phic conditions.Akaad (1959)suggested that highlymetasomatic metamorphism affecting the gneiss belttook place in two stages, namely, an early phase ofmedium-grade regional metamorphism, followed bya highly metasomatic phase. However,El-Gaby andAhmed (1980)stated that these two stages were relatedto one cycle of metamorphism and that no tectonicevents intervened between them. The micro-structuralgenerations recognized byEl-Shafei (1998)formedunder the same metamorphic conditions and show ev-idence of gradual changes in the metamorphic condi-tions as the deformation progressed. The metamorphicunits of the belt show the effects of two successivephases of regional amphibolite-facies metamorphism(M1 and M2), followed by a later thermal overprint.Specific mineral assemblages, fabric orientations andcompositions characterize each metamorphic phase(El-Shafei, 1998).

4. Mesoscopic structures of theFeiran–Solaf belt

In this section, we describe, correlate, and analyzethe field orientation data of the outcrop-scale structuresin the rocks of the Feiran–Solaf belt. Within the Feiranand Solaf Zones, 25 cross-strike transects were made,along which the available planar and linear structuralelements were measured. The most prominent planarand linear elements in the Solaf and the Feiran Zonesare shown inFigs. 3 and 4, respectively. The beltcontains a continuous, albeit highly deformed, strati-graphic sequence repeated numerous times by com-plex folds. Thrusts and other early faults locally repeatthe section, although these appear to have a minorinfluence on the structure of the belt with the impor-tant exception of the thrusts that form calc-mylonitesalong the NE margin of the belt. Based on the


Fig. 4. Structural map showing the main planar and linear structural elements of the Feiran Zone.

overprinting relations between the different fold sys-tems, three successive phases of folding are observed.

4.1. Foliations

Schistosity and gneissic foliations are among thecontinuous foliations observed in the Feiran–Solafbelt. This type is given the symbol S1. Intersection andcrenulation lineation define foliations and are giventhe symbol S2. Most foliations in the Feiran–Solaf belt

are axial-planar to folds. Quartzofeldspathic gneissesof the Solaf Zone are weakly foliated, whereas thesame rock types in the Feiran Zone are strongly foli-ated. The change in the spacing of the foliation withinthe entire belt may be related to strain variation,however, it may also be a consequence of originallithologic variations.

According to the styles of the mesoscopic folds andthe overprinting relationships, the map-scale folds ofthe belt occur as three-fold generations designated F1,


F2, and F3. Crosscutting relationships between folia-tions, folding and veins that cut them are used to derivethe relative ages of different generations of structures.However, some veins are cut by the S2 foliation andare also folded (Fig. 5b), indicating their formationafter F1 and prior to or during the second F2 foldingphase.

Gneissic foliations in the area are generally definedby medium- to coarse-grained minerals that form com-positional banding with a preferred planar orientationof platy, tabular, or prismatic minerals, and by sub-parallel lenticular mineral grains and grain aggregates.The compositional banding occurs at all scales fromthick, continuous bands and layers that can be mappedacross the entire field area, to discontinuous laminaethat pinch out within individual outcrops, hand speci-mens, or thin sections (El-Shafei, 1998). Some meso-scopic structures also are associated with thin layersand pods of granitic material, forming migmatites andagmatites in the Feiran Zone.

Foliation planes strike mainly NW–SE, roughlyparallel to the elongation of the belt, with varyingdip directions. In the eastern portion of the SolafZone, foliations have shallow dips (average 25◦NE),whereas in the central portion of the Solaf Zone fo-liations show moderate dips (45◦SE), but along thewestern part of the Solaf Zone, they show steep dips(81◦NW). In the Feiran Zone, foliations show moder-ate to steep dips (Fig. 4). The variation in strike andthe dip of foliations throughout the belt reflects theeffect of fold overprinting. The presence of inclinedaxial planar foliations of the Solaf Zone, uprightfolds, and sub-horizontal foliation of the Feiran Zonerecumbent folds suggest that these two folds may berelated to two different fold systems.

Crenulation foliations are recorded only in thebiotite-gneisses of the Feiran–Solaf belt as crenula-tions of S1 cleavage.

4.2. Lineations

Linear structures are well developed throughout thearea. They have been divided into the following types:intersection lineations, fold hinge lineations, boudinlineations, and mineral lineations. They are found innearly all rock types, but are generally best developedin migmatites, especially in the crests and troughs ofthe macroscopic folds.

The mean geometric orientation of intersection lin-eations is parallel to that of the major fold axes (F2).The preferred orientations of mesoscopic folds definefold hinge lineations. The measured mesoscopic foldaxes are treated geometrically as a regionally penetra-tive lineation. They show the presence of three clusterson the stereonets that are related to the three observedmacroscopic fold axes, as explained later.

Boudins display a wide variety of shapes in the area.Leucocratic plagioclase-rich layers are commonlysegmented forming boudins, while the surroundingmelanocratic material flowed in between them. Inthis type of boudinage the necks between boudins aresmoothly curved. The existence of pinch-and-swellstructures (Fig. 2b) is strong evidence for non-linearflow in the stiff layer (e.g.Hudleston and Lan, 1993).Some boudins are rotated about their long axes show-ing right-lateral sense of shearing (Fig. 2d; Wilson,1982). The long axes of most boudins are alignedparallel to the F2 macroscopic fold axes (recumbentfolds). Some other boudins are oriented normal tothe F2 axes, and these groups are related to post-F2folding (i.e. parallel to F3 macroscopic folds). Com-parisons of the orientation of layers that have beenshortened versus those that were lengthened andboudinaged were used to infer the sense of shear dur-ing boudin formation (Davis and Reynolds, 1996).Other boudinage structures show no evidence ofshearing (i.e. they were formed during pure sheardeformation).

Mineral lineations in the area are developed in theplane of the foliation and are typically marked by astreaky, fiber-like lineation, composed of aligned crys-tals of quartz, feldspar and hornblende. This mineralfabric (stretching lineation) is parallel to the geomet-ric axes of the macroscopic F1 (SE plunges) and F2(NW plunges) folds.

4.3. Fold style, orientation, and overprintingrelationships

Mesoscopic folds with wavelengths of tens of cen-timeters to a few meters and variable styles and orien-tations are numerous in the Feiran–Solaf belt (Figs. 3and 5). Most folds in the Feiran–Solaf belts are paral-lel Class 1B types (e.g.Fleuty, 1964; Ramsay, 1967;Hudleston, 1973; Twiss, 1988; Hudleston and Lan,1993), although more complex types are also present.


Fig. 5. Nature, style, and orientation of some mesoscopic folds recognized within Feiran–Solaf belt. All are traced from photographs. (a)Asymmetry sense of the later F2 mesofolds superimposed the F1 fold; (b) Post F1 and syn-F2 folded quartz vein; (c) type-1 interferencepattern (dome and basin); (d) isoclinal F1 fold developed in the hornblende-biotite gneiss of the Feiran Zone; (e) S-shaped fold inmigmatites of Feiran Zone; (f) Z-shaped fold developed in the calc-silicate rocks of Solaf Zone; (g) zigzag pattern type of interferenceshowing F2 fold superimposed the F1; (h) F3 fold superimposed both F1 and F2 folds; (i) dextral shearing indicated from the rotated sigmaporphyroclast, Solaf Zone; (j) sketch showing style of minor F1 and F2 folds from the Feiran Zone; (k) F3 folds superimposed on bothF1 and F2 folds from the Feiran Zone.


4.3.1. Mesoscopic foldsMesoscopic folds were analyzed in the field and

grouped according to style, orientation, and overprint-ing relationships.

NW- and SE-trending folds characterize the SolafZone. NW-trending folds generally are more steeplyplunging than those with a SE trend. NE-trending foldsare rare in the Solaf Zone. In the Feiran Zone, thenumber of SE-trending folds increases at the expenseof the NW-trending folds, both of which have moder-ate to steep axial plunges.

The earliest folds (F1) exhibit variability in attitudefrom region to region throughout the belt, but showconsiderable similarity of style (i.e. they are isoclinal)(Figs. 2d and 5g), intensity of folding, and associatedplanar and linear mineral growth. The axial planes ofthe isoclinal folds are parallel to the regional foliation,which in turn is roughly parallel to the trend of thebelt. This suggests a strong NE–SW flattening normalto the trend of the gneiss belt at this stage of defor-mation. Some folds show broad rounded hinges, sug-gesting a low ductility contrast during folding (ModelA of Ramsay, 1967; see alsoRamsay and Huber,1987), where the thickness ratio of the competent toincompetent layers is low. Elsewhere, both competentand incompetent layers are thickened in the fold hingezone and are thinned in the fold limbs (Model B ofRamsay, 1967; Fig. 5j). Some folds in the Feiran Zoneshow highly attenuated limbs (Fig. 5i) as a result ofprogressive strain. Ptygmatic folds were also encoun-tered in most of the metamorphic units. However,some mesoscopic folds display the effect of a sim-ple shear mechanism as indicated by the presence ofsigmoidal “drag” folds. Other mesoscopic folds showthe effects of flattening by ductile shearing (Fig. 2c).

The younger fold sets show a progressively moreuniform orientation through the metamorphic rocksequence, and they are nearly identical in terms ofstyle and orientation. F2 fold sets are characterizedby tight to recumbent folds, and are encountered pre-dominantly in the hornblende-biotite gneiss of theFeiran Zone. F2 fold sets have a strong and consistentsense of asymmetry; virtually all verge towards theSE (Figs. 2e and 5f) and are S-shaped when vieweddown-plunge. F2 folds refolded the F1 structuresand the variability of their geometry is ascribed toprogressive development of folds and the original ori-entation of F1 folds (Fig. 2d). F3 open folds are only

locally developed at outcrop scale (Fig. 5d). Z-shapedfolds are recognized in many parts of the study area(Fig. 2f) and are used together with S-shaped folds tolocate the large scale ones.

4.4. Geometry and mechanics of superimposedmesoscopic folds

Fold overprinting relationships are clearly rec-ognized within the metamorphic rock units of theFeiran–Solaf belt. The resulting outcrop pattern oftwo successive folding events depends entirely on: (a)the style, orientation, and scale of the individual foldsets, including the shapes of the earlier folds and theinclination of their axial planes; (b) the orientation andintensity of the F2 fold formation; and (c) the amountof flattening which accompanies the formation of F2folds and the orientation of the outcrop surface (e.g.Ramsay, 1962; Hudleston and Lan, 1993).

The metamorphic rocks of the Feiran–Solaf beltshow interference patterns between F1 and F2 folds(Fig. 2f), and among F1, F2, and F3 folds (Fig. 2g). F1folds are characterized by overturned isoclinal foldsat small scales and resulted in the development of astrong schistosity (S1) (Fig. 5e), which is defined bymica in metapelites. Broadly spaced cleavage is de-veloped in more competent lithologies such as quart-zofeldspathic gneisses. The orientation of F1 planarand L1 linear fabrics varies according to their posi-tions with relation to F2 major folds. The second setof folding (F2) is the main fold set of tight, recumbentand local similar fold styles. The mesoscopic folds ofthese sets show different geometries. The axial trendsof these folds consistently plunge between 20 and 70◦towards the NW and the associated planar fabric withthis phase of deformation consists mainly of axialcrenulations and spaced cleavage, which strikes NWand dips 25–80◦ towards the NE. L2 lineations withinthe belt are mainly boudins and intersection lineations,and plunge 25–50◦NW. F3 is a local mesoscopic foldset, characterized by broad, open folds.

In the Feiran–Solaf belt, the axial surfaces of simi-lar type folds show slight rotation or “rearrangement”of the inferred principal shortening direction. The ge-ometry of structures indicates that flattening played amajor role in the deformational history of the belt. Flat-tening probably dominated in the early stages (Fig. 2c)and gave way to local simple shear in the later stages


(Fig. 2i). The planar and linear fabrics in the metamor-phic rock units display a close geometric relationshipwith the coeval larger-scale folds (i.e. outcrop-scalelineations are parallel to map-scale fold axes;Figs. 9and 10).

4.5. Early thrust faults and calc-mylonites

A folded early thrust fault is recognized near thecontact with the pre- to syn-tectonic granitoids in theeastern part of the gneiss belt. This early thrust faultis preserved as a NW-striking belt of calc-mylonitesup to 50 m thick. The calc-mylonites are composedof diopside, plagioclase, quartz, and garnet. The gar-nets form large, spectacularly rotated porphyroblastswith deflected and rotated tails, indicating the senseof shear. The kinematic indicators from this mylonitezone show an early sense of thrusting from the NEtoward the SW (Kusky and El-Shafei, in preparation).

5. Geometrical analysis of thestructural elements

In this section, we analyze the structural geometryand sequence of folding in the study area by describ-ing the orientation of folds, fold shape and tightness,and graphically restoring folds to find the initial orien-tation of the early structural elements. Some modifi-cations have been made to improve the appearance ofthe contour diagrams, including the removal of someintermediate contour lines.

The maps of the Solaf and Feiran Zones (Figs. 3and 4) show the distribution of the main planar and lin-ear structural elements throughout the belt. The struc-tural measurements on these maps represent the meanorientation of the structural elements and some dataare eliminated due to the small scale of the map. Fo-liations, intersection lineations, mineral lineations,boudins, and mesoscopic fold hinge lineations are themain structural elements that are treated geometri-cally and statistically using stereographic projectiontechniques to calculate their original orientations.

5.1. Foliations

Field studies of the Feiran–Solaf belt indicate thatthe belt experienced multiple folding events. It is there-

fore necessary to subdivide the polyphase fold belt intosmaller, homogenous subdivisions or domains eachof which contains structures that are statistically ho-mogeneous (e.g. domains characterized by cylindricalfolds).

The crude form of macroscopic folds was deter-mined by drawing extrapolated strike lines on the mapparallel to the measured attitudes of foliations in theSolaf (Fig. 6) and Feiran (Fig. 7) Zones. These mapsshow the general forms of the macrofolds within thebelt, which cannot be deduced by standard field map-ping methods because the folds are too large to bedetected by direct observation in the field. The crudefold forms have been subdivided into seven Domains,three in the Solaf and four in Feiran Zones. This subdi-vision is based essentially on the configuration of theextrapolated strike lines, the unique orientation of bothplanar and linear elements, and the attitude of the in-cluded mesoscopic folds. For each domain, the avail-able measurements were treated separately in order toconstruct the whole complex, noncylindrical structure.The axis and the axial plane of each fold dominatingeach domain were defined.

The subdivisions displayed onFigs. 6 and 7arebased on the recognition of the rectilinear nature of theapparent trace of the hinge surfaces and other struc-tural evidence (e.g. the attitude of mesoscopic folds).A plot of the data from each domain yields the ori-entation of the folds in each homogeneous part of thelarge heterogeneous structures; the results of the anal-yses are described below.

5.1.1. Solaf ZoneThe attitudes of 235 foliation planes were measured

in Domain 1 in the eastern part of Solaf Zone (Fig. 6a).The stereogram inFig. 6ashows one distinct maxi-mum of mean orientation plunging 49◦ to S29◦W. Thecontour lines are elongated along a great circle, whichstrikes S12◦W and dips 80◦W. The pole to the girdle(i.e. the fold axis) plunges 10◦ to S77◦E. The axialplane (the great circle passing through the fold axisand the axial trace) strikes N30◦W and dips 30◦ to theNE (Fig. 8a).

The attitudes of 127 foliation planes were measuredin Domain 2 in the central portion of the Solaf Zone.The stereogram inFig. 6bshows a general concentra-tion of points in the southwest quadrant of the pro-jection, signifying that the foliations are moderately


Fig. 6. Structural orientation data from the Solaf Zone: (a–c) equal area, lower-hemisphere projections of poles to foliations and simplifiedmap showing boundaries of structural domain; (d and e) show point diagram and its contour equivalent to the Solaf Zone mesoscopic foldhinges, respectively.


Fig. 7. Structural orientation data from the Feiran Zone: (a–d) equal area, lower-hemisphere projections of poles to foliations and simplifiedmap showing boundaries of structural domains; (e) contoured diagram of poles to foliation along transect “A–B” in Wadi Feiran; and (fand g) point and contour diagrams of mesoscopic fold hinges in the Feiran Zone, respectively.


Fig. 8. Attitudes of dominant axial plane in each structural domain in the Feiran–Solaf belt.

dipping towards the east and the center of the con-toured pattern corresponds to the preferred orientationof the foliation. The contour lines are elongated alonga great circle striking S41◦W and dipping 77◦W. The

fold axis plunges 13◦ to S49◦E, and the axial planestrikes N43◦W and dips 70◦ to the NE (Fig. 6b).

The attitudes of 234 foliation planes were measuredin Domain 3 in the western part of the Solaf Zone

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Fig. 9. Structural cross-section A–B along Wadi Dehiset Abu-Talb and Wadi Um Takha, Solaf Zone.

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Fig. 10. Structural cross-section C–D through the Feiran Zone.


and the eastern part of the Feiran Zone (Fig. 6c). Thestereogram shows one distinct maximum (Figs. 6cand 8c) situated in the southwest quadrant of the netthat strikes S59◦W and dips 22◦ to the SE, signify-ing that the foliations are steeply dipping towards thenortheast. The contour lines are elongated along onegreat circle. The axial surface of the of the best-fitgreat circle strikes S15◦E and dips 22◦ to the SW andthe pole to this great circle plunges 68◦ to N75◦E.The axial plane strikes N27◦W and dips 68◦ to theNE (Fig. 8c). A point diagram and its contour equiv-alent of the mesoscopic fold hinges measured acrossthe entire Solaf Zone are shown in (Fig. 6d), which in-dicates that these mesoscopic folds are parallel to thelarger folds deduced by stereographic projection.

5.1.2. Feiran ZoneThe attitudes of 380 foliation planes measured in

Domain 4 from the area around the Feiran Oasis areplotted inFig. 7a. The diagram shows the elongationof the contour lines along a great circle striking S54◦Wand dipping 69◦NW. The pole (fold axis) to this greatcircle plunges 21◦ to S36◦E. The attitude of the axialplane strikes N22◦W and dips 55◦ to the NE (Fig. 8d).

The attitudes of 413 foliation planes were measuredin Domain 5 and are plotted inFig. 7b. The stere-ogram shows the elongation of the contour lines defin-ing a fold girdle. The attitude of the best-fit great circlestrikes N32◦E and dips 64◦ to the NW and the fold axisplunges 26◦ to S58◦E. The axial plane strikes N34◦Eand dips 26◦ to the SE (Fig. 8e). The fold axis plungesdirectly down the dip of the axial surface. Field mea-surements and the stereographic projection reveal thatthis reflects the presence of a cylindrical fold systemin which the folds have roughly the same axial trendsand axial surfaces. The attitudes of 87 foliation planeswere measured in Domain 6. The stereogram of these

Table 1Attitudes of dominant macroscopic folds in each structural domain of the Feiran–Solaf belt

D Poles no. Fold axis Axial plane Fold description

1 235 S77◦E/10◦ N30◦W/30◦E Sub-horizontal, gently inclined fold2 127 S49◦E/13◦ N45◦W/69◦E Gently plunging, steeply inclined fold3 234 N75◦E/68◦ N27◦W/68◦E Steely plunging, steeply inclined fold4 380 S36◦E/21◦ N18◦W/54◦E Gently plunging, moderately inclined fold5 413 S58◦E/26◦ N31◦E/26◦E Gently plunging, gently inclined, reclined fold6 87 S71◦E/05◦ N70◦W/81◦E Sub-horizontal upright fold7 185 S69◦E/08◦ N67◦W/67◦N Sub-horizontal steeply inclined fold

data (Fig. 7c) shows the presence of two-point max-ima, one of which is situated at the SW quadrant ofthe projection, signifying that this maximum is mod-erately dipping towards the NE, whereas the secondmaximum is located at the NE quadrant, signifying afoliation that is moderately dipping towards the SW.The two maxima are aligned together along a greatcircle that strikes S19◦W and dips 85◦W, and whosepole (the fold axis) plunges 5◦ to S71◦E. The axialplane strikes N70◦W and dips 82◦ to the NE (Fig. 8f).

Domain 7 is located in the western portion of theFeiran Zone. The attitudes of 185 foliation planes weremeasured within this domain (Fig. 7d). The stereogramshows one distinct maximum, which is situated in thesouthwest quadrant of the net and steeply dipping to-wards the northeast. The contour lines are elongatedalong a best-fit great circle striking S21◦W and dipping82◦W, whose pole (fold axis) plunges 8◦ to S69◦E.The axial surface strikes N66◦E and dips 67◦ to theNE (Fig. 8g).

Table 1 exhibits the net result of analyses of alldomains and the description of the resultant folds onthe basis of the geometric relationship between axialsurfaces and fold axes. Domains 1, 6, and 7 containsubhorizontal to gently plunging folds that are gen-tly inclined (Domain 1), steeply inclined (Domain 7)or upright (Domain 6) while Domains 2, 3, 4, and 5show gently plunging folds that are steeply inclined(Domains 2 and 3), moderately inclined (Domain 4),or gently inclined, reclined folds (Domain 5).

Mesoscopic fold hinges encountered in the FeiranZone are plotted inFig. 7e. The diagram shows thatthese mesoscopic folds are parallel to the larger foldsdeduced by domain analysis.Fig. 7f is a contour dia-gram of 146 foliation planes measured along profilesA–B (Fig. 7) in Wadi Feiran. The fold axis plunges23◦ to S49◦E, which nearly represents the mean axial


trend of the F1 fold set. The diagram shows the ef-fect of the F2 folds, which deform the F1 trends alonga girdle indicated by the elongation of the contourlines.

5.2. Lineations

The most common lineations encountered in theFeiran–Solaf belt include intersection lineations, min-eral lineations, boudins, and fold hinge lineations.

The attitudes of 156 intersection lineations, minerallineations, and the long axes of boudins are plottedin Fig. 3 (inset). The diagram shows the presence ofthree distinct clusters. The first cluster is situated inthe southeastern quadrant of the net, which is parallelto the direction of the geometric F1 axes of the macrofolds. The second cluster is located in the northwest-ern quadrant parallel to the axes of major F2 folds(Fig. 6b). The third cluster is located in the northeast-ern quadrant and coincides with F3 axes, whose trendis N75◦E and plunges 68◦ (Fig. 6c).

The attitudes of 29 mesoscopic fold hinges withinthe Solaf Zone are plotted inFig. 6c and d. Fig. 8dshows that the hinges are distributed along a great cir-cle striking NW–SE and dipping NE, coinciding withthe axial plane of the geometric folds (seeFigs. 6and 8). Fig. 6e shows the presence of two maxima.The first is located in the southeastern quadrant andit coincides with the major F1 axis. The second max-imum is situated in the northwestern quadrant and isparallel to the F2 axis.Fig. 6dalso shows the best-fitgreat circle controlling the projected hinges. The poleto this circle plunges 13◦ to S42◦W, which is the meanpole of the foliation planes in the Solaf Zone. A thirdgroup of mesoscopic fold hinges also appear in thenortheastern quadrant and have the same orientationas the geometric F3 fold axis (Fig. 6c).

The attitudes of 59 fold hinges measured in theFeiran Zone are shown in the point diagram inFig. 7fand contour diagram inFig. 7g. The hinges are con-figured along a great circle and the pole to that cir-cle plunges 26◦ to S55◦W, i.e. consistent with that inthe Solaf Zone (Fig. 6d). Fig. 7f also shows the den-sity of hinges in the southeastern quadrant of the net.These hinges coincide with the geometric F1 axis. Thehinges in the northwestern quadrant are parallel to theF2 axis, whereas those in the northeastern quadrantrepresent the F3 axis.

6. Discussion

6.1. Structural interpretation

The analyses of the planar and linear structuralelements in the Feiran–Solaf metamorphic belt showclearly the presence of three phases of folding (seeFigs. 2f, g and 5a, h, i and k). Using field-overprintingdata together with the equal-area projections, themean axis of F1 plunges 13◦ to S49◦E. The F2 axisplunges 36◦ to N12◦W, while the F3 axis plunges 68◦to N75◦E. F1 and F2 account for the overall structuralpattern shown by the lithologic units, while the F3occurs mostly as mesoscopic folds.

In order to clearly display and simplify the ma-jor structures that affected the Feiran–Solaf belt, twostructural cross-sections are constructed. The first oneextends E-W for about 13 km along Wadi Um Takhaand Wadi Dehiset Abou Talb in the Solaf Zone (Fig. 9),while the second extends NW–SE for about 18 kmthrough the Feiran Zone (Fig. 10). From these struc-tural cross-sections, the larger folding geometry maybe described as a series of superimposed and alternat-ing anticlines and synclines (Fig. 10), which controlthe map distribution of the metamorphic units. Fol-lowing ductile folding, the metamorphic units weredissected by later brittle structures. The results of thestructural cross-sections are consistent with the geo-metrical and field analyses.Hegazi (1988)proposedsimilar results on his study of the area around theFeiran Oasis.

Finally, the mesoscopic structural elements, de-scribed above, expressed by fold overprinting rela-tionships are in harmony with the conclusion reachedon the macroscopic scale (Figs. 9 and 10).

6.2. Evolution of the Feiran–Solaf belt

We suggest that the parental sedimentary rocksof the Feiran–Solaf belt formed a thick sedimen-tary sequence deposited before the 804.8 ± 4.7 Ma,based on the age of pre- to syn-tectonic granitoidsthat intrude the sequence. The sequence is composedof metamorphosed mudstones, graywacke, and mi-nor calcareous sediments, with minor amounts ofarenaceous sediments and minor bands of volcanicrocks. The characteristic of these sediments stronglysuggests that the sediments represent a deep water


mudstone/graywacke (distal turbidite?) sequence andwere later cut by granitic and elongated dike-likeintrusions (e.g.Belasy, 1991).

The results of this study show that the Feiran–Solafmetamorphic belt contains five distinct tectonic unitsbounded by regional faults and granitic intrusions thathave undergone contrasting deformational and meta-morphic histories.

The main rock units in the Solaf Zone are horn-blende-biotite gneisses, biotite gneisses, quartzofelds-pathic gneiss, calc-silicates and quartzite. Migmatiticgneisses, hornblende-biotite gneisses and highly fo-liated quartzofeldspathic gneisses are the main rocktypes in the Feiran Zone. Migmatitic leucosomes oc-cur in large quantities in some locations and in smallamounts in others, which may be due to the differentaccessibilities of water during metamorphism, differ-ent compositions of the parent rocks, or differences inthe P–T conditions (e.g.Henkes and Johannes, 1980;Johannes and Gupta, 1982; Olsen, 1985; Ashworthand McLellan, 1985; Babcock and Misch, 1989;Barbey et al., 1990; Anhaeusser, 1992). The presenceof migmatized gneissic rocks in the Feiran Zone andtheir absence from the Solaf Zone can thus be at-tributed to higher-grade rocks being brought closer tothe surface in the core of the major Feiran anticlineand the presence of local heat sources such as thelater granitic intrusions.

Impure calcareous sediments that were metamor-phosed to garnetiferous calc-silicate rocks representthe final cycle of deposition and are the youngestmetamorphosed rock types in the study area. Thegranodiorite rocks to the east of the belt (Fig. 1) con-tain metamorphic inclusions and are younger than themetamorphic units. The contact between the meta-morphic rocks and the granitic rocks is intrusive.

Most of the rocks forming the Feiran–Solaf belt aredeformed and foliated, but with different intensitiesand on various scales ranging from those which arestrongly deformed (e.g. the area between Wadi Agalaand Wadi Tarr;Fig. 4) to those subjected to weakdeformation (e.g. the southeastern and northwesternportions of the belt).

Most foliations strike NW–SE throughout the belt.Slight changes in the strike direction of the foliationare ascribed to the effect of refolding. Changes in theorientation of the foliation planes along the border ofthe belt are attributed to plutonic emplacement.

Stern and Manton (1988)suggested that a thrustfault may separate the Solaf Zone and the Feiran Zone,and that the Solaf Zone metasediments may be olderthan those of the Feiran Zone. However, based on ourdetailed structural studies, there is no field or micro-scopic evidence documenting the thrust fault betweenthe two zones. The orientation data throughout thebelt show no sharp difference in the dip of the planarfabrics. However, an early thrust fault is located nearthe boundary with the igneous rocks to the NE of thebelt.

Analysis of the meso-scale fold orientations andtheir relation to the foliation planes throughout the beltsuggests that the deformational events under whichthese folds were formed were progressive. They wereof nearly constant orientation during the first deforma-tional event D1 and the formation of the first two-foldsets, F1 and F2 (Fig. 10), and then changed during thelast phase D2. F1 folds, the dominant foliation planes(NW–SE strike), and pinch and swell boudinage struc-tures are the earliest-recognized structures. The direc-tion of the maximum compressive stress (σ1) duringthe first deformational event was NE–SW, whereasσ1was directed NW–SE during the D2 phase. The resultsof stress field changes were the formation and super-imposition of F1, F2, and F3 meso- and macro-scalefold generations and the zigzag (Fig. 5h and j) anddome- and basin-type (Fig. 5c) interference patternswhich were followed by later brittle structures.

6.3. Deformational phases and structuralreconstruction

From the forgoing results, the deformational historyof the belt is a product of complex superimpositionof three-fold generations (F1, F2, and F3) associatedwith two deformational events (D1 and D2).

The early phase of deformation (D1) is character-ized by overturned, isoclinal folds (F1) with attenu-ated limbs and sharp hinges. The F1 folds, which arecompletely attenuated within the foliation, have beenobserved only on a small scale. Most of these foldsare isolated, either because they are rootless, due totectonic attenuation of limbs, or because of their ge-ometry and orientation combined with the effects oflater folding. In a number of localities, the F1 foldshave been folded around tight, typically nearly sym-metrical folds whose axial planes are largely parallel


to the foliation. The D1 deformation also resulted inthe development of a strong schistosity (S1), which isdefined by the mica in metapelites, and an axial-planarfoliation associated with F1 folds (Fig. 5e and h). Thisfoliation is generally NW-trending, but dip values fluc-tuate to define the geometry of F2 folds.

An early stage of regional metamorphism (M1) ac-companying the D1 event occurred under medium-grade amphibolite facies conditions. Chlorite, biotiteand hornblende are the main mineral assemblages,which grew parallel to the early-formed foliations.

The dominant structures of the area were generatedlate in the D1 phase, including tight, recumbent, andsimilar folds. The mesoscopic folds of the late D1phase show different geometries than those of early D1phase. The axial trends of these folds consistently dipbetween 20 and 70◦ to the NW. The planar fabric asso-ciated with late D1 is mainly an axial crenulation andspaced cleavage, which strikes NW and dips 25–80◦to the NE. L2 lineations within the belt are mainlyelongate boudins and intersection lineations plunging25–50◦ to the NW. Late D1 deformation increases to-wards the center of the belt with complicated interfer-ence patterns and more penetrative foliations. Meta-morphism (M2) coupled with this stage of deformationoccurred under high-grade regional amphibolite-faciesconditions (sillimanite-grade). The formation ofmigmatites also accompanied this stage, indicatingthe involvement of anatexis localized in the FeiranZone (El-Gaby and Ahmed, 1980; El-Shafei, 1998),while metamorphic differentiation played only aminor role.

The D2 episode is considered to have been a local-ized additional phase involving open, meso-scale fold-ing (F3). Brittle faulting and intrusion of felsic dikesexpress later deformation. M3 was the latest thermalphase of metamorphism accompanying the pluton em-placement. Garnet, diopside, actinolite and tremolitewere the main metamorphic mineral assemblages thatgrew during this phase (El-Shafei, 1998).

The D1 deformational event is interpreted to reflecta progressive deformation accompanying amphibolite-facies metamorphism, and starting as NE–SWdirected flattening deformation. The flattening de-formation produced the dominant NW–SE foliationtrends in addition to the SE-trending F1 isocli-nal folds. As the flattening deformation continued,migmatites, NW-trending folds and overprinting folds

were formed during the latest stages of D1. Openfolds followed by brittle structures represent thesecond (D2) stage, which accompanied plutonic em-placement. The D2 event is probably equivalent to thestage-III (block faulting deformation) event proposedby El-Ghawaby (1979).

7. Implications for the closure of theMozambique Ocean

The Feiran–Solaf assemblage of metamorphosedpelites, graywackes, calcareous sandstone, and rarequartz–arenites suggests that the sequence mayhave been deposited in a deep marine environment.Metacarbonates are present but rare, signifying thatthe rocks may be a metamorphosed submarine tur-bidite sequence, and the calcareous units may becalcareous turbidites or debris flows. Metavolcanicintercalations are also present but rare, and we donot have enough data at present to determine if theyare tectonic slivers or integral parts of the originalstratigraphy. The original sedimentary sequence mayhave been turbidites that were complexly folded byearly NW striking intrafolial isoclinal folds and D1recumbent tight to isoclinal folds while being off-scraped during subduction accretion into an accre-tionary wedge. Similar fabrics and structural stylesare known from many younger accretionary prisms(e.g.Kusky et al., 1997; Kusky and Bradley, 1999).

The location of the Feiran–Solaf belt between theMidyan terrane of Saudi Arabia, and the possiblycorrelative Gerf terrane of Egypt suggests that theremay be a structural and tectonic break between thesetwo terranes, and they may represent separate arcsequences. In Sinai, the Feiran–Solaf belt lines upwith and may be correlative with strongly deformedmetasedimentary and metavolcanic rocks of the WadiKid and the Sa’al-Zaghra belts, forming a relativelycontinuous belt of deformed metasedimentary andmetavolcanic rocks. This elongate belt may correlatewith the Ad Durr fault or Ajjaj shear zones in theMidyan terrane of Saudi Arabia upon closing the RedSea. If so, the Feiran–Solaf belt may represent part ofan unrecognized suture between the Gerf and Midyanterranes.

The vergence of early structures is difficult to de-termine, but the strike of the early rootless isoclinal


folds and first-generation recumbent folds may berelated to the orientation of early zones of conver-gence or subduction. The NW strikes of these fabricssuggests early NE–SW contraction, and the earlyvergence appears to indicate NE over SW thrustingduring early fabric formation and offscraping. Theformation of later, N-striking folds indicates E-Wshortening, which we relate to shortening along weakN-S zones along with movement on the NW strikingNajd faults, and extension of appropriately orientedsedimentary basins in the Arabian–Nubian Shield (seeKusky and Matsah, 2003; Johnson, 2003; Abdelsalam,1994).

8. Conclusions

The Feiran–Solaf gneisses and migmatites representa thick sequence of sedimentary rocks that are olderthan 804.8 ± 4.7 Ma. The entire sequence is markedby the alternation of thin pelitic, psammitic and limeylayers, together with minor thin basic volcanic rocks.Paragneissic rocks in the belt were deposited underdeep marine conditions between Neoproterozoic ensi-matic arc sequences.

The entire sequence was subjected to multiplephases of successive deformation and metamor-phism. Three phases of folding are identified, andthese were accompanied by medium- to high-gradeamphibolite-facies metamorphic conditions. Thelower-crustal rocks suffered partial anatexis, yield-ing granitoid and trondhjemitic migmatites, whichcrop out only in the Feiran Zone; regional foldingmay control their distribution. Subsequently, largemagmatic bodies and later dike swarms were em-placed, and were controlled by the NE–SW fracturezones. Post-folding brittle structures cut these rockunits.

Field observations, such as the presence of meta-morphic xenoliths in the granodioritic bodies and in-trusive contacts between the metamorphic rocks andthe granodiorites indicate that the metamorphic rocksare older than the 804 Ma intrusions.

Early stages of D1 deformation produced SE-trendingisoclinal folds, which were refolded by NW-trendingF2 recumbent folds, reorientation of the metamorphicfoliations, and formation of migmatites at the latestages of this event. We relate these two folding and

transposition events with initial offscraping and fold-ing of the metasediments possibly in an accretionaryprism environment. Open folds and contact meta-morphism followed by brittle structures represent thesecond (D2) stage.

We conclude that the Pan-African tectonothermalevents in the Feiran–Solaf metamorphic belt weremarked by penetrative and progressive deformationand metamorphism up to the amphibolite facies, re-sulting in the formation of migmatites. The analysesof planar and linear structural elements from theFeiran–Solaf belt clearly show the presence of threegenerations of folds (F1, F2, and F3). The mean atti-tude of F1 hinges plunges 23◦ to S56◦E, F2 plunges36◦ to N12◦W, and F3 plunges 68◦ to N75◦E. Fromthese data, it is apparent that the F1 and F2 had dom-inantly NW–SE striking axial surfaces, with gentlyplunging hinges, whereas the superimposed F3 foldsgenerally have NE orientations. Therefore, the vari-able orientations of structures in the Feiran–Solaf beltare related to the re-orientation of structures aboutlate NNE-trending fold axes.

The geometrical relationships between D1 and D2suggest that the Feiran–Solaf structures were mainlydeveloped in response to a NE–SW compressionalstress. This compressional stress may be related tooblique collision between the Arabian–Nubian Shieldand the Nile craton at∼750–650 Ma. On the otherhand, the NW–SE structures in the African plate mayreflect a structural style that is attributed to the col-lision of the Arabian–Nubian Shield with the NileCraton in the west and the Ar-Rayn micro-plate tothe east at∼670–610 Ma (Abdelsalam, 1994). Moreage data from South Sinai is required to confirm thisinterpretation. However, the youngest, cross-cutting,faults probably relate to the post- and syn-Mioceneopening of the Red Sea as they run through the belt it-self and the western Phanerozoic cover of Cretaceousage.

Acknowledgements

This research is a part of the first author’s Ph.D.thesis completed under the supervision of the secondauthor. The authors greatly appreciate the helpful sug-gestions and detailed comments of the reviewers Profs.J. Loizenbauer, U. Hargrove, and M. Abdeen.


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