Download Geochemistry of an island-arc plutonic suite

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Journal of African Earth Sciences, Vol. 24, No. 4, pp. 4 7 3 - 4 9 6 . 1997
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Geochemistry of an island-arc plutonic suite: Wadi
Dabr intrusive complex, Eastern Desert, Egypt
FAWZY F. ABU EL-ELA
Geology Department, Faculty of Science, Assiut University, Assiut, Egypt
Abstract--The Wadi Dabr intrusive complex, west of Mersa-Alam, Eastern Desert,
Egypt ranges in composition from gabbro to diorite, quartz diorite and tonalite. The
gabbroic rocks include pyroxene-hornblende gabbro, hornblende gabbro,
quartz-hornblende gabbro, metagabbro and amphibolite. Mineral chemistry data for
the gabbroic rocks indicate that the composition of clinopyroxenes ranges from
diopside to augite and the corresponding magma is equivalent to a volcanic-arc
basalt. Plagioclase cores range from AnTs to An34 for the gabbroic varieties, except
for the metagabbro which has Anl~.l 8. The brown amphiboles are primary phases
and classified as calcic amphiboles, which range from tschermakitic hornblende to
magnesiohornblende. Green hornblende and actinolite are secondary phases.
Hornblende barometry and hornblende-plagioclase themometry for the gabbroic rocks
estimate crystallisation conditions of 2-5 kb and 885-716°C.
The intrusive rocks cover an extensive silica range (47.86-72.54 wt%) and do not
exhibit simple straight-line variation on Harker diagrams for many elements (e.g.
TiO 2, AI203, FeO*, MgO, CaO, P205, Cr, Ni, V, Sr, Zr and Y). Most of these elements
exhibit two geochemical trends suggesting two magma sources.
The gabbroic rocks are relatively enriched in large ion lithophile elements (K, Rb, Sr
and Ba) and depleted in high field strength elements (Nb, Zr, Ti and Y) which suggest
subduction-related magma. Rare earth element (REE) data demonstrate that the gabbroic
rocks have a slight enrichment of light REE [(La/Yb)N= 2.67-3.91] and depletion of
heavy REE [(Tb/Yb) N= 1.42-1.47], which suggest the parent magma was of relatively
primitive mantle source.
The diorites and tonalites are clearly calc-alkaline and have negative anomalies of
Nb, Zr, and Y which also suggest subduction-related magma. They are related to
continental trondhjemites in terms of Rb-Sr, K-Na-Ca, and to volcanic-arc granites
in terms of Rb-(Y + Nb) and Nb-Y.
The Wadi Dabr intrusive complex is analogous to intrusions emplaced in immature
ensimatic island-arcs and represents a mixture of mantle (gabbroic rocks) and crustal
fusion products (diorites and tonalites) modified by fractional processes.
R6sum6--Le complexe intrusif de Wadi Dabr, & I'ouest de Mersa-Alam, Ddsert
Oriental, Egypte, est compos0 de gabbro, diorite, diorite quartzique et tonalite. Lee
roches gabbrdfques comprennent un gabbro ~ pyrox~ne-hornblende, un gabbro
hornblende, un gabbro quartzique ~ hornblende, un m(~tagabbro et une amphibolite.
Les donn6es chimiques des min6raux des roches gabbrdiques montrent que les
clinopyrox~nes varient de diopside ~ augite et que le magma correspondent est
dquivalent & un basalte d'arc volcanique. Les coeurs de plagioclase 6voluent de An75
An34 pour les varidt6s gabbrdl'ques, sauf le mdtagabbro qui contient An~11s.
L'amphibole brune est une phase primaire calcique variant de hornblende
tschermakitique ~ magndsio-hornblende. L'amphibole verte et I'actinote sont des
phases secondaires. Le barom~,tre hornblende et le thermom(~tre hornblendeplagioclase sur les roches gabbro'iques donnent des conditions de cristallisation
estimdes & 200-500 MPa et 885-716°C.
Les roches intrusives montrent un grand intervalle de teneurs en silice (47.86-72.54%
en poids d'oxydes) et ne montrent pas de simples variations lin6aires dane lee
Journal of African Earth Sciences 473
F. F. A B U EL-ELA
diagrammes de Harker (par exemple, TiO 2, AI203, FeO*, MgO, CaO, P205, Cr, Ni, V,
Sr, Zr et Y). La plupart de ces 616ments montrent deux tendances g6ochimiques
sugg6rant deux sources magmatiques.
Les roches gabbro'='quessont relativement enrichis en LILE (K, Rb, Sr et Ba) et appauvris
en HFSE (Nb, Zr, Ti et Y) ce qui sugg~re un magma de subduction. Les donn6es de
terres rares montrent que les roches gabro'iques ont un faible enrichissement en
terres rares 16g~res [(La/Yb)N=2.67-3.91] et un appauvrissement en terres rares
Iourdes [(Tb/Yb) N= 1.42-1.47], ce qui sugg6re un magma parent issu d'une source
mantellique relativement primitive.
Les diorites et les tonalites sont clairement calco-alcalines et pr~sentent des anomalies
n6gatives en Nb, Zr, Y, ce qui sugg6re aussi un magma de subduction. Elles sont
reli6es aux throndhj6mites continentales en termes de Rb-Sr, K-Na-Ca et aux granites
d'arc volcaniques en termes de Rb-(Y + Nb) et Nb-Y.
Le complexe intrusif de Wadi Dabr est analogue aux intrusions mises en place dans
des arcs insulaires ensimatiques immatures et repr6sente un m61ange des produits
de fusion de roches mantelliques (roches gabbro'iques) et crustales (diorites et
tonalites), modif6s par des processus de fractionnement.
(Received 14 May 1996: revised version received 8 February 1997)
INTRODUCTION
Although there are many reconnaissance studies
of island-arc intrusive rocks (e.g. Kesler et al.,
1977; Mason and McDonald, 1978; Hine and
Mason, 1978), detailed studies of individual
intrusions (e.g. Chivas, 1978; Perfit et al., 1980;
Kay et al., 1983; Whalen, 1985) are relatively
uncommon. An understanding of these rocks has
implications for the genesis of calc-alkaline
volcanic rocks, which may represent extrusive
equivalents. As is the case for calc-alkaline
volcanic suites, knowledge of the characteristics
of island-arc intrusive rocks has great ramifications
for tectonic interpretations in older orogenic belts
(e.g. Whalen and Currie, 1982).
Island-arc volcano-sedimentary rocks, which are
composed of weakly metamorphosed calc-alkaline
intermediate volcanics (mainly of andesites, dacites,
volcaniclastics of comparable composition and
subordinate basalts and rhyodacites), are already
established and identified in the Egyptian basement
(e.g. Stern, 1981; Abu EI-Ela, 1990, 1992; Abu EIEla and Hassan, 1992). However, the plutonism of
the island-arc in the Egyptian basement is much less
studied (e.g. AbdeI-Rahman, 1990; Abu EI-Ela,
1996). This paper addresses the question of how
plutonic rocks in the Egyptian basement are related
to the island-arc association using geology, mineral
and whole-rock chemistry.
GEOLOGY
The investigated Wadi Dabr intrusive complex
is a gabbro-diorite-tonalite suite (Fig. 1) which
was mapped as an epidiorite-complex (El Ramly
and Akaad, 1960), as metagabbros and diorites
(Akaad and Essawy, 1964; El Ramly, 1972) and
474 Journal of African Earth Sciences
as a metagabbro-diorite complex (Hassan and
Essawy, 1977). The gabbro-diorite rocks have
been a f f e c t e d by t h r e e p r o c e s s e s , viz.
hybridisation, post-magmatic (deuteric) alteration
and regional metamorphism and were closely
f o l l o w e d by e m p l a c e m e n t of s y n o r o g e n i c
granites (Hassan and Essawy, op. cir.).
The present study reveals that the gabbroic
rocks include p y r o x e n e - h o r n b l e n d e gabbro,
hornblende gabbro, quartz-hornblende gabbro,
metagabbro and amphibolite. They are dark
green, show marked variation in grain size, from
fine to coarse grained, and vary in the ratio of
mafic to felsic minerals. They are massive and
devoid of any trace of igneous layering. The
g a b b r o i c rocks in some places are h i g h l y
tectonised w i t h developed minor folds and
stretching lineations.
The diorite and quartz diorite are locally
foliated, cataclased and have a gneissic texture
along Wadi Dabr, Wadi Um Markha and Wadi
Thamili El Zarka. They contain relics of pegmatite
and quartz veins which occur as pinch and swell
textures. The coarse grained diorite, quartz
diorite and appinitic diorite are intruded into the
g a b b r o i c rocks. X e n o l i t h s of g a b b r o and
amphibolite are enclosed within the dioritic rocks.
The diorite and quartz diorite are dissected by
veins and dyke-like bodies of muscovite granites
(post-orogenic granites).
The tonalites form small masses and veins
that invaded both gabbroic and dioritic rocks.
They s h o w agmatite s t r u c t u r e and enclose
different shapes and sizes of fine gabbro,
coarse grained gabbro and quartz dolerite
xenoliths. Some tonalite veins are cataclased
and display augen texture.
Geochemistry of an island-arc plutonic suite
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Journal of African Earth Sciences 475
F. F. ABU EL-ELA
The ophiolitic melange, along Wadi Dabr
(central and southwestern parts of the map area)
and along Wadi Thamili EI-Hamra (western part
of the map area), is composed of foliated slates
and pebbly slates to pebbly metamudstones,
with fragments of different sizes of ultramafic
schists, serpentinite lenses, fine metagabbros,
metabasalts, quartzites and metagreywackes. The
contact between the ophiolitic melanges and the
Wadi Dabr intrusive complex is intrusive, where
the latter intruded along the foliation planes or
the trace of bedding of the matrix of the ophiolitic
melange, with injection of veins and veinlets of
gabbroic and dioritic rocks. Along the contacts
both the ophiolitic melange and the Wadi Dabr
intrusive complex are folded into isoclinal minor
folds.
The c o n t a c t b e t w e e n the i s l a n d - a r c
metavolcanics of Gabal Igla El Iswid and the Wadi
Dabr intrusive complex is also intrusive, where
the latter encloses xenoliths of the former (Abu
EI-Ela, 1992).
The Wadi Dabr intrusive complex in turn is
invaded by young gabbros ( p o s t - t e c t o n i c
intrusive phases) along Wadi Dabr. The young
gabbros comprise olivine gabbro, norite,
gabbro and anorthositic gabbro. They caused
a thermal metamorphic effect up to hornblende
hornfels-facies.
In addition, the Wadi Dabr intrusive complex,
young gabbros and ophiolitic melange are also
invaded by late to post-orogenic granites. The
contacts are sharp with no interaction with these
rocks, which probably indicates that these granitic
masses were emplaced at shallow depths.
PETROGRAPHY
A brief petrographic description of Wadi Dabr
intrusive complex is summarised under the
following headings.
Gabbroic rocks
Pyroxene-hornblende gabbros
These rocks are fine to coarse grained, dark
green in colour and c o m p o s e d mainly of
p l a g i o c l a s e , c l i n o p y r o x e n e and b r o w n
hornblende. Actinolite, chlorite, epidote, zoisite
and sericite are secondary components. Ilmenite
and a p a t i t e are c o m m o n a c c e s s o r i e s .
Uralitisation and saussuritisation are common.
Poikiolitic texture is characteristic.
Hornblende gabbros
These are medium to coarse grained, dark greygreen in colour and c o m p o s e d mainly of
476 Journal of African Earth Sciences
p l a g i o c l a s e and b r o w n to b r o w n - g r e e n
hornblende. Chlorite, epidote, zoisite, sericite,
calcite and quartz are secondary minerals.
Apatite, sphene and ilmenite are common
accessories. Clinopyroxene is lacking. Poikiolitic
and equigranular textures are characteristic.
Quartz-hornblende gabbros
These are similar to hornblende gabbros, except
for the presence of subordinate amounts of quartz,
and they are coarse to very coarse grained.
Metagabbros
These rocks represent the product of low-grade
regional m e t a m o r p h i s m of the previously
mentioned rock types and are represented by
the new mineral assemblage of albite, epidote,
actinolite/chlorite, quartz and sphene. The fine
grained metagabbros are schistose and the
original texture can not be traced, whereas the
coarse grained metagabbros show traces of the
original poikilitic texture.
Amphibolites
The amphibolites occur either as xenoliths within
diorites and quartz diorites or as a local outcrop
along Wadi Thamili EI-Hamra. Two main varieties
are recorded, viz. hornblende amphibolites and
biotite-hornblende amphibolites. Hornblende
amphibolites are fine grained, schistose and
composed mainly of hornblende and plagioclase
(An34). Chlorite, sericite and epidote are
secondary minerals. Sphene apatite and Fe
oxides are common accessories. Hornblendebiotite amRhibolites are similar to the previously
mentioned amphibolites except for the presence
of minor amounts of biotite and quartz.
Dioritic rocks
Coarse-grained diorites
They are composed mainly of plagioclase and
hornblende. Locally, chlorite partially replaces
hornblende and quartz is a minor constituent.
Hypidiomorphic texture is characteristic, Apatite,
zircon and Fe oxides are common accessories.
Gneissose diorites
They are coarse grained and composed mainly
of plagioclase, hornblende and minor biotite.
Gneissic texture is characteristic. Apatite, zircon
and iron oxides are common accessories.
Quartz diorites
Texturally, three varieties of quartz diorites are
distinguished, viz. hypidiomorphic quartz diorite,
cataclased quartz diorite and gneissose quartz
Geochemistry o f an island-arc plutonic suite
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478 Journal of African Earth Sciences
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Geochemistry o f an island-arc plutonic suite
diorite. They are coarse grained and composed
mainly of variable amounts of plagioclase and
hornblende with subordinate biotite and quartz.
Apatite, zircon, sphene and Fe oxides are
common accessories.
Tonalitic rocks
Cataclased microtonalites
These rocks occur as quartzo-feldspathic veins
cross-cutting the gabbroic and dioritic rocks.
They are fine grained and composed mainly of
plagioclase and quartz with minor amounts of
hornblende, chlorite and biotite. Zircon and
apatite are accessories. Augen texture is
characteristic of the plagioclase porphyroclasts.
Coarse grained tonalites
The coarse grained t o n a l i t e s are mainly
composed of plagioclase and quartz w i t h
subordinate amounts of hornblende. Chlorite,
biotite and microcline are minor constituents.
Hypidiomorphic texture is common. Locally,
some of these rocks are foliated. Zircon and
apatite are accessories.
MINERALOGY AND MINERAL CHEMISTRY
Analytical methods
Microprobe analyses of the studied minerals were
performed at the Institute of Earth Science,
Utrecht University, The Netherlands, with a Jeol
JXA 8600 superprobe and Tractor 5500 ED,
using wavelength dispersive technique for Na,
Cr, Mn and Fe, and e n e r g y d i s p e r s i v e
spectrometer for Mg, AI, Si, K, Ca and Ti.
Operating conditions were 20 kV acceleration
voltage and 10 nA sample current. Matrix
corrections were applied using ZAF program.
Plagioclase is an important phase in the gabbroic
rocks of the Wadi Dabr intrusive complex.
Chemical compositions and structural formulae
of plagioclase are listed in Table 1. Most
plagioclase shows no significant optical zoning;
for this reason only cores of plagioclase were
analysed. The core composition is presumably
representative of the original crystallisation and
should provide the best indication of magma
fractionation. Plagioclase core compositions in the
gabbroic rocks range from An~s.9 [100 Ca/
(Ca + Na + K)] to An5o for pyroxene-hornblende
gabbro, from An~. 4 to An384 for hornblende gabbro
and from An380 to An34.s for quartz-hornblende
gabbro. Metagabbros have An content ranging
from An18.3 to Anlo.9.
Clinopyroxenes occur as relict cores within the
calcic amphiboles, or as subhedral plates that
enclose poikiolitically subhedral prismatic crystals
of plagioclase, and have their peripheries altered
to actinolite. Chemical compositions and structural
formulae of relict cores of clinopyroxene are listed
in Table 2. The clinopyroxenes are classified as
diopside and augite (Wo41.o: En438:Fs73 to Wo47 s:
En4~s: Fs12.8)according to the classification scheme
of Poldervaart and Hess (1951 ). The conventional
Si02-AI203 (Fig. 2) method of Le Bas (1962) is
likely to be useful for slowly cooled igneous rocks
(Coish and Taylor, 1979). The clinopyroxenes are
located in the subalkaine field of Le Bas (1962).
In the Ti + Cr versus Ti diagram (not shown), most
of the clinopyroxenes plot in the volcanic arc basalt
field of Leterrier et al. (1982). In addition, most
of the ctinopyroxenes occupy the calc-alkali basalt
field (Fig. 3) on the Ti-AlCt~discrimination diagram
of Leterrier et al. (op. cit.).
Amphiboles are the dominant ferromagnesian
minerals in the gabbroic rocks. They generally
display well-formed crystal margins, good
cleavages and uniform brown and brownish
green colour. The brown hornblende occurs as
subhedral plates that poikiolitically enclose
plagioclase crystals, or as subhedral crystals
containing relic cores of clinopyroxene. The
brown hornblende is partially altered to green
hornblende and chlorite.
The chemical compositions and structural
formulae of amphiboles are listed in Table 3. The
amphiboles, according to the classification of
Leake (1978) and Hammarstrom and Zen (1986),
are calcic amphiboles (Fig. 4) belonging to the
t s c h e r m a k i t e - a c t i n o l i t e series. The b r o w n
hornblende in the pyroxene-hornblende gabbros
ranges from t s c h e r m a k i t i c hornblende to
m a g n e s i o h o r n b l e n d e , w h e r e a s the b r o w n
hornblende in hornblende and quartz-hornblende
gabbros is classified as magnesiohornblende. The
gabbroic rocks contain subsolidus fibres of pale
green actinolite replacing earlier clinopyroxene.
Both subsolidus actinolite and metamorphic
actinolite, associated with the metagabbros, fall
in the actinolite field of the amphibole classification
diagram (Fig. 4).
According to Leake's (1965) Si-Ti diagram, to
differentiate between igneous and metamorphic
amphiboles (Fig. 5), the brown hornblende in the
gabbroic rocks falls within the igneous amphiboles
field, w h e r e a s the green varieties (green
hornblende and actinolite) fall within the field of
metamorphic amphiboles. In addition, the Si-Ti
diagram (Fig. 5) shows that the calcic hornblendes
display decreasing Ti with increasing Si, which
may suggest continual chemical change with
magmatic differentiation.
Journal of African Earth Sciences 479
F, F. ABU EL-ELA
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Figure 2. Si02-AI203 diagram o f LeBas (1962) for
clinopyroxene relict cores of pyroxene-hornblende.gabbros.
Figure 4. Amphibole classification diagram modified after
Leake (1978) and Hammarstrom and Zen (1986) for the
gabbroic rocks of Wadi Dabr intrusive complex. Q: hornblende
from clinopyroxene-hornblende gabbros; O: hornblende from
hornblende gabbros; * : hornblende from quartz-hornblende
gabbros; x: actinolite rims around clinopyroxenes from
pyroxene-hornblende gabbros.
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for clinopyroxene relict cores o f pyroxene-hornblende
gabbros. IA T = island-arc tholeiite; CA = calc-alkaline basalt.
The hornblende barometry is based on the
pressure s e n s i t i v i t y of total AI content in
hornblende, where AI content increases with
pressure. Hornblende crystallisation pressures for
the gabbroic rocks have been calculated using
the calibration of Hammarstrom and Zen (1986),
Johnson and Rutherford (1989) and Schmidt
(1992). The pressure estimates for the gabbroic
rocks range from 2-5 kb (Table 4). A
geothermometer has been devised (Blundy and
Holland, 1990) based on the Al(iv) content of
hornblende coexisting with plagioclase. Only
those hornblendes that satisfied the igneous
480 Journal of African Earth Sciences
Figure 5. Variation of 77versus Si in hornblende for gabbroic
rocks of the Wadi Dabr intrusive complex, according to Leake
(1965). Symbols as for Fig. 6.
criteria were utilised for P-Tdeterminations (see
Fig. 5). Eight hornblende-plagioclase pairs yield
crystallisation temperatures ranging from 885716°C (Table 4).
Ilmenite is commonly found in hornblende
gabbro and quartz-hornblende gabbro. Ilmenite
analyses are listed in Table 5.
Chlorite is mostly after brown hornblende. It
is characterised by a relatively high Fe/(Fe + Mg)
ratio which ranges from 0.28 to 0.36 per formula
unit and low Si which ranges from 5.571 to
5.425 per formula unit (Table 5) and is classified
as ripidolite (Hey, 1954).
All epidote-group minerals are optically negative
and defined as epidote. Compositionally, epidote is
AI-rich (Table 5) and tool.% of pistacite (ps)= Fe/
(Fe+AI) is 0.12 which is characteristic of
metamorphic epidote. By comparison, Fe epidote
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Journal of African Earth Sciences 481
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Geochemistry of an island-arc plutonic suite
Table 5. Representative microprobe analyses of ilmenite, chlorite, epidote and
sphene from the gabbroic rocks of the Wadi Dabr intrusive complex
Rock
types
Sample
No.
SiO2
A!203
TiO2
Cr203
FeO
MnO
Quartz-hornblende
pbbro
14A
14B
llm
llm
0.000
0.000
0.000
0.000
53.040
53.630
0.040
0.000
43.360
43.680
2.750
2.660
0.000
0.000
Mgo
0.000
0.000
CaO
0.000
0.000
Na20
K20
0.000
0.000
99.190
99.970
Total
30
Cations per
0.000
0.000
Si
0.000
0.000
A!
1.011
1.013
Ti
0.001
0.000
Cr
0.919
0.917
Fe
0.059
0.057
Mn
0.000
0.000
Mg
0.000
0.000
Ca
0.000
0.000
Na
0.000
0.000
K
1.989
1.987
Sum
Metagabbro
500A
Chl
28.180
21.070
0.300
0.100
16.720
0.240
22.390
0.000
0.050
0.000
89.050
500A
Chl
27.120
21.310
0.280
0.080
16.480
0.260
22.480
0.000
0.040
0.000
88.050
14 O
2.712
2.512
0.021
0.006
1.378
0.022
3.351
0.000
0.008
0.000
10.011
of primary magmatic textural features has been
reported with composition between PSo21 to
PSo.33(Zen and Hammarstrom, 1984; Evans and
Vance, 1987; Barth, 1990; Vyhnal et al., 1991 ).
Sphene is a widespread accessory mineral
throughout the gabbroic rocks. It occurs as dusty
aggregates, intimately associated with opaque
phases, and as subhedral grains enclosed within
actinolite and plagioclase. Sphene analyses
(Table 5) are c o n s i s t e n t w i t h t h o s e of
greenschist-facies rocks in terms of SiO~, AI203,
TiO 2, FeO and CaO (Ernest, 1976).
WHOLE ROCK GEOCHEMISTRY
Thirty nine representative samples of the Wadi
Dabr gabbro-diorite-tonalite intrusive complex
were analysed for their major elements on an
ARL-34000 ICP emission spectrometer. Trace
element analyses were carried out using the XRF
automated Philips PW 14OO spectrometer at the
Institute of Earth Sciences, State University of
Utrecht, Holland. SiO 2 and LOI were determined
using the wet-chemical methods of Shapiro
2.782
2.452
0.022
0.008
1.381
0.020
3.295
0.000
0.010
0.000
9.970
500A
Ep
39.120
28.490
0.340
0.000
6.870
0.000
0.210
22.450
0.000
0.000
97.480
12.50
3.071
2.636
0.020
0.000
0.451
0.000
0.025
1.888
0.000
0.000
8.091
500A
Sp
31.790
1.410
37.040
0.000
0.930
0.030
0.000
27.970
0.000
0.000;
99.170
10 O
2.084
0.109
1.826
0.000
0.051
0.002
0.000
1.964
0.000
0.000
6.036
i
i
i
( 1 9 7 5 ) . Rare earth e l e m e n t s (REE) were
determined by INAA at IRI, Delft, using the
established techniques (De Bruin, 1983).
Whole.rock compositions of typical rock types
of the Wadi Dabr intrusive complex are shown
in Table 6. The intrusive rocks cover an extensive
silica range from 47.86 to 72.54 wt%. The main
compositional trend of the studied intrusive rocks
are shown on Harker variation diagrams (Fig.
6). Figure 6 shows that many elements do not
have straight line variations (e.g. TiO 2, AI203,
FeO*, P2Os, Cr, Ni, V, Zr, Y and St). This
suggests two different compositional trends; one
for the gabbroic rocks and the other for dioritetonalite association. Therefore, t w o magma
sources may be suggested. The compostional
trend of the gabbroic rocks is characterised by
an increase of TiO 2, AI203, Na20 + K20, P2Os,
Zr, Y, Sr and Ba with increasing SiO 2, whereas
FeO*, MgO, CaO, Cr, Ni and V decrease with
increasing SiO 2. This trend is close to the calcalkaline series except for TiO 2, AI203 and PzOs.
The compositional trend of diorite and tonalite
is characterised by a decrease of TiO 2, AI203,
Journal of African Earth Sciences 483
F. F. A B U EL-ELA
oJ =
r,j
o
=¢
.<
-
~o
|
,=~===,',';o~
=
~
=-
=,,....
=
=,-
]==.==.
...,,,==,,,==.
. --,====~-=..~.
. .
=,'-~=.=",~,"._.~",=~
X
E
o
0
E
==~ ,,_,-=""~=¢"="=~'==_
,--.
-
"0
m
e"
m
i
"0
|
=
ID
ID
0
#=
•
. e : . ~
= ~ ¢ =
N--
.~.
0
o
o¢ -
S
•
~
.
=
|
484 Journal of African Earth Sciences
~ = ~
~N
Geochemistry of an is~and-arcplutonic suite
"
Is
="
"
el
II
~
o
0,
,<
gO
,
°
~S
.<
P
i
o
~
~
,~
~,.J~
u'~ ,,o
~
=
,,
~
~
e"j P,l
E
-
u
I,,-
Journal o f African Earth Sciences 4 8 5
F. F. ABU EL-ELA
10
!
|
I
•
16
I
FeO (wt %)
x
8
14
12
10
l.Oo
6
Z~
2
Z~
;2
I
I
I
I
1
I
I
I
!
!
20
18
16
o&
4
2
0
I
,
,
,
~
1
I
I
!
OoO o
0
• o,,,,.~,%
•
°So"~Ip"°~
CaO(wt %)
8
• ~
..,
o
6
g O B "
A
•
•
•t
4
12
/%/k
2
10
5
I
I
I
I
I
I
I
I
I
I
a
0
0
TiO2(w t %)
o
•
**
I
I
I
!
i
!
I
I
P205 (wt %)
0.2
.t
•
~
~
I
55
I
I
65
•
O o
O
0.1
%
I
I
0.3
X
0
I
0.4
X
5
0
45
%
O
14
5
I
MgO(wt°l°)
2
AI 2 03 (wt %)
•
O
I
8
6
4
0
I
0.0
I
75
Si 02(w t %)
I
45
I
55
I
I
65
I
75
Si 02 (wt %)
Figure 6. (a) Plots o f m a j o r element contents versus SiO 2 f o r the Wadi Dabr intrusive complex.
FeO*, MgO, Ca•, P2Os, Cr, Ni, V and Sr with
increasing SiO 2, whereas Na20+K20 and Ba
increase with increasing SiO 2 (Fig. 6). This trend
is identical to the calc-alkaline series. The decrease
of Zr and Y contents with incresing SiO= in the
diorites and tonalites (Fig. 6) suggest that these
486 Journal of African Earth Sciences
rocks may be derived from an island-arc protolith
rather than from an evolved continental crust, as
discussed later.
A plot of the Wadi Dabr intrusive rocks on a
Na20 + K20 versus SiO 2 diagram (Fig. 7) of Irvine
and Baragar (1971) show that they fall within
Geochemistry o f an island-arc plutonic suite
3 O0
'
'
'
x
200
2501
•
• o
'
'
'
z~
z~
A
z~
O
~o~oW
*•
0
'
°o ~
ox
1501
oOe °GI)
•
-
'
•,dk
o"
••"
300
,
V (ppm)
=='
100
,
a~
l
l
J
,
,
,
az~z~ z~
501
i
i
,
,
e l , [b
01
Zr(ppm)
l
t
i
,
i
,
,
,
,
,
Ni(ppm)
40
20 C
15
x.
• '(
30
Y(ppm)
_o
20
•
••
10C
10
,.,,.x • "
o, ~ i ( ,
500
'
•
'
••
'
%,,,,,,
'
'
~
z~
~
•
,
500
Cr(ppm)
•
,
'
400
'
Oxo
%
"~i~
300
,
,
,
'
'
'
••
z~
•
o
•
o|
x
•
,%%
Z~Z~ Z ~
200
•
•
%
O0
%o°
45
A
x
O0
•
AA Z~
100
0
55
65
SiO2(wt%)
•
•
•
0
•
I00
A
~
/
•
300
••
o°
•
•
° "4
0
=o%°1O8o
Pyroxene-hornblende gobbros
75
Sr(ppm)
0
,
,
,
,
,
600
'
'
,
,
,
Z~
Z~
500
Z~
400
o Hornblende gobbros
300
•
13 Q u o r t z - h o r n b l e n d e gobbros
200
*
Me~ogobbros
x
Amphibolites
0
•
•
0
100
Ba(ppm)
e•
0
•
Diorites
Z~ T o n a l i t es
A
A
I
45
n
55
I
I
65
SiO 2 ( w t %)
I
75
Figure 6. (b) Plots o f trace element contents versus SiO 2 f o r the Wadi Dabr intrusive complex.
Journal of African Earth Sciences 487
F. F. ABU EL-ELA
s
8
J
.t
s
Alkaline
J
•
Z~
•
o
/ I
,,"
tJ
0
35
I
I
Subalkali
I
/.5
ne
55
I
I
65
I
75
S i O 2 °/,,
Figure 7. N a 2 0 + K 2 0 versus SiO 2 plots of Irvine and Baragar (1971) for the
Wadi Dabr intrusive complex. Symbols as for Fig. 6.
F
A
v
M
Figure 8. AFM diagram of Irivine and Baragar (1971) for the Wadi Dabr intrusive complex.
Symbols as for Fig. 6.
the subalkaline field. On the AFM diagram (Fig.
8) of Irvine and Baragar (op. cit.), most of the
rock units are calc-alkaline rather than tholeiitic
and show only limited Fe enrichment.
Figure 9a and b shows hygromagmatophile
element (HYGE) abundances for the Wadi Dabr
intrusive rocks normalised to the primitive mantle
abundances given by McDonough et aL (1985).
These illustrate the characteristic enrichment of
large ion lithophile elements (LILE: Sr, K, Rb, Ba)
and depletion of high field strength elements
488 Journal of African Earth Sciences
(HFSE: Nb, P, Zr, Ti, Y) in the gabbroic rocks.
LILE and HFSE abundances s h o w a steady
increase from the least evolved pyroxenehornblende gabbro to the most evolved quatrzhornblende gabbro (Fig. 9b). Figure 9c and d show
trace elements of the dioritic and tonalitic rocks
normalised to ocean ridge granites abundances
given by Pearce et al. (1984). These rocks are
enriched in K, Rb and Ba and depleted in Nb, Zr
and Y with respect to oceanic ridge granites
(ORG). The patterns are very similar to those of
Geochemistry of an island-arc plutonic suite
100 • Pyroxene-hornblende g a b b r o s
a
( 523A,515A,503C,522,50z0B, 2A, 504A, 525,
13A, 532,534A, 523C, 540,538 )
cE}
4.n
E
10
E
U3
I
I
Bo
Rb
I
K
I
I
I
I
I
I
Nb
$r
P
Zr
Ti
Y
Figure 9. (a) Spidergram of trace element concentrations for pyroxene-hornblende gabbros
normalised to primitive mantle after McDonough e t ai. (1985). (b) Spidergram of trace
element concentrations for hornblende gabbros and quartz-hornblende gabbros normalised
to primitive mantle after McDonough et al. (1985). (c) Spidergram o f trace element
concentrations for diorites normalised to ocean ridge granite (ORG) after Pearce et al.
(1984). (d) Spidergram o f trace element concentrations fo( tonalites normalised to ocean
ridge granite (ORG) after Pearce e t al. (1984).
volcanic arc granites (Fig. 1 b of Pearce et al., op.
cit.). In general, the gabbro-diorite-tonalite complex
is characterised by the depletion of HFSEs and a
marked negative Nb anomaly. HFSEs are depleted
in subduction-related magmas derived at least in
part from the mantle-wedge (Perfit et al., 1980).
Also, the low concentration of Nb in association
with low Ti is a feature of arc basalts (Saunders
et al., 1 9 8 0 ; Pearce, 1 9 8 2 ; Ellam and
Hawkesworth, 1988). The HYGE abundances of
the gabbroic rocks (Fig. 9a) are similar to those of
island-arc calc-alkaline basalt from the Taupo
Volcanic Zone (TVZ), New Zealand (Graham and
Hackett, 1987). The TVZ forms part of the TaupoHikurangi subduction system (Cole and Lewis,
1981).
The discriminant K-Na-Ca diagram (Fig. 10)
after Barker and Arth (1976) clearly shows
the trondhjemitic affinity of the diorites and
tonalites of the Wadi Dabr intrusive complex.
A plot of Rb versus Sr (Fig. 11) indicates that
the diorites and tonalites of the Wadi Dabr
i n t r u s i v e c o m p l e x p l o t in t h e field of
continental trondhjemite and quartz diorite of
Coleman and Peterman (1975) and do not
belong to the oceanic plagiogranite group. The
latter are evolved rocks, formed in association
with ophioiite complexes, and are distinguished
by extremely low Rb contents.
The c h o n d r i t e - n o r m a l i s e d REE patterns,
estimated after Wakita et al. (1 971) for the
gabbroic rocks of the Wadi Dabr intrusive
complex are reported in Fig. 12. They are
relatively enriched in light REE (LREE) [(La/
Yb),=
2.67-3.91;
Table
7],
less
fractionated,
s h o w no s i g n i f i c a n t
Eu
Journalof African EarthSciences489
F. F. ABU EL-ELA
100 o Hornblende gabbros
( 3A, 527A, 506A, 539, 506C, 502A)
b
[] Q u a r t z - h o r n b l e n d e
( 14A, 1 4 B )
gabbros
m
e"
:E
o.
10
cL
E
¢}
u3
1
I
I
I
I
I
I
I
I
I
Bo
Rb
K
Nb
Sr
P
Zr
Ti
Y
100
100
C
d
10
1C
1
1
0
t~
0.1
R
a
Figure 9. continued.
4 9 0 J o u r n a l o f A f r i c a n Earth Sciences
b
r
K20 Rb Bo
Nb
Zr
Y
Geochemistry of an island-arc plutonic suite
K
No
Ca
Figure 10. Ternary K-Na-Ca projection for diorites and tonalites of the Wadi Dabr intrusive
complex after Baker and Arth (1976). Ca" calc-alkaline trend; Tr: trondhjemitic trend.
Symbols as for Fig. 6.
sI
r
I
//
s
f
~
~.
10
jJ'
1 O0
1000
5r ppm
Figure 11. Rb-Sr variation diagram for diorites and tonalites of the Wadi Dabr
intrusive complex. Symbols as for Fig. 6.
Journal of African Earth Sciences 4 9 1
F. F. ABU EL-ELA
Table 7. REE (in ppm) in some gabbroic rocks of
the Wadi Dabr intrusive complex
0
Sample No.
523.A
4.630
9.870
1.690
0.723
0.341
1.119
0.167
2.670
1.540
1.420
1.240
La
Ce
Sm
_=
Eu
=o
x Island-arc
calc-alkaline
Tb
Yb
Lu
basalt of TVZ,
New Z e a l a n d (Cole et al., 1983)
(L=/Yb )W
I
Le Ce
I
I
I
Sm Eu
Tb
(La/Sm)N
(Tb/Yb)N
I
Yb Lu
Eu / Eu*
506A
9.110
19.260
3.730
1.290
0.636
2.017
0.380
2.92
1.40
1.47
1.08
14B
12.680
26.170
3.964
1.30
0.659
2.214
0.410
3.91
1.83
1.39
1.04
Figure 12. Chondrite-normalised REE patterns for some
gabbroic rocks of the Wad/Dabr intrusive complex. Symbols
as for Fig. 6.
1000
WPG
100
..-"
f
.s
J
O.
Q.
syn-COLG"v~////
.Q
z
10
10
1O0
1000
Y(ppm)
Figure 13. Discrimination diagram Nb versus Y after Pearce et al. (1984)
for diorites and tonalites of the Wadi Dabr intrusive complex. ORG: oceanridge basalt; syn-COLG + VAG: syn-collision granites + volcanic-arc granites;
WPG: within-plate granites. Symbols as for Fig. 6.
anomaly [ ( E u / E u * ) = 1 . 0 4 - 1 . 2 4 ] and are
mildly depleted in heavy REE (HREE) [(Tb/
Yb)N= 1.42-1.47]. Depleted HREE indicates
the presence of g a r n e t in the source
(Weaver and Tarney, 1981). Total REE
abundances ( 1 3 . 5 4 - 4 7 . 7 9 ppm) increase
from the least evolved gabbro (pyroxenehornblende gabbro) to the most evolved
gabbro (quartz-hornblende gabbro) and this
can be explained in terms of fractional
crystallisation. Minor Ce anomalies (Fig. 12)
have been widely described as typical of
492 Journal of African
Earth Sciences
volcanic-arc rocks. Negative Ce anomalies
have been explained by either the presence
of small amounts of subducted sediments
in the source (Gill, 1981; Hole eta/., 1984),
by fractionation of fluids originating from
dehydration of the subducted slab (White
and Patchett, 1984), or by hydrothermal
alteration (Brouxel et al., 1987). The REE
profile of the gabbroic rocks (Fig. 12) is
similar to those of the island-arc calcalkaline basalt of the Taupo Volcanic Zone
(TVZ), New Zealand (Cole eta/., 1983).
Geochemistry of an island-arc plutonic suite
1000
100
YwPG
syn-COLG
J
10
VAG
|
I
I
ORG
I
I IIII
I
10
I
I
IIIll
I
100
~
I
I I II1|
1000
Y,Nb(ppm)
Figure 14. Discrimination diagram of Rb versus Y + Nb after Pearce et al.
(1984) for diorites and tonalites of the Wadi Dabr intrusive complex, synCOLG: syn-collision granites; VAG: volcanic-arc granites; WPG: withinplate granites. Symbols as for Fig. 6.
TECTONIC SETTING
The REE profile of the gabbroic rocks resembles
that of island arc basalts (lABs) and is distinctive
from that of N-type mid-ocean ridge basalts
(MORB). The similarity in REE profile between
the gabbroic rocks and lAB suggests an islandarc tectonic setting.
A plot of diorites and t o n a l i t e s on the
discrimination diagram (Fig. 13) of Nb versus Y
depicts that they fall in the field of VAG + synCOLG (volcanic-arc granites and syn-collision
granites) of Pearce e t al. (1984). However,
plotting on the discrimination diagram (Fig. 14)
of Rb versus Y + Nb shows that they fall within
the VAG (volcanic-arc granites) of Pearce e t al.
(op. cit.).
S U M M A R Y AND CONCLUSION
The Wadi Dabr intrusive complex is composed
of a gabbro-diorite-tonalite suite that shows a
bimodal silica range (48.39-54.79 and 57.3172.54). The gabbroic rocks (48.39-54.79 SiO 2
%) display a subalkaline character (Fig. 7) and
calc-alkaline trend (Fig. 8) on the basis of their
major element chemistry. This is corroborated
by the behaviour of major and trace elements
on variation diagrams (Fig. 6). The spidergram
(Fig. 9a, b) suggests that the gabbroic rocks are
similar to island-arc calc-alkaline basalt from the
Taupo Volcanic Zone, New Zealand (Graham and
Hackett, 1987), where the gabbroic rocks are
enriched in LILE (Ba, Rb, K, Sr) and depleted in
HFSE (Nb, P, Zr, Ti, Y). Both LILE and HFSE
increase steadily from the least evolved gabbro
(pyroxene-hornblende gabbro) to the most
evolved gabbro (quartz-hornblende gabbro),
which may be due to magmatic differentiation.
The REE pattern for the gabbroic rocks shows
slight enrichment of LREE and depletion in HREE,
which is similar to island-arc calc-alkaline basalt
from the Taupo Volcanic Zone, New Zealand
(Cole e t al., 1983). This suggests that the parent
magma was derived from relatively primitive
mantle source. The clinopyroxene chemistry
depicts that the parent gabbroic magma is
comparable to volcanic-arc basalt. The gabbroic
rocks were crystallised, under conditions of 5-2
kb pressure and 865-716 °C temperature (Table
4), passing from the least evolved gabbro to the
most evolved gabbro. The decrease in P-T
conditions, from the least evolved to the most
evolved gabbros, may be due to concomitant
ascent, cooling and geochemical differentiation
in the magma chamber. The foregoing discussion
suggests the parent magma of the gabbroic rocks
of the Wadi Dabr intrusive complex to have been
a subduction-related magma.
The diorites and tonalites of the Wadi Dabr
intrusive complex show a clear calc-alkaline trend
on an AFM diagram (Fig. 8). The calc-alkaline
trend is supported by major and trace element
variation diagrams (Fig. 6), except for the
variations of both Zr and Y versus SiO 2 (Fig. 6).
Zirconium and Y decrease with increasing SiO 2,
which suggests that the diorites and tonalites
Journal of African Earth Sciences 493
F. Fo ABU EL-ELA
Calc-alkaline and tholeiiti¢ lavas
Diorite - tonal~ te / t rondhj em
Fusion of amoh'~bolitized
thole'l'lti c
Oceanic
lithosphere
Hontle fusion
Mantle
~onatlon of basaltic
IO
lie flux
Figure 15. Magma-forming processes and magma types formed during the
evolution of an oceanic island-arc, based mainly on Ringwood (1974), Greene
(1982) and Brown (1982) for the Wadi Dabr intrusive complex.
may have been derived from an island-arc
protolith rather than from evolved continental
crust. In support of this view, both diorite and
tonalite
have the chemistry
of the
trondhjemitic trend (Fig. 10) of Baker and Arth
( 1 9 7 6 ) , the c o n t i n e n t a l t r o n d h j e m i t e and
quartz diorite field (Fig. 11) of Coleman and
Peterman (1 975) and volcanic-arc granite (Figs
9c, d, 13 and 14) of Pearce e t al. (1984).
Therefore, the parent magma of diorites and
tonalites of the Wadi Dabr intrusive complex
has similar features to a subduction-related
magma.
A proposed model for the plutonism within an
island-arc, which is controlled by magmatic
processes related to subduction (Ringwood,
1974; Brown, 1982), is suggested for the Wadi
Dabr intrusive complex (Fig. 15). The model of
ensimatic island-arc development occurs when
the crust is sufficiently thick to retard the upward
m o v e m e n t of t h o l e i i t i c b a s a l t i c m a g m a s .
Crystallisation of such magmas near to the base
of the crust will involve amphibole, pyroxene,
magnetite and sphene (Greene, 1982). Crystalliquid fractionation will curtail the Fe enrichment
trend and enhance the calc-alkaline magmatic
trend. The emplacement of magma in the lower
crust also causes melting of the amphibolitised
tholeiitic protolith. The first felsic melts produced
in this way have diorite-tonalite or trondhjemitic
affinities. In this w a y , the protolith of the
gabbroic rocks of the Wadi Dabr intrusive
complex is of mantle source and the diorites
and tonalites are of tholeiitic crustal source.
494 Journal of African Earth Sciences
Marzouki et al. (1982) and Jackson (1986)
have also demonstrated that the 9 0 0 - 7 0 0 Ma
diorite-tonalite complexes in the Arabian Shield
were produced by mantle-derived magmas that
were emplaced in an island-arc setting.
ACKNOWLEDGEMENTS
A c k n o w l e d g e m e n t is made to the D u t c h
Government for the donation of my scholarship
and to the Institute of Earth Sciences, State
University of Utrecht, for the support of this
research.
REFERENCES
AbdeI-Rahman, A. M. 1990. Petrogenesis of Early-Orogenic
Diorite, Tonalite and Post-Orogenic Trondhjemites in the
Nubian Shield. Journal Petrology 31, 1285-1312.
Abu EI-Ela, F. F. 1990. Biomodal volcanism of a volcanosedimentary sequence around Gabal Um Halham, Central
Eastern Desert, Egypt. Bulletin Faculty Science Assiut
University, Egypt 19 (l-F), 37-60.
Abu EI-Ela, F. F. 1992. Bimodal volcanism of the Igla EliswidUm Khariga metavolcanics, Eastern Desert, Egypt. Journal
African Earth Sciences 14, 477-491.
Abu EI-Ela, F. F. 1996. The petrology of the Abu Zawal
gabbroic intrusion, Eastern Desert, Egypt: an example
of an island-arc setting. JournalAfrican Earth Sciences
22, 147-157.
Abu EI-Ela, F. F. and Hassan, M. A. 1992. Geology and
geochemistry of bimodal volcanism north of Gabal Zabara,
Eastern Desert, Egypt. Egyptian Journal Geology 36, 253271.
Akaad, M. K. and Essawy, M. A. 1964. The metagabbrodiorite complex northeast of Gabal Atud, Eastern Desert,
and the term of "epidiorite'. Bulletin Science Technology
Assiut University, Egypt 7, 83-108.
Geochemistry of an island-arc plutonic suite
Barker, F. and Arth, J. G. 1976. Generation of trondhjemitictonalitic liquids and Archean bimodal trondhjemite-basalt
suites. Geology 4, 596-600.
Barth, A. P. 1990. Mid-crustal emplacement of Mesozoic
plutons, San Gabriel Mountains, California, and implications
for the geologic history of the San Gabriel terrane, In: The
Nature and Origin of Cordilleran Magmatism (Edited by
Anderson, J. L.) Geological Society American Memoir 174,
33-45.
Blundy, T. D. and Holland, J. J. B. 1990. Calcic amphibole
e q u i l i b r i a and a n e w a m p h i b o l e - p l a g i o c l a s e
geothermometer. Contributions Mineralogy Petrology 104,
208-224.
Brouxel, M., Lapierre, H., Michard, A. and Albarede, F. 1987.
The deep layers of a Paleozoic arc: Geochemistry of the
Coply-Balaklala series, northern California. Earth Planetary
Science Letters 85, 386-400.
Brown, G. C. 1982. Calc-alkaline intrusive rocks - their
diversity, evolution and relation to volcanic arcs. In:
Andesites (Edited by Thorpe, R. S.) pp437-461. John Willy,
New York.
Chivas, A. R. 1978. Porphyry copper mineralisation at the
Koloula igneous complex, Guadalcanal, Solomon Island.
Economic Geology 73, 645-677.
Coish, R. A. and Taylor, L. A. 1979. The effect of cooling
rate on texture and pyroxene chemistry in DSDP leg 34
basalt: A microprobe study. Earth Planetary Science Letters
42, 389-398.
Cole, J. W. and Lewis, K. B. 1981. Evolution of the TaupoHikurangi subduction system. Tectonophysics 72, 1-21.
Cole, J. W., Cashman, K. V. and Rankin, P. C. 1983. Rareearth element geochemistry and the origin of andesites
and basalts of the Taupo Volcanic Zone, New Zealand.
Chemical Geology 38, 255-274.
Coleman, R. G. and Peterman, Z. E. 1975. Oceanic plagiogranite.
Journal Geophysical Research 80, 1099-1108.
DeBruin, M. 1983. Instrumental neutron activation analysis
- a routine method. Ph.D. dissertation 270p. Delft
University, the Netherlands.
Ellam, R. M. and Hawkesworth, C. J. 1988. Elemental and
isotopic variations in subduction related basalts: evidence
for a three component model. Contributions Mineralogy
Petrology 98, 72-80.
El-Rarely, M. F. and Akaad, M. K. 1960. The basement
complex in the Central Eastern Desert of Egypt. Geological
Survey, Cairo, Egypt, Paper 8, 35p.
Ernset, W. G. 1976. Mineral chemistry of eclogites and
related rock from the Voltri group, Western Liguria, Italy.
Schweizer Mineralogische Petrographische Mitteilung 66,
293-343.
Evans, B. W. and Vance, J. A. 1987. Epidote phenocrysts
in dacite dikes, Boulder Country, Colorado. Contributions
Mineralogy Petrology 96, 178-185.
Gill, J. B. 1981. Orogenic Andesites and Plate Tectonics.
390p. Springer, Berlin.
Graham, I. J. and Hackett, W. R. 1987. Petrology of calcalkaline lavas from Ruapehu volcano and related vents,
Taupo Volcanic Zone, New Zealand. Journal Petrology
28, 531-567.
Greene, T. H. 1982. Anatexis of mafic crust and high
pressure crystallisation of andesite. In: Andesites (Edited
by Thorpe, R. S.) pp477-487. John Wily, New York.
Hammarstrom, J. M. and Zen, E.-An. 1986. Aluminum in
Hornblende: an empirical igneous geobarometer. American
Mineralogist 71, 1297-1313.
Hassan, M. A. and Essawy, M. A. 1977. Petrography of the
metagabbro-diorite complex of Wadi Mubarak-Gabal Atud
area, Eastern Desert, Egypt. Journal University Kuwait
(Science) 4, 203-213.
Hey, M. H. 1954. A n e w revision of the chlorites.
Mineralogical Magazine 30, 277-292.
Hine, R. and Mason, D. R. 1978. Intrusive rocks
associated with porphyry copper mineralisation in New
Britain, Papua New Guinea, Avak, Alaska. Economic
Geology 73, 749-760.
Hole, M. J., Saunders, A. D., Marriner, G. F. and Tarney, J.
1984. Subduction of pelagic sediments: implications for
the origin of Ce-anomalous basalt from the Mariana islands.
Journal Geological Society London 141,453-472.
Irvine, T. N. and Baragar, W. R. A. 1971. A guide to the
classification of the common volcanic rocks. Canadian
Journal Earth Sciences 8, 523-548.
Jackson, N. J. 1986. Petrogenesis and evolution of Arabian felsic
plutonic rocks. JournalAfrican Earth Sciences4, 47-59.
Johnson, M. C. and Rutherford, M. J. 1989. Experimental
calibration of the aluminum-in-hornblende geobarometer
with application to Long Valley caldera (CalifOrnia) volcanic
rocks. Geology 17, 837-841.
Kay, S. M., Kay, R. W., Brueckner, H. K. and Rubenstone,
J. L. 1983. Tholeiitic Aleutian arc plutonism: the Finger
Bay pluton, Avak, Alaska. Contributions Mineralogy
Petrology 82, 99-116.
Kesler, S. E., Lewis, J. F., Jones, L. M. and Walker, R. L.
1977. Early island arc intrusive activity, Cordillera Central,
Dominican Republic. Contributions Mineralogy nd Petrology
66, 91-99.
Leake, B. E. 1965. The relationship between composition of
calciferous amphibole and grade of metamorphism. In:
Controls of Metamorphism (Edited by Pitcher, W. S. and
Flynn, G. W.) pp299-318. Oliver and Boyd, London.
Leake, B. E. 1 9 7 8 . N o m e n c l a t u r e of a m p h i b o l e s .
Mineralogical Magazine 42, 533-563.
Le Bas, M. J. 1962. The role of aluminium in igneous
clinopyroxenes with relation to their parentage. American
Journal Science 260, 267-288.
Leterrier, J., Maury, R. C., Thonon, P., Girard, D. and Marchal,
M. 1982. Clinopyroxene compositions as a method of
identification of the magmatic affinities of Paleo-volcanic
series. Earth Planetary Science Letters 59, 139-154.
Marzouki, F. M. H., Jackson, N. J. and Ramsay, C. R. 1982.
Composition, age and origin of t w o Proterozoic dioritetonalite complexes in the Arabian shield. Precambrian
Research 19, 31-50.
Mason, D. R. and McDonald, J. A. 1978. Intrusive rocks
and porphyry copper occurrences of the Papua New
Guinea-Solomon Islands region: a reconnaissance study.
Economic Geology 73, 857-877.
McDonough, W. F., McCulloch, M. F. and Sun, S.-S. 1985.
Isotopic and geochemical systematics in Tertiary-Recent
basalts from southeastern Australia and implications for
the evolution of the s u b - c o n t i n e n t a l lithosphere.
Geochimica Cosmochimica Acta 49, 2051-2067.
Pearce, J. A. 1982. Trace element characteristics of lavas
from destructive plate boundaries. In: Andesites (Edited
by Thorpe, R. S.) pp525-548. John Wiley, New York.
Pearce, J. A., Harris, N. B. and Tindle, A. G. 1984. Trace element
discrimination diagrams for the tectonic interpretation of granitic
rocks. Journal Petrology 25, 956-983.
Perfit, M. R., Brueckner, H., Lawrence, J. R. and Kay, R. W.
1980. Trace element and isotopic variations in a zoned
pluton and associated volcanic rocks, Unalaska Island,
Alaska: a model for fractionation in the Aleutian calc-alkaline
suite. Contributions Mineralogy Petrology 73, 69-87.
Poldervaart, A. and Hess, H. H. 1951. Pyroxenes in the
crystallisation of basaltic magma. Journal Geology 59,
472-489.
Ringwood, A. E. 1974. The petrological evolution of island arc
systems. Journal GeologicalSociety London 130, 183-204.
Saunders, A. D., Tarney, J. and Weaver, S. D. 1980.
Transverse geochemical variations across the Antractic
Peninsula: implications for the genesis of calcalkaline
magmas. Earth Planetary Science Letters 46, 344-360.
Journal of African Earth Sciences 495
F. F. ABU EL-ELA
Schmidt, M. W. 1992. Amphibole composition in tonalite
as a function of pressure: an experimental calibration of
the AI-in-hornblende barometer. Contributions Mineralogy
Petrology 110, 304-310.
Stern, R. G. 1981. Petrogenesis and tectonic setting of late
Precambrian ensimatic volcanic rocks, CED of Egypt.
Precambrian Research 16, 195-230.
Vyhnal, C., McSween, H. Y., Jr. and Speer, J. A. 1991.
Hornblende chemistry in southern Appalachian granitoids:
Implications for aluminium hornblende thermobarometery
and magmatic epidote stability. American Mineralogist
76, 176-188.
Wakita, H., Rey, P. and Schmitt, R. A. 1971. Abundances
of the 14 rare earth elements and 12 other trace elements
in Apollo 12 samples: five igneous and one breccia rocks
and four soils. Lunar Science Conference, 2nd,
Proceedings, pp1319-1329.
Weaver, B. L. and Tarney, J. 1981. The Scourie dyke suite:
Petrogenesis and geochemical nature of the Proterozoic
sub-continental mantle. Contributions Mineralogy
Petrology 78, 175-188.
496 Journal of African Earth Sciences
Whalen, J. B. 1985. Geochemistry of an island-arc plutonic
suite: the Uasilau-Yau Yau intrusive complex, New Britain,
PNG. Journal Petrology 26, 603-632.
Whalen, J. B. and Currie, K. L. 1982. Volcanic and plutonic
rocks in the Rainy Lake area, Newfoundland. In: Current
Research, part A, Canadian Geological Survey Paper 821A, 17-22.
White, W. M. and Patchett, J o 1984. Hf-Nd-Sr isotopes and
i n c o m p a t i b l e e l e m e n t abundances in island arcs:
implications for magma origin and crust mantle evolution.
Earth Planetary Science Letters 67, 167-185.
Zen, E.-An. and Hammarstrom, J. M. 1984. Magmatic
epidote and its petrologic significance. Geology 12,
515-518.
Geological map
A new geological map for the basement rocks in the
Eastern and Southwestern Desert of Egypt; 1:1 000
000. 1972. Compiled by El Ramly, M. F. Annals
Geological Survey Egypt 2, 1 - 18.