Geological and Geochemical Characterization of the Neoproterozoic Derudieb Metavolcanic Rocks, Red Sea Hills, Sudan

Geological and Geochemical Characterization of the Neoproterozoic Derudieb Metavolcanic Rocks, Red Sea Hills, Sudan
Geological and Geochemical Characterization of the Neoproterozoic
Derudieb Metavolcanic Rocks, Red Sea Hills, Sudan
*1Albarra M.N. Satti, 2Khalil I. Khalil, 3Ahmed M. ElMakky
1Mining and Economic Geology Department, Faculty of Earth Sciences, Red Sea University, Sudan.
2Geology Department, Faculty of Science Alexandria University, Egypt.
3Department of Geological and Biological Sciences, Faculty of Education, Alexandria University, Egypt.
The metavolcano - sedimentary sequences in the northern part of the Red Sea Hills comprise a
sequence of metamorphosed rocks at low green schist facies of metamorphism consisting of lava
flows, tuffs to breccias and agglomerates range in composition from basalts and andesites to
rhyolites. Geologically the meta volcano sedimentary sequences is divided into metavolcanic
rocks and metasediments. The metavolcanic rocks range in composition from mafic to felsic. The
metasediments are represented by banded schist, quartzite and marble. The samples collected
for study lie within the field of sub-alkaline rocks except one mafic volcanic sample, which plot
near the boundary in the alkaline field and thus follow a transitional tholeiitic to calc-alkaline trend
(increasing FeO* relative to MgO). The behavior of the large ion lithophile element (LILE) in the
studied metavolcanics confirms the early fractionation of plagioclase. These rocks display
negative Nb anomalies, suggesting that the melt source was modified by subduction-related
fluids. Tectonically all felsic samples fall in the field of volcanic arc granitoids whereas the mafic
units plot firmly within the plate margin field.
Key words: Meta- volcano sedimentary, mafic volcanic, felsic volcanic, Red Sea Hills, Derudieb.
INTRODUCTION
The study area is located in the southern part of the Red
Sea Hills, northern Sudan. It occurs at about 80 km to the
northwest of the Sudanese Eritrean boundaries. Derudieb
area is situated within the physiographic limits of the Red
Sea Hills. It covers about 30 km2 and generally constitutes
a rugged terrane characterized by hills and vallies with
different sizes in most of its parts. The metavolcano-
sedimentary rocks represent part of an early island arc
system formed during the late Proterozoic evolution of the
Arabian-Nubian Shield. They comprise stratified and
folded successions of greenschist to lower amphibolites
facies metamorphosed rocks intruded by granitoid
complexes (Vail, 1988) (Fig 1.1). The metavolcano-
sedimentary sequences are previously termed Oyo series,
Nafirdeib and Awat series (Abu Fatima, 1992). The
eruptive rocks consist of lava flows that range in
composition from basalts and andesite's to rhyolites, in
addition to tuffs, breccias and agglomerates. These rocks
are strongly deformed and show gradational contacts
against the rocks of the greenschist facies grade. No age
and tectonic setting data are available but the styles of
deformation sequences are very clear to be of late
Precambrian age (Nour, 1983).
In this paper, we report geological and geochemical data
of Neoproterozoic metavolcano-sedimentary rocks
(Derudieb area, Red Sea Hills. Sudan), which tectonically
locates in the Haya terrain. The main aim is to study the
geological and geochemical features of the meta volcano
sedimentary rocks to evaluate their tectonic environment.
*Corresponding Author: Dr. Albarra M.N. Satti; Mining
and Economic Geology Department, Faculty of Earth
Sciences, Red Sea University, Sudan. Email:
albarrasatti78@yahoo.com, Tel: 00249116328528;
Co-Authors Email: 2
kebeid@yahoo.com;
3
ahmedelmakky@yahoo.com
Research Article
Vol. 5(3), pp. 297-308, November, 2019. © www.premierpublishers.org. ISSN: 3019-8261
nternational Journal of Geology and MiningI

Satti et al. 298
Fig.1.1: Geological sketch map of NE Sudan showing the
main lithological units (modified after Vail 1983).
RESEARCH METHODOLOGY
Research methodologies, which are used to accomplish
the objectives of the present work, are mainly: (1) fieldwork
and sampling of the different rock units (2) preparation of
thin section for most of the collected samples (3) chemical
analyses of major, minor and trace elements. In the field
trip, sampling was conducted by collecting representative
rock samples from specific outcrops in the study area.
These specific outcrops include some belts of
metasediments and metavolcanics (6 samples) (Table
1.1). 6 thin sections representing the meta volcano
sedimentary sequence, were prepared at the Department
of Geology, Faculty of Science, Alexandria University,
Egypt. The microscopic study allows to investigate the
petrographic and mineralogical characteristics of the
different rock types. 6 samples were analyzed for major
and some selected trace elements by inductively coupled
plasma mass spectrometry (ICP-MS). The remaining trace
elements and rare earth elements (REE) were analyzed by
inductively coupled plasma-atomic emission spectrometry
(ICP-AES). All the analyses were carried out at the ACME
Analytical Laboratories Ltd.
Table 1.1: The coordinate of the samples which was
collected from the study area.
Sample Number Latitude Longitude
C 13-1 36.28055556 17.49205556
C4 36.26347222 17.5205
B7-2 36.35938889 17.61552778
E 7 36.21463889 17.54575
9 36.21777778 17.55916667
42 36.42388889 17.5438889
Regional setting
The Arabian Shield is a part of a larger geological
ensemble, the Arabian–Nubian Shield, which covers
several countries, mainly Egypt, Eritrea, Ethiopia, Saudi
Arabia, Somalia, Sudan and Yemen (2200 km NS 1200 km
EW). These different areas were accreted during the
Neoproterozoc and share a very similar geological
evolution (Stern and Johnson, 2010). The Arabian-Nubian
shield (Fig1.2) is composed of imbricated meta-
sedimentary, meta-volcanic, and ophiolitic rock
assemblages that evolved in island arc, back-arc, and
oceanic settings, and were episodically deformed,
intruded, and metamorphosed together during the late
Proterozoic Pan-African orogeny (e.g. Greenwood et al.
1976; Gass 1977,Kroner et al. 1987; Pan &- African in the
sense of Berhe ( 1990). The Red Sea Hills of NE Sudan
are considered to be the north eastern extension of the
Mozambique belt (Kröner, 1977). They occupied the area
between the Red Sea in the east and Nile valley in the west
(Vail, 1979). The Pan-African rocks in the Red Sea Hills
are mainly arc volcanic, immature sediments, ophiolites
and back arc basins, which are predominantly,
metamorphosed in the greenschist facies. Towards the
west, they pass into high grade metamorphic lithologies.
This change in metamorphic grade has been interpreted
as indicating pre Pan-African origin of the high-grade rocks
(Vail, 1979). Structurally (Kroner, 1987) subdivided the
Red Sea Hills into five intra-oceanic-arc terrains. These
are: Gerf, Gabgaba, Gebiet, Haya and Tokar terrains that
are separated by east to northeast trending ophiolite–
decorated sutures formed during the Pan African Orogeny
between 900-550 Ma ago (Kröner 1977), (Fig 1.2). The
terrains comprise blocks of similar rock types, which
display complex and protracted tectonic histories due to
their interaction and collision. The study area occurs within
Haya terrain.
Geological setting
The metavolcano-sedimentary sequences have many
local names according to previous geological literature, but
the most used name is Nafirdieb Series (Abu Fatima
1992). These sequences are generally characterized by
low grade greenschist facies regional metamorphism, but
occasionally metamorphism has witnessed the
amphibolite facies, especially around igneous intrusions
(Ruxton 1956). The metavolcano-sedimentary rocks cover
most of the western and southwestern parts of the study

Int. J. Geol. Min. 299
Fig. 1.2: Map of the Arabian Nubian Shield showing the main suture zones and terranes (Johnson and Wolehaimanot,
2003).
area. They consist mainly of meta-sediments (schist,
marble and quartzite), and metavolcanic rocks of different
rock types including rhyolite, andesite, basaltic andesite
and basalt (Fig. 1.2). They usually form hills of variable
dimensions, with moderate to high relief, and may reach
up to mountain size.
Based on their field and microscopic criteria, the
metavolcanic rocks in the study area have been classified
into intermediate volcanic rocks, acidic lavas and tuffs.
Rhyolite tuff unit occurs in the western part of the study
area, near Khor Awagtieb, and extends as intermittent and
isolated outcrops to the SW of the study area. The rhyolite
outcrops are slightly tectonized, weakly foliated rocks and
cut by some veinlet of pegmatites, which composed of
coarse-grained crystals of quartz and potash feldspar. In
the central part of the study area, near Khor Tagotieb,
there is an outcrop of low relief rhyodacite tuff, which is
highly weathered and kaolinized in some parts. The
rhyodacite tuffs have disseminated iron oxide and exhibit
reddish colour on the surface of the rock (Fig. 1.3 A,B).
The metavolcanics are dominated by acid lavas, tuffs and
intermediate (meta-andesite) to basic (metabasalt)
varieties. Andesitic rock unit occurs in the central part of
the study area near the camp of Ariab Company
(Fig.1.3C). The outcrop is characterized by massive to
weakly foliated metavolcanic rocks and sharp contact with
gabbroic rocks. The metabasalts are massive, moderately
relief and contact with post tectonic intrusion rocks in the
study area (Fig 1.3 D). The metasediments in the study
area occur as elongated belt on the east and west sides of
the area. In the northern bank of Khor Derudieb, the
metasediment belt extends northwards for about four
kilometers in an ENE-WSW direction. This belt represents
the large one in the study area and consists of highly
foliated quartz- mica schist containing very small lenses of
metavolcanic (Fig. 1.3 E, F). Quartzite occurs as large
outcrop in the western and central parts of the study area.
It also presents as small, elevated and massive outcrops
with smoky to grey colour in the central part of the area.
There is also a chain of intermittent outcrops of massive
and low elevated white quartzite (Fig. 1.3 G). Moreover, to
the West of Shagoneen village (Fig. 1.2), there is a black
quartzite outcrop extended for more than one kilometer.
Fig.1.2. Field photographs of quartzite in the study area,
(G1) intermittent outcrops of white, massive and low
elevated quartzite (G2) close up view showing massive
white quartzite stained with iron oxides

Satti et al. 300
Fig.1.2: Simplified geological map of the meta volcano sedimentary sequence in the study area.
Marble occurs at the Shagoneen village, near the gossan
outcrop, in the central part of the study area. It occurs as
three high-standing ridges (Fig.1.3H) surrounded by
granite. The length of the marble bands is about 3
kilometer with widths ranging between 50-150 m. The
Shagoneen marble varies in color from grey to smoky or
white. It is also highly fractured and jointed (Fig.3.10B) with
some elephant skin in the surface of the rock.
Fig. 1.3: Field photographs of the metavolcanics and
metasediments rocks in the study area, (A,B) highly
weathered to kaolinized rhyodacite tuffs near K.Tagotieb
with reddish color surface, (C) meta andesite outcrops
near the camp of Ariab company and (D) meta basalt.
(E,F) strongly foliated metasediment near Khor Derudieb,
(G) field photographs of quartzite in the study area, (G1)
intermittent outcrops of white, massive and low elevated
quartzite (G2) close up view showing massive white
quartzite stained with iron oxides. (H) Field photographs of
Marble in the study area, (H1) high standing ridges of
marble, (H2) highly fractured and jointed marble.

RESULTS
Petrography
The metavolcanic rocks occupy the central and western
parts of the study area as moderately to highly elevated
outcrops in contact with the intrusive rocks (Fig 3.6). The
metavolcanics are dominated by acid lavas, tuffs and
intermediate (meta-andesite) to basic (metabasalt)
varieties.
The metabasalts are massive, in spite of the presence of
some veinlets filled with calcite and epidote and occasional
quartz amygdales. The metabasalts consist of plagioclase
feldspar, hornblende, actinolite, epidote, and chlorite as
well as accessory apatite and opaque minerals. The
texture is mainly porphyritic (Fig.2.1A) with phenocrysts
dominated by plagioclase, actinolite pseudomorph and
occasionally relict pyroxene. Aphyric basalts are also
common.
The presence of some fresh, colourless to pale green,
clinopyroxene microphenocrysts (augite) in some samples
surrounded by actinolite and chlorite suggest that the
actinolite phenocrysts are pseudomorphic after
clinopyroxene. The plagioclase phenocrysts are partially
or completely saussuritized. The saussuritization of the
plagioclase may be either epidote-sericite or sericite-
chlorite. The original composition of the plagioclase, as
indicated from the fresh relicts is mainly andesine (An35-
45). The microcrystalline groundmass is dominated by
saussuritized plagioclase laths, mafic minerals
pseudomorphosed by actinolite, chlorite and opaque
minerals. Aphyric metabasalts contain flow-oriented
plagioclase laths together with actinolite, chlorite and
opaque oxides (Fig. 2.1B).
The meta-andesite in the study area is very rare. It consists
of plagioclase feldspar, actinolite, and subordinate
amounts of quartz, biotite, chlorite and apatite. Plagioclase
is the major constituent in the meta-andesite rock. It varies
in composition from oligoclase to andesine. The
plagioclase occur in two forms; coarse-grained prismatic
phenocrysts with grain sizes up to 3 mm embedded in a
fine grained matrix of idiomorphic plagioclase laths (up to
0.2 mm long), actinolite, biotite and opaque minerals. The
plagioclase phenocrysts (Fig.2.1C) show combined albite-
Carlsbad twinning and sometimes are partially to
completely saussuritized. Actinolite form lath-like
idiomorphic to subhedral prismatic crystals and granular
aggregates in the groundmass. It is generally pale green
and weakly pleochroic and occasionally shows simple
twinning. In some samples, actinolite exhabit slight
alteration to chlorite along the crystal margins. Biotite
occurs as fine flakes, which are partially replaced by
chlorite and show distinct pleochroism from dark brown to
pale brown. Apatite as an accessory mineral is present as
cracked elongated grains in the matrix or as inclusions in
the plagioclase and actinolite crystals. Quartz is
represented by fine-grained crystals, which forms part of
the groundmass.
The metavolcanic units are dominated by felsic tuffs and
lava, which occur in the eastern part of the study area. The
felsic tuffs are mainly composed of crystal fragments up to
0.2 mm long of plagioclase and occasionally actinolite and
quartz together with few rock fragments (up to 0.5 mm
across), (Fig. 2.1D). The crystal and rock fragments are
set in a tuffaceous felsitic matrix primarily composed of
quartz and feldspar with few streaks of chlorite, epidote
and calcite. Minor and scarce amounts of epidote,
magnetite, ilmenite, and apatite are also common as
groundmass components.
The felsic lava is mainly meta-rhyolite, which is generally
fine-grained to porphyritic. The main constituent minerals
are: K-feldspar, quartz, plagioclase feldspar and some
biotite (Fig.2.1E). Zircon, apatite, and magnetite are
accessory minerals. Additionally, sericite and calcite are
secondary minerals. The rhyolites are fine-grained with
allotrimorphic texture, but porphyritic and granophyric
textures are also common. Quartz crystals occur in two
distinct types.
The first type is fine-grained anhedral with granular form
constituting the main components of the groundmass.
Some crystals show micro-phenocrysts imparting to the
rock microporphyritic texture. Plagioclase feldspar (An10 –
An15) and K-feldspar are fine-grained, anhedral with
granular form. Biotite crystals occur as fine-grained
discrete grains sporadically scattered in the rock or as
interstitial constituent in the groundmass. They are
partially to completely alter to chlorite and iron oxides.

Satti et al. 302
Fig 2.1: Photomicrographs of metavolcanics in the study area showing metabasalt (A) plagioclase phenocrysts embedded
in a groundmass of plagioclase laths and chlorite.CN. (B) Showing chlorite actinolite with opaque minerals as iron oxide
and clinopyroxene, PPL. The meta-andesite (C) showing the porphyritic texture of the rock with plagioclase phenocrysts
embedded in a groundmass consisting of plagioclase laths, biotite, chlorite , actinolite and opaque minerals; CN. The meta
rhyolite (D) plagioclase, quartz, muscovite and biotite as main constituent minerals; CN. (E) Shows the accessory and
secondary minerals; PPL.
The metasediments in the study area are represented by
schist bands and marble belt. The schist bands are of
various mineralogical composition and textures and are
well exposed in the south eastern part of the study area
(Fig 1.3). They are generally well foliated and fine- to
medium-grained. The schist bands consist of quartz,
garnet, biotite, epidote and chlorite (Fig. 2.2 A).
Chlorite and epidote are secondary minerals that formed
due to the alteration of biotite and plagioclase feldspar,
respectively. Quartz appears as anhedral rounded grains
characterized by wavy extinction due to the effect of
deformation or stress. Garnet occurs as small rounded
crystals, which are pale pink to colourless in plane
polarized light. Biotite occurs as flakes of brown colour and
is sometimes partially altered to chlorite. Very fine-grained
iron oxides are crystallized in the schist and occur as
streaks parallel to the main schistosity fabric (Fig 2.2 B).
The metasediments in the study area are also represented
by marble which occurs in the central part near Tagotieb
gossan in the Shagoneen village (Fig 1.2).
Microscopically, marble is dominantly composed of
equigranular and well crystalline calcite. Feldspar grains
and biotite-muscovite flakes do occur but are very rare.
Accessory minerals are represented by some sulphide
grains, which are decomposed and replaced by iron oxides
(Figs. 2.3A&B).
Fig. 2.2: Photomicrographs of the schist showing: (A) quartz , garnet , chlorite , biotite and epidote , CN. (B). Showing fine
grained of iron oxide, PPL.

Fig.2.2: Photomicrographs of the marble showing (A) calcite crystals, opaque minerals, (B) epidote minerals.
Geochemistry
Based on field and petrographic investigation, 6
representative samples were selected for chemical
analyses of major and trace elements. The samples were
selected to cover all the petrographic varieties (mafic
volcanic and felsic volcanic) that have been encountered
in the study area and to show the minimum effect of post
magmatic alteration. The distribution of the analyzed
samples (6 samples) from the different rock types of
metavolcanics as follows: mafic volcanic (3 samples) and
felsic volcanic (3 samples).
The Metavolcanic Rocks:
Major and trace element analyses of 6 representative
samples, covering the metavolcanic varieties are listed in
(Table 1.1). According to the chemical data, the
metavolcanics are divided into two main groups, which are
mafic metavolcanic rocks (SiO2 = 46- 48 wt. %) and felsic
metavolcanic rocks (SiO2 = 73- 84 wt. %). The mafic
metavolcanics have narrow to moderate ranges of MgO
(5.45–6.20 wt. %), CaO (7.59–10.35 wt. %), total iron as
Fe2O3 (14.10–16.57 wt. %), Al2O3 (12.94–15.09 wt. %)
and TiO2 (2.28–2.88 wt. %). Their Na2O (1.7–3.35 wt. %)
and K2O (0.1–0.84 wt. %) contents are highly variable.
The felsic metavolcanics have wide ranges of MgO (0.02–
0.47 wt. %), CaO (0.03–3.33 wt. %), total iron as Fe2O3
(0.16–2.60 wt. %), Al2O3 (11.92–19.12 wt. %) and TiO2
(0.20–0.62 wt. %). Their Na2O (0.02–4.43 wt. %) and K2O
(0.09–4.23 wt. %) contents are highly variable. The total
alkalis vs. SiO2 (TAS) geochemical classification diagram,
which relies on SiO2 vs Na2O+ K2O (Le Bas et al, 1986),
shows that the mafic metavolcanic samples are low
Na2O+ K2O basalts (Fig. 3.1). The felsic volcanic samples
on the other hand, show moderate to high range of Na2O+
K2O (Table. 1.1) and are classified as rhyolites. According
to the classification of (Irvine and Baragar1971), all felsic
and mafic metavolcanic samples lie within the field of sub-
alkaline rocks except one mafic volcanic sample, which
plot near the boundary in the alkaline field and thus follow
a transitional tholeiitic to calc-alkaline trend (increasing
FeO* relative to MgO) (Fig. 3.1). This trend may be due to
olivine and pyroxene fractionation.
Fig. 3.1: Total alkalis (Na2O + K2O) vs SiO2 diagram (Le
Bas et al 1986) for the chemical classification of the
studied metavolcanic rocks. The curve separating alkaline
and subalkaline fields is from Irvine and Baragar (1971).

Satti et al. 304
Table 1.1: Major (wt %), trace elements (ppm) and REE
elements (ppm) data of the metavolcanics in the study
area.
Mafic volcanic Felsic volcanic
C13-1 C4 B7-2 E7 9 42
SiO2 47.65 48.22 46.07 78.33 73.84 77.35
TiO2 2.76 2.28 2.88 0.20 0.32 0.62
Al2O3 12.94 13.06 15.09 11.92 3.00 13.90
Fe2O3 16.57 16.32 14.88 1.43 2.60 0.84
MnO 0.29 0.27 0.19 0.03 0.11 0.03
MgO 5.90 6.20 5.45 0.47 0.19 0.34
CaO 10.35 9.15 7.59 1.20 3.33 0.05
Na2O 1.70 2.52 3.35 4.43 4.33 0.23
K2O 0.23 0.12 0.84 0.79 0.91 4.23
P2O5 0.27 0.18 0.72 0.03 0.09 0.02
LOI 1.0 1.4 2.6 1.1 1.2 2.3
Sum 99.66 99.72 99.66 99.93 99.92 99.91
Cr 177 157 75 95 13 13
Ni 12.0 16.4 25.7 3.0 4.8 0.4
Sc 51 50 23 5 6 8
Ba 331 132 330 232 397 947
Be 1 2 3 0.5 0.5 2
Co 40.2 40.3 46.0 2.3 2.4 2.2
Cs 0.5 0.5 0.6 0.1 0.1 0.5
Ga 20.6 19.4 21.8 11.6 13.9 8.1
Hf 4.0 3.4 5.2 4.6 3.4 4.4
Nb 2.6 1.6 11.2 5.2 3.7 4.3
Rb 1.9 0.8 12.1 10.9 13.2 53.8
Sn 2 2 2 1 1 4
Sr 138 160 638 111 271 31
Ta 0.1 0.2 0.7 0.5 0.2 0.3
Th 0.3 0.1 0.7 2.9 1.8 1.6
U 0.1 0.2 0.4 0.7 0.8 0.6
V 468 420 265 28 15 40
W 0.8 0.7 0.4 1.2 0.8 2.0
Zr 143 119 224 144 113 149
Y 49 40 32 24 27 26
C13-1 C4 B7-2 E7 9 42
La 6 5.1 20.4 7.4 10.9 17.3
Ce 18.2 14.1 51 33.9 24.4 40.5
Pr 3.17 2.46 7.31 2.52 3.2 4.08
Nd 17.1 13.8 34.2 10.4 13.5 14.1
Sm 6.04 4.76 8.06 2.66 3.64 2.97
Eu 2.23 1.79 2.51 0.66 1.11 0.48
Gd 8.29 6.33 8.09 3.16 4.11 3
Tb 1.45 1.18 1.22 0.57 0.7 0.53
Dy 8.69 7.35 6.63 3.98 4.15 3.31
Ho 1.96 1.55 1.25 0.93 0.96 0.78
Er 5.73 4.88 3.37 3.16 3.02 2.43
Tm 0.82 0.65 0.46 0.5 0.47 0.43
Yb 5.42 4.27 3.14 3.83 3.19 3.13
Lu 0.83 0.66 0.43 0.59 0.49 0.53
ΣREE 85.93 68.88 148.07 74.26 73.84 93.57
(La/Yb)n 0.79 0.86 4.66 1.39 2.45 3.96
(La/Sm)n 0.64 0.69 1.63 1.80 1.93 3.76
(Gd/Yb)n 1.27 1.23 2.13 0.68 1.07 0.79
(Eu/Eu*) 0.96 1.00 0.95 0.70 0.88 0.49
DISCUSSION
The geochemical behavior of trace elements during the
evolution of magma depends on their partitioning between
solid and liquid phases. Elements which are retained in the
residual solid during partial melting or substitute major
elements during crystallization are termed high
temperature (compatible) elements, for example Cr and
Ni. Some trace elements are strongly enriched in the
residual melt during crystallization and are termed
incompatible elements such as Sr, Rb, Ba, Zr, Ti and Y
(Wilson, 1989).
The elements Ni, Cr, V, Co, and Sc, which are termed
compatible elements, are present in high concentrations in
the studied metabasalt rocks (Cr=75-274ppm; Ni=8-
26ppm; Sc=23-50ppm; V=265-468ppm; Co=36-46ppm,
Table 1.1). The high contents of these elements in the
metabasalt may attribute to the presence of
ferromagnesian mineral phases such as olivine, pyroxene
and titano-magnetite in these rocks. The strong depletion
of these elements in the acid metavolcanic (Ni=0.4-5ppm;
Sc=2-8ppm; V=15-40ppm; Co=1.3-2.4ppm, Table 1.1)
may coincide with the virtual absence of mafic phases in
the rhyolite samples.
The behavior of the LILE in the studied metavolcanics
confirms the early fractionation of plagioclase. The Rb
concentration is higher in the felsic metavolcanic rocks
(11-54 ppm in rhyolite) compared to the mafic
metavolcanic rocks (0.9-12ppm in basalt). The Sr
concentration varies widely but decrease in basaltic rocks
(Fig. 2.3).
The behavior of Sr contrasts with K and Rb variation,
suggesting that Sr was probably removed in plagioclase
substituting Ca. The decrease of Sr and CaO with
increasing Rb (Fig. 2.3) confirms plagioclase fractionation.
The contents of the incompatible HFSE like Zr (25-224
ppm), Nb (1-11 ppm), Hf (0.7-5.3 ppm), Ta (<0.1–0.2
ppm), and Y (2.5–50 ppm) in the studied metavolcanics
show wide variation within the mafic and felsic
metavolcanics (Fig. 3.3). They show a positive correlation
when plotted against each other suggesting that they are
a group of coherent elements. Other strongly incompatible
elements like U, Th, show the same behavior of HFS
elements.

Fig. 3.2: Rb vs. Ba, K, Sr and CaO binary variation
diagrams for the studied metavolcanic rocks.
Fig. 3.3: Variation of Zr vs. Nb, Hf, and Y in the studied
metavolcanic rocks. .

Satti et al. 306
Rare Earth Element (REE) patterns of representative
samples normalized chondritic values of Sun and
McDonough (1989) are shown in (Fig. 3.4). The REE
patterns show that the mafic and felsic metavolcanics are
variably light-REE enriched according to rock type. The
mafic metavolcanics are less fractionated than those of the
felsic metavolcanics. The mafic metavolcanics
(metabasalts) are characterized by low to moderate total
REEs (24–148ppm, Table 1.1) and weakly fractionated
patterns [(La/Yb) n=0.8–4.7; (La/Sm)n=0.64-1.63; (Gd/Yb)
n=1.22-2.13)] with no Eu-anomalies (Eu/Eu*=0.95–1.06).
The felsic metavolcanics (rhyolites) have higher REE
contents (34–94ppm) and show relatively more
fractionated REE patterns [(La/Yb)n=0.63–3.96] with weak
to moderate negative Eu anomalies (Eu/Eu*=0.5–0.9)
(Table 1.1). Generally, the REE-patterns of all
metavolcanics clearly show an increase of the total REE
contents (mainly the LREE) and the negative Eu
anomalies from the mafic to the felsic volcanics.
These variations testify to the importance of fractional
crystallization in the evolution of the metavolcanics.
Primordial mantle-normalized incompatible element
profiles of the metavolcanic rocks (Fig. 3.5) display
negative Nb anomalies, evidence that the melt source was
modified by subduction-related fluids (Pearce, 1983). The
rhyolites have ―spiked multi-element patterns and
variably negative Ba, Sr, P, Eu, and Ti anomalies, which
may reflect plagioclase, K-feldspar, apatite, and Fe–Ti
oxide fractionation.
Fig. 3.4: Chondrite-normalized REE-patterns of the studied metavolcanic rocks. Normalization values are from Sun
and McDonough (1989).
Fig. 3.5: Primordial mantle-normalized trace element patterns for the studied metavolcanic rocks. Normalizing values are
from Wood (1979).
Tectonic discrimination diagrams for the investigated
metavolcanic rocks are discrimination of the felsic
volcanics and Ti/Y – Zr/Y discrimination diagram (Pearce
and Gale, 1977) for the mafic volcanic. For the investigated
felsic volcanic rocks, all samples plot in the field of volcanic
arc granitoids (Fig. 3.6). On the Ti/Y – Zr/Y diagram which
discriminate between plate margin and within-plate
basalts, the data of the studied mafic volcanic rocks plot
firmly within the plate margin field (Fig. 3.7). All the studied
metavolcanic rocks are characterized by low Zr/Y ratios
and high Zr contents (Fig. 3.8), which are typical for basalts
from oceanic arc tectonic environments (Pearce 1983).

Fig.3.6: Y vs. Nb discrimination diagram of Pearce et al
(1984) for the tectonic discrimination of the felsic volcanic
rocks; WPG=within plate granite, ORG=ocean ridge
granite, VAG=volcanic arc granite and COLG=collision
granite
Fig. 3.7: Ti/Y – Zr/Y diagram (Pearce and Gale, 1977) for
the tectonic discrimination of the mafic metavolcanics.
Fig. 3.8: Zr/Y vs. Zr discrimination diagram Pearce (1980)
showing the oceanic arc character of the studied
metavolcanic rocks in the Tagotieb area.
CONCLUSION
The metavolcanic rocks can be broadly classified into
mafic metavolcanics and felsic metavolcanic. The mafic
metavolcanics are mainly metabasalt and meta-andesite,
which occur as massive to weakly foliated bodies, usually
interlayered with metasediments of variable types of
schist, marble, and quartzite. They are greyish green with
the primary volcanic textures (porphyritic and sometimes
amygdaloidal) still recognizable. The felsic metavolcanics
are rhyolites, which occur as variably deformed rocks often
with pink colour. They are composed mainly of quartz, K-
feldspar and albite and minor sericite, chlorite and/or
epidote.
All the studied metavolcanic rocks are characterized by
low Zr/Y ratios and high Zr contents , which are typical for
basalts from oceanic arc tectonic environments (Pearce
1983).The felsic volcanic rocks were produced through
fractional crystallization of basaltic melts.
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Accepted 22 May 2019
Citation: Satti AMN, Khalil I. Khalil IK, ElMakky AM (2019).
Geological and Geochemical Characterization of the
Neoproterozoic Derudieb Metavolcanic Rocks, Red Sea
Hills, Sudan. International Journal of Geology and Mining
5(3): 297-308.
Copyright: © 2019: Satti et al. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.

Geological and Geochemical Characterization of the Neoproterozoic Derudieb Metavolcanic Rocks, Red Sea Hills, Sudan

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