Continental Flood Basalts and Rifting: Geochemistry of …

Loading...

Taking too long?

Reload document

| Open in new tab

International Journal of Geosciences, 2013, 4, 1459-1466
Published Online December 2013 (http://www.scirp.org/journal/ijg)
http://dx.doi.org/10.4236/ijg.2013.410143

Continental Flood Basalts and Rifting: Geochemistry of
Cenozoic Yemen Volcanic Province

M. A. Mattash1,2, L. Pinarelli3, O. Vaselli3,4, A. Minissale3, M. Al-Kadasi5, M. N. Shawki6, F. Tassi3,4
1HCCGSR, Mukalla, Yemen
2Ministry of Oil and Minerals, Geological Survey and Mineral Resources Board, Aden, Yemen
3CNR, Institute of Geosciences and Earth Resources, Florence, Italy
4Department of Earth Sciences, University of Florence, Florence, Italy
5Department of Geology, Sana’a University, Sana’a, Yemen
6Department of Geology, Taiz University, Taiz, Yemen
Email: lapina@igg.cnr.it

Received August 2, 2013; revised September 6, 2013; accepted October 3, 2013

Copyright © 2013 M. A. Mattash et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accor-
dance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of the intellectual
property M. A. Mattash et al. All Copyright © 2013 are guarded by law and by SCIRP as a guardian.

ABSTRACT

Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces,
being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of
the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in
Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene
Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS).
Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the
Red Sea and the Gulf of Aden (30 – 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase
(10 – 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic
rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields
of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges,
but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes
dominate geochemical variations of both series. Primitive magmas (MgO > 7.0%) are enriched in incompatible ele-
ments and LREEs with respect to primitive mantle, but YVS are more enriched than YTS. To first order, the different
geochemical patterns agree with different degrees of partial melting of an astenospheric mantle source: 25% – 30% of
partial melting for YTS and 10% – 3% for YVS. Secondly, the higher degree of enrichment in incompatible elements of
YVS reflects also greater contribution of a lithospheric mantle component in their source region.

Keywords: Continental Flood Basalts; Continental Rifting; Geochemistry; Yemen; Cenozoic

1. Introduction

The Tertiary continental magmatism of Yemen was as-
sociated to the early opening phases of the Red Sea and
the Gulf of Aden, and was part of the Afro-Arabian rift
system (AARS), which included the Ethiopian Rift and
the Afar Triangle (Figure 1(a)).

During Late Eocene to recent, the geological evolution
of North Africa was dominated by the development of
the Red Sea-Gulf of Aden-East Africa Rift System that
resulted in the separation of the Arabian plate. The open-
ing of narrow, elongated oceanic domains along the Gulf

of Aden and the Red Sea from Miocene times resulted in
the separation and northwards drift of the Arabian plate,
allowed by sinistral movement along the Levant-Dead
Sea fault zone. Rifting initiated in the Early Oligocene in
several small, en echelon E-W to ESE-WNW trending
basins in the Gulf of Aden province. By the Oligocene-
Miocene transition, rifting had spread to Afar and through-
out the Red Sea system. The onset of continental rifting
began ~22 Ma ago, and encompassed the whole length of
the present-day Red Sea basin and Gulf of Aden [1].
Strong magmatic activity predated and accompanied rift
tectonics, favouring extension by weakening the litho-

Open Access IJG

1460

M. A. MATTASH ET AL.

sphere. Oceanic spreading followed advanced continental
rifting about 5 Ma ago with volcanic (mainly basaltic)
activity [1].

In the late Oligocene-early Miocene through to the
present time, large volumes of flood basalts emplaced at
discrete eruptive centres along the western margin of the
Arabian plate from the Gulf of Aden to the Mediterra-
nean. These plateau basalts are concentrated on the Ara-
bian side of the Red Sea without matching counterparts
on the Nubian plate (Figure 1(a)), and represent one of
the largest areas of predominantly alkali-olivine basalts
in the world.

In Yemen, Oligo-Miocene to Recent (pre-/syn-rift) vol-
canic complexes were emplaced in the western and south-
western parts (Figure 1(b)).The area of this volcanism,
which included Continental Flood Basalts, occupied ap-
proximately one-tenth of the total area of the country,
and approximately 28% of the total area of the Arabian
Plate volcanic rocks. The Yemen flood volcanics are
characterized by: 1) large volumes of magmatic activity;
2) large-scale crustal extension; 3) mildly alkaline basalts
and 4) bimodal distribution of basic and acid magma
products. Volcanic products from Yemen are akin to
coeval volcanic rocks from Djibouti, Ethiopia, and some
parts of the Kenyan rift.

This work presents a review of petrological data for

the rift-related volcanic rocks of Yemen.

2.1. Yemen Trap Series (YTS)

The YTS represent the lowest part of the Cenozoic Yemen
volcanic province, and mainly overly the Cretaceous
Tawilah Group sandstones and the Paleogene lateritic
paleosols, and in some cases the metamorphic basement
rocks. They had been developed during the Oligocene-
early Miocenic pre- and sin-rift phases.

The YTS consists of thick bimodal volcanics, includ-
ing alkaline to transitional basalts and peralkaline rhyo-
lites and their associated ignimbrites, tuffs and rhyolitic
obsidian flows, which cover an area of about 3000 km2.
The volume of acidic to basic volcanic products is greater
than 0.5. Thickness of the YTS varies from >2000 m in
the west down to hundreds to tens of meters in the east.
The older units of this series are intruded by gabbro, al-
kali granite and syenite bodies. The majority of the felsic
rocks are of peralkaline type (A/CNK > 1) with a comen-
ditic character (normative-quartz > 20%) and are very
poor in normative-mafic minerals.

Quoted ages for the YTS volcanism range from 31 to
16 Ma (see review in [1]). Within this large period, the
peak of activity occurred between 30.9 and 26.5 Ma. In
addition, some pre-Oligocenic ages [e.g. 2] could suggest
early beginning of the volcanism in an Eocenic pre-Trap
phase of magmatic activity, in agreement with Cenozoic
igneous activity in the neighbouring Arabia and Gulf of
Aden.

2. The Yemen Continental Flood Basalts

2.2. Yemen Volcanic Series (YVS)

The Cenozoic Yemen volcanic province can be divided
into: 1) the late Oligocene-early Miocene Yemen Trap
Series (YTS), separated by an unconformity from 2) the
late Miocene-Recent Yemen Volcanic Series (YVS).

The YVS was firstly defined by [3-5] on the basis of both
geochronological and geochemical evidence. They were
generated and developed through the post-rift stage (Mio-
cene to Recent), and are separated by an unconformity

(a) (b)

Figure 1. (a) Generalized map of the Afro-Arabian rift system, comprising the Read Sea, the Gulf of Aden, the Ethiopian Rift
and the Afar triangle. (b) Sketch map of the southwestern part of Yemen showing the main Tertiary magmatic rocks.

Open Access IJG

M. A. MATTASH ET AL.

1461

Northern YTS and East-of-Aden YVS

from the older YTS. Volcanic cones, domes, sheets and
lava flows are the typical occurrences of this series. They
are composed mainly of basaltic lavas, stratified basic
tuffs and agglomeratic pyroclastics, and less common
differentiated rock-types, except the Al-Lisi volcano (5
km E of Dhamar city), which is entirely composed of
rhyolitic lava flows.

Published K-Ar ages for the YVS volcanism range

from 11.3 to 0.04 Ma ([2] and references therein).

There are eight well-known volcanic fields situated
along the Gulf of Aden coast. They are mainly composed
of individual volcanoes characterized by central vent erup-
tions. There are geological, chronological and geochemi-
cal differences between those outcropping West- and East-
of Aden [4]. The former (West-of-Aden) are older (10 – 5
Ma), include the Island of Perim, Jabal Kharaz, Jabal
Al-Birkah, Ras Imran, Little Aden, and Aden, and are
stratoid volcanoes characterized by transitional-mildly
alkaline basalt to peralkaline rhyolite. The latter (East-of-
Aden) are younger (5 – 0 Ma); include Shuqrah (Al
Urkoob-Ahwar), Bir Ali, Ataq, as well as smaller basaltic
fields in Hadramawt and Al-Mahrah in the farther east
(Qusaier, Er-Raidah, Musayna’h-Hadhathem, Hesay-
Thamnoon, and the southern part of Wadi Al-Masilah),
and the inland volcanic fields (Marib, Amran, Dhamar).
They are low cones (basalts and basic pyroclastics),
mostly characterized by an alkaline affinity.

3. Geochemistry of the Yemen Flood

Volcanism

The following sections present a review of geochemical
and isotope data of the Oligocene-Recent volcanic rocks
from Yemen [2,3,6-19], along with their age equiva- lent
from Saudi Arabia and Ethiopia [20-23].

The chemical characterization of the Yemen flood vol-
canism is illustrated in the total alkali versus silica (TAS)
diagram of Figure 2. The volcanic rocks from northern
YTS (Figure 2(a)) range in silica from 40% to 75%,
witha marked bimodal distribution (SiO2 < 50% or >60%)
and alkaline character in the mafic part of the sequence.
The southern YTS (Figure 2(b)) have only mafic litho-
types with the same SiO2 range of mafic northern YTS,
but tend to be lower in alkalies and their rock types are
mainly transitional olivine basalt.

The East-of-Aden YVS (Figure 2(a)) have only mafic
lithotypes with alkaline connotation comparable to the
mafic northern YTS, whereas the West-of-Aden YVS
(Figure 2(b)), show instead a continuous variation of
silica from basalt to rhyolite, and have transitional char-
acter comparable to the southern YTS.

On the basis of several tectonic discrimination dia-
grams, not shown, the YTS and YVS basalts have within
continental plate (WPB) character.

Southern YTS and West-of-Aden YVS

(a)

(b)

Figure 2. Total alkalis vs. silica diagram showing (a) the
Northern YTS (closed squares) along with the East-of Aden
YVS (open squares). (b) the Southern YTS (closed squares)
along with the West-of-Aden YVS (open squares = Aden;
open diamonds = Little Aden).

Binary diagrams of major elements versus MgO are
reported in Figure 3. Despite the considerable scatter for
most elements, the YTS and YVS have similar ranges of
MgO, CaO and P2O5, even if YVS tend to have, on av-
erage, higher MgO contents (7.0% vs. 6.6, respectively).
Al2O3, Na2O and K2O are higher, and TiO2 lower, in the
YVS than in the YTS. There is similarity in major ele-
ment contents and distributions between the YTS and
their age equivalent series in Ethiopia, and between the
YVS and their age equivalent alkaline basalts in Saudi
Arabia. Indeed, the Ethiopian basalts mainly overlap to
the YTS, with rough positive correlation of CaO and
rough negative correlations of Na2O, K2O, and P2O5 ver-
sus MgO. And the Saudi Arabian basalts tend to trace the
YVS distributions, with rough positive correlation of
CaO, rough negative correlation of Na2O, and bell shaped
patterns of K2O, and Al2O3, versus MgO. The marked
variation in MgO suggests olivine fractionation through-
out the sequences.

Fractionating ol + plag could generate the decline in
CaO observed with decreasing MgO, but this is incon-
sistent with the lack of decrease in Al2O3 observed with

Open Access IJG

1462

M. A. MATTASH ET AL.

Figure 3. Major oxides versus MgO for YTS (closed squares) and YVS (open). The fields of Ethiopian (dark grey) and Saudi
Arabian (light grey) basalts are shown for comparison.

decreasing MgO in most but the evolved samples. Thus,
this decrease in CaO also requires significant clinopy-
roxene fractionation. In summary, differentiation trends
indicate crystallization of ol + cpx throughout the frac-
tionation sequence, with plagioclase also a significant
fractionating phase only in the most evolved part of the
series (MgO < 6 - 7 wt%).These conclusions agree with quantitative fractionation modelling [e.g. 12]. The West-of-Aden YVS, which show a continuous variation of lithotypes from basalt to rhyolite, were con- sidered separatelyin the major elements vs. Differentia- tion Index plots of Figure 4. The samples show well- defined negative correlations of TiO2, MgO, CaO, and FeO, and a tight positive correlation of alkalies, with DI. These variations, taken together, point to olivine + cli- nopyroxene fractionation. Trace element normalized concentrations of two rep- resentative primitive basalts from YTS and YVS were reported in Figure 5. The YTS are enriched with respect to normalizing primitive mantle, with increase of Large Ion Lithophile Elements (LILE) over High Field-Strength Elements (HFSE), and pronounced negative spikes of K and Pb. The pattern of the YVS is similar to that of YTS, but with even higher LILE/HFSE. 4. Discussion The Cenozoic Yemen volcanic rocks are rift-related, and their formation and evolution is the result of syn- and post-rift phases of the formation and development of the Gulf of Aden and the Red Sea. Magmas of the YTS were erupted during the syn-rift phase and correlate with the Figure 4. Major oxides versus DI (Differentiation Index) for the West-of-Aden YVS, which show a continuous variation of lithotypes from basalt to rhyolite. Open squares = Aden; open diamonds = Little Aden. DI is the normative weight ratio: (Qz + Or + Ab + Ne)/Total). first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas magmas of the YVS were ascended during the post-rift phase (10 - 0 Ma). These differences in tectonic settings are reflected in ana- logue differences in geochemical characterization of the two rock series. YTS are bimodal, less alkaline, less en- riched in incompatible elements and LREEs with respect to the YVS. The most primitive magma types in the YTS are transitional to alkali olivine basalts, in the YVS only alkali olivine basalt. The geodynamic setting influences the magma-gen- Open Access IJG M. A. MATTASH ET AL. 1463 100 10 1 e l t n a M e v i t i m i r P / k c o R 0.1 YTS YVS HIMU EM II EM I N-MORB (a) (b) Cs Ba U Ta La Pb Nd Zr Sm Gd Dy Y Tm Lu Rb Th Nb K Ce Pr Sr Hf Eu Tb Ho Er Yb Figure 5. Spider diagrams displaying the normalized con- centrations of trace elements ordered by increasing com- patibility. Normalizing values after [24]. A representative pattern for MORB [24], and examples of HIMU (St. Helena, [25]), EM I (Tristan da Cunha, [25]), and EM II (Society Islands, [26]), are also reported for comparison. eration process in the rift zones. In high-volcanicity rifts, the rates of crustal extension are higher, corresponding to higher degrees of lithospheric attenuation and hence more asthenospheric penetration into the lithosphere [27]. In this context, mafic magmas are derived by partial melting of asthenospheric mantle ascending beneath the rift axis, and possibly mixed with partial melts from the litho- spheric mantle during their rise to the surface. The greater is the crustal extension rates and mantle upwelling, the higher are the partial melting degrees of the astheno- sphere. Regarding the Yemen volcanism, major element geochemistry denoted the effects of fractional crystalli- zation processes. In order to clarify the relative role of partial melting and fractional crystallization, trace ele- ment discrimination diagrams, availing the different be- haviour of moderately and strongly incompatible ele- ments, were used (Figure 6). The ratios of highly to mildly incompatible elements (Th/Yb and Th/Hf in Fig- ures 6(a) and (b)) remain approximately constant during closed system fractional crystallization, whereas they de- crease for increasing melting degrees. The distribution of the Yemen volcanic rocks suggests that YTS can be the result of higher degrees of partial melting of the mantle source with respect to YVS. This is confirmed by calcu- lations made with equilibrium partial melting model [28], starting from an astenospheric mantle composition [29- 32], which indicate 25% - 30% of partial melting for YTS and 10% - 3% for YVS (Figure 6). However, de- parture of the YTS trend from the partial melting trend (Figures 6(c) and (d)) corroborates a consistent role of fractional crystallization in the more differentiated part of YTS. As regards the nature of the mantle source, previous studies identified several distinct mantle domains con- (c) (d) Figure 6. (a) Th/Yb versus Th; (b) Th/Hf versus Th; (c) Yb versus Th; (d) Hf versusTh reporting the fields of YTS and YVS mafic rocks, along with the result of calculations made with equilibrium partial melting model, starting from an astenospheric mantle composition. Numbers marked by asterisks along the solid lines are the degrees of partial melting. tributing to magma genesis in the AARS. To first order, these components include a mantle plume, broadly thought to consist of 1) an HIMU (High m) [e.g. 33] or FOZO (Focus Zone) [e.g. 15] component; 2) a depleted mantle reservoir, interpreted as the source region for N-MORB, and 3) one or two enriched (EMI = Enriched Mantle I - EMII = Enriched Mantle II) mantle components [15,33 among others]. In the spider diagrams of Figure 5, pro- gressively higher contents of alkalies, incompatible ele- ments and LREEsare evident passing from YTS to YVS. This could agree with alarger contribution of enriched mantle components in the source of the YVS with respect to the YTS. Published Sr, Nd, Pb, and O isotope studies pointed out that part of the YTS and YVS underwent assimilation of heterogeneous Pan-African crust. This is consistent with the high heat flow that characterizes active rift zones, where elevated crustal temperatures give rise to the gen- eration of acidic magmas by crustal melting, or mixing of crustal and mantle partial melts. On this basis, higher degrees of crustal contamination could be hypothesized as the agent of the enrichment in incompatible elements and LREEs of YVS with respect to YTS. To ascertain this hypothesis, the (La/Sm)N versus Ba/Nb patterns of the YTS and YVS, along with the Red Sea MORB, and the main mantle and crustal components, were reported in the plot of Figure 7. To minimize the effects of frac- tional crystallization, only samples with MgO > 7% were
considered. It can be seen that crustal rocks have much
higher Ba/Nb than all mantle components, whilst have
(La/Sm)N higher than those of N-MORB, but similar to

Open Access IJG

M. A. MATTASH ET AL.

1464

6.0

5.0

4.0

N

3.0

)

m
S
a
L
(

/

2.0

1.0

YVS
YVS

YTS

U
M
H

I

t
n
e
m
e
h
c
i
r
n
e

e
l
t
n
a
M

B
R
O
M
E

–

B
R
O
M

a
e
S

d
e
R

t
s
u
r
C

r
e
p
p
U

l

a
t
n
e
n
i
t
n
o
C

k
u
B

l

t
s
u
r

C

Lower
Crust

Crustal contamination

N-MORB

0.0

0

10

20

30

40

Ba

/Nb

50

Figure 7. (La/Sm)N versus Ba/Nb plot reporting: YTS and
YVS, Red Sea MORB [2 and references therein], N-MORB
[24], E-MORB and HIMU [25,34], Upper Crust, Lower
Crust, Bulk Continental Crust [35].

those of mantle sources like E-MORB or HIMU. Thus
crustal contamination paths should afford a simultaneous
increase of both Ba/Nb and (La/Sm)N (Figure 7). The
ranges of Ba/Nb of basalts from both YTS and YVS
show instead restricted variations, comprised in the range
of mantle values, and do not show the increases expected
for crustal contamination. As regards to the (La/Sm)N, it
is interesting to note that YTS are similar to the Red Sea
MORB, and are displaced towards enriched components
with respect to N-MORB. The YVS are still more en-
riched than YTS, and their (La/Sm)N encompass those of
E-MORB, but without a concomitant increase of Ba/Nb,
denoting a process of source enrichment rather than magma
contamination.

Schilling [33] suggested, on the basis of combined Nd-
Sr-Pb isotopes, that the Afar mantle plume material may
consist mainly of HIMU component and explained the
isotope variations of the Cenozoic basalts from the Gulf
of Aden by three components mixing including Afar plume
material (HIMU), depleted mantle (DM) and an hybrid
enriched mantle (EM I-EMII). However, the typical
HIMU signatures are not found in the Cenozoic Yemen
volcanics [15]. Indeed, in the 143Nd/144Nd versus 87Sr/
86Sr plot (Figure 8), the Yemen flood volcanic rocks ap-
pear to plot within the mixing area of three components:
Depleted mantle, Enriched Lithospheric Mantle (ELM,
as defined by [15]), and C, an intermediate component
between DM and HIMU. Although assimilation of het-
erogeneous crust has the major control on large-scale
isotope variability, the least contaminated samples of the
Yemen flood volcanics have radiogenic isotope ratios

Figure 8. 143Nd/144Nd versus 87Sr/86Sr plot reporting YTS
(closed symbols) and YVS (open symbols). Shaded areas
outline data of the Red Sea [36-39], Gulf of Aden, and Afar
plume [33,40]. C: Common component defined by [41].
ELM: Enriched Lithospheric Mantle defined by [33].

that approach those inferred for the Afar plume (field
circled with dashed line in Figure 8).

5. Summary and Conclusions

In summary, the following conclusions can be drawn:

1) The Cenozoic Yemen flood volcanic province can
be divided in: Oligo-Miocenic bimodal transitional to
alkaline Yemen Trap Series, YTS, and Miocene-Recent
alkaline Yemen Volcanic Series, YVS. Magmas of the
YTS were erupted during the synrift phase and correlate
with the first stage of sea-floor spreading of the Red Sea
and the Gulf of Aden (30 – 15 Ma), whereas magmas of
the YVS were ascended during the post rift phase, con-
sistent with the sea-floor spreading model (10 – 0 Ma).

2) The YTS are contemporaneous with, and geochemi-
cally similar to, the Ethiopian Trap Series, whereas the
more alkaline YVS are geochemically similar to the Saudi
Arabian volcanics.

3) A continental within plate character is recognized
for both the YTS and YVS basalts. The two rock series
have similar SiO2 ranges, but YVS tend to have, on av-
erage, higher alkalis and MgO contents than YTS. Frac-
tional crystallization processes dominate geochemical
variations of both series.

4) Primitive magmas (MgO > 7.0%) from both series
are enriched in incompatible elements and LREEs with
respect to primitive mantle, but YVS are more enriched
than YTS. To first order, the different geochemical pat-
terns agree with different degrees of partial melting of
the mantle source: 25% – 30% of partial melting for YTS
and 10% – 3% for YVS. Secondly, the higher degrees of
enrichment in incompatible elements of YVS reflect also
a greater contribution of an enriched component (E-
MORB) to the mantle source.

5) The large-scale Sr-Nd-Pb-O isotope variability of
the Cenozoic Yemen flood volcanism is mostly accounted
by crustal contamination. However, the least contami-
nated samples have radiogenic isotope ratios that ap-

Open Access IJG

proach those inferred for the Afar mantle plume.

461. http://dx.doi.org/10.1093/petrology/11.3.433

M. A. MATTASH ET AL.

1465

6. Acknowledgements

We are deeply indebted to Gianluca Bianchini and an
anonymous referee for their useful and invaluable sug-
gestions. Particular thanks are due to Gyorgy Buda, Uni-
versity of Budapest, Hungary for providing all the possi-
bilities to make this work successful. We also acknowl-
edge Professors of the University of Idaho, USA, for
their continuous help and cooperation.

REFERENCES

[1] B. Bosworth, P. Huchon and K. McClay, “The Red Sea
and Gulf of Aden basins,” Journal of African Earth Sci-
ence, Vol. 43, No. 1-3, 2005, pp. 334-378.
http://dx.doi.org/10.1016/j.jafrearsci.2005.07.020

[2] M. A. Mattash, L. Pinarelli, O. Vaselli, A. Minissale, M.
C. Jaimes-Viera, M. Al-Kadasi, M. N. Shawki and F.
Tassi, “Geochemical Evolution of Southern Red Sea and
Yemen Flood Volcanism: Evidence for Mantle Hetero-
geneity,” Arabian Journal of Geosciences, in press.

[3] M. A. Mattash, “Study of the Cenozoic Volcanic Rocks
and Their Associated Intrusive Rock in Yemen in Rela-
tion to Rift Development,” PhD Dissertation, Hungarian
Academy of Sciences and Eötvös L. Univ., Budapest,
1994.

[4] M. A. Mattash and K. Balogh, “K-Ar Radiometric Age
Data on Cenozoic Volcanics and Their Associated Terti-
ary Intrusions from Yemen,” Acta Mineralogica-Petro-
graphica, Vol. 35, 1994, pp. 83-92.

[5] Z. R. Beydoun, M. L. As-Saruri, H. El-Nakhal, I. N. Al-
Ganad, R. S. Baraba, A. O. Nani and M. H. Al-Aawah,
“International Lexicon of Stratigraphy,” Republic of Ye-
men IUGS Publication, London, Vol. III, 1998, p. 245.

[6] M. L. Kabesh, A. K. A. Salem and M. H. A. Higazy, “Con-
tributions to the Petrochemistry and Geochemistry of
Some Quaternary Basaltic Rocks, Northern and Southern
Yemen,” Acta Mineralogica-Petrographica, Vol. 26, 1984,
pp. 171-186.

[7] USGS (United States Geological Survey), “Geology of
Dhamar Area,” Internal Report for the Geological Survey
of Yemen, 1985, p. 32.

[8] S. Chiesa, L. Civetta, M. De Fino, L. La Volpe and G.
Orsi, “The Yemen Trap Series: Genesis and Evolution of
a Continental Flood Basalt Province,” Journal Volca-
nological and Geothermal Research, Vol. 36, No. 4, 1989,
pp. 337-350.
http://dx.doi.org/10.1016/0377-0273(89)90078-4

[9] M. A. Mattash and Gy. Buda, “The Evolution of Yemen
Basalts in Relation to Rift Development and the Chemis-
try of Their Mineral Constituents,” Bulletin of the Geo-
logical Society of Greece, Vol. 28, No. 2, 1992, pp. 499-
514.

[10] K. G. Cox, I. G. Gass and D. I. J. Mallick, “The Peralka-
line Volcanic Suite of Aden and Little Aden, South Ara-
bia,” Journal of Petrology, Vol. 11, No. 3, 1970, pp. 433-

[11] J. A. Baker, M. F. Thirlwall and M. A. Menzies, “Sr-Nd-
Pb Isotope and Trace Element Evidence for the Crustal
Contamination of Plume-Derived Flood Basalts: Oligo-
cene Flood Volcanism in the Western Yemen,” Geochi-
mica et Cosmochimica Acta, Vol. 60, No. 14, 1996, pp.
2559-2581.
http://dx.doi.org/10.1016/0016-7037(96)00105-6

[12] J. A. Baker, M. A. Menzies, M. F. Thirlwall and C. G.
Macpherson, “Petrogenesis of Quaternary Intraplate Vol-
canism, Sana’s, Yemen: Implications for Plume-Litho-
sphere Interaction and Polybaric Melt Hybridization,”
Journal of Petrology, Vol. 38, No. 10, 1997, pp. 1359-
1390. http://dx.doi.org/10.1093/petroj/38.10.1359

[13] M. T. S. Heikal, E. M. M. Lebda, Y. Orihashi and A.
Habtoor, “Petrogenetic Evolution of Basaltic Lavas from
Balhaf-Bir Ali Plio-Quaternary Volcanic Field, Arabia Sea,
Republic of Yemen,” Arabian Journal of Geosciences.

[14] J. A. Baker, C. G. Macpherson, M. F. Menzies, M. F.
Thirlwall, M. Al-Kadasi and D. P. Mattey, “Resolving
Crustal and Mantle Contributions to Continental Flood
Volcanism, Yemen; Constraints from Mineral Oxygen
Isotope Data,” Journal of Petrology, Vol. 41, No. 12,
2000, pp. 1805-1820.
http://dx.doi.org/10.1093/petrology/41.12.1805

[15] Y. Orihashi, K. Nagao, A. Al-Jailani and B. B. Hanan,
“Primordial Helium Isotope Signature from Plio-Quarter-
nary Alkaline Basalts in Yemen,” The Island Arc, Vol. 10,
2001, pp.145-157.
http://dx.doi.org/10.1046/j.1440-1738.2001.00315.x

[16] R. G. Coleman and A. V. McGuire, “Magma Systems Re-
lated to the Red Sea opening,” Tectonophysics, Vol. 150,
No. 1-2, 1988, pp. 77-100.
http://dx.doi.org/10.1016/0040-1951(88)90296-X

[17] M. Menzies, K. Gallagher, A. Yelland and A. J. Hurford,
“Volcanic and Non Volcanic Rifted Margins of the Red
Sea and Gulf of Aden: Crustal Cooling and Margin Evo-
lution in Yemen,” Geochimica et Cosmochimica Acta,
Vol. 61, No. 12, 1997, pp. 2511-2527.
http://dx.doi.org/10.1016/S0016-7037(97)00108-7

[18] Y. Orihashi “Evolution of the Afar Mantle Plume,” Ph.D.
Dissertation, Hokkaido University, Hokkaido, 1997.

[19] J. A. Baker, M. A. Menzies, M. F. Thirlwall and C. G.
Macpherson, “Petrogenesis of Quaternary Intraplate Vol-
canism, Sana’s, Yemen: Implications for Plume-Litho-
sphere Interaction and Polybaric Melt Hybridization,”
Journal of Petrology, Vol. 38, 1997, pp. 1359-1390.
http://dx.doi.org/10.1093/petroj/38.10.1359

[20] V. E. Camp and M. J. Roobol, “The Arabian Continental
Alkali Basalt Province: Part I. Evolution of Harrat Rahat,
Kingdom of Saudi Arabia,” Bulletin of the Geological
Society of Am