Bossworth, that the Red Sea was an evolving

Bossworth, 2015

(Intro)

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            Red
sea is  recognized as one component of a
continent scale rift system that reaches from the Dead Sea to Mozambique. The
rift system is popularly known as Afro- Arabian rift system. Red Sea and Gulf
of Sden are suggested to be oceanic rifts at divergent plate boundaries with a
triple junction with East African Rift at Afar.

(Nature of red sea crust- diff arguments)

            In
1972 wells of Glomar Challenger Leg 23B in and near axial trough con?rmed that
basalts and ?uids with mantle-derived lead isotopes have been emplaced into the
sediment column along the Red Sea axis. This supported the hypothesis that the
Red Sea was an evolving oceanic rift . Based on this Coleman (1972) compiled a geological map of
the entire Red Sea Basin and argued some interesting points about the nature of
the crust of the Red Sea. According to him oceanic crust was restricted to the
axial trough in the southern Red Sea and the rest of the margin was continental
crust intruded by tholeiitic gabbros and basalt dike swarms. From geophysical
data sets Girdler 1958;
Drake and Girdler 1964;Lowell and Genik 1972 developed similar
interpretations  that support Coleman
(1972). But this was contradicting the arguments done by McKenzieet al. (1970)
model that envisioned a pre-rift coast-to-coast restoration with the entire Red
Sea underlain by oceanic crust . Girdler 1966,1970; Girdler and Darracott 1972 also proposed  numerous intermediate models

 

(nature of crust in S,C and N red sae)

            The
striped magnetic anomaly patterns recognized along the southern red sea axis
give the most convincing evidence of oceanic rifting (Phillips 1970; Girdler and Styles 1974;Röser1975;
Searle and Ross 1975; Hall et al. 1977; Cochran 1983). There are also
many other geophysical and geochemical evidences  that support true oceanic spreading scenario
in the Red sea area.

 

            It
is suggested that although the southern red sea is purely an oceanic rift, the
northern end of the rift (Gulf of suez) is purely continental in nature (Steckler 1985; Jarrige et al.
1986;Courtillot et al. 1987; Girdler and Southren 1987; Joffe andGarfunkel
1987; Moretti and Chénet 1987) . However the central and  northern red sea that make the intervening
area does not meet with similar agreement. in terms of stratigraphy and
underlying basement lithologies  they
have similarities in In outcrop and in offshore exploratorywells with the Gulf
of Suez (Colemen 1974;
Tew?k and Ayyad 1984; Barakat andMiller 1984; Beydoun 1989; Beydoun and
Sikander 1992;Bosworth 1993). But along axial trough there are some
important similarities with the southern red sea. Thus it is suggested that the
northern and central red sea regions are transitional in nature between the
aborted continental rifting in the northern end and purely oceanic spreading in
the southern red sea

 

(Evolution of red sea in context of
evolution of African plate)

            The
evolution of the Red Sea should be considered in the context of the evolution
of entire  African plate which is a
remnant of Gondwana, that began to break up during the Late Carboniferous.  The break up lasted several  hundred million years through a series of
rifting processes and basin formation . The Red Sea–Gulf of Aden rift system,
with the East African rifts, is part of this ongoing process (Bumby andGuiraud
2005; Bosworth et al. 2005).

The driving mechanism for the breakup of a
continental mass has been attributed mainly to two process-one being the plume
or hotspot activity impinging on the base of the lithosphere (Anderson 1982) which
plays a main role in active rifting, the second one being the slap pull forces
as a result of the nearby subduction zone that becomes the major reason of
passive rifting processes. (Daviesand
Richards 1992; Lithgow-Bertelloni and Richards 1998;Collins 2003; Reilinger
andMcClusky 2011) . In most cases both plume activity and slap pull
forces contribute to the rifting process. As reviewed by Bossworth et al 2005 both
plumes and nearby subduction zone processes played key roles in the evolution
oof red sea. Plumes can weaken continental lithosphere and strongly influence
the location of lithospheric failure, while plate boundary forces can drive
extension.

            In
The above stated perspective the evolution of red sea was happened as a part of
tectonic evolution of African plate where the rifting processes and  passive continental margin formation has been
happened for last 300 Myr as a result of various tectonic processes. But
according to Burke 1996
there is some modification in the ongoing rifting processes that leads to the
evolution of African plate during the most recent 30 Myr.  Geologists have recognized that Africa
possesses a distinctive basin and swell geomorphology (Krenkel 1922, 1957; Argand 1924; Holmes 1965).
According to Krenkel, Burke and Wilson (1972) This topography was generated by
mantle processes when Africa stays stationary with repect to underlying mantle
circulation pattern  during the recent 30
MYr. The stationary Africa (Burke
1996) became part in the intensified collision with Eurasia  and/or irruption of the Afar plume. The
impingement of Afar plume is possibly in conjunction with the Principe and
other plumes acted to pin the base of the lithosphere to the upper mantle (Burke 1996) .Burke
suggested that arresting of Africa plate motion lead to extensive intraplate
volcanism and renewed rifting i.e. Afro- Arabian rift system including Red
sea-Gulf of Aden- East African rift. In the tectonic history of Africa there is
a 35 Ma gap of intraplate extension between the end of Cretaceous and arresting
of Africa. This gap was the period of major peneplanation including the
development of extensive laterites and paleosols across the Arabian–Nubian shield
(Coleman 1993) .
Red sea was later started evolving on the surface thus formed.

 

(Geomorphology)

Axial trough

            The
most prominent feature is the deep axial trough of around 1000m or greater
depth along the basin axis and the elevations along its rifted shoulders. The
trough is seen continuous from just south of Ras Mohammed in southernmost Sinai
to the vicinity of the Zubayr Islands offshore Yemen. Isolated deeps of 2000m
or greater depths are notices along the main trough and are containing hot
brine pools and basaltic cones((Pautot 1983; Pautot et al. 1984; Bicknell et al. 1986) . These
deeps are considered as related to the evolution of oceanic spreading centres (Cochran 1983; Bonatti 1985; Martinez
and Cochran 1988; Cochran and Martinez 1988, reviewed in Cochran 2005; Cochran
and Karner 2007 ) According to Cochran (2015) 
in the Northern red sea axial trough strikes 5°–10° more to the
northwest than the overall trend of the marine basin. This as a reflection of
an adjustment to extension parallel to the Gulf of Aqaba tran sform boundary
can be a consequence of the
two Eulerian pole Red Sea opening models as proposed by many authers (Joffe and Garfunkel 1987)

marine shelf and coastal plains

            The
marine shelf and coastal plains of the area are variable in width. The
tectonic, sedimentary and biotic activity together played important roles in
the formation of them.  The present
climat of the red sea area is arid, with some exceptions, and no permanent
rivers are flowing to the basin except some intermittent rivers such as the
Barka (Baraka) . Such rivers provide a very little sedimentary input to the
basin. But it is found that they were permanently flowing rivers in past and
contributed significantly to the sedimentaion.  The southern coastlines of Red Sea are
curvilinear and paired.  North of about
24O latitude the shorelines are straight on both sides.

            High
elevation areas are common immediately adjacent to the coastline along most of
the red sea. There is an unbroken erosional escarpment from Taif (Saudi Arabia)
to Taizz (Yemen) along the Arabian margin that bounds the high terrain with
highest peaks exceeding 3000m. In Ethiopia the escarpment marks the eastern
boundary of Ethiopian Plateau with peaks exceeding 2000m. The geomorphology of
Afar area is marked by the famous Afar depression and the Danakil horst near
the coast. Along the Sudan margin elevation of the Red sea hills becomes less
to typically greater than 1000m. Upto Egypt and 
along western margin of gulf of Suez this relief continues with isolated
basement peaks of elevation greater than 2000m

           

(Take

 fig 1

fig 2)

 

Initial burst of oceanic crust accretion in the Red
Sea due to edgedriven mantle convection

Marco Ligi et al., 2016

            Rifting
of continental blocks and subsequent formation of oceans and their life cycles
are explained as Wilson cycle. The overall process takes place as a result of
the interaction of tectonic and magmatic processes. The mechanism of rifting
and initial stages of ocean spreading is an important area of interest. Red sea
is the area were continental rift and opening of new ocean basin are occurring
today by the separation of African and Arabian plates. The rift system that
fragments the Arabian Nubian shield was formed since late Oligocene- Miocene
time. Although there has been little volcanism within the central-northern Red
sea rift since the Early Miocene, The impingement of the Afar mantle plume from
below, starting ca. 40 Ma, may haveinfl uenced the evolution of the system (Ebinger and Sleep, 1998)

 

Geomorphology

There is a nearly continuous axial valley carpeted
by basaltic oceanic crust along the southern Red Sea. Vine-Matthews magnetic anomalies
as old as 5 Ma extends for ~400 km are flanking the axial trough in the
southern Red Sea (Roeser,
1975). In the Central Red Sea the initial emplacement of oceanic crust
occurs in discrete axial cells and thus the axial trough becomes discontinuous
in the Central Red sea (Bonatti,
1985).    In the Northern Red sea the axial trough is
almost absent. Only some scattered basaltic intrusions have been observed there
(Cochran, 2005).

 

Le Pichon and Francheteau(1978)

Since the time of formulation of continental drift
by Alfred Wegner the area encompassing Red Sea, Gulf of Aden and east African
rift has been a type example of early stages of the ocean formation.

The amount of extension in the area is no more than
200-300 km. which is twice the width of transition from a fully continental to
a fully oceanic crust in a well-developed continental margin (Worzel 1965,1968 ) .
Consequently it is difficult to evaluate what part of the total extemsion is
due to crustal thinning and what part is due to the production of oceanic
crust.  (This is a gap)

Two groups have been developed among the people who
studies tectonic evolution of the area. The first one mainly deals with
kinematic data as represented by Mckenzie (1970) . For solving the total plate motion of the area
they assume that Red Sea and Gulf of Aden area are entirely floored by newly
formed oceanic crust from coastline to coastline, that the plates bounding the
area are perfectly rigid, and that there is a clear boundary from undeformed
continental shield crust to a seafloor spreading type crust. These assumptions
help easily working out the kinematics of the total plate motions since the
beginning of break-up. Mckenzie et al. showed that four main plates are
necessary in this process to explain the kinematics of the area-Nubian plate,
Arabian plate, Somalian plate and Sinai plate. Among this the relative motion
of Arabia and Nubia are obtained by fitting the coastlines of Red Sea. Relative
motions of the other pairs were obtained from the data of Gulf of Aden and East
African Rift. Simplicity of the solution by McKenzie et al. leads to a rigorous
treatment and easy testing of the problem. Several variants of the solution by
McKenzie et. al. have been proposed by various authors. Differences lie in the
lines that are used to fit to calculate the relative plate motions.

 The McKenzie
et al solution was independently supported by the magnetic anomalies on the
southern marginal portions of the Red Sea trough. Girdler and Styles(1974,1976) have shown magnetic anomaly patterns that can be
dated as 34-42 M.y over the shelf westwards very close to the shoreline between
14.5O N and 16 O N. Thet could correlate similar anomalies near 17 O N on both
sides of the axial trough. Girdler
and Styles (1974, 1976) and Roeser (1975) argue that the total
magnetisation necessary to produce this type of magnetic lineations should be
very high and it timplies the existence of the presence of an ocean type
crust.  If more geological and geophysical
data comes supporting the solution of McKenzie et al. a solution close to it
will have to be accepted , the iontepretation of the plate kinematics in the
area will be more simplified and also the morphological fit of the coastlines
of the Red sea will be convincingly explained.

(Include morphological fitting of
the red sea from library book and more detaile about the kinematics of the red
sea. This can be shown as a problem we are addressing)

Although the McKenzie et al.
solution is a simplest way of approach to the problem there are some
difficulties created by this at both ends of the Red Sea. For example, the
solution implies that, to the south, the whole of the Afar triangle, to the
foot of the Ethiopian escarpment is newly created lithosphere. But the area
includes about 110 km wide Danakil Jurassic basement.

 

Age

another difficulty to be faced by
mcKenzie et al. solution is regarding the age of the main part of the Red Sea. Between
60 and 65% of the Red Sea floor was emplaced from Late Eocene to

Earliest Oligocene (Girdler and Styles 1974,1976).
But, although there is evidence that tectonic activity in the Red Sea and Gulf
of Aden was begun in Jurassic or Cretaceous (Karpoff 1957, whiteman 1965, Azzaroli 1968) , the
separation started in Early Middle (or Late) Miocene after Oligo- Miocene phase
of uplift and faulting (Beydoun,
1970). The Oligocene and earliest Miocene volcanism in the Red sea area
is very important as a precursor of the major episode of Red sea rifting. The
presence of Middle Miocene sediments just above the acoustic basement close to
2000 meter isobath and just beyond the correlatable magnetic anomalies, as
resulted from Joides leg 24 (Fisher et al.,1974) agrees with the results.

            Independently,
from the dating of volcanic formations within and on the edges of the Afar
triangle, Jones (1976) concluded that it is in the earliest Miocene (25-23 m.y.) the
volcanism that accompanies the the initial fragmentation in this area occurred.
Barberi et al. (1975) and
Barberi and Varet (1976) supports this observation. They assume that
from 25 to 4 my ago is the first stage 
that was essentially a continental rifting stage. The second stage is
during the last 3.5 m.y. when the oceanic crust has been emplaced.  All the above works disagrees with a Late
Eocene to earliest Oligocene age of formation of oceanic crust.

            Similarly,
the depth of oceanic basement as predicted from McKenzie et al. solution does
not agree with the actual depth .

            These
disagreements and difficulties  led
another group of people to assume that the total amount of creation of oceanic
crust in the Red Sea is very small and limited to the presently volcanically
active axial trough (Lowell
and Genik,1972: Ross and Schlee,1973). Also the assume that most of the
Afar triangle as well as the main Red sea trough are floored by continental
crust which has been thinned by normal faulting and intruded by volcanics. The
observation of Barberi et
al. (1975) and Barberi and Varet (1976) that oceanic crust in Red Sea
and Afar triangle has been only produced in the last 3.5  m.y that is over a width not exceeding 70
k.m.. But this solution does not agree with the width ocean floor creation in
Gulf of Aden ,which is more than 70 k m as implied by marine magnetic anomaly
as well as seismic data.

            On
a concluding note, both of the solutions are supported by some evidences and
are in disagreement with some other observations. If the first type of solution
is correct , it implies that  the 100-150
km wide transitional cru

st zone that corresponds to a
mature continental margin will have to be developed mainly by subsidence and
possibly also by hot creep of the lower part of the continental crust (Le Pichon et al., 1973),
in a later stage of the opening of ocean. If the second solution is correct,
the transitional crust zone is produced in the early rifting stage by tectonic
and volcanic activities that modified the continental crust. After the maximum
amount of extension has been produced within the continental crust, new oceanic
crust appears. However, the two groups of interpretations agrees that oceanic
crust has been created in the Red sea, the Afar triangle and the Gulf of Aden
for the last 3.5 m.y.

           

Wiki

Red Sea has been evolving as a sea water
inlet of the indian ocean. It is connected to the Indian ocean through Bab el
Mandeb strait and Gulf of Aden. To the north of the Red Sea lie the Sinai
Peninsula, Gulf of Aqaba and Gulf of Suez which is connected to Mediterranean
Sea through the artificial Suez Canal. The surface area of the Sea is around
438,000 km^2, length about 2250 km and maximum depth 3040 m in the Central
Suakin trough. Appr. 40 % of the Red sea is under 100 m depth and about 15% is
above 1000 m depth. The marine shelves are extensively shallow and shelf breaks
are marked by coral reefs.

The Red Sea contains a spreading
center between the African and Arabian plates , extending from the Dead sea
fault system and ending at Afar triple junction . The Red Sea is a type example
of transition from continental rift to oceanic drift. From the magnetic
anomalies the spreading rate on either side of the main rift about 1 cm/year. The
African plate has a rotation rate of 0.9270 degrees/Ma, while the Arabian plate
has a rotation rate of 1.1616 degrees/Ma. (McKenzie et al. (1970))