T
he thin, solid crust on which we live represents
only about 1% of the distance to the Earth’s
centre: 5–10 km thick under the oceans and
25 –70 km thick under the continents. Yet its
evolution and movement, and its interaction
with the underlying mantle, give rise to almost all the geolog-
ical events of signiicance to us, including earthquakes, volcanic
eruptions and the formation of mineral deposits, oil and gas
reserves, underground lakes, mountains and oceans.
The crust and upper mantle is broken into a jigsaw of moving
tectonic plates. Their movement crushes them together, pulls
them apart and makes them slide past each other. Some are
pushed down under neighbouring plates in a process known as
subduction.
While we have learned a lot about the movement of conti-
nents and what happens when they crash into one another, the
formation of ocean crust – a major force that drives plate
tectonics and regenerates the plates – remains one of the least
understood processes related to plate tectonics.
However, recent research into the geology and geophysics of
the Red Sea has overturned the conventional view that ocean
crust formation is a continuous process whereby a rift opens in
the ocean loor like a zipper and magma bubbles up from the
underlying mantle to push it apart. Instead, sealoor formation
actually happens in bursts separated in geography and time.
Ten years ago I was keen to become a leading authority on
the evolution of the Australian plate. My research had focused
on understanding the architecture and geological evolution of
Australia’s ancient crust, which is more than a billion years old.
So how is it that today one of my major research interests is
to understand the evolution of the Red Sea, the one place on
the planet where continental crust is transitioning from a conti-
nental rift to a juvenile ocean basin?
It all began with a knock on my door. Khalid Almalki, astudent with PhD sponsorship from Saudi Arabia, was looking
for a supervisor and wanted to continue studying the Farasan
Islands in the southern Red Sea with the intention of mapping
out the salt domes that often form the walls of oil reservoirs. It
wasn’t my area of expertise, and I remember thinking that I
would probably not see Khalid again.
But Khalid liked my group’s approach of combining struc-
tural geology and geophysical interpretation and modelling to
explore the geometry of the Earth’s crustal elements and show
how rocks deform under stresses. He joined our research group
and began researching salt dome tectonics in the Red Sea.
The Red Sea has a special place in plate tectonics because it
represents the only example where a continental rift is transi-
tioning to a juvenile ocean basin (Fig. 1). The southern part of
the Sea is undergoing active sealoor spreading, driving Africa
and Arabia apart. But while there is a continental rift in the
northern part of the Red Sea, Africa and Arabia remain irmly
attached –a single plate yet to be split apart.
This offers a unique opportunity to understand how conti-
nental plates split apart to make separate plates, and provides
hints about the geological processes involved. It is an active
tectonic setting where low-level earthquakes and tremors contin-
ually occur in response to separation.
The continental margin of Saudi Arabia and the Afar Depres-
sion in East Africa record 30 million years of volcanic and
igneous activity, and there are large topographic escarpments
and small mountain ranges that have formed as the continents
continue to split apart.
Young geoscientists are introduced to the Red Sea in text-
books because it represents one arm of a classic triple junction
where the African, Arabian and Indian plates all meet. This
junction is centred in Ethiopia above the Afar Plume, a buoyant
upwelling from the deep mantle that interacts with the base
of the Earth’s rocky crust and upper mantle.
Until now, the opening of the Red Sea and the separation
of the Arabian and African plates has been interpreted as a rela-
tively simple process driven by the upward pressure of this
plume. This is what I also believed when I irst met Khalid. As
it turns out, I couldn’t have been more wrong.
Our research started in the Farasan Islands, an archipelago
of Pleistocene to Pliocene (< 5 million years) islands and lime-
stone reefs lifted above sea level by the pressure of buoyant salt
domes beneath. The story became really interesting when Khalid
started presenting us with magnetic and gravity data collected
over the Farasan Islands and the adjacent Miocene sediments
(5–23 million years old) between the islands and the Saudi
Arabian coastal plains.
High resolution airborne magnetic data showed the pres-
ence of magnetic stripes in the ocean crust beneath the sedi-
ments. These stripes form as magnetic minerals align with the26 | JUNE 2016
Birth of the
RED SEA
PETER BETTSNew evidence about the creation of the
Red Sea has fundamentally changed how
geologists understand the birth of oceans.