Red Sea seafloor spreading and tectonic plate dynamics

Red Sea Spreading Seafloor

The spreading of the seafloor under the Red Sea offers researchers a chance to study several important areas of science and apply what is learned to a better understanding of earth, earth's history, and perhaps other planets in the Solar System such as Mars. This paper reviews and examines existing science related to the tectonic plates (African and Arabian plates) beneath the Red Sea, the explanation for their movement apart and the dynamics of the hydrothermal activities that are part of the plate spreading itself. The Red Sea is of particular interest to scientists and this paper provides thorough reviews of the research conducted to date and why that research is of great value to science and to an understanding of how the Earth was formed.

INTRODUCTION:

The sea floor beneath the Red Sea is of great interest to geologists, oceanographers, seismologists and other scientists mainly because of the fact that the tectonic plates - that are the reason the Red Sea was formed in the first place - and are pulling apart ("separating") slowly but surely over geologic time. This dynamic is of great interest to the world of science in part because research into the formation of the oceans is important; what happens in one area of the world where plates are separating has vital implications for other areas of the world with similar geologic dynamics. Also, in an active tectonic region there is always the possibility of large earthquakes that could be generated within the tectonic region (and also the likelihood of a tsunami resulting from a large temblor. And moreover, the Red Sea is important to study because the seas and oceans are "inextricably interconnected" (www.ngsednet.org.oceans);theseas and oceans are sometimes seen as "indestructible" but they are not, and the more research that goes into the present day - and historical - issues associated with seas and oceans, the wiser the decisions mankind will be able to make through the process.

RED SEA GEOLOGIC EVOLUTION: ROBERT C. COLEMAN'S BOOK:

Author Robert C. Coleman (Geologic Evolution of the Red Sea) writes that hot brine pools were discovered on the seafloor of the Red Sea in 1966, which excited scientists. At that time the discovery of hot brine pools served as a "catalyst" in the sense of stimulating more collaborative research studies (Coleman p. 6); the evolving understanding of plate tectonics received a great boost when the Research Vessel (R/V) Glomar Challenger went into the Red Sea in 1972 and drilled into the seafloor at six sites around the "axial rift" (the separating tectonic plates under the Red Sea). The conformation soon followed that indeed, Coleman explains on page 6 of his book, the axial trough was "an active spreading center," which in fact was producing the "hot heavy metal brines." Still that drilling by the crew of the Glomar Challenger did not go deep enough to penetrate the "thick evaporite sequence along the edge of the axial trough" and hence, the nature of what lay beneath remained "enigmatic."

Among the "vexing problems" that has puzzled scientists trying to understand the Red Sea dynamics has been "trying to characterize the crust underlying the marginal trough and coastal plain" (Coleman, 7). In 1979 the U.S. Geological Survey and the Saudi Arabian Directorate General of Minerals conducted a research project - a "deep seismic refraction profile" - across western Saudi Arabia and well into the southeastern Red Sea. That research was discussed in a workshop involving some 46 seismologists from around the world; all 46 of these scientists had been given data from the USGS and Saudi Arabian research ahead of time. There were a variety of interpretations of this data, as might be expected, but the consensus among the scientists was that there was great concern by the fact that the "continental crust" (on land in Saudi Arabia) was 48 km deep while the oceanic crust dropped to just 17 km (Coleman, 7).

From that point on, the Red Sea has been considered (designated) a "key environment" because of its "great scientific and ecological importance," Coleman explains.

Some facts about the Red Sea: the Red Sea is an "elongate depression" that is more than 200 kilometers long; in the north, the shorelines are just 180 kilometers apart, while in the south of the Red Sea the shorelines - while much more irregular - are as far apart as 350 kilometers. There are volcanic centers within the axial zone, and the axial zone is surrounded by "fault terraces" that are nearly vertical and the walls rise up to 800 meters high from the bottom of the axial zone. At the time of the publishing of this book (1993) the rift was about four to five kilometers wide at about 2,000 meters deep into the Red Sea, Coleman explains (p. 18).

Large open fissures appear in clusters along the extrusive zone," and those clusters break up the "silt-lava sequences" and at times "transect" the ancient volcanoes. The fact that the sediments are not very deep on the volcanic features of the axial zone is clear evidence, Coleman writes, of its "youthfulness" in geologic terms. The "most spectacular manifestation of volcanism" is found along the axial ranges that have been discussed earlier in this paper. But Coleman asserts that eruptions in the Late Oligocene period - continuing "sporadically" up to the Late Miocene epoch - formed an "apron" that was 40 kilometers wide and extended more than 100 kilometers along the axis.

Meantime the southern portion of the Red Sea reveals "many sub-parallel faults" which are very similar, Coleman explains (p. 89), to mid-ocean patterns of tectonic faulting and spreading. The Red Sea spreading centers were fairly straight zones roughly 30 to 50 kilometers long and 3 to 20 kilometers across. In the northern portion of the Red Sea seafloor though is a place where dramatically irregular faulting makes the spreading center very different from the trends in the south. The faults along the spreading in the north are marked by zigzagging; the lack of "obvious transform faults," the author goes on, is "puzzling"; but it also reveals to scientists that the Red Sea has a "diachronous history of spreading" (Coleman, 89). Diachronous means there are various and widely differing ages of rock in the same zone.

Although this paper has alluded to the Red Sea as a place where two tectonic plates are slowly being pushed apart by the upward surge of hot magma, Coleman, and other scholars, refer to the Red Sea as having a "triple junction" - the African (Nubian) and Arabian tectonic plates are interacting with the Gulf of Aden oceanic spreading centers. The Gulf of Aden oceanic spreading center enters the gulf of Tadjura, and meets with the north-moving East African rift system, according to Coleman.

On page 123 author Coleman points to the belief that in geologic reality, four, not three, rigid plates are interacting dynamically in the Red Sea region; as discussed, the Arabian plate and the African (Nubian) plate are part of the picture; and Coleman adds to that stew the Sinai and Somalia plates. There is certainly rifting and spreading under the Red Sea, but Coleman writes in his Epilogue (p. 151-152) that there was - at the time his book was published - "No geologic evidence" that supports the existence of a "large dome centered" under the Red Sea Basin during the initial stages of rifting. In other words, there is no known "initial hot spot" where a volcano blasted molten rock and ash up through the rift. What he can say with certainty though is that the Red Sea "will continue to grow" through a combination of volcanic activity and faulting (the volcanic activity he refers to is the upward pushing of magma from deep in the earth's core, not a blast of volcanic ash exploding up from the seafloor).

However, it is "reasonable" Coleman posits, to assume there will be "future seismic and volcanic events" under the Red Sea, which makes the Red Sea "a unique ecosystem" and offers an "unparalleled" opportunity for continuing research of oceanic spreading and tectonic plate movement. The author warns against attempts by nations or corporations to exploit the Red Sea for "heavy metal deposits" or "petroleum" within the axial trough - prior to additional research.

SPREADING SEAFLOOR DYNAMICS BENEATH the OCEANS & SEAS

Prior to delving into the specifics relative to the Red Sea seafloor, a review of the dynamics of seafloor spreading is worthy and timely. There is an impressive volume of information with reference to the spreading of a seafloors and the movement of tectonic plates that respond by spreading when pushed by magma. The outermost layer of earth, earth's crust that is also alluded to as the upper mantle, is technically called the lithosphere.

Rosanna L. Hamilton, a professional scientist at Los Alamos National Laboratory ("The Lithosphere & Plate Tectonics") (www.solarviews.com) explainsfirst of all that there are eight large tectonic plates (African, Antarctic, Eurasian, Indian-Australian, Nazca, North American, Pacific and South American plates), and "two dozen smaller ones that are drifting above the mantle at the rate of two to four inches a year."

Hamilton explains that while Continental Lithosphere is as much as 93 miles thick, the "Oceanic Lithosphere" is much thinner - up to perhaps six miles. Indeed, the oceanic crust makes up only 0.099% of earth's mass, according to Hamilton. Oceanic lithosphere is a product of the volcanic magma that pushes up to force tectonic plates aside. As new oceanic lithosphere is actually formed the heat that comes up with the magma "escapes the interior as this new lithosphere emerges from below" in the Red Sea and elsewhere where there are tectonic plates spreading.

As the lithosphere cools, it contracts and then "moves away from the ridge, traveling across the seafloor to subduction zones." This process is technically called "seafloor spreading." After the lithosphere has been on the Red Sea floor for a while, it thickens up, Hamilton writes, and as it becomes even denser than the mantle just below it, it sinks into the earth (called "subduction") at a "steep angle" which cools the interior below the tectonic plates.

As a side note to undersea spreading, Hamilton mentions that as a rule all continents drift laterally along the "...convecting system of the mantle away from hot mantle zones toward cooler ones"; this is called continental drift, and "most" continents are either moving toward cooler parts of the mantle of earth. Or they are sitting on a cooler part of the earth's mantle. Africa is the one exception to this geologic rule, Hamilton continues. Africa was at one time - several hundred million years ago - the "core" of Pangaea, the "supercontinent" that broke into the continents that make up the earth's main land masses today.)

Meantime, the New York Times reported in 1987 that information about the spreading of sea floors is easier to come by thanks to "remote-controlled instruments and a new generation of manned deep-diving vessels." These technological developments have helped - and will continue to help - scientists learn more about how oceans and continents are being split apart. The training for proper use of these technologies was given in the late 1980s to 3,500 scientists from 78 countries; during the training session it was projected by Rodey Batiza of Northwestern University that they may be "a million volcanic mountains on the floor of the Pacific Ocean," most directly related to tectonic plate movement and magma surging upwards.

Among the 3,500 scientists there was "wide agreement" that the energy that is pushing the tectonic plates apart under seas and oceans comes "chiefly from the heat of radioactive decay inside the earth." Moreover, two scientists (Dr. R.W. Girdler of the University of Newcastle-upon-Tyne in England and P.R.K. Simpson) stated that magnetic instruments have indicated that the Africa plate and Arabian plate are "an unusual case" in which a "sea-floor spreading penetrates deep into a continent" (more on this topic will be discussed later in the paper).

This article was written, and the conference was held, well before the confirmation of the split under the Red Sea; still, at the time of the conference the scientists reported that the rift under the Red Sea was spreading at the rate of "about one inch per year"; and the rifting continues north through the gulf of Aqaba into the Dead Sea rift valley; that spreading rate is only have of the rate under the Red Sea.

RED SEAFLOOR RUPTURING: RECENT RESEARCH

The National Sciences Foundation (NSF) (Fall, 2006) MARGINS Newsletter No. 17, reports on the rupturing continental lithosphere dynamics in the northern and central Red Sea. In the narrative references are made to a recent an initiative launched to better understand "continental expansion" and how that transcends into ocean spreading. In this report - with data gathered from scientists from Massachusetts Institute of Technology, Penn State University and the University of Kansas - scientists explain that before studying the rupturing issues beneath the seafloor of the Red Sea, logistical and political issues had to be ironed out. The scientific collaborations that had been planned for this project - with scientists from Egypt, Sudan, Jordan, Eritera, and Saudi Arabia, were not workable.

Unfortunately due to the current security situation and political climate in the Middle East, the NSF...could not longer consider U.S.-led marine geophysical experiments in the Red Sea at this time" (Reilinger, 2006). This political dilemma sheds light on the fact that there is a great deal of tension, first, between the Muslim states in the Middle East and the West in general, and secondly, the United States is engaged in a controversial war in Iraq - and the U.S. supports Israel of course - which contributes to the deep rift (not unlike the tectonic rift beneath the Red Sea) between the Arab / Muslim states and U.S. And unfortunately, science becomes involved even though the empirical studies proposed for the Red Sea had nothing whatsoever to do with politics or gathering intelligence.

Still several aspects of the geophysical dynamics under the Red Sea are explored in the 2006 NSF report, based on significant research conducted prior to the Red Sea region (not just the sea but the surrounding and bordering territories) being designated an "ancillary site." The beginning of the separation of the Arabia from the Nubia (African tectonic plate) is believed to have happened in the Miocene epoch. This separation was a kind of "counterclockwise rotation of Arabia relative to Nubia," Reilinger et al. report.

That counterclockwise rotation continues to this day, the report explains, and it directly results in "increasing spreading rates" and also a "total extension from north to south" in the Red Sea. The scientists in this report characterize the spreading as "characterized by the early stages of continental breakup." The mid-ocean ridge and the magnetic anomalies associated with the ridge is so well developed, the report continues, that it has become "an ideal location to study the transition from rupturing continental lithosphere to full ocean spreading."

Also included in the MARGIN Newsletter No. 17 (Fall 2006) is a report by scientists (Stocki, et al., 2006) that points out there has been "Limited knowledge of how extensional strain is spatially and temporally distributed along the continental margins" of the rift under the Red Sea. That is to say, the story of how the rift technically and specifically took place has been hampered by the "scarcity of datable...volcanic rocks," and the gathering of this information has been hampered by fact that the "post-rift sedimentary rocks" are buried deeply with the rift.

Meanwhile, the Saudi Arabian Geological Survey has cooperated with the National Science Foundation (notwithstanding the prevention [because of political tensions] of addition research into the Red Sea mentioned earlier in this paper) to launch a "comprehensive low-temperature thermochronometric investigation...to determine the timing, origin, and geometry of extensional faulting and rift flank exhumation." This research was done primarily along the central and northern portion or the Red Sea that is actually within the territory of Saudi Arabia.

This is important, recent research, and the report indicates that more than 400 samples were taken (thermochronometric samples) to attempt to solve the puzzle of when the faulting (rifting) actually occurred. The results of those samples have not been released, but the detailed narrative that describes the process and the importance of this science adds to the theme of this paper that indeed the seafloor and its rifting beneath Red Sea is one of the most fascinating and important geological resources on the planet.

RECENT RED SEA SCIENCE: DISCUSSION

The most recent revelations regarding the Red Sea allows for a thoughtful discussion of what is happening today along the faults and cracks in the earth that are part of the tectonic activities of the African (Nubia) and Arabian plates. Indeed, the National Geographic reported in July, 2006, that scientists have determined "...a recent tear in Earth's continental crust near the [Red Sea] is the largest single rip seen since satellite monitoring began" (Lovgren, 2006)). The report explains that over the past 30 million or so years, the Arabian tectonic plate has been moving away from the African (also known as the "Nubian" plate) plate. This is a well-known part of the factual resume of the Red Sea and the Arabian and African tectonic plates. Within the area that the two plates are moving apart there is a "rift"; rifting is the process of the slow opening of a gap between two tectonic plates. Rising hot magma from the center of the earth drives up the Arabian plate and the African plate from below and they reportedly actually began drifting apart approximately 55 million years ago, according to sources reported by.

But what makes the recent discovery fascinating, of great concern to science, and worthy of scientific discussion, is that the rift - in its stretching and thinning process - is not happening as smoothly as it once was. While normally the movement apart is very tedious and slow, only able to be measured in geologic time, something happened to alert scientists all over the world. The possibility of a volcanic eruption, or a massive earthquake that could create a tsunami, is very real based on the newest research.

Indeed, in September of 2005 the tectonic plates "split apart along a 37-mile (60-kilometer) section in Afar, Ethiopia," which is located near the southern portion of the Red Sea.

This dynamic may prove to be a textbook learning opportunity for scientists. By researching this recent tear, or split, scientists hope to learn more about how and why tectonic plates split apart in the first place, and how new crust forms under the seas and oceans. The study alluded to by journalist Stefan Lovgren in National Geographic suggests that "the splitting is due to the injection of underground magma" - which is molten rock - "into the rift rather than earthquakes" that are occurring on those tectonic fault lines. It has already been reported in this paper that the magma is known to be pushing upwards, shoving the two tectonic plates aside. But this new split may offer new clues into what is happening beneath the Red Sea. Tim Wright is an earth and environmental scientist at the University of Leeds in the United Kingdom; he is quoted in the National Geographic article as saying that "...it is clear the rise of molten rock through the plate is enabling the breakup of Africa and Arabia."

The research that is going into this recent split is being done from space, on the ground, and under the Red Sea. The European Space Agency's Envisat radar satellite has analyzed how the ground moved in Ethiopia during the split, and they are comparing and contrasting that with the split that occurred in Iceland between 1975 and 1984. That split in Iceland took about nine years and "20 individual splits," Lovgren writes, to create the same size gap that was created in Ethiopia (and under part of the Red Sea) in "just a few weeks."

The two tectonic plates in Ethiopia moved apart some 26 feet (8 meters) over a few weeks' time, which is a very significant movement along a tectonic plate. As those plates were splitting apart by twenty-six feet an estimated 0.6 cubic mile of magma was "injected into a vertical crack known as a dyke" (Lovgren). That 0.6 cubic mile of magma was enough to fill about 2,000 football stadiums, a very significant amount.

One would naturally expect that there were earthquakes that resulted from the action of the earth's lithosphere cracking open by that amount; the Lovgren article states that "more than 160 earthquakes" were felt and measured by seismographs during that event. As for the human toll, over 10,000 African people were "displaced," and several goats and camels fell into the open fissures resulting from the split. When the plates shifted, and the split opened up, above the dyke the faults moved by "several meters" as the ground opened up.

Lovgren makes clear in the article that the process of the infusion of magma into the area where the split occurred is responsible for determining how far the plates will spread, not the crack itself. In other words, the magma's force from deep under the earth's crust is the key factor in the shifting of these plates under and astride the Red Sea. The entire event was, according to Gezahegn Yirgu, a co-author of the study, "...a vivid expression of the unimaginable amount of stored energy the Earth releases from time to time." The power that it takes to split apart continents (through tectonic plate movement) is something that lay people have a difficult time coming to terms with.

Tim Wright added that the movement under the Red Sea was similar to the process in the mid-ocean ridge under the Atlantic Ocean; the magma pushes up and the crust grows, eventually building up to the point of creating islands such as Iceland. In the case of the Arabian and African tectonic plates, they are moving apart at about "the same speed that fingernails grow," Lovgren writes, which amounts to a few centimeters per year. Is it possible that an ocean will be formed in the place that the Red Sea is now located? Wright says "the prospects are good" but it may take "a million years before the port can be built."

CONCLUSION:

The Red Sea has become a geologic destination of preference for many scientists who are interested in plate tectonics, seafloor spreading, hydrothermal dynamics, the creation of minerals are ores from undersea activities, and more. As research continues using the latest technologies, students and other interested individuals will become informed and enlightened about the Red Sea and the implications for other undersea areas. It is vital for the health and well-being of the citizens on the planet for scientists and scholars to learn as much as possible about how the earth was formed and what it is doing at this stage in its evolution. The Red Sea is unlocking some of those mysteries, and will continue to reveal answers about the sea and the changing planet as time moves forward.