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Posts: 131433
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Ocean Birth
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 Scientists suggest new age for East African Rift

The Great Rift Valley of East Africa - the birthplace of the human species - may have taken much longer to develop than previously believed, according to a new study published this week in Nature Geoscience that was led by scientists from James Cook University and Ohio University.
The team's findings suggest that a major tectonic event occurred in East Africa as far back as 25-30 million years ago, rearranging the flow of large rivers such as the Congo and the Nile to create the unique landscapes and climates that mark Africa today.

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East African Rift
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Satellites see the earth move

The East African Rift extends for over 3000 km, from Mozambique to Djibouti; many of the volcanoes are in remote areas which can be hard to access on the ground and even fewer have ground-based monitoring networks.
Satellite measurements offer a unique opportunity to study the East African Rift on the plate-boundary scale, giving us insight into the development of magma activity as the rift matures and the behaviour of individual volcanic systems.
Even where available, ground-based measurements of surface deformation are taken at a limited number of stations (usually less than 10 per volcano) so satellite images give a much higher measurement density.

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Tanzania's Great Rift Valley
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Des chercheurs du laboratoire Géosciences Azur et du laboratoire Domaines océaniques, en collaboration avec des géophysiciens et géologues basés aux Etats-Unis, au Luxembourg, en Belgique et en Tanzanie, ont pour la première fois détecté et caractérisé de manière quantifiée un événement d'injection de magma (« dyking ») dans un rift continental actif, en Afrique de l'Est. Grâce à la mise en place d'un réseau sismologique temporaire français (Lithoscope, un des quatre parcs d'instrumentation sismologique portable de l'INSU-CNRS), les équipes françaises ont pu décrire cette crise sismo-magmatique et interpréter la succession des phases de déformation. Publiés le 11 novembre dans la revue Nature, les résultats de la comparaison des mesures géodésiques (GPS), interférométriques (Envisat), sismologiques et géologiques ont ainsi révélé que la plus grande partie de la déformation observée pendant la crise au sud du rift de Natron a été relâchée asismiquement, étayant le rôle prépondérant de l'intrusion de magma en profondeur pendant les stades initiaux du rifting continental, bien avant l'amincissement lithosphérique sous le rift.

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RE: Ocean Birth
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The Evolution of Ethiopia's Afar Depression
Formation of an ocean is a rare event, one few scientists have ever witnessed. Yet this geophysical nativity is unfolding today in one of the hottest and most inhospitable corners of the globe.

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Plate Tectonics
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The continuous overturning, melting and re-casting of Earth's crust over the eons may have started with a massive asteroid impact in Earth's infancy, suggests one geologist.
The unusual and iconoclastic hypothesis, if true, could help point the way to how and why plate tectonics did or did not get started on other worlds in our solar system and beyond. That's important because one of the critical ingredients of life on Earth is a constantly recycling crust.

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Future Sea
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African Rift Signals Future Sea



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Ethiopia's rift valley
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Africa is being torn apart. And as Ethiopia's rift valley grows slowly wider, an international team of scientists is taking a unique opportunity to plot the progress of continents on the move.
The 28-strong team is led by University of Leeds geophysicist Dr Tim Wright, who has secured a £2.5 million grant from the Natural Environment Research Council (NERC) to study the seismic events taking place in the remote Afar desert of Northern Ethiopia.
It's here that two mighty shelves of continental crust, the African and Arabian plates, meet – and are tearing the landscape apart.
For most of the time, this happens at around the same speed that human fingernails grow – about 16mm a year. But the gradual build-up of underground pressure can lead to occasional bursts of cataclysmic activity.
The most dramatic event came in September 2005, when hundreds of deep crevices appeared within a few weeks, and parts of the ground shifted eight metres, almost overnight. More than two billion cubic metres of rising molten rock – magma – had seeped into a crack between the African and Arabian tectonic plates, forcing them further apart.
And it has given Dr Wright's team a unique opportunity to witness plate tectonics – the science of how continents are formed and move – at first hand.

"Much of the activity between the continental shelves takes place deep underwater at the mid-ocean ridges. Ethiopia is the only place on the planet where we can see a continent splitting apart on dry land."

Dr Wright and his colleagues will use satellite radar imaging to measure how the ground deforms.

"In its simplest form, you are taking two snapshots of the same place, separated by a period of time, to see how far they have moved apart."

His team, which includes experts from Oxford, Cambridge, Bristol and Edinburgh universities, as well as international researchers from the US, New Zealand, France and Ethiopia, will also use GPS, seismometers, and other geophysical and geochemical techniques to determine the properties of rock and magma below the surface, and to monitor the crust's movement. They will use the data to create a 3D computer model of how magma moves through the Earth's crust to make and break continents.
As the sides of the Ethiopian rift move apart, the gap between them is being plugged with molten rock, which then cools to form new land. And in around one million year's time the Red Sea could come flooding into the sinking region, re-shaping the map of Africa forever.
Much of the team's work will be on the ground in the Afar region of Ethiopia, also known as the Danakil depression. It's a barren, inhospitable, but beautiful part of the world.
Scientists from the University of Addis Ababa who are working on the project will undertake collaborative research visits to the UK. The research will establish a firm link between the two universities, with Leeds supporting two Ethiopian students on a PhD programme which will include a year in the UK.

Source University of Leeds


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Posts: 131433
Date:
Ocean Birth
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The largest tear in the Earth's crust seen in decades, if not centuries, could carve out a new ocean in Africa, according to satellite data.

Geologists say a crack that opened up last year may eventually reach the Red Sea, isolating much of Ethiopia and Eritrea from the rest of Africa.



The 60km-long rift was initially sparked by an earthquake in September.

Follow-up observations reported in the journal Nature suggest the split is growing at an unprecedented rate.

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