Breakup of continents with two speed: Continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.phases
Present-day continents were shaped hundreds of millions of years ago as the supercontinent Pangaea broke apart. Derived from Pangaea’s main fragments Gondwana and Laurasia, the current continents move at speeds of 20 to 80 millimeters per year characterizing today’s plate tectonics.
The extension velocity of tectonic plates increases rapidly during continental separation. The reason is that plate speed is dependent on the strength of the rift zone, which decreases abruptly during continental stretching – similar to a rupturing rope. (Fig: GFZ, S.Brune , G. Schwalbe , S. Riedl)
Continental breakup is still not completely scientifically understood. New research, published in the scientific journal "Nature" shows that the continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.
Of course these processes have to be seen from the geological perspective: we are talking about plates moving slowly over long time periods, centimeters per year and millions of years, respectively. South America for instance separated from Africa over a period of approximately 40 million years.
The separation process, called 'rifting' by geoscientists, began about 150 million years ago, while the two tectonic plates diverged only with 5 to 7 millimeters per year. This slowly thinned the earth's crust and led to the formation of a basin. Before the two continents separated, however, the rift velocity increased six-fold to around 40 millimeters per year. Today Africa and South America drift apart annually with about 35 millimeters per year.
"Imagine the rope snapping during a tug-of-war" describes Sascha Brune from the GFZ German Research Centre for Geosciences, lead author of the study. "At first the rope strains slowly and imperceptibly, when one fiber breaks the overall strength of the rope doesn’t change much; but rupture of the last few rope fibers occurs very abruptly."
Together with colleagues from the University of Sydney the scientist has investigated numerous different rift zones worldwide and found that many continental breakups proceeded according to this two-phase speed evolution: "Most dramatic was the case of the separation of North America and Africa," says Brune. "Roughly 240 million years ago, divergence began very slowly with only one millimeter per year." 200 million years ago, however rifting accelerated by 20 times.
Intriguingly, rift acceleration typically began about ten million years before the actual rupture of the continent, as seen during the separation of Australia and Antarctica, North America and Greenland, Africa and South America, in the North Atlantic or the South China Sea.
Therefore, the newly formed continental margins are significantly shaped by both speed stages: first, slow rifting formed the shelf regions that today are located not far below sea level and near to the coast. In the second phase the distal, deep-water domains of the continental margin were formed at higher rift velocity inducing enhanced faulting and greater volcanic activity.
The new geoscientific results have important implications for the theory of plate tectonics: today's movements of the tectonic plates are known to be governed by the descent and collision of plates and by the currents of Earth’s deep mantle. During the breakup of continents, however, rapid plate accelerations are controlled by the weakening of the continent itself and not primarily by processes in the deep interior of the Earth.
Sascha Brune, Simon E. Williams, Nathaniel P. Butterworth, and R. Dietmar Müller: ”Abrupt plate accelerations shape rifted continental margins”, Nature AOP, 18.07.2016, DOI 10.1038/nature18319
Dipl.Met. Franz Ossing | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Receding glaciers in Bolivia leave communities at risk
20.10.2016 | European Geosciences Union
UM researchers study vast carbon residue of ocean life
19.10.2016 | University of Miami Rosenstiel School of Marine & Atmospheric Science
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences