Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A new theory on the formation of the oldest continents

13.03.2012
Geologists at the Universities of Bonn and Cologne have come up with a new idea as to how the earliest continents were formed

The earth's structure can be compared to an orange: its crust is the peel supported by the earth's heavy mantle. That peel is made up of a continental crust 30 to 40 kilometers thick. It is much lighter than the thinner oceanic crust and protrudes from the earth's mantle because of its lower density, like an iceberg in the sea.

"According to the current theory, the first continental crusts were formed when tectonic plates would collide, submerging oceanic crusts into the earth's mantle, where they would partially melt at a depth of approximately 100 kilometers. That molten rock then ascended to the earth's surface and formed the first continents," says adjunct professor Dr. Thorsten Nagel of the Steinmann Institute of Geosciences at the University of Bonn, lead author of the study. The theory has been supported by the oldest known continental rocks – approximately 3.8 billion years old – found in western Greenland.

Following trace elements

The composition of the continental crust corresponds to a semiliquid version of the oceanic crust melted by 10 to 30 percent of its original state. Unfortunately, the concentrations of the main chemical components in the re-solidified rock do not provide much information about what depth the fusion occurred at. "In order to find that out, you have to know what minerals the remaining 70 to 90 percent of the oceanic crust consisted of," explains Prof. Dr. Carsten Münker of the Institute of Geology and Mineralogy at the University of Cologne.

Researchers from Bonn and Cologne have now analyzed the Greenlandic rocks for different elements occurring at various high concentrations, also know as trace elements. "Trace elements provide geologists with a window to the origin of continental crust," says Prof. Münker. "With their help, we can identify minerals in the residual rock that were deposited in the depths by the molten rock."

Before the magma separated from the bedrock, the semifluid rock and the leftover solid minerals actively exchanged trace elements. "Different minerals have characteristic ways of separating when trace elements are smelted. In other words, the concentration of trace elements in the molten rock provide a fingerprint of the residual bedrock," explains Dr. Elis Hoffmann from Bonn, coauthor of the study. The concentration of trace elements in the oldest continental rock allows geoscientists to reconstruct possible bedrock based on their minerals and thus determine at what depth the continental crust originated.

The oceanic crust did not have to descend

Using computers, the scientists simulated the composition of bedrock and molten rock that would emerge from partially melting the oceanic crust at various depths and temperatures. They then compared the data calculated for the molten rock with the actual concentration of trace elements in the oldest continental rocks. "Our results paint a surprising picture," Dr. Nagel reports. "The oceanic crust did not have to descend to a depth of 100 kilometers to create the molten rock that makes up the rocks of the first continents." According to the calculations, a depth of 30 to 40 kilometers is much more probable.
The primeval oceanic crust could have 'oozed' continents

…it could definitely have had the power to do so in the Archean eon. Four billion years ago, the gradually cooling earth was still significantly warmer than it is today. The oceanic crust could have simply 'oozed' continents at the same time that other geological processes were occurring, like volcanism, orogeny, and the influx of water. "We think it is unlikely that the contents were formed into subduction zones. Whether or not tectonic plates of the primordial earth had such zones of subsidence is still a matter of debate," says the geologist from Bonn.

Publication: Generation of Eoarchean tonalite-trondhjemite-granodiorite series from thickened mafic arc crust, Geology, DOI: 10.1130/G32729.1

A photo for this press release can be found at:
http://www3.uni-bonn.de/Pressemitteilungen/060-2012
Contact:

Adjunct Professor Dr. Thorsten Nagel/Dr. J. Elis Hoffmann
Steinmann Institute of Geosciences
University of Bonn
Tel. 0228-732760
Email: tnagel@uni-bonn.de
Prof. Dr. Carsten Münker
Institute of Geology and Mineralogy
University of Cologne
Tel. 0221-4703198
Email: c.muenker@uni-koeln.de

Professor Dr. Thorsten Nagel | EurekAlert!
Further information:
http://www.uni-bonn.de

More articles from Earth Sciences:

nachricht The Wadden Sea and the Elbe Studied with Zeppelin, Drones and Research Ships
19.09.2017 | Helmholtz-Zentrum Geesthacht - Zentrum für Material- und Küstenforschung

nachricht FotoQuest GO: Citizen science campaign targets land-use change in Austria
19.09.2017 | International Institute for Applied Systems Analysis (IIASA)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

Im Focus: Silencing bacteria

HZI researchers pave the way for new agents that render hospital pathogens mute

Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Molecular Force Sensors

20.09.2017 | Life Sciences

Producing electricity during flight

20.09.2017 | Power and Electrical Engineering

Tiny lasers from a gallery of whispers

20.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>