Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earth's crust was unstable in the Archean eon and dripped down into the mantle

30.12.2013
Model calculations indicate that the extreme density of the base of the thickened primary crust caused it to subside into the Earth's mantle

Earth’s mantle temperatures during the Archean eon, which commenced some 4 billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle.


Computer simulation of the processes in the Earth's mantle
Ill.: Institute of Geosciences, JGU

This is the conclusion reached by Dr. Tim E. Johnson who is currently studying the evolution of the Earth's crust as a member of the research team led by Professor Richard White of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU). According to the calculations, this dense primary crust would have descended vertically in drip form.

In contrast, the movements of today's tectonic plates involve largely lateral movements with oceanic lithosphere recycled in subduction zones. The findings add to our understanding of how cratons and plate tectonics, and thus also the Earth's current continents, came into being.

Because mantle temperatures were higher during the Archean eon, the Earth's primary crust that formed at the time must have been very thick and also very rich in magnesium. However, as Johnson and his co-authors explain in their article recently published in Nature Geoscience, very little of this original crust is preserved, indicating that most must have been recycled into the Earth's mantle.

Moreover, the Archean crust that has survived in some areas such as, for example, Northwest Scotland and Greenland, is largely made of tonalite–trondhjemite–granodiorite complexes and these are likely to have originated from a hydrated, low-magnesium basalt source. The conclusion is that these pieces of crust cannot be the direct products of an originally magnesium-rich primary crust. These TTG complexes are among the oldest features of our Earth's crust. They are most commonly present in cratons, the oldest and most stable cores of the current continents.

With the help of thermodynamic calculations, Dr. Tim E. Johnson and his collaborators at the US-American universities of Maryland, Southern California, and Yale have established that the mineral assemblages that formed at the base of a 45-kilometer-thick magnesium-rich crust were denser than the underlying mantle layer. In order to better explore the physics of this process, Professor Boris Kaus of the Geophysics work group at Mainz University developed new computer models that simulate the conditions when the Earth was still relatively young and take into account Johnson's calculations.

These geodynamic computer models show that the base of a magmatically over-thickened and magnesium-rich crust would have been gravitationally unstable at mantle temperatures greater than 1,500 to 1,550 degrees Celsius and this would have caused it to sink in a process called 'delamination'. The dense crust would have dripped down into the mantle, triggering a return flow of mantle material from the asthenosphere that would have melted to form new primary crust. Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to provide a source of the tonalite–trondhjemite–granodiorite complexes. The dense residues of these processes, which would have a high content of mafic minerals, must now reside in the mantle.

Publication:
Tim E. Johnson et al.
Delamination and recycling of Archaean crust caused by gravitational instabilities
Nature Geoscience 7, 47–52. Published online 1 December 2013
DOI: 10.1038/ngeo2019
Contact:
Dr. Tim E. Johnson
Metamorphic Geology division
Institute of Geosciences
Johannes Gutenberg University Mainz
D 55099 Mainz, GERMANY
phone +49 6131 39-26825
e-mail: tjohnson@uni-mainz.de
http://www.geowiss.uni-mainz.de/843_ENG_HTML.php
Professor Dr. Boris Kaus
Geophysics division
Institute of Geosciences
Johannes Gutenberg University Mainz
D 55099 Mainz, GERMANY
phone +49 6131 39-24527
e-mail: kaus@uni-mainz.de
http://www.geowiss.uni-mainz.de/934_ENG_HTML.php
Weitere Informationen:
http://www.geowiss.uni-mainz.de/360_DEU_HTML.php
(Geophysics and Geodynamics at Mainz University)

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2019.html
(Article)
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2033.html
(Archean drips)

Petra Giegerich | idw
Further information:
http://www.geowiss.uni-mainz.de/934_ENG_HTML.php

More articles from Earth Sciences:

nachricht Research icebreaker Polarstern begins the Antarctic season
09.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

nachricht Far fewer lakes below the East Antarctic Ice Sheet than previously believed
08.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

Im Focus: Coping with errors in the quantum age

Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly

The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...

Im Focus: Nanorobots propel through the eye

Scientists developed specially coated nanometer-sized vehicles that can be actively moved through dense tissue like the vitreous of the eye. So far, the transport of nano-vehicles has only been demonstrated in model systems or biological fluids, but not in real tissue. The work was published in the journal Science Advances and constitutes one step further towards nanorobots becoming minimally-invasive tools for precisely delivering medicine to where it is needed.

Researchers of the “Micro, Nano and Molecular Systems” Lab at the Max Planck Institute for Intelligent Systems in Stuttgart, together with an international...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

In focus: Peptides, the “little brothers and sisters” of proteins

12.11.2018 | Life Sciences

Materials scientist creates fabric alternative to batteries for wearable devices

12.11.2018 | Materials Sciences

A two-atom quantum duet

12.11.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>