An international research group with Dr. Longjian Xie from the Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI) of the University of Bayreuth has succeeded for the first time in measuring the viscosity that molten solids exhibit under the pressure and temperature conditions found in the lower earth mantle.

The data obtained support the assumption that a bridgmanite-enriched rock layer was formed during the early history of the earth at a depth of around 1,000 kilometres - at the border to the upper mantle.

In addition, the data also provides indications that the lower mantle contains larger reservoirs of materials that originated in an early magma ocean and have remained unchanged to this day. The researchers have presented their findings in the scientific journal "Nature Communications".

For the viscosity measurements, the scientists used a heating element they developed, based on a boron-doped and therefore electrically conductive diamond. For example, they were able to examine material samples in a multi-anvil press at pressures of up to 30 giga-pascals and at temperatures of almost 3,000 degrees Celsius - i.e. under conditions similar to those prevailing in the lower mantle of the early earth.

The samples were selected for composition similar to the main minerals present in the lower mantle. Using a super-fast camera (1000 frames/second), the melting processes taking place in the multi-anvil press were observed, and the viscosity of the molten material was measured.

The data obtained proved to be particularly revealing with regard to the magma ocean, from which the earth's mantle formed over the course of the earth's history. Based on their viscosity measurements, the researchers were able to show that the crystallization of the magma ocean was largely dependent on the level of pressure. This resulted in a so-called fractional crystallisation at a depth of around 1,000 kilometres.

"Our measurement data support the assumption that a rock layer containing a high proportion of the mineral bridgmanite was formed at this depth due to crystallization processes. This layer could be responsible for the high viscosity observed at this depth in previous geophysical investigations," explains Dr. Longjian Xie, a post-doctoral researcher at BGI and lead author of the study now published.

The other members of the international team of authors are working in Japan, at Okayama University and the electron synchrotron Spring-8, and in France at Universite Clermont Auvergne and the synchrotron SOLEIL in Saint Aubin.

Research paper

Related Links
University of Bayreuth
Tectonic Science and News

Tweet

Thanks for being here; We need your help. The Space Media Network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceMediaNetwork Contributor $5 Billed Once credit card or paypal		SpaceMediaNetwork Monthly Supporter $5 Billed Monthly paypal only

New insights into the formation of Earth's crust
Rochester NY (SPX) Dec 30, 2019
New research from Mauricio Ibanez-Mejia, an assistant professor of Earth and environmental sciences at the University of Rochester, and Francois Tissot, an assistant professor of geochemistry at the California Institute of Technology, gives scientists better insight into the geological processes responsible for the formation of Earth's crust. In a paper published in the journal Science Advances, Ibanez-Mejia and Tissot studied the isotopes of the element zirconium. Most elements in the periodic ta ... read more