1000 km deep in the Earth's mantle: Conditions simulated in the laboratory for the first time

Figure: The mantle (light green) is the vast region of the Earth interior between the crust and the core (grey). It mainly consists of peridotite rocks (green). However, the dense and cold oceanic lithosphere made of peridotite and a basaltic crust (brown) can sink deeply in the mantle. Our experiments help us to understand how peridotite rocks deform at different depths in the mantle (the red and green boxes). In particular we infer how the minerals of peridotite, depicted in the green and red circles, change their orientation due to the stress and heat in these remote regions of our planet. Bridgmanite crystals (blue) align to one another, while ferropericlase crystals (red) do not.

The deepest boreholes in the Earth just reach a few kilometers into the depths. Our knowledge of the nature of the Earth's mantle and the plastic deformation of the rocks there has so far been based on the investigation of seismic waves and their splitting or deceleration on their way through the Earth's interior. Now scientists have succeeded in simulating the extreme conditions of the Earth's mantle at a depth of about 1000 km in the laboratory for the first time. The scientists exposed the mineral olivine to 400,000 times our ambient pressure in the "Extreme Conditions Beamline" of the DESY X-ray source PETRA III, compressed it and also heated it to over 700 degrees Celsius at the same time. In the process, they created the minerals bridgmanite, which is typical for the Earth's mantle and accounts for 40 percent of the volume of the Earth, and ferropericlase, another very common mineral.

The grain-to-grain interactions between bridgmanite and ferropericlase showed an unusual behavior, which may eventually explain why certain directional differences (anistropies) are observed when earthquake waves propagate through the earth. With the investigations it will be easier to understand the behavior of molten rocks when they rise from the Earth's mantle. Convection in the Earth's mantle determines plate tectonics and is thus directly related to the volcanic and earthquake activity of our planet. The study is currently considered the closest approximation for deformed samples of the composition of the lower mantle. It has recently been published in the scientific journal Frontiers in Earth Science.

Original study: Couper S, Speziale S, Marquardt H, Liermann H-P and Miyagi L (2020) Does Heterogeneous Strain Act as a Control on Seismic Anisotropy in Earth’s Lower Mantle?. Front. Earth Sci. 8:540449. doi:10.3389/feart.2020.540449

Scientific contact:
Dr. Sergio Speziale  
Chemistry and Physics of Earth Materials
Helmholtz Centre Potsdam GFZ - German Research Centre for Geosciences
14473 Potsdam
Phone: +49 331 288-1848

Media contact
Josef Zens  
Head of Public and Media Relations
Helmholtz Centre Potsdam GFZ - German Research Centre for Geosciences
14473 Potsdam
Phone: +49 331 288-1040

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