By looking at the electronic spin state of iron in a lower-mantle mineral at high temperatures and pressures relevant to the conditions of the Earth’s lower mantle, Lawrence Livermore National Laboratory researchers and colleagues have for the first time tracked down exactly where this occurs.
The Earth’s mantle is a 2,900-kilometer thick rocky shell that makes up about 70 percent of the Earth’s volume. It’s mostly solid and overlies the Earth’s iron-rich core. The lower mantle, which makes up more than half of the Earth by volume, is subject to high pressure-temperature conditions with a mineral collection made mostly of ferropericlase (an iron-magnesium oxide) and silicate perovskite (an iron-magnesium silicate). The Earth’s lower mantle varies in pressure from 22 GPa (220,000 atmospheres) to 140 GPa (1,400,000 atmospheres) and in temperatures from approximately 1,800 K to 4,000 K. (One atmospheres equals the pressure at the Earth’s surface).
The scientists identified the ratios of the high-spin and low-spin states of iron that define the spin transition zone. By observing the spin state, scientists can better understand the Earth’s structure, composition, and dynamics, which in turn affect geological activities on the surface.
“Locating this pressure-temperature zone of the spin transition in the lower mantle will help us understand its properties, in particular, how seismic waves travel through the Earth, how the mantle moves dynamically and how geomagnetic fields generated in the core penetrate to the Earth’s surface,” said Jung-Fu Lin, a Lawrence fellow in LLNL’s Physics and Advanced Technologies Directorate.
“The spin transition zone (STZ) concept differs from previously known structural transitions in the Earth’s interior (e.g., transition zone (TZ) between the upper mantle and the lower mantle), because the spin transition zone is defined by the electronic spin transition of iron in mantle minerals from the high-spin to the low-spin states.”
The research appears in the Sept. 21 issue of the journal, Science.
Lin and colleagues determined that the simultaneous pressure-temperature effect on the spin transition of the lower mantle phase is essential to locating the exact place where this occurs.
The scientists studied the electronic spin states of iron in ferropericlase and its crystal structure under applicable lower-mantle conditions (95 GPa [950,000 atmospheres] and 2,000 K) using X-ray emission spectroscopy and X-ray diffraction with a laser-heated diamond anvil cell. The diamond cell is a small palm-sized device that consists of two gem-quality diamonds with small tips pushing against each other. Because diamonds are the hardest known materials, millions of atmospheres in pressure can be generated in the small device. The sample between the tips was then heated by two infrared laser beams, and the spin states of iron in ferropericlase were probed in situ using synchrotron X-ray spectroscopes at the nation’s Advanced Photon Source at Argonne National Laboratory.
Ferropericlase (which is made up of magnesium, iron and oxygen) is the second most abundant mineral in the lower mantle and its physical properties are important for understanding the Earth’s structure and composition. A high- to low-spin transition of iron in ferropericlase could change its density, elasticity, electrical conductivity and other transport properties. Pressure, temperature and characteristics of the spin transition of ferropericlase are therefore of great importance for the Earth sciences, Lin explained.
“The spin transition zone of iron needs to be considered in future models of the lower mantle,” said Choong-Shik Yoo, a former staff member at LLNL and now a professor at Washington State University. “In the past, geophysicists had neglected the effects of the spin transition when studying the Earth’s interior.
Since we identified this zone, the next step is to study the properties of lower mantle oxides and silicates across the zone. This research also calls for future seismic and geodynamic tests in order to understand the properties of the spin transition zone.”
“The benchmark techniques developed here have profound implications for understanding the electronic transitions in lanthanoid and actinoid compounds under extreme conditions because their properties would be affected by the electronic transitions,” said Valentin Iota, a staff member in LLNL’s Physics and Advanced Technologies Directorate.
Anne Stark | EurekAlert!
Ice cave in Transylvania yields window into region's past
28.04.2017 | National Science Foundation
Citizen science campaign to aid disaster response
28.04.2017 | International Institute for Applied Systems Analysis (IIASA)
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences