Large magma eruptions have produced great floods of basalt lava on the continents during Earth’s history. Conventionally, the largest flood basalt eruptions are thought to be possible only in regions where the continental tectonic plates are unusually thin, so that deep mantle material can rise close to the Earth’s surface. In such low-pressure environments, the melting of the hot mantle can generate very large amounts of magma.

A new study by researchers from the University of Helsinki and Aarhus University challenges this widely held view.

"The idea that flood basalt eruptions generally require melting of the mantle under low-pressure conditions is largely based on the trace element compositions of the erupted magmas", explains Dr. Jussi Heinonen, University of Helsinki, the lead author of the recent Journal of Petrology article describing this study.

He specifies further that the relative amounts of rare earth elements in many flood basalts point to magma formation in the presence of low-pressure mantle minerals.

Support from supercomputing

The new study was carried out as part of a research project focusing on the origin of flood basalts that erupted in southern Africa and Antarctica when these continents were attached as parts of Pangaea some 180 million years ago.

"We became curious about the occurrence of most flood basalts in regions where the African and Antarctic tectonic plates are thick rather than thin", describes Dr. Arto Luttinen, leader of the University of Helsinki team. "Moreover, we found that many flood basalts that have rare earth element compositions, suggesting high-pressure formation conditions, are located in thin regions of the tectonic plates."

The idea of an alternative hypothesis started forming after the team discovers a type of flood basalt in Mozambique that shows compositional evidence for exceptionally high eruption temperatures.

"These flood basalts made us consider the possibility that melting of exceptionally hot mantle could lead to the formation of high-pressure magmas with trace element features similar to those of low-pressure magmas", adds Ph.D. student Sanni Turunen from the University of Helsinki.

The researchers decided to test their hypothesis using the geochemical modeling tool REEBOX PRO, which enables realistic simulation of the behavior of minerals, melts and their trace element contents during mantle melting.

"We were thrilled to find out that the simulations supported our hypothesis by predicting total consumption of garnet, a diagnostic mineral of high-pressure conditions when mantle melting occurred at the high temperatures indicated by the flood basalts", says Dr. Eric Brown, Aarhus University, a co-author of the article and one of the developers of the REEBOX PRO tool.

Magmas formed at high pressure can thus chemically resemble low-pressure magmas when the mantle source is very hot. Furthermore, the results indicated the survival of garnet at relatively low pressures when a different kind of mantle source was selected for the modeling.

"Our results help us to understand the apparent controversy between the occurrences of southern African and Antarctic flood basalts and their trace element characteristics. Most importantly, we show that voluminous flood basalts can form in regions of thick tectonic plates and that the trace element compositions of flood basalts are unreliable messengers of magma generation depths unless the influences of mantle temperature and composition are accounted for", the authors conclude.

The transformation between skyrmions and bimerons has now been realized by scientists at Japan's Shinshu University

Skyrmions and bimerons are fundamental topological spin textures in magnetic thin films with asymmetric exchange interactions and they can be used as information carriers for next generation low energy consumption memory, advanced neuromorphic supercomputing, and advanced quantum supercomputing as they have multiple degrees of freedom that can carry information. The transformation between isolated skyrmions and bimerons will be an essential operation for future computing architecture based on multiple different topological bits. Therefore, the community needs to find effective ways to realize the creation, transformation, and manipulation of skyrmions and bimerons in magnetic materials.

In a recent study published in Nano Letters, the group led by Xiaoxi Liu, a Professor in the Department of Electrical and Computer Engineering at Shinshu University in Japan and their international collaborators demonstrate in experiments and simulations that the creation of isolated skyrmions and their subsequent transformation to bimerons are possible in a magnetic disk surrounded by a current-carrying and omega-shaped microcoil, where the electric current-induced Oersted field and temperature-induced perpendicular magnetic anisotropy variation play important roles in the transformation between skyrmions and bimerons. Researchers find that the current injected into the microcoil can generate an Oersted field to switch the magnetization of the magnetic disk in the out-of-plane directions. Meanwhile, the current injected into the microcoil can heat the magnetic disk and increases the device's temperature. As a result, a temperature-induced decrease of magnetic anisotropy is realized in the magnetic disk, which leads to the magnetization reorientation from the out-of-plane direction to the in-plane direction and thus, fosters the transformation from skyrmions to bimerons. Researchers also find deformed skyrmion bubbles and chiral labyrinth domains during the transformation between skyrmions and bimerons.

The researchers’ results demonstrate the possibility that two different types of topological spin textures can be hosted by the same magnetic film with asymmetric exchange interactions, which may provide guidelines for building novel spintronic applications based on different types of topological spin textures.

“Our experiment clarified for the first time the transformation between different topological spin textures,” explains Liu. He also mentions, “Skyrmions and bimerons are two most important information carriers for next-generation memory and advanced computing architectures. Our research has a fundamental physical interest. It is also important for future data storage and computing community”.

Researchers will try to study magnetic and spintronic device applications based on the transformation of different types of topological spin textures. An example is voltage-gated spintronic devices based on skyrmions and bimerons. “Our ultimate goal is the application of topological spin textures for low energy consumption, high-density memory, and advanced neuromorphic computing,” says Liu.