Basalt is a kind of volcanic rock that’s shaped when lava with a excessive content material of mafic minerals (resembling pyroxene and olivine) cools and solidifies. Basalt lava eruptions happen when this molten rock is erupted from a volcano and comes into contact with the Earth’s floor. These eruptions might be explosive, producing ash and tephra, or they are often extra effusive, flowing slowly and steadily over lengthy intervals of time. Basalt lava is often extra fluid than different kinds of lava, which permits it to stream simply and canopy massive areas.
n the previous, huge magma eruptions have led to the creation of enormous floods of basalt lava on the continents. It was beforehand believed that a lot of these eruptions may solely happen in areas the place the continental tectonic plates are skinny, permitting deep mantle materials to rise near the floor. The low stress in these areas permits for the melting of scorching mantle, which may generate a big quantity of magma.
However, a brand new research by researchers from the University of Helsinki and Aarhus University challenges this standard understanding.
“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 creator of the current Journal of Petrology article describing this research.
He specifies additional that the relative quantities of uncommon earth parts in lots of flood basalts level to magma formation within the presence of low-pressure mantle minerals.
The flood basalts in Dronning Maud Land, Antarctica, originate from an exceptionally deep mantle supply. Credit: Arto Luttinen
Support from laptop simulation
The new research was carried out as a part of a analysis venture specializing in the origin of flood basalts that erupted in southern Africa and Antarctica when these continents had been hooked up to one another as elements of Pangaea some 180 million years in the past.
“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, chief of the University of Helsinki staff. “Moreover, we found that many flood basalts that have rare earth element compositions, suggesting high-pressure formation conditions, are actually located in thin regions of the tectonic plates.”
The concept of another speculation began forming after the staff’s discovery of a kind of flood basalt in Mozambique that exhibits compositional proof for exceptionally excessive 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”, provides Ph.D. scholar Sanni Turunen from the University of Helsinki.
The researchers determined to check their speculation utilizing the geochemical modeling software REEBOX PRO, which permits real looking simulation of the habits of minerals, melts and their hint aspect contents throughout 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.
Reference: “Heavy Rare Earth Elements and the Sources of Continental Flood Basalts” by Jussi S. Heinonen, Eric L. Brown, Sanni T. Turunen and Arto V. Luttinen, 27 September 2022, Journal of Petrology.
DOI: 10.1093/petrology/egac098
