Marked by earthquakes, these two huge anomalies that lie beneath the Earth’s mantle continue to puzzle scientists. However, a new study suggests that they may be much older than we thought. This results in the work of convection flowing across the screen.
On the surface, nothing suggests their existence. And yet, the earthquake is official. Under the Pacific Ocean and under Africa, at the bottom of coatcoatthere are two very large thermal anomalies. Thanks to the analysis of seismic waves generated during a powerful earthquake, it IrregularitiesIrregularities The larger the continents the less the larger provinces are named VitesseVitesse Earthquake (for Provinces of large low seismic velocity, or LLSVP). They actually correspond to parts of the mantle in which waves propagate unusually slowly compared to the surrounding mantle. A rapid anomaly that may conflict with the temperature of the rocks: Kot would be unusually hot compared to what is expected in this region of Kot Nar Kot, which is more than 2,000 km deep.
Still very mysterious structures
We still know very little about these two LLSVPs: their nature, their origin, their age and their effects on coat dynamics are still poorly constrained. Their presence raises a number of questions, particularly about the dynamics of the mantle. We know that the coat is animated by the complex flow in which it participates MovementsMovements Tectonic plates on the surface. This way the whole coat will be “ready”, albeit on the scales for a very long time. , in this diagram, how to explain the presence of LLSVP?
A team of researchers has thus attempted to better explain these anomalies, specifically by observing the way in which seismic waves are “amorized” when crossing them. This moisture has been linked to damageEnergyEnergy That the waves know as they travel. However, in contrast, the researchers observed much less damping of seismic waves as they passed through the LLSVP. Generally, hot stuff has strong moisture. LLSVP so show a signature The bodyThe body Which cannot be explained only by their high temperature. For researchers, these signatures can however provide clues about grain size MineralsMinerals Within these anomalies.
Probably very old structures that have survived the mantle plume
The smaller the grain size, the higher the number of grains in one VolumeVolume is long So the number of boundaries between grains is also important and this leads to a strong damping. And vice versa! In the case of LLSVP, less damping will involve some grain boundaries, and hence larger grains.
However, the presence of large grains suggests that LLSVP is much older than these, and much harder! Many features that suggest that the content that composes them do not participate convectionconvection A result presented in the journal Remain Mental The nature And who suggests that, unlike what they usually offer, the coat won’t be completely mixed, allowing the LLSVP to survive. Thus these massive structures may be at least half a billion years old.
Important new data that may make it possible to better understand the evolution of our planet, and especially the evolution of its volcanoes. Hot spots, these great plumes that give rise to the surface The ArchipelagosThe Archipelagos Like Hawaii, volcanoes can actually be developed on LNSVP slots.
