Deep magma facilitates the movement of tectonic plates

October 21, 2020

A small amount of molten rock located under tectonic plates encourages them to move. This is what scientists from the Laboratoire de géologie de Lyon: Terre, planètes et environnement (CNRS/ENS de Lyon/Université Claude Bernard Lyon 1) have recently discovered. Their new model takes into account not only the velocity of seismic waves but also the way in which they are attenuated by the medium they pass through. The velocity of tectonic plates near the surface is thus directly correlated with the quantity of magma present. This research is published on October 21, 2020 in Nature.

The lithosphere, the outer part of the Earth, is made up of the crust and part of the upper mantle. It is subdivided into rigid plates, known as tectonic or lithospheric plates. These move on a more fluid layer of the mantle, the asthenosphere. The lower viscosity of the asthenosphere allows the tectonic plates to move around on the underlying mantle, but until today the origin of this low viscosity remained unknown.

Seismic tomography produces three-dimensional images of the Earth's interior by analysing millions of seismic waves recorded at seismological stations spread across the surface of the globe. Since the 1970s, seismologists have analysed these waves with a view to identifying a single parameter: their propagation speed. This parameter varies with temperature (the colder the medium, the faster the waves arrive), composition, and the possible presence of molten rocks in the medium the waves pass through. Seismologists from the Laboratoire de géologie de Lyon: Terre, planètes et environnement (CNRS/ENS de Lyon/Université Claude Bernard Lyon 1) instead studied another parameter, wave attenuation, alongside the variation in wave propagation speeds. This analysis, which provides new information on the temperature of the medium traversed by the waves, makes it possible to ascertain the quantity of molten rock in the medium the waves pass through.

Their new model made it possible, for the first time, to map the amount of molten rock under tectonic plates. This work reveals that a small amount of molten rock (less than 0.7% by volume) is present in the asthenosphere under the oceans, not only where this was expected, i.e. under ocean ridges and some volcanoes such as Tahiti, Hawaii or Reunion, but also under all oceanic plates. The low percentage of molten rock observed is enough to reduce the viscosity by one or two orders of magnitude underneath the tectonic plates, thus "decoupling" them from the underlying mantle. Moreover, the seismologists from Lyon observed that the amount of molten rock is higher under the fastest-moving plates, such as the Pacific plate. This suggests that the melting of the rocks encourages the plates to move and the deformation at their bases. This research improves our understanding of plate tectonics and how it works.
-end-


CNRS

Related Plate Tectonics Articles from Brightsurf:

Lost and found: UH geologists 'resurrect' missing tectonic plate
A team of geologists at the University of Houston College of Natural Sciences and Mathematics believes they have found the lost plate known as Resurrection in northern Canada by using existing mantle tomography images.

Plate tectonics goes global
A research team led by Dr. WAN Bo from the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences has revealed that plate tectonics went global 2 billion years ago.

Remixed mantle suggests early start of plate tectonics
New Curtin University research on the remixing of Earth's stratified deep interior suggests that global plate tectonic processes, which played a pivotal role in the existence of life on Earth, started to operate at least 3.2 billion years ago.

Why the Victoria Plate in Africa rotates
The East African Rift System is a newly forming plate tectonic boundary at which the African continent is being separated into several plates.

Evidence for plate tectonics on earth prior to 3.2 billion years ago
New research indicates that plate tectonics may have been well underway on Earth more than 3.2 billion years ago, adding a new dimension to an ongoing debate about exactly when plate tectonics began influencing the early evolution of the planet.

Upper-plate earthquakes caused uplift along New Zealand's Northern Hikurangi Margin
Earthquakes along a complex series of faults in the upper plate of New Zealand's northern Hikurangi Subduction Margin were responsible for coastal uplift in the region, according to a new evaluation of local marine terraces.

Breathing? Thank volcanoes, tectonics and bacteria
A Rice University study in Nature Geoscience suggests Earth's first burst of oxygen was added by a spate of volcanic eruptions brought about by tectonics.

What drives plate tectonics?
Scientists found ''switches'' between continental rupture, continental collision, and oceanic subduction initiation in the Tethyan evolution after a reappraisal of geological records from the surface and new global-scale geophysical images at depth.

Plate tectonics may have driven 'Cambrian Explosion, study shows
The quest to discover what drove one of the most important evolutionary events in the history of life on Earth has taken a new, fascinating twist.

Zipingpu Reservoir reveals climate-tectonics interplay around 2008 Wenchuan earthquake
A new study led by Prof. JIN Zhangdong from the Institute of Earth Environment (IEE) of the Chinese Academy of Sciences provided a new insight on the interplay between climate and tectonics from a sediment record in the Zipingpu Reservoir around the 2008 Wenchuan earthquake.

Read More: Plate Tectonics News and Plate Tectonics Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.