The contributions of magma originated in events subsequent to subduction, when one tectonic plate is inserted under another, come from the Earth’s mantle and not from recycling the crust, as was thought until now. This has been demonstrated experimentally by research from the National Museum of Natural Sciences (MNCN), the Andalusian Institute of Earth Sciences (IACT) —both CSICs—, and the University of Salamanca. This discovery, published in Earth and Planetary Science Lettersrepresents an important advance in the knowledge about the mechanisms that cause the growth of the continents and therefore a better understanding of the planet.
The finding changes the scientific model that explained how new continental crust is created. The earth’s crust has been slowly but steadily increasing in size since its formation, about 3.5 billion years ago. Until now, the scientific paradigm attributed this contribution of new material to the processes linked to the subsidence of the oceanic crust under the continental crust or tectonic processes of subduction, as occurs in the Andes.
“When this occurs, there is a contribution of new material to the crust, but also the part that sinks into the mantle is lost. This leads to a mass deficit because, in the end, about the same crust is gained at subduction zones as lost. So, where does the new crust come from?” is the question asked by the MNCN researcher. daniel gomez.
how continents grow
On the other hand, there are large granite formations that grow from the magmatism produced millions of years after the subduction tectonic movements take place, after the collision of two continents.
Its about post collisional magmatism, in which magma formed at great depth is introduced into the crust and cools little by little, without coming to the surface, as occurs in volcanic eruptions. These events generate batholithslarge masses of granite that cool slowly becoming part of the earth’s crust and thus increasing the size of the continents.
The Gredos mountain range, in Spain, is an example of these formations. “What we have shown through petrological experiments is that these magmas, which were previously attributed to recycling of the crust, come from the melting of the mantle. This would imply continental growth during magmatic episodes and would explain the origin of the excess material that is generated and that is not attributable to subduction movements,” he explains. antonio castroMNCN and IACT researcher.
The material generated after a continental collision comes directly from the Earth’s mantle.
To prove their hypothesis about the growth of the continents, the research team reproduced the composition and mineralogy of post-collisional batholiths no need to include recycled bark material. “Having reproduced the characteristics of the batholiths in this way indicates that the material generated after a continental collision comes directly from the Earth’s mantle,” says Gómez.
“This finding could bring us closer to understanding where the continents come from and substantially change the models of their origin that, until now, underestimated the role of post-collisional magmatism,” he concludes.
This article was first published on SYNC