New study reveals how Earth recycles continents deep underground

• Continental crust - the Earth’s thick, outer layer of rock - can be dragged deep underground during continental collisions and later rise again through ‘relamination’ 

• Relaminated crust mixes with deeper mantle rocks, creating a new source of magma long after continents collide 

• Laboratory experiments reproduced the chemical signatures seen in natural post-collisional plutonic rocks worldwide 

Scientists have uncovered new evidence that Earth’s continents are continuously reworked deep beneath the surface, offering fresh insight into how continents have evolved over billions of years.  

The study focuses on what happens after two continental plates collide to form major mountain ranges such as the Himalayas and the Alps. While geologists have long known that continental collisions build mountains and deform the crust, the new research shows that portions of continental crust can also be dragged deep into Earth during subduction before rising again and mixing with mantle rocks. 

Daniel Gómez Frutos from the University of Portsmouth’s School of the Environment and Life Sciences is lead author of the study. He said: “Our results show that continental collisions do far more than lift mountains. They also create deep hybrid zones where crust and mantle materials blend together, producing magmas that fundamentally build the continents.” 

This process, known as ‘relamination’, creates a hybrid crust–mantle source that can later generate post-collisional magmas, plutonic rocks that appear millions of years after continental collisions took place. 

Plutonic rocks are a type of igneous rock that forms when magma (molten rock) cools and solidifies deep beneath the Earth's surface.

Daniel, who worked on the research while at the National Museum of Natural Sciences in Madrid, Spain, said: “We used a combination of advanced thermomechanical computer simulations and laboratory melting experiments to demonstrate that magmas produced from this hybrid source closely match the chemical composition of post-collisional igneous rocks found around the world.” 

The findings may also help solve a longstanding geological puzzle: why many younger post-collisional plutonic rocks resemble ancient rocks known as sanukitoids, which formed during the Archean Eon roughly 3 billion years ago. 

The origin of modern-day plate tectonics is an ongoing matter of controversy for the scientific community. According to the researchers, this similarity suggests that crust–mantle hybridization has been a fundamental process for billions of years, potentially pinpointing the earliest stages of plate tectonics on Earth. 

“This implies that complex plate tectonic interactions involving continental subduction and crust-mantle mixing may have been active much earlier in Earth’s history than previously understood,” added Daniel. 

The research offers new insight into how continents evolve over geological time and may help scientists better interpret the chemical record preserved in ancient rocks across the globe. 

The paper Continental evolution influenced by relamination of deeply subducted continental crust is published in Nature Geoscience.