Beneath the surface of Iran, an immense rock plate is tearing apart in two different places.
The phenomenon is taking place beneath the southeast of the country, at depths no one can reach directly. Researchers have nevertheless managed to reconstruct its contours. Their study, published in Nature Geoscience, reveals two distinct ruptures in the Arabian Plate.
Zagros Mountains forest steppe ecoregion. This map represents the boundaries of the Zagros Mountains forest steppe ecoregion (magenta outline)
Image Wikimedia
The Earth's surface moves: it is divided into large plates that advance a few centimeters per year. When they meet, one can plunge beneath the other. This very slow movement can eventually make an ancient ocean floor disappear.
In this region, part of the Arabian Plate once belonged to an ocean called Neotethys. Its relatively dense rocks continue to sink beneath the Makran region. Farther west, continental rocks, which are less dense, resist this subduction more strongly. Iran's Zagros Mountains lie in this collision zone.
This exerts different forces on neighboring parts of the same plate. The oceanic section plunges deeper, while the continental section sinks less easily. Over time, the rocks can separate, even if they appear perfectly solid at our scale.
Evolution of the plates
The scientists analyzed vibrations produced by earthquakes and recorded by monitoring stations. These waves travel through Earth's depths at varying speeds depending on the materials they encounter. By comparing their paths, the research team reconstructed an image of Earth's interior.
The results indicate that the oceanic section descends to at least 450 km below the surface. The continental section studied does not extend beyond 300 km. The researchers distinguish a first tear, as well as a second tear farther south.
These two ruptures probably did not begin in the same place or for the same reasons. They could nevertheless eventually join as they progress.
The study also offers a possible explanation for some of the region's ancient volcanic activity. When pieces of a plate separate at depth, hotter rocks can rise through the spaces left behind. The researchers are therefore seeking to clarify how these ruptures alter the movement of materials beneath the continents.