How does subduction of oceanic plates turn into collision of continental plates? Chinese scientists reveal secrets

The subduction of oceanic plates slowly turns into the collision of continental plates. What changes will happen deep underground? This has always been a difficult mystery in earth science. If you want to see this transformation process clearly, the Zagros-Makran area in southeastern Iran is an excellent natural observation site. Recently, a scientific research team from the Institute of Geology and Geophysics of the Chinese Academy of Sciences, together with scientists from Iran and France, found direct evidence of double tearing of plates here, uncovering the deep mystery of the transition from oceanic subduction to continental collision. The results were published today (4th) in the international academic journal Nature Earth Sciences.

The Zagros-Mokran area is a key area where the ancient Neo-Tethys Ocean slowly closed and oceanic plates transitioned into collisions with continental plates. Scientific researchers have deployed a large number of mobile seismic monitoring equipment here, continuously collected seismic signals for 18 months, and analyzed nearly 57,000 sets of seismic wave data. Using seismic tomography technology is equivalent to doing a CT scan of the Earth's interior, allowing us to see clearly what the plates look like hundreds of kilometers underground.

Monitoring shows that the plate shapes on the east and west sides of this area are very different: the oceanic plate in Moklan in the east first penetrates 300 kilometers underground gently, and then steepens and continues to sink, reaching a maximum depth of 450 kilometers; in the west is the continental plate in Zagros, which subducts downward to a limited depth of 300 kilometers at most. There is also a remnant of an ancient oceanic plate hidden underneath.

The study found that there were two tears here, with completely different causes. The Zagros side is tearing horizontally: the oceanic plate is heavier and will keep sinking; the continental plate is light and does not go down easily. The two are pulled apart, tearing a hole horizontally, and the continental plate and the deep oceanic plate are separated. The other is a vertical tear, which occurs at the junction of Zagros and Mokran. It is not a pattern familiar to academic circles in the past. It began to crack about 8 million years ago and has extended 200 kilometers southward. It was caused by the continuous northward extrusion of the continent. The two tears were not completely severed, but there was still a connecting link between them. This connection structure stabilizes the gentle subduction of the Maklan plate; and the gap opened by the tear leaves a channel for high-temperature underground materials to surge up, affecting local volcanic and magmatic activities. The two kinds of tearing cooperated with each other, causing the oceanic and continental plates that were originally connected to slowly separate, changing the underground stress and mantle flow, and also causing obvious differences in deformation and magmatic activity at different locations in this orogenic belt.

This study has sorted out a set of models that illustrate that horizontal and vertical plate tearing will occur simultaneously and cooperate with each other, providing an important theoretical reference for us to understand the geological process of the transition from oceanic subduction to continental collision.