Introduction
The collision between the Indian and Eurasian tectonic plates is one of the most spectacular geological events on Earth, giving rise to the Himalayas and the Tibetan plateau. However, the fate of the Indian plate as it slides under Eurasia is still a matter of debate among geologists. Some suggest that the plate remains intact and horizontal, while others propose that it bends and breaks into pieces. A new study, based on seismic data from across southern Tibet, reveals a surprising scenario: the Indian plate is splitting in two, with its lower part sinking into the mantle and its upper part continuing to move northward.
Evidence of delamination
The researchers, led by Lin Liu from Ocean University of China, used data from 94 broadband seismic stations to measure how earthquake waves travel through the crust and mantle below Tibet. They combined different types of waves, such as P-waves, S-waves and shear-wave splitting, to obtain a more detailed picture of the structure and deformation of the Indian plate. They found that the plate is not uniform, but rather shows signs of delamination: a process in which the denser lower part of the plate detaches from the lighter upper part and sinks into the deeper mantle. This explains why some parts of the plate appear to be more buoyant and resist subduction, while others are more prone to plunge into the mantle.
Implications for mountain building
The delamination of the Indian plate has important implications for understanding how the Himalayas and the Tibetan plateau formed and evolved over time. The researchers suggest that the delamination is driven by gravitational forces, as the lower part of the plate becomes heavier due to cooling and metamorphism. As this part peels off and sinks, it creates a downward pull on the upper part, which in turn causes it to stretch and thin. This stretching may create fractures and tears in the crust, which could be potential sites for future earthquakes. The delamination may also affect the uplift and erosion of the mountains, as well as the climate and ecology of the region.
Conclusion
The study by Liu and colleagues provides a new perspective on the complex dynamics of continental collision beneath Tibet. It shows that the Indian plate is not a rigid block, but rather a composite structure that is undergoing delamination due to differential density and stress. This process has significant consequences for mountain building, seismic activity and environmental change in one of the most geologically active regions on Earth.