Oceanic plate between Arabian and Eurasian continental plates is breaking away

When two continents converge over millions of years, the oceanic floor between them slides to great depths beneath the continents. Eventually, the continents collide, and masses of rock from their edges are lifted up into towering mountain ranges. Over millions of years, the immense weight of these mountains causes the Earth's surface around them to bend downward. Over time, sediments eroded from the mountains accumulate in this depression, forming plains such as Mesopotamia in the Middle East. The researchers modelled the downward bend of the Earth's surfaces based on the Zagros Mountain's load where the Arabian continent is colliding with Eurasia. They combined the resulting size of the depression with the computed topography based on the Earth's mantle to reproduce the unusually deep depression in the southeastern segment of the study area. The researchers found that the weight of the mountains alone cannot account for the 3-4 km deep depression that has formed and been filled with sediment over the past 15 million years.

"Given the moderate topography in the north-western Zagros area, it was surprising to find out that so much sediment has accumulated in the part of the area we studied. This means the depression of the land is greater than could be caused by the load of the Zagros Mountains," said Dr Renas Koshnaw, lead author and Postdoctoral Researcher at Göttingen University's Department of Structural Geology and Geothermics. Researchers propose that this is caused by the additional load of the sinking oceanic plate that is still attached to the Arabian plate. Koshnaw adds: "This plate is pulling the region downward from below, making space for more sediment accumulation. Towards Turkey, the sediment-filled depression becomes much shallower, suggesting that the slab has broken off in this area, relieving the downward pull force."

The geodynamic model developed in this research will benefit other fields as well. "This research contributes to understanding how the Earth's rigid outer shell functions," explains Koshnaw. Such research can lead to practical applications in the future by providing information for exploring natural resources such as sedimentary ore deposits and geothermal energy, and better characterization of the earthquake risks.

This research was made possible thanks to funding from the Alexander von Humboldt Foundation.