The powerful processes that occurred in the ancient Tethys Ocean may have played an important role in shaping the Central Asian landscape during the Cretaceous period. This conclusion was made by scientists from the University of Adelaide (Australia) after analyzing hundreds of models of the region's thermal history published over the past 30 years (this is a reconstruction of how rocks in an area warm and cool over millions of years and what these temperature changes reveal about geological processes). The research results are presented in the journal Communications Earth & Environment.
Traditionally, the development of the Central Asian terrain is associated with a combination of tectonic movements, climate change and processes in the Earth's mantle over the past 250 million years. However, as the new analysis shows, the contributions of climate and mantle dynamics turn out to be relatively small.
According to Dr. Sam Boone, one of the authors of the work, this area spends most of its time in an arid climate, which limits the influence of erosion and precipitation on landform formation.
Instead, the researchers identified a direct link between the dynamics of the distant Tethys Ocean and short-term periods of mountain building in Central Asia.
This ancient ocean existed during the Mesozoic-Cenozoic era, gradually closing due to tectonic processes; Its modern “remnant” is considered the Mediterranean Sea.
The modern appearance of Central Asia was largely formed later – by the collision of the Indian and Eurasian plates and their ongoing convergence. However, in the Cretaceous period, when dinosaurs still existed on Earth, the area had distinctly mountainous terrain.
Complex geological relationships
Scientists think that the expansion of the Tethys Ocean, caused by the retreat of subduction zones of the oceanic crust, triggered ancient faults in the Earth's crust. This led to the formation of a system of nearly parallel mountain ranges in Central Asia – up to several thousand kilometers from the future Himalayan impact zone.
A subduction zone is the area where one oceanic tectonic plate sinks beneath another plate and into the mantle. Imagine the ancient Tethys Ocean between major continents. Along its edge, one oceanic plate slowly moves under another – this is normal subduction. At some point, this diving zone begins to shift toward the ocean. This plate still goes deep into the Earth, but the place where it “dives” is gradually moving away. Therefore, it is not compression that occurs above the plate, but tension: the earth's crust seems to begin to be pulled in different directions.
This stretching affects not only the ocean floor but also the neighboring continent. Tensions are transmitted long distances, deep into the continent. The continental crust already has old cracks and faults left over from previous eras. When the cerebral cortex begins to stretch, it is these weak spots that react first. Faults “wake up”: some parts of the crust go down, others rise.
As a result, the flat surface gradually turns into a series of parallel ridges and depressions. These are mountains formed not by continents colliding head-on, but by stretching and fracturing the crust. According to researchers, this is exactly how the mountainous terrain of Central Asia could have been formed in the Cretaceous period – under the influence of tectonic processes in the distant Tethys Ocean, thousands of kilometers from the future Himalayas.
Simulation method
The main research tool is thermal history models based on the thermochronological method. They allow us to monitor how rocks cool as they rise to the surface and then erode. The authors compared such models with plate tectonic reconstructions of the Tethys Ocean, as well as with data on ancient climate and convection in the mantle.
According to the study's co-authors, the same approach could be applied to other regions of the planet, where the cause and timing of mountain formation or rifting (the appearance of faults) is still unknown. The authors believe that combining large amounts of geological data with modeling of tectonic processes allows us to take a fresh look at the role of ancient oceans in shaping continental landforms and clarify the Earth's evolutionary history.
