More than 400 million years ago, an upwelling of hot rock from the Earth’s mantle caused the Earth’s crust in Mongolia to tear apart. This created an ocean that lasted for 115 million years.
The geological history of this ocean could help researchers understand the Wilson cycles, or the process by which supercontinents break apart and come together. These are slow, large-scale processes that progress at less than a centimeter per year, according to the study’s co-author Daniel Pastor-Galana geoscientist at the National Spanish Research Council in Madrid.
“It tells us about processes in the Earth that are not that easy to understand and that are not that easy to see,” Pastor-Galán told LiveScience.
Geoscientists can reconstruct the breakup of the last supercontinent fairly accurately. Pangea, 250 million years ago. But before that, it’s difficult to model exactly how the mantle and crust interacted.
In a new study, researchers were intrigued by volcanic rocks in northwestern Mongolia from the Devonian period (419 million to 359 million years ago).
The Devonian was the ‘Age of Fish’, when fish dominated the oceans and plants began to spread over the land. At the time, there were two major continents, Laurentia and Gondwana, as well as a long series of microcontinents that would eventually grow into what is now Asia. These microcontinents gradually collided with each other and merged in a process called accretion.
The researchers began fieldwork in 2019 in northwestern Mongolia, where rocks from these continental collisions are exposed at the surface, studying the age and chemistry of the ancient rock layers. They found that between about 410 million and 415 million years ago, an ocean called the Mongol-Okhotsk Ocean opened up in the region. The chemistry of the volcanic rocks that accompanied this rift revealed the presence of a mantle plume – a flow of extremely hot, buoyant mantle rock.
Related: Columbia, Rodinia, and Pangea – A History of Earth’s Supercontinents
“Mantle plumes are usually involved in the first phase of the Wilson cycle: the breakup of continents and the opening of oceans, such as the Atlantic Ocean,” said lead author of the study. Mingshuai Zhua professor of geology and geophysics at the Chinese Academy of Sciences told LiveScience.
In many cases, this happens right in the middle of a solid piece of continent, tearing it apart. In this case, however, the geology is particularly complex because the plume tore apart the crust that had previously come together through accretion. Weak spots between the accreted microcontinents, combined with the plume, likely contributed to the ocean’s formation, Zhu said. The researchers published their findings in the journal on May 16 Geophysical research letters.
The ocean closed at the same place it opened, which is a common pattern in ocean life cycles, Pastor-Galán said, but researchers in this study only looked at a snapshot of the ocean’s opening.
“The good thing is that a hotspot is relatively stable, so they can stay in the same place for many millions of years,” says Pastor-Galán. As continents in the crust move over the mantle hotspot, the hotspot leaves behind volcanic rocks and telltale chemistry; this helps researchers track plate movements over millennia, he said.
Asia is no longer adding new microcontinents, Pastor-Galán said, but the formation of the Mongol-Okhotsk Ocean was likely similar to what we see today at the Red Sea, where the crust expanded by about 0.4 inches (1 centimeters) per year. . The Red Sea is part of a larger continental divide that could create a brand new ocean in East Africa in tens of millions of years, although geologists don’t yet know whether other continental forces will prevent that ocean from fully opening, the researchers said. Eos magazine.
Zhu and his colleagues now plan to use their data to create computer models that can better describe the complex tectonics of the ancient Devonian Ocean.