Over 400 million years ago, an upwelling of hot rocks from the Earth's mantle split the crust in Mongolia, creating an ocean that survived for 115 million years.
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The geological history of this ocean could help researchers understand Wilson cycles , or the process by which supercontinents break up and come together. These are slow, large-scale processes that progress less than an inch per year, said study co-author Daniel Pastor-Galán, a geoscientist at the Spanish National Research Council in Madrid.
Geoscientists can reconstruct with some accuracy the breakup of the last supercontinent, Pangaea, 250 million years. But before that, it's difficult to model exactly how the mantle and crust interacted.
In a new study, researchers focused on volcanic rocks in northwestern Mongolia from the Devonian period (419 million to 359 million years ago), discovering an ocean.
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The Devonian was the "Age of Fishes," when fish dominated the oceans and plants began to spread onto land. At that time, there were two large continents, Laurentia and Gondwana, as well as a large section of microcontinents that would eventually become what is now Asia. These microcontinents gradually collided with each other and merged in a process called episedimentation.
Researchers began fieldwork in northwestern Mongolia, where rocks from these continental collisions are exposed at the surface, in 2019, studying the age and chemistry of the ancient rock layers. They found that between about 410 and 415 million years ago, an ocean called the Mongolian-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 stream of extremely hot, buoyant rock.
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 complicated because the superelevation was tearing apart crust that had previously been joined together through subduction. The weak spots between the accreted microcontinents, combined with the superelevation, likely helped form the ocean. The researchers published their findings May 16 in the journal Geophysical Research Letters.
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The ocean closed at the same point it opened, which is a common pattern in ocean life cycles, Pastor-Galán said, but the researchers only looked at one snapshot of the ocean opening in this study.
Source: space.com
