Privileged Planet: deep ocean plate tectonics (Introduction)

by David Turell , Thursday, March 18, 2021, 19:42 (1346 days ago) @ David Turell

A new discovery based on maps of ocean plate movements:

https://www.sciencedaily.com/releases/2021/03/210317141719.htm

"First, the geological formations that are most important for its understanding lie at the bottom of the oceans. Secondly, forces controlling the processes act below the seafloor and are hence hidden from our view. Many details of plate tectonics are therefore still unclear today.

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"It is about so-called transform faults. "These are large offsets in the mid-ocean ridges. So far, they have been assigned a purely passive role within plate tectonics. However, our analyses show that they are definitely actively involved in shaping the ocean floors," explains Prof. Ingo Grevemeyer from GEOMAR, lead author of the study.

"A look at a global overview map of the ocean floors helps to understand the study. Even at low resolution, several tens of thousands of kilometres long mid-ocean ridges can be recognised on such maps. They mark the boundaries of the Earth's plates. In between, hot material from the Earth's interior reaches the surface, cools down, forms new ocean floor and pushes the older ocean floor apart. "This is the engine that keeps the plates moving," explains Prof. Grevemeyer.

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"The authors of the current study have now looked at available maps of 40 transform faults in all ocean basins. "In all examples, we could see that the transform valleys are significantly deeper than the adjacent fractures zones, which were previously thought to be simple continuations of the transform valleys," says co-author Prof. Colin Devey from GEOMAR. The team also detected traces of extensive magmatism at the outer corners of the intersections between transform valleys and the mid-ocean ridges.

"Using sophisticated numerical models, the team found an explanation for the phenomenon. According to this, the plate boundary along the transform fault is increasingly tilted at depth, so that shearing occurs. This causes extension of the seafloor, forming the deep transform valleys. Magmatism at the outer corners to the mid-ocean ridges then fills up the valleys, so that the fracture zones become much shallower. Oceanic crust that forms at the corners is therefore the only crust in the ocean that is formed by two-stage volcanism. What effects this has on its composition or, for example, the distribution of metals in the crust is still unknown.

"Since transform faults are a fundamental type of plate boundary and frequent phenomenon along active plate boundaries in the oceans, this new finding is an important addition to the theory of plate tectonics and thus to understanding our planet. "Actually, the observation was obvious. But there are simply not enough high-resolution maps of the seafloor yet, so no one has noticed it until now," says Prof. Grevemeyer."

Comment: There must be mechanisms that keep the plates moving, maintaining the subduction processes that cause the recycling of various elements vital to our staying alive.