Rocks from the Earth's mantle are found more than 1,000 miles from where they originated.
The opening may allow a flow of mantle materials from beneath the Galpagos Islands to beneath Panama.
This form of transport may help explain why Panama has very few active volcanoes. Subduction is a process in which the Cocos tectonic plate dives down and pushes the continental crust under it.
The Central American Volcanic Arc is where lava pushes through the boundaries. The volcanism stops in western Panama, which is on the Panama plate, according to David Bekaert, a scholar at the Woods Hole Oceanographic Institute.
This relative peace has been a mystery for a long time. A new study published in the journal Proceedings of the National Academy of Sciences suggests that the culprit may be a window-like opening in the Cocos tectonic plate that's being pushed down toward Earth's center.
Anomalies are being tracked.
Bekaert and his colleagues are trying to understand how subduction works. The Cocos plate under North America has the capacity to cause large earthquakes, including the one in Oaxaca that killed dozens.
The researchers collected volcanic rock samples, gas and fluid samples from hot springs, and analyzed them to learn more. They were interested in looking at the ratios of the same atoms with different numbers of neutrons in their nuclei. The researchers focused on the isotopes of lead and helium.
Different sources of geological material have different compositions, so we can track the contribution from different regions of the mantle.
The mantle is made up of rocks with a particular structure of oxygen and Silicon. The composition can vary a lot over small distances. There were some strange anomalies in Central America.
In western Panama and behind the volcanic arcs in Costa Rica, we have some exotic signatures that are very similar to what you find in the Galpagos Islands.
There was no way to explain how mantle elements from the Galpagos could get to Panama. The researchers used earthquake waves to map what's beneath the surface, and then used computer modeling to try to understand what was happening.
The buried portions of the Cocos plate may hold the answer. The subducting plate that slides under another plate doesn't just disappear, it retains its structure as it grinds down into the mantle.
There is a window through the slab that allows for the influx of this mantle component.
The window may be the result of a pre-existingFracture in the subducting Cocos crust, or it may be a place where the crust snapped during subduction. It allows materials to pass through from one side of the plate to the other.
The question was what was driving the breeze.
Two possibilities were found by the researchers. The materials are moving through the Panama Fracture Zone, a zone of cracking in the crust and upper mantle that connects the Galpagos to Panama. It's hard to see what would drive long-distance transport through that area. It's not clear if such transport is possible.
The researchers found that the typical circulation of the mantle simply drives materials through the opening in the subducting slab.
"You expect the deep global mantle flow when you model the mantle circulation in this place," Bekaert said.
The lack of active volcanoes in Panama can be explained by the window mantle.
Water locked into the subducting slabs tends to promote the formation of volcanoes because it lowers the melting point of rocks. The opening under Panama means there is a gap in the water-rich crust, which makes it harder to get melty magma flowing there.
There are unexplained anomalies in the chemistry of the mantle all over the world, Bekaert said, but the mantle flow is under-studied. The team wants to expand the method around the globe, but they want to conduct a similar analysis in Chile next.
"No one has thought about this process before, so I want to consider all the data," Bekaert said.
There are related content.
The 'Lost' plate is hidden under the Pacific.
The oldest minerals on Earth are plate tectonics.
What happens to Earth's disappearing crust is a mystery for scientists.
The article was published by Live Science. The original article can be found here.
