Key and his co-authors peered into this mysterious zone beneath the northern East Pacific Rise, a fast-spreading mid-ocean ridge near Costa Rica.
Plates pull apart, make new crust
Their new image is akin to a sonogram of the Earth, but instead of sound waves, the researchers used a technique called electromagnetic imaging, which looks for subtle variations in Earth's naturally occurring electric and magnetic fields. The variations reveal different layers and liquid beneath the surface.
Key discovered a symmetrical, narrow melt zone beneath the East Pacific Rise. This implies the mantle is simply filling space created by spreading plates, he said. If the rising mantle were pushing the plates apart, there would likely be evidence of localized convection, such as broader, asymmetrical melting.
The study supports one of the dominant theories (the passive flow model) of how mid-ocean ridges work, the researchers said. Earth's crust is like a giant conveyor belt, with plates spreading apart at mid-ocean ridges and diving into the mantle for recycling at subduction zones, Key explained. The plates ride on giant convection cells in the mantle, but mid-ocean ridges aren't linked to these massive swirls. Instead, the ridges' localized melting comes from the space created by slip-sliding tectonic plates, geologists think. However, there's ongoing debate as to whether the driving force is pull at subduction zones - the passive flow model - or push from magma coming up at ridges. [Infographic: Tallest Mountain to Deepest Ocean Trench]