Copper chains: Study reveals Earth`s deep-seated hold on copper
Earth is clingy when it comes to copper. A new Rice University study this week in the journal Science finds that nature conspires at scales both large and small — from the realms of tectonic plates down to molecular bonds — to keep most of Earth`s copper buried dozens of miles below ground.
Finding copper is more than an academic exercise. With global demand for electronics growing rapidly, some studies have estimated the world`s demand for copper could exceed supply in as little as six years. The new study could help, because it suggests where undiscovered caches of copper might lie.
Earth scientists have long debated whether an oxygen-rich atmosphere might be required for continent formation. The idea stems from the fact that Earth may not have had many continents for at least the first billion years of its existence and that Earth`s continents may have begun forming around the time that oxygen became a significant component of the atmosphere.
In their search for answers, Lee and colleagues set out to examine Earth`s arc magmas — the molten building blocks for continents. Arc magmas get their start deep in the planet in areas called subduction zones, where one of Earth`s tectonic plates slides beneath another. When plates subduct, two things happen. First, they bring oxidized crust and sediments from Earth`s surface into the mantle. Second, the subducting plate drives a return flow of hot mantle upwards from Earth`s deep interior. During this return flow, the hot mantle not only melts itself but may also cause melting of the recycled sediments. Arc magmas are thought to form under these conditions, so if oxygen were required for continental crust formation, it would mostly likely come from these recycled segments.
This garnet pyroxenite xenolith from Sierra Nevada, California, is an example of the deepest products of crystallization within the magmatic belts of subduction zones. Rice University`s Cin-Ty Lee and colleagues showed that most of the copper in arc magmas eventually end up in these deep-seated rocks.
Because sulfides are also heavy and dense, they tend to sink and get left behind in the deep parts of arc systems, like a blob of dense material that stays at the bottom of a lava lamp while less dense material rises to the top.
Lee noted that a high school intern played a role in the research paper. Daphne Jin, now a freshman at the University of Chicago, made her contribution to the research as a high school intern from Clements High School in the Houston suburb of Sugarland.
The research was funded by the National Science Foundation.
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