In Dasgupta's high-pressure lab, volcanic rocks are windows to the planet's interior. The researchers crush tiny rock samples that contain carbon dioxide to find out how deep magma forms.
"We have all the necessary tools to simulate very high pressures--to nearly 750,000 pounds per square inch--and temperatures," he said. "We can subject small amounts of rock to these conditions to see what happens."
The geologists use powerful hydraulic presses to partially melt rocks that contain tiny amounts of carbon, simulating what they believe is happening under equivalent pressures in the mantle.
"When rocks come from deep in the mantle to shallower depths, they cross . . . the solidus [boundary], where rocks begin to undergo partial melting and produce magmas," Dasgupta said.
"Scientists knew the effect of a trace amount of carbon dioxide or water would lower this boundary, but our new estimation made it 150-180 kilometers deeper from the known depth of 70 kilometers," he said.
"What we are now saying is that with just a trace of carbon dioxide in the mantle, melting can begin as deep as around 200 kilometers.
"When we incorporate the effect of trace water, the magma generation depth becomes at least 250 kilometers."
The extent of magma generation is larger than previously thought, he said, and, as a consequence, has the capacity to affect the geophysical and geochemical properties of the entire planet.
|Contact: Cheryl Dybas|
National Science Foundation