Scientists aboard the research drilling ship JOIDES Resolution have, for the first time, drilled into a fossil magma chamber under intact ocean crust. There, nearly a mile beneath the sea floor, they have recovered samples of gabbro – a hard, black rock that forms when molten magma is trapped beneath Earth's surface and cools slowly.

The scientists, affiliated with the Integrated Ocean Drilling Program (IODP), an international marine research drilling program dedicated to advancing scientific understanding of the Earth by monitoring and sampling sub-seafloor environments, published their findings on April 20 in Science Express, the online edition of the journal Science.

Although gabbro has been sampled elsewhere in the oceans where faulting and tectonic movements have brought it closer to the seafloor, this is the first time gabbro has been recovered from intact ocean crust.

The borehole into the magma chamber took nearly five months to drill, and required the use of 25 hardened steel and tungsten carbide drill bits. Getting there "is a rare opportunity to calibrate geophysical measurements with direct observations of real rocks," says geophysicist Doug Wilson of the University of California at Santa Barbara, lead author on the Science Express paper. "Finding the right place to drill was probably the key to this success."

Wilson and his IODP colleagues found that place by identifying a region of the Pacific Ocean that formed some 15 million years ago when the East Pacific Rise was spreading at a "superfast" rate of more than nearly 8 inches per year, faster than any mid-ocean ridge on Earth today.

"We planned to test the idea that magma chambers should be closest to the Earth's surface in crust formed at the fastest spreading rate," says Wilson.

"These results confirm ideas about the way in which fast-spreading oceanic crust is built," says Jamie Allan, IODP program director at the U.S. National Science Foundation, which co-funds the program. "This new understanding opens the way to understanding the origin of oceanic crust, which we can best do by deep drilling."