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  Research
U-M scientist part of team that digs up scientific first

A U-M scientist is part of an international team that has, for the first time, recovered black rocks known as gabbros from intact ocean crust—items which ultimately will help scientists determine how new ocean crust is formed.

Working for the Integrated Ocean Drilling Program aboard the research drilling ship JOIDES Resolution in the Pacific Ocean about 500 miles west of Costa Rica, the team drilled through the volcanic rock that forms the Earth's uppermost crust to reach a fossil magma chamber lying almost a mile beneath the sea floor.

The team's findings were published in the April 20 issue of Science Express.

"By sampling a complete section of the upper oceanic crust, we've accomplished a major goal scientists have pursued for over 40 years, since the days of Project MoHole," says Damon Teagle, National Oceanography Centre, University of Southampton, UK, and co-chief scientist of the drilling expedition. "Our achievement will ultimately help science answer an important question, 'How is new ocean crust formed?' The formation of ocean crust is a key process in the cycle of plate tectonics and constantly 'repaves' the surface of our planet, builds mountains, and leads to earthquakes and volcanoes."

Project MoHole, begun in the 1950s, endeavored to drill through the ocean crust and into the Earth's mantle.

"Having this sample from the deep fossil magma chamber will allow us to compare its composition to the overlying lavas," says U-M research scientist Jeff Alt, also a co-chief scientist on the expedition. "It will help explain whether ocean crust, which is about six to seven kilometers (about four miles) thick, is formed from one high-level magma chamber or from a series of stacked magma lenses."

Geophysical theories have projected that oceanic magma chambers freeze to form the coarse-grained, black rocks known as gabbros, commonly used for facing stones on buildings and kitchen countertops. Although gabbros have been sampled elsewhere in the oceans, where faulting and tectonic movement have brought them closer to the seafloor, this is the first time gabbros have been recovered from intact ocean crust.

Three years of research and multiple trips to the site laid the groundwork for the expedition. The borehole that rendered the magma chamber is more than 1,500 meters (about nine-tenths of a mile) deep and took nearly five months at sea to drill. Twenty-five hardened steel and tungsten carbide drill bits were used before the scientists' work was complete. The rocks directly above the frozen magma chamber were extremely hard because they had been baked by the underlying magmas, much like tempered steel.

Scientists plan to return to the site of the magma chamber and explore deeper, in hopes of finding more secrets hidden within the ocean's crust.

The program is an international marine research drilling project dedicated to advancing scientific understanding of the Earth, the deep biosphere, climate change and Earth processes by monitoring and sampling sub-seafloor environments. It is supported by the U.S. National Science Foundation and Japan's Ministry of Education, Culture, Sports, Science, and Technology.

U.S.-sponsored drilling operations are conducted by the JOI Alliance, comprised of the Joint Oceanographic Institutions—of which U-M is a member—Texas A&M University Research Foundation, and Lamont-Doherty Earth Observatory of Columbia University.

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