Scientists, technicians, and drillers with the Integrated Ocean Drilling Program have recovered rocks from 1415.5 meters (>4644 feet) below the seafloor that will provide valuable information on the composition of the Earth. Onboard the scientific ocean drilling vessel JOIDES Resolution, they drilled from mid-November until early March to create the third deepest hole ever in the basement (area below the sediment cover) of the oceanic crust. Benoit Ildefonse (Université Montpellier), a co-chief scientist on one of the two related expeditions, explained the significance of the project, “Deep coring in the ocean crust/lithosphere is a challenging endeavor, and has been a long-term goal of the geoscience community since the end of the 1950s. Post-cruise research to be conducted by the sailing scientists will undoubtedly expand our scientific knowledge of processes at slow spreading mid-ocean ridges, a key component of the global Earth dynamics.”
Staff scientist Jay Miller, Texas A&M University, who spent 115 days at sea obtaining these cores, continued, “We have a preconceived notion of how the Earth evolved that is based on geophysical data. Ocean drilling is needed to obtain samples to determine if these remote sensing tools accurately describe the composition of the Earth. The types of rocks recovered show that the interpretation of the geophysical data is oversimplifying features. Each time we drill a hole, we learn the structure of Earth is more complex and are changing our understanding of how the Earth evolved.”
Co-chief scientists Donna Blackman (Scripps Institution of Oceanography), Ildefonse, Barbara John (University of Wyoming), and Yasuhiko Ohara (Hydrographic and Oceanographic Department of Japan), and IODP staff scientist Jay Miller led the expeditions, which drew scientists from IODP’s members (U.S., Japan, European Consortium for Ocean Research Drilling, and China) in 18 countries. The two consecutive cruises (known as 304 and 305) were designed to drill the Atlantis Massif, which is located at the intersection between the Mid-Atlantic Ridge and the Atlantis fracture zone. The central portion of this domal massif displays characteristics representative of an “oceanic core complex,” a shallow seafloor feature. The ‘core’ of the complex is presumably comprised of lower crustal and upper mantle rocks, providing a unique opportunity to sample the mantle.
John explained the types of rocks recovered, “The gabbroic rocks have compositions that represent some of the most primitive lower crust ever sampled in ocean drilling. Whereas most similar types of rocks have undergone some alteration, intervals of these rocks are very fresh, locally with less than 1 or 2% alteration. They are unique in the ocean drilling records, and provide and unprecedented opportunity to learn about crustal growth in a slow spreading environment.”
Ohara continued, “The ~1.4 km sequence of gabbroic rocks cored during the expeditions is inconsistent with the initial assumption that they would find rocks typical in an uplifted mantle section. A more complex model is required.”
Scientists will continue in-depth research after the expedition to learn more about these features. In addition, more drilling could take place in this location — at the end of Expedition 305, the hole is open, in good condition, and ready to be deepened in the future.
Photos from the expedition are available here. Additional high-resolution images are available on request.
The Integrated Ocean Drilling Program (IODP) is an international marine research drilling program dedicated to advancing scientific understanding of the Earth by monitoring and sampling subseafloor environments. Through multiple platforms, scientists explore IODP’s principal themes: the deep biosphere, environmental change, and solid earth cycles. IODP drilling platforms are operated by the Joint Oceanographic Institutions Alliance (JOI, Texas A&M University, and Lamont-Doherty Earth Observatory of Columbia University), Japan’s Center for Deep Earth Exploration, and the European Consortium for Ocean Research Drilling. IODP’s initial 10-year, $1.5 billion program is supported by two lead agencies, the U.S. National Science Foundation and Japan’s Ministry of Education, Culture, Sports, Science, and Technology; by ECORD, and China’s Ministry of Science and Technology.