An international team of scientists has completed an ocean drilling expedition in the eastern Pacific, more than 600 miles west of the Galapágos Islands. Here, the complex tectonic activity of the Pacific, Cocos and Nazca Plates has created a large, craggy underwater rift valley known as Hess Deep.
At the center of this rift, the layers of the ocean’s crust have been peeled away, like an onion sliced in half and pulled apart, revealing deep layers of oceanic crust that are difficult to access anywhere else. Drilling into these layers provided the scientists with rare and valuable samples that will help determine how the Earth’s ocean crust is formed.
Integrated Ocean Drilling Program (IODP) Expedition 345 (Hess Deep Plutonic Crust) returned to Hess Deep almost exactly 20 years after the JOIDES Resolution first drilled there on Ocean Drilling Program (ODP) Leg 147. Co-Chief scientists Kathryn Gillis (University of Victoria, Canada) and Jonathan Snow (University of Houston) led a team of 30 scientists hailing from 10 different countries. Three Education Officers joined the team as well, and helped to communicate the science of the expedition to audiences around the world.
“These rocks represent one of the first reference sections for oceanic lower crust in a known tectonic setting,” says Snow. “Future studies in other settings will be measured and compared against this one, and past ones re-assessed. These samples could not have been acquired through any other means, highlighting the importance of ocean drilling as a technique for studying the evolution of our planet.”
The samples include nearly 200 feet of rock cores made primarily of gabbro, a type of igneous rock formed when magma cools within the crust. Simply retrieving these rocks is a noteworthy achievement; unlike softer sedimentary deposits, drilling cores from hard rock is technically demanding. The work is complicated further when the seafloor sits beneath nearly three miles of water.
“Drilling into hard rock with a very thin sediment cover and water depths greater than 4800 meters was a remarkable feat for IODP,” says Gillis.
The Hess Deep Rift is named for Harry H. Hess, a pioneer in the study of plate tectonics. First discovered in the 1970s, the rift has exposed parts of the ocean crust that normally sit two or three miles below the seafloor. Hess Deep provided the opportunity for the JOIDES Resolution to drill directly into these rocks, providing long-sought clues about how magma from the Earth’s mantle finds its way into the ocean crust.
Until now, the study of ophiolites has provided one of the best opportunities for learning about these processes. Ophiolites are sections of ancient seafloor that have been uplifted and deposited onto continental surfaces. While these formations are easier to access for study, questions still remain about their origin.
This is why the rock samples from Hess Deep, known to form at the fast-spreading East Pacific Rise, are so important. They will help the expedition scientists address fundamental questions about how fast-spreading ocean crust forms and interacts with hot hydrothermal fluids.
“The recovered core has confirmed a long held paradigm that the lower ocean crust is composed of layered gabbros,” Gillis explains. “Their chemistry will allow scientists to test models of how melt is transported from the mantle through the lower crust and ultimately erupted onto the seafloor.”
The Integrated Ocean Drilling Program (IODP) is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring, and monitoring the subseafloor.
The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Together, Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University, and the Consortium for Ocean Leadership compose the USIO. IODP is supported by two lead agencies: the U.S. National Science Foundation (NSF) and Japan’s Ministry of Education, Culture, Sports, Science, and Technology. Additional program support comes from the European Consortium for Ocean Research Drilling (ECORD), the Australia-New Zealand IODP Consortium (ANZIC), India’s Ministry of Earth Sciences, the People’s Republic of China (Ministry of Science and Technology), the Korea Institute of Geoscience and Mineral Resources, and Brazil’s Ministry of Education (CAPES). For more information, visit www.iodp.org.
For more information about IODP Expedition 345 (Hess Deep Plutonic Crust), visit http://iodp.tamu.edu/scienceops/expeditions/hess_deep.html
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