The Earth's oceanic crust is formed from magma bodies located beneath mid-ocean ridges. Although axial magma chambers, magma bodies located in the mid-crust, are known to be responsible for generating the upper oceanic crust, it has so far been unclear if the lower crust is formed from the same source or if it primarily arises from deeper "magma lenses" -- smaller bodies located at or near the base of the crust.
Researchers from Lamont-Doherty as well as the Scripps Institution of Oceanography and the Woods Hole Oceanographic Institution collected seismic data of the oceanic crust beneath the seafloor off the coast of Washington, Oregon and northern California. To form the images, they analyzed sound waves that bounced off of structures deep in the Earth, a process similar to that of creating an ultrasound image. The resulting images are the first of their kind showing solidified lenses and sills, narrow lateral intrusions of magma, embedded within the crust/mantle boundary known as the Moho transition zone. The presence of such bodies that deep near a mid-ocean ridge suggests that the lower crust is at least partially formed from several smaller sources of magma rather than from a single large source located in the middle of the crust.
"This demonstrates quite strongly that the process of crustal formation is more complex than generally believed," said Mladen Nedimovic, lead author on the study and a Doherty Associate Research Scientist at Lamont-Doherty. "It also favors the emerging view that volcanoes have a complicated plumbing system consisting of many interconnected sills and magma conduits. We obviously still have a lot to learn about what goes on beneath the surface of the Earth."
The study was funded by grants from the Doherty Foundation and the National Science Foundation.
The Lamont-Doherty Earth Observatory, a member of The Earth Institute at Columbia University, is one of the world's leading research centers seeking fundamental knowledge about the origin, evolution and future of the natural world. More than 200 research scientists study the planet from its deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean. From global climate change to earthquakes, volcanoes, nonrenewable resources, environmental hazards and beyond, Observatory scientists provide a rational basis for the difficult choices facing humankind in the planet's stewardship. For more information, visit www.ldeo.columbia.edu.
The Earth Institute at Columbia University is the world's leading academic center for the integrated study of Earth, its environment and society. The Earth Institute builds upon excellence in the core disciplines--earth sciences, biological sciences, engineering sciences, social sciences and health sciences--and stresses cross-disciplinary approaches to complex problems. Through research, training and global partnerships, the Earth Institute mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world's poor. For more information, visit www.earth.columbia.edu.