UVic’s associate dean of science cracks the Earth’s crust

During a two-month expedition on the JOIDES Resolution, Dr. Kathy Gillis, associate dean of the Faculty of Science at UVic, was one of two chief scientists that helped confirm and refine hypotheses about how the ocean crust was formed.

The crew of scientists aboard the JOIDES Resolution, a large ocean drilling boat, consisted of 34 people from universities in 12 different countries. Gillis and Jonathan Snow, from the University of Houston, were the two chief scientists.

Expedition 345, as it is officially named by the Integrated Ocean Drilling Program (IODP), took place at the Hess Deep Rift. The rift is located 900 kilometres west of the Galapagos Islands. “There are very few places in the world,” says Gillis, “where the geology has exposed deep rocks more than four kilometres below the sea floor and on the sea floor, if that makes sense.” She goes on to explain, “In this area of Hess Deep, plate tectonics have formed a deep rift valley, and if you were to go down in a submersible, along the walls of this rift, you see the upper four kilometres of the ocean’s crust exposed.” It is a very unique place, because these deep rocks are exposed on the ocean floor. Deep rifts such as this are considered a fast-spreading ridge, and they are responsible for forming three quarters of the ocean floor.

Gillis has been with the IODP for over 20 years and, in that time, has been majorly involved with two expeditions. “The other one was 20 years ago in the same location,” says Gillis, “but with different objectives. We were still drilling into the ocean crust but at a different level within the crust.”

The ocean’s crust is made up of layers. Gillis says the rocks collected “tell us a lot about how the ocean’s crust gets built.” It’s made up of a top layer of lavas and sediment, a layer of a basaltic sheeted dike (sheets of volcanic rock), and then a layer of gabbro. Gabbro is magma that has cooled under the earth’s crust. Although it starts out as magma, like the basalt, it is noticeably different from the layer that covers it. Because of how it cools under the earth’s crust, it forms small crystals. The Hess Deep Rift is special because it has sections that have direct access to the gabbro layer and the ophiolites that make it up. They were able to drill into this layer thanks to the IODP.

Now back at UVic, Gillis says, “The next thing for me is not to go back on the ship, but to go back with new eyes to these ophiolites, and that’s what I plan to do next year when I’m on my sabbatical.”

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