A recent drilling operation to a depth of 1,268 metres in the Earth’s mantle from the Mid-Atlantic Ridge has revealed new insights into its mineral composition and processes, challenging current geological models and underscoring the role of deep-sea drilling in scientific discovery.
A record-breaking 1,268-meter (4,160-foot) fossil sample collected from the Mid-Atlantic Ridge in the North Atlantic has provided a deep and detailed mineralogical glimpse into the oceanic mantle. The findings reveal new insights into the composition of the mantle, the deep geology of Earth, and the possible biochemical conditions involved in the origins of life.
Understanding the Earth’s mantle is crucial to understanding important details of the Earth system, including the Earth’s molten rocks, the composition of the crust, and the cycling of elements between the Earth’s interior, hydrosphere, atmosphere, and biosphere. Much of what we know is based on rocks extracted from the ocean floor.
However, these samples often lack crucial geological context and are subject to mineral changes due to igneous processes and seafloor erosion, including transformation into serpentine rocks. And while cores of rocks from deep peridotites—the bedrocks in the Earth’s upper mantle—can provide a continuous record, drilling the kilometer-deep holes required to obtain them has proven difficult.
Final drilling success
Now, Johan Lissenberg and colleagues report the recovery and characterization of a nearly continuous 1,268-meter-long drill core of serpentinite peridotite from the Mid-Atlantic Ridge. The core core was collected in 2023 during the International Ocean Discovery Program (IODP) Expedition 399, from a hydrothermally active region called the Atlantis Block. And others. Large mineral variations have been documented throughout the core at various levels, including serpentinite levels.
The pyroxene content of the sample was also unexpectedly low compared to other peridotite samples worldwide, possibly due to high degrees of depletion and dissolution of pyroxene during melt flow. Contrary to popular models, the melt migration was found to be biased upward into the mantle. The authors observed hydrothermal fluids interacting with rocks throughout the core, with oxidative weathering occurring down to 200 m depth. Gabbroic intrusions were also found to play an unexpected role in hydrothermal alteration and in regulating fluid compositions from peridotite-hosted hydrothermal vents, which have been proposed as models for environments where biochemistry might have led to the development of life on early Earth and other planetary bodies.
“Decades of ocean-bottom sampling by dredging have painted a rough mineral picture of the mantle. Yet each new drilling mission reveals surprising insights into the mantle and the composition of the oceanic crust,” Eric Hillebrand wrote in a related Perspective article. “More ambitious drilling projects will reveal important pieces for understanding the biogeochemical effects of the oceanic mantle.”
References: “A Long Section of Serpentinized Peridotite” by C. Johan Lissenberg, Andrew M. McCaig, Susan Q. Lang, Peter Bloom, Natsuo Abe, William J. Brazelton, Remi Coltat, Jeremy R. Deans, Kristen L. Dickerson, Margaret Goddard, Barbara E. John, Frieder Klein, Rebecca Cohn, Kuan Yu Lin, Haiyang Liu, Ethan L. Lopez, Toshio Nozaka, Andrew J. Parsons, Vamdev Pathak, Mark K. Regan, Jordyn A. Robari, Ivan B. Savov, Esther M. Schwarzenbach, Olivier J. Sissman, Gordon Southam, Feng Ping Wang, C. Jeffrey Witt, Leslie Anderson and Sarah Treadwell, August 8, 2024, sciences.
DOI: 10.1126/science.adp1058
“A Deeper Dive into the Earth’s Mantle” by Eric Hillebrand, August 8, 2024, sciences.
DOI: 10.1126/science.adr2490
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