Journal
NATURE GEOSCIENCE
Volume 15, Issue 7, Pages 591-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41561-022-00963-w
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Funding
- European Research Council [339442 TransAtlanticILAB]
- German Science Foundation (DFG)
- Deep Earth Imaging Future Science Platform, CSIRO
- Pawsey Supercomputing Centre
- Australian Government
- Government of Western Australia
- S-CAPAD at IPGP
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Oceanic crust is formed through a combination of magmatic and tectonic processes, with the formation of the lower crust still under debate. Seismic data from young crust formed at the Mid-Atlantic Ridge reveal alternating layers of high and low velocities, with the uppermost low-velocity layer associated with hydrothermal alteration. The layering supports the intrusion of melt as sills at different depths to form the lower crust, indicating a stable process of lower crustal accretion.
Oceanic crust forms at mid-ocean spreading centres through a combination of magmatic and tectonic processes, with the magmatic processes creating two distinct layers: the upper and the lower crust. While the upper crust is known to form from lava flows and basaltic dykes based on geophysical and drilling results, the formation of the gabbroic lower crust is still debated. Here we perform a full waveform inversion of wide-angle seismic data from relatively young (7-12-Myr-old) crust formed at the slow-spreading Mid-Atlantic Ridge. The seismic velocity model reveals alternating, 400-500 m thick, high- and low-velocity layers with +/- 200 m s(-1) velocity variations, below similar to 2km from the oceanic basement. The uppermost low-velocity layer is consistent with hydrothermal alteration, defining the base of extensive hydrothermal circulation near the ridge axis. The underlying layering supports that the lower crust is formed through the intrusion of melt as sills at different depths, which cool and crystallize in situ. The layering extends up to 5-15 km distance along the seismic profile, covering 300,000-800,000 years, suggesting that this form of lower crustal accretion is a stable process.
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