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Episodic magmatism and serpentinized mantle exhumation at an ultraslow spreading centre.

Grevemeyer, I. and Hayman, N.W. and Peirce, C. and Schwardt, M. and van Avendonk, H.J.A. and Dannowski, A. and Papenberg, C. (2018) 'Episodic magmatism and serpentinized mantle exhumation at an ultraslow spreading centre.', Nature geoscience., 11 . pp. 444-448.

Abstract

Mid-ocean ridges spreading at ultraslow rates of less than 20 mm yr−1 can exhume serpentinized mantle to the seafloor, or they can produce magmatic crust. However, seismic imaging of ultraslow-spreading centres has not been able to resolve the abundance of serpentinized mantle exhumation, and instead supports 2 to 5 km of crust. Most seismic crustal thickness estimates reflect the depth at which the 7.1 km s−1 P-wave velocity is exceeded. Yet, the true nature of the oceanic lithosphere is more reliably deduced using the P- to S-wave velocity (Vp/Vs) ratio. Here we report on seismic data acquired along off-axis profiles of older oceanic lithosphere at the ultraslow-spreading Mid-Cayman Spreading Centre. We suggest that high Vp/Vs ratios greater than 1.9 and continuously increasing P-wave velocity, changing from 4 km s−1 at the seafloor to greater than 7.4 km s−1 at 2 to 4 km depth, indicate highly serpentinized peridotite exhumed to the seafloor. Elsewhere, either magmatic crust or serpentinized mantle deformed and uplifted at oceanic core complexes underlies areas of high bathymetry. The Cayman Trough therefore provides a window into mid-ocean ridge dynamics that switch between magma-rich and magma-poor oceanic crustal accretion, including exhumation of serpentinized mantle covering about 25% of the seafloor in this region.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1038/s41561-018-0124-6
Date accepted:12 April 2018
Date deposited:16 April 2018
Date of first online publication:14 May 2018
Date first made open access:14 November 2018

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