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Seismic structure and segmentation of the axial valley of the Mid-Cayman Spreading Center.

Van Avendonk, H.J.A. and Hayman, N.W. and Harding, J.L. and Grevemeyer, I. and Peirce, C. and Dannowski, A. (2017) 'Seismic structure and segmentation of the axial valley of the Mid-Cayman Spreading Center.', Geochemistry, geophysics, geosystems., 18 (6). pp. 2149-2161.

Abstract

We report the results of a two-dimensional tomographic inversion of marine seismic refraction data from an array of ocean-bottom seismographs (OBSs), which produced an image of the crustal structure along the axial valley of the ultraslow-spreading Mid-Cayman Spreading Center (MCSC). The seismic velocity model shows variations in the thickness and properties of the young oceanic crust that are consistent with the existence of two magmatic-tectonic segments along the 110 km-long spreading center. Seismic wave speeds are consistent with exhumed mantle at the boundary between these two segments, but changes in the vertical gradient of seismic velocity suggest that volcanic crust occupies most of the axial valley seafloor along the seismic transect. The two spreading segments both have a low-velocity zone (LVZ) several kilometers beneath the seafloor, which may indicate the presence of shallow melt. However, the northern segment also has low seismic velocities (3 km/s) in a thick upper crustal layer (1.5-2.0 km), which we interpret as an extrusive volcanic section with high porosity and permeability. This segment hosts the Beebe vent field, the deepest known high-temperature black smoker hydrothermal vent system. In contrast, the southern spreading segment has seismic velocities as high as 4.0 km/s near the seafloor. We suggest that the porosity and permeability of the volcanic crust in the southern segment are much lower, thus limiting deep seawater penetration and hydrothermal recharge. This may explain why no hydrothermal vent system has been found in the southern half of the MCSC.

Item Type:Article
Full text:Publisher-imposed embargo
(AM) Accepted Manuscript
File format - PDF (Copyright agreement prohibits open access to the full-text)
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1002/2017GC006873
Publisher statement:Van Avendonk, H. J. A., N. W. Hayman, J. L. Harding, I. Grevemeyer, C. Peirce, and A. Dannowski (2017), Seismic structure and segmentation of the axial valley of the Mid-Cayman Spreading Center, Geochemistry, Geophysics, Geosystems, 18, doi: 10.1002/2017GC006873. To view the published open abstract, go to https://doi.org/ and enter the DOI.
Date accepted:16 May 2017
Date deposited:31 May 2017
Date of first online publication:16 June 2017
Date first made open access:16 December 2017

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