Spreading-rate dependence of melt extraction at mid-ocean ridges from mantle seismic refraction data

Daniel Lizarralde (), James B. Gaherty, John A. Collins, Greg Hirth and Sangmyung D. Kim
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Daniel Lizarralde: Georgia Institute of Technology
James B. Gaherty: Lamont-Doherty Earth Observatory of Columbia University
John A. Collins: Woods Hole Oceanographic Institution
Greg Hirth: Woods Hole Oceanographic Institution
Sangmyung D. Kim: Georgia Institute of Technology

Nature, 2004, vol. 432, issue 7018, 744-747

Abstract: Abstract A variety of observations indicate that mid-ocean ridges produce less crust at spreading rates below 20 mm yr-1 (refs 1–3), reflecting changes in fundamental ridge processes with decreasing spreading rate. The nature of these changes, however, remains uncertain, with end-member explanations being decreasing shallow melting3 or incomplete melt extraction2, each due to the influence of a thicker thermal lid. Here we present results of a seismic refraction experiment designed to study mid-ocean ridge processes by imaging residual mantle structure. Our results reveal an abrupt lateral change in bulk mantle seismic properties associated with a change from slow to ultraslow palaeo-spreading rate. Changes in mantle velocity gradient, basement topography and crustal thickness all correlate with this spreading-rate change. These observations can be explained by variations in melt extraction at the ridge, with a gabbroic phase preferentially retained in the mantle at slower spreading rates. The estimated volume of retained melt balances the ∼1.5-km difference in crustal thickness, suggesting that changes in spreading rate affect melt-extraction processes rather than total melting.

Date: 2004
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DOI: 10.1038/nature03140

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