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

Publication Type  Journal Article
Year of Publication  2004
Authors  Lizarralde, D.; Gaherty, J. B.; Collins, J. A.; Hirth, G.; Kim, S. D.
Journal Title  Nature
Volume  432
Issue  7018
Pages  744-747
Journal Date  Dec 9
ISBN Number  0028-0836
Accession Number  ISI:000225597200045
Key Words  oceanic ridges; anisotropy; crust; constraints; tomography; generation; velocity; beneath; rocks

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 melting(3) or incomplete melt extraction(2), 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 similar to1.5-km difference in crustal thickness, suggesting that changes in spreading rate affect melt-extraction processes rather than total melting.


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URL  <Go to ISI>://000225597200045
DOI  Doi 10.1038/Nature03140