Abstract
Recent field and experimental evidence is used to produce a model which explains the generation and characteristics of the basalts found on the Mid-Atlantic Ridge. Multiple cycles of partial melting of the upper mantle, related to tectonic patterns beneath the axis of the Ridge, are thought to generate the different magma types. The sudden stress releases due to faulting on the Median Rift Valley result in considerable partial melting of a pyrolite mantle, which initiates a volcanic cycle with the subsequent extrusion of tholeiitic lava. As the original energy is consumed, the extent of partial melting possible is gradually reduced, so that smaller quantities of magma, progressively enriched in alkalis, are generated. The last extrusions of a volcanic cycle consist of small quantities of alkaline olivine basalt. Since the magmas extrude onto an actively spreading ocean floor, there results a distribution of the different basalt types which can be correlated to the topographic features of the Median Rift Valley.
Published Version
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