Oceanic spreading rates and magma production
The Mantle convects, and depending on its position relative to the convection cells, a rock rises or falls at variable speeds. In the figure above, we have simulated the exhumation, at variable speeds, of a rock at a depth of 100km, using MetaMod, software.
For low exhumation rates (u = 1 mm/year), the rock cools slowly, but remains in the solid domain, to the left of the dry mantle solidus (i.e. at lower temperatures). When the black curves are crossed, transformations take place in the solid state (they are metamorphic).
For fast exhumation rates (u = 10 mm/year), at the vertical of the ridge, temperature only decreases significantly at shallow depths. In that case, the rock crosses the mantle solidus and partially melts, producing the magma that forms the oceanic crust. At rates of between 1 et 10 mm/year, the path increasingly " enters " beyond the solidus, implying higher and higher rates of partial melting of the mantle.
As a result, the magmatic input in the slow-spreading ridges is lower than in the fast-spreading ones.
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