Discontinuous melt extraction and weak refertilization of mantle peridotites at the Vema Lithospheric Section (Mid Atlantic Ridge)

Melting processes beneath the Mid-Atlantic Ridge were studiedin residual mantle peridotites sampled from a lithospheric sectionexposed near the Vema Fracture Zone at 11N along the Mid-Atlantic Ridge. Fractional and dynamic melting models were testedbased on clinopyroxene rare earth element and high field strengthelement data. Pure fractional melting (non-modal) cannot accountfor the observed trends, whereas dynamic melting with critical mass porosity <001 fits better the measured values. Observed microtextures suggest weak refertilization with 01–1% quasi-instantaneous or partially aggregated melts trapped during percolation. The composition of the melts is evaluated, together with their provenance, with respect to the garnet–spinel transition. Partial melts appear to be aggregated over short but variable intervals of the melting column.Deep melts (generated within the garnet stability field at the base of the melting column) escape detection, being separated from theresidues by transport inside conduits or fractures. The temporalevolution of the melting process along the exposed section shows a steady increase of mantle temperature from 20 Ma to present.