Glass compositions, plume–ridge interaction, and hydrous melting along the Galápagos Spreading Center, 90.5°W to 98°W. Geophys

[1] The Galápagos Spreading Center (GSC) between 90.5W and 98W manifests its interaction with the nearby Galápagos plume by way of variations in lava geochemistry, crustal thickness, and morphology along the ridge axis. Natural glasses from stations with9 km average spacing were analyzed for major and minor elements, H2O, and CO2. Samples can be classified as enriched mid-ocean ridge basalts (E-MORB), transitional MORB (T-MORB), or normal MORB (N-MORB) on the basis of K/Ti ratios. E-MORB dominate the GSC east of 92.6W. T-MORB are mainly found between 92.6W and 95.5W. West of the propagating rift tip at 95.5W, N-MORB dominate. High K/Ti E-MORB also have higher H2O, Al2O3, and Na2O and lower FeO*, SiO2, and CaO/Al2O3 relative to N-MORB at similar values of MgO, characteristics consistent with lower mean extents of partial melting relative to N-MORB. We examine the melting process along this section of the GSC with a set of equations that simulate a deep zone of hydrous melting related to the depression of the mantle solidus by H2O. This model constrains the range of mantle source compositions, the depth of the additional hydrous melting zone, the melt productivity in the hydrous region, and the ratio of mantle flow rate through the hydrous zone relative to the anhydrous zone (Uw/U0) that can explain the measured crustal thickness as well as the fractionation-corrected concentrations of K, Na2O, H2O, and Ti along the GSC. Far from the hot spot, the measured crustal thickness and N-MOR