NEAR-AXIS SEAMOUNTS AS PROBES OF MANTLE MELTING AT THE EAST PACIFIC RISE

Understanding how melts are generated and focused from the upper mantle to mid-ocean ridges is imperative to understanding how the majority of Earth’s lithosphere is formed. The classic paradigm is that, as melts are produced due to decompression at mid-ocean spreading centers, they migrate 100’s of kilometers to the ridge axis where they are erupted on the sea floor to form new oceanic crust. However, it is very difficult to test the hypothesis of three-dimensional melt migration because the majority of mid-ocean ridge basalt samples come from the ridge axis. Near-axis seamounts provide excellent opportunities to test hypotheses of melt distribution and variation in melt sources because they act as geochemical ‘probes’ that tap into the melt of the upper mantle as it rises to the ridge axis. The region of interest in this study is the East Pacific Rise and the seamount chains located between 14ºN and 4ºN. Here, a total of eight near-axis chains have been sampled and analyzed for basalt lava composition. Major element data derived from glass and whole rock analyses are used to produce chemical variation diagrams and liquid lines of decent plots for the seamount rock suites. Geodynamic models that combine mantle convection, melt generation, and melt migration are used to predict the composition variation that is expected at the East Pacific Rise. Real world data are combined with the model predictions to investigate near-axis melt migration processes. We compare the data and the models to test the hypotheses for melt migration and creation of near-axis seamounts. The results provide a view of the complexities of melt migration and the formation of new crust at mid-ocean ridges.