Abstract

Data from a suite of closely spaced lava flows recovered within the axial summit caldera and on the crestal plateau of the East Pacific Rise around lat 9°31′N indicate that eruptions on this fast-spreading part of the mid-ocean ridge occur throughout the crestal region and are not restricted to the axis. These eruptions contribute to a complex distribution of basalts of various ages and a significant thickening of seismic layer 2A away from the axis in our study area. Small-scale (<600 m) diversity and nonsystematic distribution of lava types may reflect rapid changes in magma chemistry that occur during crystallization and replenishment in small magma lenses, coupled with the effects of frequent low-volume eruptions both within and outside of the axial summit caldera.

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