SMALL-SCALE SPATIAL AND TEMPORAL VARIATIONS IN MIDOCEAN RIDGE CREST MAGMATIC PROCESSES

Data from a suite of closely spaced lava flows recovered within the ax ial summit caldera and on the crestal plateau of the East Pacific Rise around lat 9-degrees 31'N indicate that eruptions on this fast-spread ing part of the mid-ocean ridge occur throughout the crestal region an d are not restricted to the axis. These eruptions contribute to a comp lex distribution of basalts of various ages and a significant thickeni ng of seismic layer 2A away from the axis in our study area. Small-sca le (< 600 m) diversity and nonsystematic distribution of lava types ma y reflect rapid changes in magma chemistry that occur during crystalli zation and replenishment in small magma lenses, coupled with the effec ts of frequent low-volume eruptions both within and outside of the axi al summit caldera.