PETROLOGY AND ERUPTION STYLES OF KICKEM-JENNY SUBMARINE VOLCANO, LESSER-ANTILLES ISLAND-ARC

Basaltic magmas erupted from the Kick'em-Jenny submarine volcano have assimilated amphibole-bearing crustal material. The MgO content of the basalts ranges from similar to 12 to similar to 4 wt.%, and some of t he more evolved members of the suite may have eventually become satura ted with amphibole as well as olivine, plagioclase, clinopyroxene, and titanomagnetite. Major-element and trace-element compositions are con sistent with processes dominated by assimilation-fractional crystalliz ation. Analysis of glassy melt inclusions (MgO similar to 2.9 wt.%) in olivine phenocrysts suggests that pre-eruption melt water contents ma y have been as high as similar to 5 wt.%. Glass compositions are inter preted to reflect eruption-related loss of water. Submersible observat ions and dredge sampling of the volcano have revealed two styles of er uption: explosive, tephra-producing eruptions, and non-explosive, dome -forming lava eruptions. The contrasting styles of eruption are though t to be due principally to the rate and extent of eruption-related deg assing of less than or equal to 5 wt.% juvenile H2O, although magma in teractions with external water may also play a role in explosive erupt ions.