Loihi (Y. Orihashi and T. Matsumoto)

Loihi Seamount is the southernmost of the Hawaiian shield volcanoes and is the most recent volcano produced by the Hawaiian hotspot. Magmatic activity of the Loihi provides an extremely rare opportunity to investigate how the earliest magmatism at mantle plume would proceed. We have carried out several submersible dives along the southrift zones and searched hydrothermal activities and collected many rock samples. Part of outcomes derived from our 1999-2000 project was already published (e.g., Umino et al., 2001, AGU Monograph). However, in order to fully understand the evolutional history of this volcano, more information is required, not only from the currently most active rift zones, but also from the interior of the volcano which is exposed now in steep eastern and western flanks of Loihi due to masswasting. Thus, in the 2002 cruise, we have proposed to three ubmersible dives on both flanks to obtain geological information and collect rock samples of probable older generation than those erupted along the rift zones. Collected samples will be examined for major and trace elements and isotopic compositions of Sr, Nd, Pb, N, C and noble gases (and possibly more elements). We are expecting to draw clearer picture, based on the information obtained from multi-isotope studies, about the source and composition of the Loihi’s parent magma through its earlier to recent stage.