HYDROTHERMAL METHANE AND MANGANESE VARIATION IN THE PLUME OVER THE SUPERFAST-SPREADING SOUTHERN EAST PACIFIC RISE

Onboard analyses of dissolved CH, and Mn were conducted on the water c olumn along the southern East Pacific Rise between 13 degrees 50' and 18 degrees 40'S during the 1993 RIDGE FLUX Cruise. Many hydrothermal p lumes were identified by chemical anomalies which overlie more than ha lf of the surveyed ridge crest. The CH4/Mn ratio in the plumes shows w ide variability ranges from about 0.05 to 3.9 due to wide range of CH4 concentration. The CH4-rich plumes were detected in the region of 16 degrees 00'-18 degrees 40'S where vigorous magmatic budget was confirm ed by previous studies. Moreover, the CH4/Mn ratio of the plumes is hi ghly correlated with other volatile/metal parameters such as the S/Fe ratio in plume particulate. These results strongly suggest that volati le input caused by magmatic perturbation to hydrothermal systems is re sponsible for the CH4/Mn variability in the southern EPR plumes, based on analogy of the case at the EPR 9 degrees 50'N site. The detection of several volatile-rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the su perfast spreading southern EPR. Copyright (C) 1997 Elsevier Science Lt d.