Hydrothermal exploration along the northern Central Indian Ridge, 8°-12° S: Preliminary results of hydrothermal plume and volcanic lava

Abstract

Hydrothermal exploration aboard the R/V Onnuri was performed along the northernCentral Indian Ridge (CIR) between 8°S and 12°S in January 2010. The main objectives ofthis first Korean research cruise on mid ocean ridge system was 1) to understand the nature of spreading segments of the northern CIR area, where no systematic surveys have been operated before, by mapping and sampling of volcanic rocks and 2) to discover new hydrothermal vents along the spreading center of northern CIR. During the first leg (IR09 Leg1) bathymetric data, in ~50 km width, were collected by multibeam echo sounding system (EM120), which reveals the exact location and structure of axial rift valley of northern CIR between ~8°S and 17°S. Then, rock sampling and CTD casts and tows were performed in northern half of the mapped area in the second leg (IR09 Leg2). The preliminary result of geochemical analyses of basaltic glasses show geographic trend of increasing of incompatible elements north to south along the spreading axis, which might be influenced by Reunion hotspot plume. However, local but clear enrichment of incompatible elements is observed in volcanic lava from segment 2, which suggests possible local mantle heterogeneity of uncertain source. Along the spreading axis of the northern CIR, significant hydrothermal plume signatures were detected by CTD casts and tows. Plume signatures occur at all 5 surveyed segments, suggesting vigorous hydrothermal activities along the northern CIR. However, the optical signals (light transparency and backscattering) of the nearly every cast along the axial valley of the CIR showed increased background level, which might be due to higher level of suspended particles within the axial valley not only by widespread hydrothermal plumes but also by other processes like resuspension of sediments. Onboard dissolved methane analysis indicates that the greater part of the plume signals are originated from the hydrothermalventing, not from the resusp