Ocean core complexes and non transform offsets on the Central Indian Ridge between 8°S and 18°S
Sang Joon Pak(electrum@kiost.ac.kr),Seung-Kyu Son(skson@kiost.ac.kr), Se-Jong Ju (sjju@kiost.ac.kr), Hyun-Sub kim, Kyeong-Young Lee
We report prominent ocean core complexes (OCCs) and non-transform offsets (NTOs) observed in the middle portion of Central Indian Ridge (CIR) based on high-resolution bathymetry and discuss possibility of seafloor hydrothermal venting over those areas. The CIR between 8°S and 18°S reveals slow-spreading ridge by geomagnetic study. The ridge is divided into six segments by six major transform offsets including Vema fracture zone (9°30'S), Argo fracture zone (13°30'S) and Marie Celeste fracture zone (17°S). These first-order segments can be subdivided by NTDs into second-order segments. OCCs in the area are generally recognized with mantle rocks as well as corrugation structures. OCCs at 13°S and 15°30'S show the uplifted and elongated-shape NTDs where serpentinite and/or gabbroic rocks were recovered. In bridge-shaped NTD of 13°S, identical to OCC structure, either ends of the NTD link with other OCCs at rifting valley flanks. Northern part of this OCC is mostly composed of gabbroic rocks whereas serpentine rocks were dominantly sampled in the southern part of OCC. At 15°30'S OCC is featured by septum structure which separates southern part of segment into two small segments. Gabbroic rocks and serpentinite are predominant at the eastern part and western part of NTD, respectively. OCCs in NTDs at 13°S and 15°30'S are unusual shape because those OCCs are characterized by elongated and narrow structures. Hydrothermal plumes were detected and seafloor massive sulfide ores were recovered at the OCCs. Plume along the spreading center were weak and no sulfide ores were recovered on axial valley. But hydrothermal sulfides were recovered at 13°S OCC. The hydrothermal ores are fragments of Cu-bearing massive sulfides (or their relatives), low-temperature Zn-Ba chimneys and/or hydrothermal Fe-Mn oxides. High methane concentrations with low particulates anomaly on OCCs indicate that those plumes creadted by ultramafic rock and seawater interaction, i.e. serpentinization.
