Geochemical characters of hydrothermal sediments in the northern Central Indian Ridge (CIR) and their implications

Abstract

Several multiple-box and piston sediment core samples were retrieved at rift valley about 4~5 km from spreading center of the northern part of Central Indian Ridge (CIR), which is characterized by very slow spreading rate. The sediments are mostly consisted of yellowish calcareous sediments with a range of 30~70% in calcium carbonate contents, but low opal contents (average 8%). Sedimentation rates of the cores range from 70 to 110 mm/ky the established age model reveals that the box cores extend to approximately 7 ka BP and the piston core extend to 35 ka BP. Hydrothermal materials in the CIR sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Especially, Fe and sometrace elements (e.g., Cu, Co, Ni, and Hg) are suggested as useful tracers for better understanding of spatiotemporal variations of hydrothermal system. In the study area, notably, the most active hydrothermal eruptions have occurred between 3.5 and 6 ka BP, and have waned rapidly since then. Meanwhile, the 35 ka-sediment core contains several continuous and discernible pyroclastic layers of 1~5 cm thick, which consist of glassy, angular blocky particles frequently including bubble wall shards, indicating a series of volatile, explosive ocean-ridge volcanic eruptions. Interestingly, the volcanic eruptions in this area are sparse during the last glacial maximum (LGM), but significantly increase during the last de