National Institute Of Oceanography( NIO ) - Signatures of degassing and hydrothermal alteration of recent origin in Central Indian Basin

Signatures of degassing and hydrothermal alteration of recent origin in Central Indian Basin

Since the time of discovery of submarine hydrothermal vents in the Pacific Ocean in late seventies, several deep-sea hydrothermal systems have been discovered along the divergent or convergent plate boundaries such as the mid-oceanic ridges and island arc-trench systems. East Pacific Rise, Mid-Atlantic Ridge and the subduction zones at Southwest Pacific are known to host the majority of hydrothermal systems. Hydrothermal mineralization sites are rarely found in the intra-plate regions basically because of lack of heat source. Some of the seamounts which are located within a plate in the Pacific Ocean such as Macdonald, Loihi , Vailulu'u (Samoan Hotspot related) were found to be hydrothermally active. Extensive bathymetric studies using both single and multi-beam echosounders by NIO have revealed a number of seamounts and abyssal hills in the Central Indian Basin. Sampling in the vicinity of these topographic highs has yielded volcanogenic-hydrothermal material at one location (Iyer, Prasad and Gupta, 1997) in the past. Further, native aluminium of hydrothermal origin were reported from two locations in the Central Indian Basin (Iyer, Mascarenhas-Pereira and Nath, 2007). In a latest study, NIO scientists have identified signatures of recent hydrothermal fluid flow through the sediments at the base of a seamount in the Central Indian Basin through several geochemical and isotopic tracers in a core located close to the southern end of 75^o30'E fracture zone, which defines the trace of Indian Ocean triple junction movement. Isotopic (²¹⁰Pb, ²³⁸U-²³⁰Th, ¹⁰Be), major and trace elements, and micromorphological and microchemical data, were used to identify recent (~100 yrs) hydrothermal alteration of a >200 kyr sedimentary record. Collaboration with scientists from the Uppsala University, Sweden for AMS based ¹⁰Be studies and Mossbauer spectroscopy and from Dr. K. S. Krishnan Geomagnetic Research Laboratory, Allahabad for magnetic properties has yielded valuable supporting data. Although the earlier studies have reported the occurrence of hydrothermally derived sediments at intra-plate seamounts in the Central Indian Basin, degassing events of recent origin as reported here were not known. Emanation of hydrothermal fluids and consequent alteration of the sediments may be a widely prevalent phenomenon in the Central Indian Ocean than that is known currently, in view of possible fluid ascent along the conduits in the faulted areas of the well defined fracture zones. Reactivation of tectonic activity at the fracture zones may be responsible for the hydrothermal activity. Systematic geochemical studies along the fracture zones may help identify more such areas. This was recovered while collecting the basin-wide benthic environmental data to help model the dispersal pattern of plume to be generated during deep-sea mining. Currently an interdisciplinary study with the biologists at NIO is being carried out to look at the benthic and microbial community structures in these geologically special areas.

To consult original article, refer :
Nath, B. N., D. V. Borole, A. Aldahan, S. K Patil, M. B. L. Mascarenhas-Pereira, G. Possnert, T. Ericsson, V. Ramaswamy, and S. M. Gupta (2008), ²¹⁰Pb, ²³⁰Th, and ¹⁰Be in Central Indian Basin seamount sediments: Signatures of degassing and hydrothermal alteration of recent origin, Geophys. Res. Lett., 35, L09603, doi:10.1029/2008GL033849

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