Pranab Das

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Genesis of Central Indian Ocean basin seamounts: morphological, petrological, and geochemical evidence

International Journal of Earth Sciences, 2018

We present the petrological investigation carried out of the seamounts located between water dept... more We present the petrological investigation carried out of the seamounts located between water depths of 4300 and 5385 m in the Central Indian Ocean Basin (CIOB). The seamounts have variable shapes (conical and elongated) and heights (625-1200 m). The basalts have a glassy veneer that forms the outer rind, while the holocrystalline interior shows variable textures. The basalts are plagioclase phyric and compositionally have low FeO* (8.0-10.5 wt%) and TiO 2 (1.3-2.0 wt%), and variable K 2 O (0.1-1.0 wt%) contents and are slightly enriched in the light rare-earth elements. These characteristics are similar to the basalts from the CIOB seafloor and the Central Indian and Southeast Indian Ridges. These facts attest to the simultaneous formation of the CIOB seafloor and associated seamounts that shared a common source between 56 and 51 Ma when the spreading (half) rate was 95 mm/year. Similar to the East Pacific Rise (EPR), the source melt was perhaps ferrobasalts which over a period of time fractionated to N-MORB during the emplacement of the seamounts. The production of the seamounts may have involved a periodic tapping of a regularly replenished and shallow seated source melt. These basalts from the older seamounts of the CIOB are analogous to their present-day counterparts that form at the fast-spreading EPR and other locales in the world oceans.

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Seamounts – windows of opportunities and the Indian scenario

Seamounts are manifestations of crustal tectonics and volcanism, and are also sites of biodiversi... more Seamounts are manifestations of crustal tectonics and volcanism, and are also sites of biodiversity and hydrothermal events. Although the population of seamounts is estimated to be in thousands, a large number of these have not been thoroughly studied. Globally, several seamounts are being exploited by the fishery industries, whereas a few have been demarcated for conservation and serve as underwater observatories. We provide a summary of the seamounts related to their discovery, distribution, nature and influence in the marine environment. In addition, we review the findings of seamounts in the Indian Ocean and the need to have a multi-disciplinary approach to explore them. A TRAVERSE perpendicular to the coast into the sea would reveal, amongst others, continental shelves and margins, abyssal plain, mid-ocean ridges (MORs), plateaus and seamounts that may emerge to form islands. Studies of seamounts help understand their petrological and morpho-logical variations, which in turn sh...

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Morphological characteristics and emplacement mechanism of the seamounts in the Central Indian Ocean Basin

Tectonophysics, 2007

The morphotectonic features of the Central Indian Ocean Basin (CIOB) provide information regardin... more

Distribution and Origin of Seamounts in the Central Indian Ocean Basin

Marine Geodesy, 2005

Approximately 200 seamounts of different dimensions have been identified, from multibeam bathymet... more

Microtexture and Distribution of Minerals in Hydrothermal Barite-Silica Chimney from the Franklin Seamount, SW Pacific: Constraints on Mode of Formation

Acta Geologica Sinica - English Edition, 2014

Extinct hydrothermal barite-silica chimney from the Franklin Seamount of Woodlark basin was inves... more Extinct hydrothermal barite-silica chimney from the Franklin Seamount of Woodlark basin was investigated for mineral distribution and geochemical composition. Six layers on either side of the orifice of a chimney showed significant disparity in colors, mineral assemblages and major element composition. Electron microscope (SEM) images reveal that peripheral wall of the chimney is composed of colloform silica suggesting incipient precipitation of silica-saturated hydrothermal fluid initiated the development of chimney-wall. Intermediate layers, between exterior wall and inner fluid-orifice, dominate with barite and sulfides. Low Sr to Ba ratios (SrO/BaO = 0.015-0.017) indicate restricted fluid-seawater mixing causes relatively high temperature formation of intermediate layers. While, innermost layer bordering the chimney-orifice is characterized with more silica and higher Sr to Ba ratio (SrO/BaO = 0.023), could have formed due to paragenetic shift from high temperature active phase to cooler waning stage of the chimney formation. Paragenetic shift is also responsible for the change in mineral formation mechanism that results in textural variation of barite and morphology of colloform silica developed during different growth phases of this barite-silica chimney.

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Petrological Characteristics and Genesis of the Central Indian Ocean Basin Basalts

Acta Geologica Sinica - English Edition, 2012

The Central Indian Ocean Basin (CIOB) basalts are plagioclase rich while olivine and pyroxene are... more The Central Indian Ocean Basin (CIOB) basalts are plagioclase rich while olivine and pyroxene are very few. The analyses of forty five samples reveal high FeO T (~10-18 wt%) and TiO 2 (~1.4-2.7 wt%) indicating these a ferrobasaltic affinity. The basalts have typically high incompatible elements (Zr 63-228 ppm; Nb ~1-5 ppm; Ba ~15-78 ppm; La ~3-16 ppm), a similar U/Pb (0.02-0.4) ratio as the N-MORB (0.16±0.07) but the Ba/Nb (12.5-53) ratio is much higher than that of the normal mid-oceanic ridge basalt (N-MORB) (~5.7) and Primitive Mantle (9.56). Interestingly almost all of the basalts have negative Eu anomaly (Eu/Eu* = 0.78-1.00) that may have resulted by the removal of feldspar and pyroxene during crystal fractionation. These compositional variations suggest that the basalts were derived through fractional crystallisation together with low partial melting of a shallow seated magma.

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Seamounts – characteristics, formation, mineral deposits and biodiversity

Seamounts represent crust-mantle activities and are areas of petrological deviations, biodiversit... more Seamounts represent crust-mantle activities and are areas of petrological deviations, biodiversity, seismicity and hydrothermal events. An estimated ~50 million tons/year of basalts are required to produce seamounts suggesting intense oceanic volcanism. Seamounts either occur as chains perpendicular to the ridge or as isolated entities or in clusters. Seamounts may host basalts, hyaloclastites, gabbros and serpentinites and these variants perhaps evolve from multiple melting domains as a consequence of large-scale thermal structure and mantle lithology. Nonhotspot seamounts on a young, thin and hot lithosphere host tholeiites whereas the plume related ones on thick, older lithosphere may be either tholeiitic or alkaline. Seamounts may bear hydrothermal deposits (Fe, Mn, Co) rare metals and phosphorites. The resistance of seamounts to subduction could trigger slides; while shearing of seamounts buried in subduction zones leads to seismicity, both of which could cause tsunamis. Seamou...

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Petrological Characteristics and Genesis of the Central Indian Ocean Basin Basalts

by Sugata Hazra, Pranab Das, and Sridhar Iyer

... PETROLOGICAL CHARACTERISTICS AND GENESIS OF CENOZOIC ALKALI RICH PORPHYRY IN WEST YUNNAN, CHI... more

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