Biswajit Ghosh

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• PhD
• Professor (Associate) at University of Calcutta

Ophiolites are widely studied to unravel how new subduction zones form. They may contain crustal and mantle rocks that formed during juvenile stages of intra-oceanic subduction, modifying the pre-existing oceanic lithosphere within which subduction started, and in which a magmatic arc formed upon subduction maturation. Previous geochemical work on...

Although occurring as an accessory phase in mafic-ultramafic rocks, the universal presence of chrome spinel in ophiolitic settings bears importance in deciphering the tectonic setting of the ophiolite. Compositional and textural modification of chrome spinel via post-magmatic processes (metamorphism and fluid-induced alteration) is widely reported...

Owing to the lack of persistent magma chamber and the complex interplay between magmatism and tectonism at slow- to ultraslow-spreading ridges, the likeliness of fractional crystallization being the predominant process of evolution of crustal magmas is weak. Here, we report a detailed petro-geochemical investigation from the lower crustal gabbroic...

Igneous microtextures are significant tracers of magmatic processes as these provide important information about magma evolution. Oxy-symplectite intergrowth of orthopyroxene (host) with Fe-Ti oxide (lamellae) is described from the Atlantis Bank, an Oceanic Core Complex (OCC) along the ultraslow spreading Southwest Indian Ridge (SWIR). This texture...

This study aims to investigate the earliest imprint of Deccan rift magmatism as preserved in alkali basalts from the northwestern Indian shield. The alkali basalts are petrographically classified as nephelinites and basanites. They are silica undersaturated and their high Mg#, CaO/Al 2 O 3 , Cr and Ni indicate their primitive character. Geochemical...

The present study investigates the tectonic evolution of the western extremity of Chhotanagpur Gneissic Complex (CGC), within the eastern part of E-W trending Central Indian Tectonic Zone (CITZ). The study has been done along a N-S stretch (mostly within Chhattisgarh, India) extending from Sanawal in the north to Pali in the South. The reportedly M...

Analysis of Mare Fecunditatis with hyperspectral data derived from ISRO’s Chandrayaan-1 Moon Mineralogy Mapper (M3) pre-sents a detailed spectral analysis of the basalts comprising the Fecunditatis basin, revealing a complex geological history marked by mul-tiple episodes of volcanism and varied mineral compositions. The analysis, based on M3 data,...

The forearc and back-arc region of the Andaman-Nicobar-Sumatra Subduction Zone are mainly submarine and poorly understood. To gain new insights sixty representative volcanic rocks were collected from the Andaman Sea region. Rock types range from basalt, basaltic andesite, andesite, dacite to rhyolite reflecting calc-alkaline, intermediate to acidic...

Here, we report the occurrence of relict Neoarchean silico-carbonatites from the Elagiri complex (12°31′N: 78°35′E), Southern Granulite Terrane, Indian Shield, where they occur within leucosyenites as enclaves. Trace elements suggest that the silico-carbonatites and leuco-syenite are related through melting–crystallization episodes. U–Pb zircon age...

The Ramagiri greenstone terrane (RGT) of Central Dharwar craton, India, is recognized as remnants of Archean oceanic crust squeezed between ancient proto‐continental terranes. The granites and gneisses formed as a result of partial melting, resisted subduction and collided, sinking the intervening ocean basin. The geochemical characteristics of the...

The LA-ICP-MS data on clinopyroxene from the gabbroic intrusives from the Western Iron Ore Group Basin(21°50' N to 22°39' N and 85°00' E to 85°45' E) Singhbhum Craton, Eastern India was used to assess the petrogenetic history. The clinopyroxene belongs to the "QUAD" group as per the Q-J relation and typically signifies an "augitic nature" in the Wo...

Symplectitic intergrowth of orthopyroxene (host) with magnetite and minor ilmenite (lamellae) are recorded from Atlantis Bank, an Oceanic Core Complex on Southwest Indian Ridge. The texture is typically developed in oxide-rich gabbros recovered from the lower crustal section in this region and formed at the expense of olivine. Usually, the intergro...

Intracrystalline exsolution textures in alkali feldspar are common in lithotypes from many alkaline complexes of the Eastern Ghats Granulite Belt (EGGB), India. However, the parentage of these textures and their compositional evolution is not well documented from this granulite belt. This study on the Koraput Alkaline Complex (KAC) in the EGGB docu...

The present study reports the occurrence of orthopyroxene megacrysts from the Chilka Lake anorthosite massif, Eastern Ghats, India. An insight into the mineral chemistry of different phases, coupled with detailed field and petrographic evidences from this study, shed light on a long debate on the origin of orthopyroxene megacrysts in anorthosite ma...

We report multistage geochemical evolution of off-cratonic subcontinental lithospheric mantle by studying mantle xenoliths hosted in alkali basalts from the northwestern part of the Deccan volcanic province in Kutch. The xenolithic fragments are peridotites, composed of Cr-rich diopside, Mg-rich olivine, orthopyroxene and aluminous spinel. Composit...

The Andaman and Nicobar ophiolites, in the forearc of the western Sunda subduction zone, underwent enigmatic, rapid Cenozoic vertical motions: shallow-water sediments with abundant arc debris characterize the middle Paleocene–middle Eocene and are under- and overlain by significantly deeper sediments. Recent paleomagnetic results revealed a near-eq...

In this study, we have implemented a band shape algorithm (BSA) to identify the surface distribution of different minerals on parts of the Aristarchus Plateau using selected bands of Clementine and hyperspectral Moon Mineralogy Mapper (M3) data. BSA mineral maps derived using spectral bands of Clementine and M3 sensors could determine broadly simil...

Magma migration and differentiation processes are key to understanding the development and evolution of oceanic magma reservoirs. To provide new quantitative geochemical constraints on these processes, we applied a high‐resolution approach to study an interlayered section of the lower oceanic crust sampled at Atlantis Bank, on the (ultra)slow‐sprea...

A report on first direct evidence of Dacite crust from West Sewell Ridge, Andaman Sea https://www.gsi.gov.in/webcenter/portal/OCBIS/pageQuickLinks/pageNews?_adf.ctrl-state=qg79qw5cp_30&_afrLoop=8164890249664493#!%40%40%3F_afrLoop%3D8164890249664493%26_adf.ctrl-state%3Dqg79qw5cp_34

We have studied the microstructure, texture and seismic anisotropy of a foliated blueschist-eclogite rock in the Naga Hills Ophiolite (NHO) complex, North-East India. The rock is composed essentially of omphacite, sodic amphibole (glaucophane), sodic-calcic amphibole (barroisite), phengite, and garnet, and represents oceanic crust that experienced...

Laser ablation MC-ICP-MS was used to measure the Os-isotope compositions of single sulfide grains, including laurite (RuS2) and pentlandite [(Fe,Ni)9S8], from two chromitite bodies and host lherzolites from ophiolites of North Andaman (Indo-Burma-Sumatra subduction zone). The results show isotopic heterogeneity in both laurite (n = 24) and pentland...

A comprehensive whole-rock geochemical study of peridotites and volcanic rocks from the Indo-Myanmar Ranges (IMR) ophiolites deduces the source and extent of mantle melting and role of subduction components in modifying its melt composition. Melt modelling yields partial melting in the range of ~5–25% (with a maximum up to 20%) from a depleted MORB...

Subduction polarity reversal during arc‐continent collision has been proposed as a key mechanism to initiate new subduction zones. Despite often interpreted, well‐exposed geological record that document the reversal is sparse. The ophiolitic lithounits of the Andaman and Nicobar Islands have been proposed to have formed during the initiation of a n...

The Andaman Ophiolite remained little explored for long but recent studies yielded important first-order findings that hold promise for further research. Here we summarise these first-order constraints on the structure, geochemistry, and evolution of the Andaman Ophiolite and identify key frontiers for future research. The uniqueness of Andaman Oph...

Andaman subduction complex is thecentral part of 5000km long Burma-Java subduction complex where Indian plate is subducting obliquely below the Burma(Myanmar) microplate. The Andaman and Nicobar group of Islands represent the positive landform expression of the accretionary prism in outer arc and turbidites of fore arc setting, developed due to con...

809 deep IODP Hole U1473A at Atlantis Bank, SWIR, is 2.2 km from 1,508‐m Hole 735B and 1.4 from 158‐m Hole 1105A. With mapping, it provides the first 3‐D view of the upper levels of a 660‐km² lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer‐s...

Oceanic crust accreted at mid-ocean ridges represents ~70% of Earth's surface; nevertheless magmatic processes implicated in the formation of the lower crust remain poorly understood. Fossilized sections document its complexity in structure and composition, and recent studies show that melt migration and interactions within a crystallizing mush are...

Layered portions of gabbros were described at slow-spreading environments in at least two different Oceanic Core Complexes (OCC), which are interpreted as exhumed portions of lower crust at the ridge axis. Two ODP-IODP Holes drilled into the Atlantis Bank OCC (SW Indian Ridge) present locally such features, which provide essential insights on melts...

Felsic rocks are minor in abundance but occur ubiquitously in International Ocean Discovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolv...

The Moho Transition Zone (MTZ) within the suboceanic lithosphere records an episode of multiple magmatic exchanges between the underlying mantle and the overlying oceanic crust. This study investigated a fossilized MTZ from the Naga Hills Ophiolite (NHO) by characterizing its lithology and describing the petrogenesis of various rock types. Like the...

The Moho Transition Zone (MTZ) within the suboceanic lithospheres, records an episode of multiple magmatic exchange between the underlying mantle and the overlying oceanic crust. This study investigated a fossilized MTZ from the Naga Hills Ophiolite (NHO) by characterizing its lithology and describing the petrogenesis of various rock types associat...

The Andaman Ophiolite, India, is located at the southeastern end of the Tethyan ophiolites. We examine petrology and mineralogy of two lherzolites and a completely serpentinized dunite associated with lherzolite from the middle Andaman Island. Major and trace element compositions of minerals in the lherzolites suggest their residual origin after lo...

We examine ultramafic and olivine-rich troctolite blocks of the East Taiwan Ophiolite (ETO) in the Lichi Mélange. Although ultramafic rocks are extensively serpentinized, the primary minerals, such as olivine, orthopyroxene, clinopyroxene, spinel and plagioclase can be identified. The ultramafic rocks are classified into harzburgite (± clinopyroxen...

The Amami Plateau, Daito Ridge, and Oki-Daito Ridge of the northwestern Philippine Sea Plate are remnants of Mesozoic island arcs. We have newly recovered samples of peridotite and peridotite-derived minerals from the Daito Ridge. The peridotite samples are composed of serpentinized/altered olivines, orthopyroxene porphyroclasts, small clinopyroxen...

The volcanic section of the Manipur Ophiolite (MO), representing the crustal portion of the Neo-Tethyan oceanic lithosphere occurs as basalt, basaltic trachyandesite, and dacite in the Gamnom-Phangrei sector, Manipur, at 25°01′N–25°09′N and 94°24′E–94°27′E. They associate with cherts and ultramafics. The clinopyroxene compositions of basalt and bas...

We have collected, processed and analysed the reflec-tance spectra of representative chromitite samples of spot type, clot type and disseminated type textural variants to understand the diagnostic spectral features of each of these samples. We have found that the reflec-tance spectrum of each textural variant is distinct from the spectra of other v...

ABSTRACT In the present study, Advanced Space borne thermal emission and reflection radiometer (ASTER) data have been processed using ASTER resampled reflectance spectra of mafic cumulates to detect them within anorthosite pavement in the Sittampundi Layered Complex (SLC), Tamilnadu. Spectral map of mafic cumulates has been derived using match filt...

The volcanic section of the Manipur Ophiolite (MO), representing the crustal portion of the Neo-Tethyan oceanic lithosphere occurs as basalt, basaltic trachyandesite, and dacite in the Gamnom-Phangrei sector, Manipur, at 25°01’N-25°09’N and 94°24’E-94°27’E. The clinopyroxene compositions of basalt and basaltic trachyandesite, obtained through elect...

Serpentinization is pervasive in the ultramafic rocks of Manipur ophiolite belt (MOB), Northeastern India. Electron microprobe data of a serpentinite from the Ukhrul-Nungbi sector of MOB shows Ni-rich serpentine mineral (NiO = 33.4-33.9 wt %, SiO 2 = 37.55-38.96 wt %, MgO= 14.83-16.89 wt %). The composition and X-ray diffraction pattern characteriz...

The Naga-Manipur Ophiolite (NMO) belt is a Tethyan-type of ophiolite in the Indo-Myanmar Ranges, Northeastern India, emplaced due to the convergence of the Indian plate with the Myanmar plate [1]. The wide variation in clinopyroxene composition of the mafic volcanics from Manipur area of this belt is evident through Electron Probe Micro Analytical...

Titanium-bearing (hydro)andradites from hydrothermally altered mantle section of the Nagaland ophiolite, India have been investigated for mineral chemical study. In serpentinized peridotite they occur in association with accessory chromites or dusty magnetites and the TiO2 content in them is relatively low (< 0.35 wt%). (Hydro)andradites in magneti...

Mineralogical studies on the mantle and crustal sections of the Manipur Ophiolite Belt (MOB) lead to important findings pertaining to its genesis and controlling tectonic milieu. The wide compositional gap in the Cr# and Mg# content of spinel in the mantle peridotites of MOB implies upper mantle melting in two different tectonic settings. The tecto...

Andaman–Nicobar Ophiolites (ANO) occur as discontinuous bodies along the eastern margin of the Andaman and Nicobar Islands, the exposed parts of the outer-arc ridge of the present Sunda subduction system. The lithospheric architecture starts with mantle rocks overlain by crustal rocks with a thin transition zone in between. The mantle peridotites a...

The natural resources of the Andaman–Nicobar Islands and surrounding seas are discussed. Rocks and minerals found on the Andaman Islands include magnetite, pyrite-chalcopyrite, chromite, gold, nickel, sulphur, coal and limestone, but in most cases their concentrations are sub-economic. Lensoid bodies of algal-biohermal limestones of Palaeogene age...

The onset of the end-Mesozoic continental rift magmatism in the Deccan volcanic province (DVP), India is marked by alkali magmatism. Lithospheric fragments occurring as xenoliths/xenocrysts entrapped in alkaline basalts from the Kutch area of the DVP preserve reaction microtextures giving an insight into the processes linked to their origin. We int...

Plastic deformation in chromite is not frequently reported in literature. We present a detailed microstructural analysis of this mineral from the massive chromitite of the Neoarchaean Sittampundi Complex, southern India. The study reveals intracrystalline plasticity is dominantly active in this mineral, and it produces distinctive features correspo...

International Ocean Discovery Program (IODP) Expedition 360 was the first leg of Phase I of the SloMo (shorthand for "The nature of the lower crust and Moho at slower spreading ridges") Project, a multiphase drilling program that proposes to drill through the outermost of the global seismic velocity discontinuities, the Mohorovičić seismic disconti...

The aim of this paper is to provide a report on the IODP expedition 360 to the Polish geoscientific community. Expedition 360 to the Atlantis Bank along the Southwest Indian Ridge was Leg 1 of the SloMo Project. The primary objective of the SloMo Project is to test competing hypotheses on the nature of the Moho at the slow-spreading oceanic lithosp...

We analyzed reflectance spectra of chromitite samples and its associated rocks using quantitative mineralogical data to identify the diagnostic absorption features of these rocks. Further, we derived few new indices to delineate chromitite and associated ultramafites in satellite image acquired by Advanced Spaceborne Thermal Emission Reflection Rad...

The Oligocene-aged sandstone-shale turbidites of the Andaman Flysch are best exposed along the east coast of the South Andaman Island. Previously undocumented sandstone-shale geochemistry, investigated here, provides important geochemical constraints on turbidite provenance. The average 70.75 wt% SiO2, 14.52 wt% Al2O3, 8.2 wt% Fe\(_{2}\textit {O}_{...

The Barren Island volcano in the Western Sunda Arc has displayed explosive Strombolian eruptions for more than two decades. This recent explosive event, together with the historic and prehistoric volcanic landforms, present reliable information about explosive Strombolian eruptions and the volcanological evolution of the Barren Island volcano. This...

Black sands rich in chromian spinel commonly occur in pockets along the eastern shoreline of Andaman Island where various types of peridotites and volcanics belonging to the Andaman ophiolite suite are exposed in close vicinity. The chemistry of these detrital chromian spinels has been extensively used here in identifying the source rocks vis-à-vis...

We examined the composition and lithological variability from a road section in south-Andaman which represents a pathway to the crustal section of the Cretaceous Andaman ophiolite. Like other well-studied ophiolites worldwide this transition zone is marked by association of olivine-rich troctolite, wehrlite, pyroxenite and gabbroic rocks. The miner...

In this study, Alpine-type (ophiolite hosted) podiform chromitites from the lherzolite dominant mantle sequence of the Andaman ophiolite, India are described. The mantle host rocks for the chromitite pods show features of melt-mantle interaction. The chromites of the podiform chromitites have high-Cr# (= Cr/[Cr + Al] atomic ratio) ranging between 0...

Detailed mapping of a rocks 110 km(2) area of the Rutland Island has demarcated four dismembered thrust slices of Cretaceous ophiolite which are interleaved with Eocene sediments. The ophiolite sequence is represented by tectonite, chromitite pods, transitional peridotite, layered ultramafic-mafic, intrusives of plagiogranite-diorite suite and extr...

The mantle section of the Andaman Ophiolite between Rutland Island in the south and north Andaman in the north has been studied. The restitic peridotite of Rutland Island is comprised of depleted harzburgite to clinopyroxene-bearing harzburgite whereas that in middle and north Andaman is mostly less-depleted, lherzolite-dominated mantle. Chromian s...

Dismembered bodies of Cretaceous ophiolite slices occur in the eastern part of the Andaman Island and continues further south in the Rutland Island. The mantle tectonites of this ophiolite suite are represented by a broad spectrum of variably depleted peridotitic rocks that hosts impersistently developed podiform chromite and records a systematic v...

Detailed microstructural observations on natural chromite samples from the Sittampundi Layered Anorthosite Complex (SLAC), southern India reveal intracrystalline plastic deformation. The SLAC was formed in Neoarchaean and was subjected to eclogite facies metamorphism (>1000 C and >20 kbar), later exhumed in the latest Neoproterozoic-Cambrian. Befor...

Along the east coast of the Andaman Islands, abundant detrital chromian spinels frequently occur in black sands at the confluence of streams meeting the Andaman Sea. The mineral chemistry of these detrital chromian spinels has been used in reconstructing the evolutionary history of the Andaman ophiolite. The chromian spinels show wide variation in...

We describe the textural evolution of chromites from the Neoarchaean Sittampundi anorthosite complex in southern India. A series of micro-structural developments in chromites with increasing temperature is recorded. The intracrystalline deformation started with a high strain rate at elevated temperature. At higher temperature, crystal plastic defor...

A brief petrological account of six basalt flows from northern part of Jhabua district, Madhya Pradesh, central India is presented. The lowest flow with a thick red bole horizon at the bottom resting over the Precambrian Aravalli Supergroup of rocks is a giant plagioclase basalt (GPB) flow. The second flow is distinctly porphyritic containing augit...

Zincian spinels (gahnites) from the Mamandur Zn-Pb-Cu prospect of the Southern Granulite Terrain have been studied. Gahnites in the quartzofeldspathic gneiss occur either as (a) porphyroblastic grains closely in association with cordierite and sphalerite or as (b) inclusions in poikiloblastic quartz grains, restricted within quartz veinlets. Compos...

Compositions of chromium-bearing garnet with little grossular content belong to the uvarovite-andradite solid-solution series. They are extremely rare in nature. Here, we report the occurrence of chromian andradite with up to 50 mol.% uvarovite component from hydrothermally altered podiform chromitite of the Rutland ophiolite, Andaman Island, India...

The Elagiri complex (12°31′ N: 78°35′ E) represents one of the important silica — oversaturated syenite plutons of the Southern Granulite Terrane of the Indian shield. This article for the first time reports the mineral chemistry of the Elagiri complex and brings out important petrogenetic significance. The litho-members of Elagiri complex are intr...

The Barren Volcano located in the volcanic chain of Burma–Java subduction complex became active during 2005–2006 initially as Strombolian and later on as sub-Plinian type ejecting out ash laden grey smoke and coarse pyroclasts. The pyroclasts are represented by vesiculated (20–30 vol.% vesicle) porphyritic basaltic rock where the phenocrysts consti...

The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies: – white massive tuff with ill-defined bedding contacts (facies-A) and – dominantly green tuff exhibiting well-developed turbidite sequence with up-section change from a massive unit to plane laminated units to ripple drift lamination (facies-B). The felsic tuff...

We report here exsolved phase with unusual composition (SiO 2: 14-22 wt%, CaO: 4-10 wt% and Cr 2O 3: 17-21 wt%) from mantle peridotite of the Cretaceous ophiolite of Rutland Island in the Andamans. This high-Si, high-Ca bearing spinel-like phase occurs in two modes as fine blebs (<1-3 μ) within exsolved blebs of diopside and fine lamellae (<1-7 μ)...

Felsic volcaniclastic rock forms part of host rock sequences in many of the base metal prospects in the Betul belt. However, the volcanic facies, fragmenta-tion processes and depositional environments in min-eralized areas are poorly understood because of the effects of synvolcanic hydrothermal alteration and subsequent regional metamorphism. A...

Chromites occurring in different modes have been characterized from ophiolites of Rutland Island, a part of Burma-Andaman-Java subduction complex in the Bay of Bengal. Chromite mainly occurs as massive chromitite pods in mantle ultramafic tectonite and as thin massive chromitite bands together with minor disseminations in crustal ultramafic cumulat...

The chromite bearing ultramafic rocks of Roro-Jojohatu areas in the Singhbhum Craton within the metasediments of the Iron Ore Group (IOG) is a part of Archaean greenstone terrain of Eastern India. In this area since all the primary silicates are altered, chromite has been used for host rock petrogenesis. Chromite occurs in different forms viz. (a)...

Zn-bearing minerals that act as indicator minerals for base metal sulphide mineralization from the Proterozoic Betul Belt, central India with special emphasis on their genetic significance have been discussed. Sulphide mineralisation is hosted by the felsic volcanic rocks and has similarities with volcanic-hosted massive sulphide deposits in other...

The ophiolite assemblage around Mayodia, Dibang Valley, Arunachal Pradesh falls in the eastern extension of the Indus suture belt and is represented by peridotite tectonite, homblendite (dyke) and amphibolite. The entire succession is overlain by metabasalt carapace interlayered with metapelitic pelagic sedimentary rocks. The basal peridotite may b...

The origin of gahnite and its relationship with coexisting porphyroblasts of garnet and staurolite (zinc-bearing) was studied in metamorphosed syn-volcanic hydrothermally altered rocks associated with base metal mineralization from the Proterozoic Koparpani Zn-Pb-Cu sulfide occurrence, Betul Belt, central India. Gahnite and zincian staurolite are t...

Multiple origin of gahnite of different generations and their relationship with other coexisting minerals like garnet, biotite, chlorite and sphalerite were studied in metamorphosed synvolcanic hydrothermally altered rock associated with base metal mineralisation from the Proterozoic Bhuyari prospect, Betul Belt, Central India. The present assembla...

Sulphide mineralisation and syn-volcanic hydrothermal alteration in the Betul Belt is associated with submarine bimodal volcanism. Felsic volcaniclastics form the favourable host rocks in most areas. Alteration zones have been metamorphosed to middle to upper-amphibolite facies giving rise to various metamorphic mineral assemblages. Based on metal...