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 %, SiO2 = 37.55-38.96 wt %, MgO = 14.83-16.89 wt %). The composition and X-ray diffraction pattern characterize this Ni-rich serpentine mineral as nepouite which is suggested to be a hydrothermal alteration product of NiO-rich olivine in a fore-arc peridotite. The genesis of this NiO-rich olivine is attributed to the melt-rock interaction in a supra-subduction zone setting.

JYOTISANKAR RAY

Geology

BISWAJIT GHOSH

THUNGYANI N OVUNG

DEBABRATA MANDAL

PALLAB DASGUPTA

MADHUPARNA PAUL

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of the Geological Society of India

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 basaltic trachyandesite, obtained through electron microprobe analyzer, were used as a petrogenetic indicator to identify the parent magma-types and their tectonic settings. Based on the variable content of major oxides, they are classified as high- and low-Ti clinopyroxenes. High Ti and Al contents with relatively lower silica saturation are observed in the former group and vice versa in the latter. The TiDCpx/rock values in low- and high-Ti clinopyroxene are comparable with island-arc basaltic andesite and MORB, respectively, which confirms that the clinopyroxene composition is primarily related to the host magma-type and its tectonic setting. Clinopyroxene thermometry (ranging 1150–605 °C) suggests progressive differentiation of the parent magmas. Several bivariate and tectonic discrimination diagrams depict MORB (non-orogenic setting) and island-arc boninitic magma affinities (orogenic setting) for the high- and low-Ti clinopyroxenes, respectively. The coexistence of both MORB and island-arc boninitic magma-types in the volcanic section of Manipur Ophiolite as characterized by their varying Ti, Al, and Si contents may indicate either juxtaposition of rocks formed in diverse tectonic settings (i.e., due to transformation of tectonic setting from mid-ocean ridge to supra-subduction zone) or, a change in magma composition in a subduction zone setting. However, field relationships coupled with the mineral–chemical signatures implies a supra-subduction zone setting for the evolution of the crustal section of MO. © 2017, Springer-Verlag GmbH Germany.

International Journal of Earth Sciences

Clinopyroxene composition of volcanics from the Manipur Ophiolite, Northeastern India: implications to geodynamic setting

The mantle peridotites of the Naga-Manipur ophiolite belt, India host concordant podiform chromitite bodies that preserve various magmatic and deformation structures. Magmatic structures preserve evidence of a gradual transition from nodular to massive varieties. Nodular types are least affected by deformation. Deformation structures, restricted mainly in massive types include intracrystalline features of brittle as well as crystal plastic processes within chromite. Brittle deformation is preserved as grain fracturing and intense microbrecciation along narrow zones forming protocataclasite. Crystal plastic deformation has generated chromite subgrains and new grains in response to recovery and recrystallization processes. Subgrains are polygonal in shape and the boundaries between them are commonly straight forming a mosaic with most meeting at triple junctions. Subgrains are commonly internally zoned and the mosaics formed by them correlate well with the compositional maps. Subgrains show high Al at their cores and high Fe at their boundaries in response to differential, diffusive chemical re-equilibration. We discuss how this compositional resetting related to deformation is significant in various geologic studies related to tectonic setting and thermobarometric evolution of an area. Deformation mechanisms are likely to have started with crystal plastic processes and later switched over to the brittle regime. The preservation of all grain-scale deformation structures in the chromitite bodies of the Naga-Manipur ophiolite belt is suggestive of mantle dynamics, vertical accretion and horizontal movement in particular. © 2013 Elsevier B.V.

Ore Geology Reviews

Grain-scale plastic deformation of chromite from podiform chromitite of the naga-manipur ophiolite belt, india: Implication to mantle dynamics

Mineralogy and Petrology

Petrogenesis of chromites from the Manipur ophiolite belt, NE India: evidence for a supra-subduction zone setting prior to Indo-Myanmar collision

South East Asia Research

Thinking about Transitional Justice in Myanmar

Garnierites and garnierites: Textures, mineralogy and geochemistry of garnierites in the Falcondo Ni-laterite deposit, Dominican Republic

A Petrographic Atlas of Ophiolite

Ophiolite Around the Indian Plate Margin

Occurrence of Nepouite in the Serpentinite of the Manipur Ophiolite Belt, Northeastern India: Implication for Melt-rock Interaction in a Supra-subduction Zone

Journal	Data powered by TypesetJournal of the Geological Society of India
Publisher	Data powered by TypesetSPRINGER INDIA
ISSN	0016-7622
Open Access	No