Chrome-spinels of anorthosite-hosted chromitite bodies from Sittampundi layered igneous complex, southern India, metamorphosed under eclogite-facies condition have been studied. Besides anorthosites as the dominant rock type discontinuous layers of peridotite, pyroxenite and lenses of gabbroic granulite/eclogite occur at the bottom of the complex. Chromite grains are deformed exhibiting features of intracrystalline deformation and exsolved needle shaped rutile inclusions. Chrome-spinels are of refractory grade with Cr2O3 and Al2O3 contents varying between 34-40wt.% and 23-28wt.% respectively. In the bivariate Cr# (=Cr/[Cr+Al]) vs. Mg# (=Mg/[Mg+Fe2+]) diagram, Sittampundi chromitites show close affinity with the Archean Fiskenaesset type deposit. The calculated Al2O3 values for the parental melt of Sittampundi chromitites are consistent with the Al2O3 content of mid-ocean ridge basalts whereas the values for FeO/MgO ratio are higher. It is suggested that an initial basic magma, similar to that of mafic granulite composition evolved in the magma chamber through fractionation of peridotite and pyroxenite to Fe,Al-rich basaltic melt, parental to the chromitite bands. © 2011 Elsevier Ltd.

BISWAJIT GHOSH

Geology

R KONAR

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 Asian Earth Sciences

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 Radiometer (ASTER) sensor. The spectral indices were derived based on the ASTER sensor convolved laboratory derived reflectance spectra of these rocks. Analysis of ASTER convolved laboratory spectra of these rocks revealed that chromitite had higher reflectance in band 2 of ASTER data in comparison to band 1 and band 3. Mineralogical analysis of chromitite spectra was used as reference to understand the mineralogical importance of this signature. On the other hand, reflectance of metaultramafite was relatively higher in band 3 in comparison to band 1 of ASTER sensor. Based on above spectral contrast, two new indices termed as ASTER based Chromitite Index ((band 2∗band 2)/(band 1 + band 3)) for chromitite and ASTER based Ultramafic Index ((band 1/band 3)) for meta-ultramafite were proposed. We utilized these indices with other popular ASTER indices for gneiss ((band 5 + band 7)/band 6)) and metabasalt (band 6/band 8) and serpentine rich rock s ((band 7 + band 9)/band 8) to spatially delineate chromitite - ultramafic-mafic rock assemblage of the study area. In this regard, few index derived false color composite (I-FCC) were derived. Results of index based delineation were validated with reference geological map and field data on locations of rock exposures. We also validated two new indices (ACI, AUI) based on spectral parameters in addition to geological validation of these indices and its FCC images. Further, we also made eigenvector based analysis of principal components (PC) derived from aforementioned indices to identify fewer PC's than the number of indices used to spatially map the rocks of the study area. We found PC-2 was suitable for delineating meta-ultramafite from chromitite; PC-4 was suitable for delineating metabasalt and PC-5 for gneiss. © 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

Advances in Space Research

Implementation of reflection spectroscopy based new ASTER indices and principal components to delineate chromitite and associated ultramafic-mafic complex in parts of Dharwar Craton, India

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

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 deciphering the source characteristics. The composition of the chromian spinels (Cr#: 0.20–0.88, Mg#: 0.26–0.77, Al2O3: 5.04–48.21 wt.%, TiO2: up to 1.39 wt.% and Fe2+/Fe3+: 1.73–9.12) varies widely signifying multiple sources, of which mantle peridotites and volcanic rocks are relevant in an ophiolitic terrain. The volcanic chromian spinels are relatively fresh, commonly euhedral, sometimes with compositional variations, and contain inclusions in contrast to the mantle peridotitic chromian spinels which are rounded, extensively fractured, and altered. We used a number of geochemical bivariate plots in order to know the provenance protoliths. The volcanic chromian spinels show geochemical characters of MORB, related to spreading centers (either MOR or back-arc) and also boninites/arc-tholeiites, related to active subduction. On the other hand, the peridotitic spinels indicate partially depleted lherzolite and depleted harzburgite source of the ophiolite suite. © Indian Academy of Sciences.

Fulltext

Journal of Earth System Science

Chromian spinel-rich black sands from eastern shoreline of Andaman Island, India: Implication for source characteristics

In this article, we have processed Landsat-8 spectral bands, ground gravity, and magnetic data for delineating the mafic cumulates within the anorthositic-layered complex in Sittampundi, Tamilnadu, India. In this regard, surface anomaly map of mafic cumulates was derived by processing spectral bands of Operational Land Imager (OLI) sensor using matched filtering method. Residual gravity, magnetic anomaly maps are also derived. Spatial position of geophysical anomalies corroborate well with the spectral anomalies. A promising zone of chromitite occurrences is identified at the eastern fringe of the study area based on the concurrence of spectral and geophysical anomalies. Spatial profiles of geophysical and spectral anomalies around this promising zone are similar to the respective spatial profiles observed around the known chromite bearing mafic cumulates. Depth continuity of the mafic cumulates is confirmed by deriving of gravity and magnetic anomaly map at different depth using upward continuation filters to confirm concealed deposit. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

Geocarto International

Conjugate utilization of Landsat-8 OLI, ground gravity and magnetic data for targeting mafic cumulates within anorthositic-layered complex of Sittampundi, India

Chemical Science Transactions

Geogenic Assessment of Water Quality Index for the Groundwater in Tiruchengode Taluk, Namakkal District, Tamilnadu, India

Gondwana Research

A Neoarchean dismembered ophiolite complex from southern India: Geochemical and geochronological constraints on its suprasubduction origin

An overview of the geochemistry of Eoarchean to Mesoarchean ultramafic to mafic volcanic rocks, SW Greenland: Implications for mantle depletion and petrogenetic processes at subduction zones in the early Earth

Late Triassic subduction-related ultramafic–mafic magmatism in the Amasya region (eastern Pontides, N. Turkey): Implications for the ophiolite conundrum in Eastern Mediterranean

The Chimalpahad anorthosite Complex and associated basaltic amphibolites, Nellore Schist Belt, India: Magma chamber and roof of a Proterozoic island arc

Journal	Data powered by TypesetJournal of Asian Earth Sciences
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ISSN	1367-9120
Open Access	No