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Glass and Mineral Chemistry of Northern Central Indian Ridge Basalts:Compositional Diversity and Petrogenetic Significance

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Acta Geologica Sinica(English Edition) 2009年第6期83卷 1122-1135页

作者： Dwijesh RAY Ranadip BANERJEE Sridhar D IYER Basavaraju BASAVALINGU subir mukhopadhyay4 National Centre for Antarctic and Ocean Research National Institute of Oceanography CSIR Department of Studies in Geology University of Mysore Department of Geological Sciences Jadavpur University

The glass and mineral chemistry of basaits examined from the northern central Indian ridge （NCIR） provides an insight into magma genesis around the vicinity of two transform faults： Vityaz （VT） and Vema （VM）. The studied mid-ocean ridge basalts （MORBs） from the outer ridge flank （VT area） and a near-ridge seamount （VM area） reveal that they are moderately phyric plagioclase basalts composed of plagioclase （phenocryst [An60-90] and groundmass [An35-79]）, olivine （Fo81-88）, diopside （Wo45-51, En25-37, Fs14-24）, and titanomagnetite （FeOt -63.75 wt% and TiO2 -22.69 wt%）. The wholerock composition of these basalts has similar Mg# [mole Mg/mole（Mg＋Fe2＋）] （VT basalt： -0.56-0.58; VM basalt： -0.57）, but differ in their total alkali content （VT basalt： -2.65; VM basalt： -3.24）. The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the ∑REE of magma also increased with fractionation, without any change in the （La/ Yb）N value. Glass from the VM seamount shows more fractionated characters （Mg#： 0.56-0.57） compared to the outer ridge flank lava of the VT area （Mg#： 0.63-0.65）. This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure 〉10 kbar, followed by Fe-rich olivine at 〈10 kbar pressure.

关键词： mineral chemistry fractional crystallization petrogenesis northern central Indian ridge

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Lakshanhatti stromatolite, India： Biogenic or abiogenic？

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Journal of Palaeogeography 2016年第3期5卷 292-310页

作者： Adrita Choudhuri subir Sarkar Wladyslaw Altermann Soumik mukhopadhyay Pradip K.Bose Department of Geological Sciences Jadavpur University Kolkata 700032 India Department of Geology University of Pretoria Pretoria 0002 South Africa

Abstract The extraordinary lateral continuity of isopachous stromatotite laminae in the -87 m-thick Mesoproterozoic Lakshanhatti Dolomite （India） evinces chemical precipitation. Fan-shaped crystals grown on tamina surfaces further corroborate this contention; growth of fan-shaped crystats under the overhanging stromatolite column-margin indicates direct carbonate precipitation from ambient waters. The fan-shaped crystats are stacked up, separated onty by thin dark micritic taminae. In a retativety upper stratigraphic in- terval of the formation, tighter laminae characterized by a dotted texture and traversed by numerous winding tubutar voids change graduatty upwards into dark micritic taminae. Some sporadicatty distributed lenticutar intraciastic beds also have the similarly dark micritic coatings. Ctear carbonate cement crusts atso occur between laminae and between successive dark micritic coats around intraciasts. DuU cathodotuminescence （CL） characterizes this cement as weU as the cement lining within earty dia^enetic voids, in contrast, the taminae with dotted textures show dirty orange luminescence, white the dark micritic taminae and the dark micritic grain-coats display dear bright orange luminescence. Pyrite and its pseudomorphs are preferabty concentrated along the dark micritic laminae. Carbon content in these dark micritic components, whether laminae or coats, is much higher than in the lighter components, exceeding what can be accounted for their CaMg（COs）2 composition. A large part of this carbon is kerogen, ptausibly biogenic. The dark components are, therefore, reasonably, though not unequivocally, assumed to be microbial mats. Degradation of the mats might have given rise to the tight laminae with dotted textures. The fuzzy-margin tubes within the tight laminae probabty manifest the escape of gases generated during organic matter decomposition. Si-At-rich terrigenous fines thinty draping the dark carbonaceous taminae was possibty the resutt of baft

关键词： StromatoHte Lamina continuity Mesoproterozoic Lakshanhatti Dolomite Member Inorganicprecipitation Kerogen enrichment Filamentous microbiota

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A New Report of Serpentinites from Northern Central Indian Ridge(at 6°S)—An Implication for Hydrothermal Activity

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Acta Geologica Sinica(English Edition) 2008年第6期82卷 1213-1222页

作者： Dwijesh RAY Ranadip BANERJEE Sridhar D.IYER subir mukhopadhyay Geological Oceanography Division National Institute of OceanographyGoa 403004India Department of Geological Sciences Jadavpur UniversityKolkata 700 032India

Serpentinites from the inside corner high （6°38.5′S/68°19.34′E） from the Northern Central Indian Ridge （NCIR） are comprised mainly of high Mg-rich lizardite and chrysotile pseudomorphs with varying morphologies. ＇Mesh rim＇, ＇window＇, ＇hourglass＇ and ＇bastite＇ are the most common textures displayed by both chrysotile and lizardite. Numerous chrysotile veins in association with cross cutting magnetite veins indicate an advanced stage of serpentinisation. The relatively high abundance of chrysotile and lizardite suggest their close association and formation at a temperature below 250℃. Abundant ＇mesh rim＇ and ＇bastite＇ texture and variegated matrix reveal that the present serpentinites might have formed due to the interaction of harzburgite and seawater. Positive Eu anomaly （Eu/Eu^＊ up to ＋3.38）, higher La/Sm （up to 4.40） and Nb/La （up to 6.34） ratios suggest substantial hydrothermal influence during the formation of the serpentinites.

关键词： serpentinite serpentinisation hydrothermal alteration

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Mineralogical and geochemical variation in hydrothermal sulfides from Vienna Woods field,Manus Basin,Papua New Guinea：constraints on their evolution

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Acta Oceanologica Sinica 2018年第4期37卷 22-33页

作者： RAY Durbar BANERJEE Ranadip MAZUMDER Aninda PAROPKARI Anil L. mukhopadhyay subir BALAKRISHNAN Srinivasan CSIR-National Institute of Oceanography Dona Paula Goa 403004 India Department of Geological Sciences Jadavpur University Kolkata 700032 India Department of Earth Sciences Pondicherry University Puducherry 605014 India

Polymetallic sulfides from two hydrothermal chimneys and talus deposit from the Vienna Woods field of Manus Basin were studied for mineralogy,elemental composition,and S-isotope ratio to understand their *** factors including the nature of source fluid,mineral paragenesis,and related geochemical processes have been *** and elemental concentration of Cu and Fe-rich large chimney at the central part of this hydrothermal field was completely different from the smaller Zn-rich peripheral chimney and Fe-rich talus deposit,suggesting the variable degree of alterations generate physico-chemically different source fluids responsible for these hydrothermal ***,S-isotope ratios also indicate chemically diverse fluids and different modes of precipitation were involved in their *** mineral zonings and associated elemental and isotopic compositions within individual deposit confirm paragenetic shifts were involved during their growth process.

关键词： Manus Basin hydrothermal chimney talus geochemistry mineralogy

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Petrographic Characteristics of Manganese Bearing Rocks of Banswara Manganese Ores Belt, District Banswara, Rajasthan (India)

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Open Journal of Geology 2017年第7期7卷 1047-1062页

作者： Mohd Shaif F. N. Siddiquie subir mukhopadhyay Department of Geology Aligarh Muslim University (AMU) Aligarh India Department of Geological Sciences Jadavpur University Kolkata India

In this paper, we described the petrographical characters of the Mn-bearing rock types outcropping in the Kalakhuta, Ghatia, Gararia, Itala, Wagaicha, Tambesara and Talwara villages of Banswara district. The Mn associated rocks in the study area are phyllite, schist, quartzite and limestone. The mineral assemblage in phyllite formed under greenschist facies metamorphism. Petrographic studies of various phyllite samples also reveal that porphyroblasts of biotite sat in the fine-grained micaceous matrix (Biotite, muscovite, chlorite) along with quartz, opaque and ore minerals. Petrographic studies of schist reveal its formation under prograde metamorphism. Mineral assemblages observed in schist are typical of greenschist to lower amphibolite facies. The various schist samples at places show clusters made up of perfect rhombshaped garnets which suggest the increase in the grade of metamorphism. The quartzites are disposed conformably with the phyllites, and are at times brecciated and re-cemented by secondary chert and manganese. These Mn-bearing quartzites are with sutured/serrated and straight grain boundaries. The quartzite samples are fully composed of quartz showing undulose extinction with subordinate feldspar, micas and carbonatic materials. The petrographic characteristics explain that mostly limestones are the dolomitic composition but some ferruginous varieties are also noticed at places. The purer variety of limestone consists of calcite, dolomite and some magnetite but tremolite, quartz and some minute flakes of biotite also occur in impure variety.

关键词： Petrographical Characters Banswara Manganese Ores Belt Lunavada Aravalli Garnet Modal Analysis

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