Petrology and geochemistry of metapelites and basic granulites from Sonapahar region of Shillong Meghalaya gneissic complex, North East India

Dwivedi, Shridhar; Theunuo, Kevilhoutuo

doi:10.1007/s12594-013-0100-0

Cited by 9 publications

(5 citation statements)

References 33 publications

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“…There is a general decrease from LREE to HREE in the pelitic gneiss (unmigmatized), but since LREE are incompatible elements ( Henderson, 1984 ), they are likely to be partitioned more into the liquid melt than the coexisting restite; hence the enrichment of LREE to HREE in partially melted pelitic gneiss. The extreme enrichment of LREE could be due to metamorphic differentiation and the retention of REE accessory minerals such as monazite ( Christidis, 1998 ; Dwivedi and Theunuo, 2013 ). During partial melting, there is retention of plagioclase in the restite and thus depletion in the melt which gives rise to negative Eu anomaly of the melt.…”

Section: Discussionmentioning

confidence: 99%

Geochemistry and mineral chemistry of pelitic gneiss of Ikare area, southwestern Nigeria

Oziegbe

Ocan

Costin

et al. 2021

Heliyon

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This study conducts Electron Probe Microanalysis (EPMA), X-ray Fluorescence (XRF) and Laser Ablation Inductively Coupled Plasma Spectrometry (LA-ICP-MS) analysis on the pelitic gneiss of the Basement complex of Nigeria. Phase equilibrium modeling was undertaken in the MnO-NaGarnet has inclusions of sillimanite, biotite, and quartz. There is a very close association between biotite and sillimanite. Fibrolitic and prismatic sillimanite are both present. Fibrolitic sillimanite surrounding biotite could have possibly formed through melt-residue back reactions involving crystallization of melt. Garnet has almandine higher than 60 % and pyrope less than 33 %. Plagioclase feldspar has anorthite content between 29 and 39 %, comprising of both oligoclase and andesine. Microtextures such as cordierite corona round garnet, symplectite and kinked biotite were observed. The textural association indicates that cordierite was formed at the expense of garnet and sillimanite; garnet þ sillimanite þ plagioclase ¼> cordierite þ melt/fluid. Metamorphic peak conditions of 770-840 C and 5.5-7 kbar were obtained for the mineral assemblage garnet-biotite-sillimanite-K-feldspar-quartz indicating medium-pressure granulite facies metamorphism.

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Section: Discussionmentioning

confidence: 99%

Geochemistry and mineral chemistry of pelitic gneiss of Ikare area, southwestern Nigeria

Oziegbe

Ocan

Costin

et al. 2021

Heliyon

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“…The Proterozoic metasedimentary rocks and the basement gneisses are composed of amphibolite-to granulite-facies rocks derived from Neoarchaean-Palaeoproterozoic gneissic rocks (Chatterjee, 2017 and references therein). The Sonapahar area is composed of granulite-facies metapelites and quartzofeldspathic gneisses, including sillimanite-bearing gneisses, basic granulites, amphibolites and granite gneisses (Lal et al 1978;Nandy, 2001;Dwivedi & Theunuo, 2013, 2017. However, the Sonapahar area has a significant occurrence of metapelitic granulites and has experienced multiple phases of deformation (Chatterjee et al 2007;Chatterjee, 2017).…”

Section: Geological Settingmentioning

confidence: 99%

“…Ghosh & Saha (1954) and Lal et al (1978) reported sapphirine-bearing granulites from Sonapahar. The exposure of the basement rocks in the SMGC is limited; thus, granulite-facies rocks are reported only from some parts of the plateau, namely, the Sonapahar area (Lal et al 1978;Chatterjee et al 2007;Dwivedi, 2011;Dwivedi & Theunuo, 2013, 2017, Goalpara Hills (Chatterjee et al 2007(Chatterjee et al , 2011 and Patharkhang (Dwivedi & Theunuo, 2011).…”

Section: Introductionmentioning

confidence: 99%

Characterization and metamorphic evolution of Mesoproterozoic granulites from Sonapahar (Meghalaya), NE India, using EPMA monazite dating

2020

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This paper presents three different age domains, obtained by electron microprobe monazite dating, for granulitic gneisses collected from the Shillong-Meghalaya Gneissic Complex in Sonapahar, NE India, which contain radioactive materials, e.g. thorium (3.32–7.20 wt %), uranium (0.133–1.172 wt %) and lead (0.101–0.513 wt %). The microprobe analyses of monazite grains in the rock samples show that the monazites have three different ages ranging from Mesoproterozoic to Neoproterozoic. The oldest age (1571 ± 22 Ma) represents a peak metamorphic event, the youngest dominant age indicates the Pan-African tectonic event (478 ± 7 Ma) and the intermediate age marks the Grenvillian orogeny (1034 ± 91 Ma) or may be a mixing artefact; these ages are located at the cores, rims and intermediate parts of the monazite grains, respectively. The equilibrium mineral phases calculated for the granulitic gneisses from Sonapahar lie in a P–T range from 5.9 kbar/754 °C to 8.3 kbar/829 °C in the NCKFMASH system. Plotting the P–T conditions of the granulitic gneisses reveals a clockwise P–T path. Two major metamorphic events are observed in Sonapahar. The M1 metamorphic stage is represented by peak mineral assemblages of prograde garnet-forming reactions (8.2 kbar/∼713 °C) during Mesoproterozoic time (1571 ± 22 Ma). The M2 metamorphic stage featured decompression (3.9 kbar/∼701 °C) in which garnet–sillimanite broke down to form cordierite along an isothermal decompression path during the Pan-African tectonic event (478 ± 7 Ma).

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“…Major oxides of the Mg-Al granulites display the following compositional variation of enriched Na 2 O (0.84-0.87 weight percentage) and P 2 O 5 (0.33-0.36 weight percentage) which is totally different from the major oxide and trace element data pattern of the metapelites and basic granulites of the study area (Dwivedi and Theunuo 2013). The Mg-Al granulites are rich in compatible elements Cr (279-359 ppm), Ni (140-141 ppm), Sc (57-60 ppm), V (237-261 ppm) like basic granulites and low in incompatible elements, U (1.39-1.4 ppm), Th (bdl) and Nb (14.7-15.9 ppm) and abnormally high in Zn content (1119-1148 ppm).…”

Section: Geochemistrymentioning

confidence: 73%

Occurrence of wagnerite in Mg–Al granulites of Sonapahar, Meghalaya

Dwivedi

Theunuo

2017

J Earth Syst Sci

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We report for the first time the occurrence of rare phosphate wagnerite as a stable phase from the Mg-Al granulites of Sonapahar. The wagnerite bearing assemblages consist of the spinel, phlogopite, brucite and corundum. The wagnerite appears in the Mg-Al granulites due to the breakdown of spinel and fluorapatite. The mineral chemistry of the phases has been discussed from the EPMA data, which reveals that the fluorine content of the wagnerite is relatively low due to the exchange of F to coexisting phases. The major oxide analysis of the rocks show the low content of Ca, which is the requisite for the occurrences of wagnerite.

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Petrology and geochemistry of metapelites and basic granulites from Sonapahar region of Shillong Meghalaya gneissic complex, North East India

Cited by 9 publications

References 33 publications

Geochemistry and mineral chemistry of pelitic gneiss of Ikare area, southwestern Nigeria

Geochemistry and mineral chemistry of pelitic gneiss of Ikare area, southwestern Nigeria

Characterization and metamorphic evolution of Mesoproterozoic granulites from Sonapahar (Meghalaya), NE India, using EPMA monazite dating

Occurrence of wagnerite in Mg–Al granulites of Sonapahar, Meghalaya

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