• S B DWIVEDI

      Articles written in Journal of Earth System Science

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

      S B Dwivedi K Theunuo

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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 break-down 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.

    • A new occurrence of two-pyroxene granulites at Chicholi from Betul supracrustal belt in Central Indian Tectonic Zone (CITZ), MP, India

      MANISH SRIVASTAVA S B DWIVEDI S P SINGH

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      We report the new occurrence of two-pyroxene granulites from Chicholi, the Betul Group of the Central Indian Tectonic Zone (CITZ). The common mineral assemblage observed within different thin sections is orthopyroxene–clinopyroxene–hornblende–plagioclase–biotite–quartz. The textural relationship of these mineral phases shows the reaction: hornblende + quartz = orthopyroxene + clinopyroxene + plagioclase. The estimated $P–T$ condition of metamorphism of the two-pyroxene granulites is $901 \pm 30^{\circ}\rm{C}$ and $8.68 \pm 1.4$ kbar.

    • EPMA monazite geochronology of the granulites from Daltonganj, eastern India and its correlation with the Rodinia supercontinent

      RAVI RANJAN KUMAR S B DWIVEDI

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      We report the monazite dates of the granulites from Daltonganj (Palamau), Chhotanagpur granite–gneiss complex (CGGC) which covers the significant part of the granulite blocks in central India by using an electron micro probe analyser dating. The monazite grain varies between 70 and 80 $\mu\rm{m}$ and shows the distribution of U, Th and Pb in all monazite grains of both samples. Two different dates were obtained from different monazite grains; the first age suggests that the granulite from CGGC preserves the first remnant of the protolith of the Mesoproterozoic era at $\sim 1424$ Ma and second one at $\sim 972$ Ma which provides evidence of metamorphism of the protolith. The CGGC rocks preserve four regional metamorphic events, namely $\rm{M_{1}, M_{2}, M_{3}}$ and $\rm{M_{4}}$. But in this work, two different ages from the Daltonganj granulites were obtained which are similar to the $\rm{M_{2}}$ (<1500 Ma, i.e., the age of protolith of the granulitic gneiss) and $\rm{M_{3}}$ (1200–930 Ma) metamorphic events as reported in the CGGC. The $\rm{M_{3}}$ metamorphism attained its average $P–T$ condition at $\sim 7.35\,\rm{kbar/792^{\circ}C}$, and it represents the prograde metamorphic event. The $\rm{M_{3}}$ metamorphic event supported the Grenville-orogeny, and it was responsible for the metamorphism of the magmatic protolith of granulitic gneiss from the CGGC at the time of amalgamation of the Rodinia supercontinent. The Rodinia assembly had occurred through the global Grenville-orogenic events between 1100 and 900 Ma, with continental blocks which exist at that time.

    • Analysis of the groundwater scenario with respect to the crop water productivity for the Betwa–Dhasan river basin, Bundelkhand using remote sensing techniques

      RAJARSHI BHATTACHARJEE ABHINANDAN CHOUBEY NILENDU DAS ANURAG OHRI S B DWIVEDI SHISHIR GAUR

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      Excessive water use in the agricultural sector in the Betwa–Dhasan basin of the Bundelkhand region is becoming the cause of irrepressible drawdown in the groundwater level. These changing dynamics are becoming the cause of water scarcity in the basin and increasing difficulty in fulfilling the water demand ofthe area. For incorporating the water-saving agricultural practices in the region, it is essential to have a precise estimation of the crop water productivity (CWP) and evapotranspiration (ET) at the basin scale. In this analysis, the Kharif and Rabi seasons of 2004–2005, 2009–2010, and 2013–2014 have been included.The ET and CWP have been calculated for all the seasons. The MODIS satellite imageries have been used for calculating the ET using the surface energy balance algorithm for land (SEBAL) algorithm. The highest CWP has been recorded as 2.56 kg/m$^3$ for the Rabi season 2014. With the increase in the demand for water for irrigation and agricultural purposes, the groundwater gets depleted. The decadal groundwater Cuctuation map of the Rabi season (2005–2014) shows that groundwater gets depleted by more than 30 m within this period in some of the river basin regions situated in the Jhansi and Tikamgarh districts.

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