• Naresh Chandra Pant

      Articles written in Journal of Earth System Science

    • Insights into the P–T evolution path of TsoMorari eclogites of the north-western Himalayas: Constraints on the geodynamic evolution of the region

      Preeti Singh Ashima Saikia Naresh Chandra Pant Pramod Kumar Verma

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      The present study is on the Ultra High Pressure Metamorphic rocks of the Tso Morari Crystalline Complex of the northwestern Himalayas. Five different mineral associations representative of five stages of P–T (pressure–temperature) evolution of these rocks have been established based on metamorphic textures and mineral chemistry. The pre-UHP metamorphic association 1 of Na-Ca-amphibole + epidote ± paragonite ± rutile ± magnetite with T–P of ∼500° C and 10 kbar. This is followed by UHP metamorphic regime marked by association 2 and association 3. Association 2 (Fe< Mg< Ca-garnet + omphacite + coesite + phengite + rutile ± ilmenite) marks the peak metamorphic conditions of atleast 33 kbar and ∼750° C. Association 3 (Fe< Mg< Ca-garnet + Na-Ca amphibole + phengite ± paragonite ± calcite ± ilmenite ± titanite) yields a P–T condition of ∼28 kbar and 700°C. The post-UHP metamorphic regime is defined by associations 4 and 5. Association 4 (Fe< Ca< Mg-garnet + Ca-amphibole + plagioclase (An05) + biotite + epidote ± phengite yields a P–T estimate of ∼14 kbar and 800°C) and association 5 (Chlorite + plagioclase (An0.5) + quartz + phengite + Ca- amphibole ± epidote ± biotite ± rutile ± titanite ± ilmenite) yields a P–T value of ∼7 kbar and 350°C.

    • Chemical dating of monazite: Testing of analytical protocol for U–Th–total Pb using CAMECA SXFive tactis EPMA at the National Centre for Earth Science Studies, Thiruvananthapuram, India


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      Major and trace element analyses of monazite by electron probe microanalyzer (EPMA) are routinely carried out for several decades. U–Th–total Pb method of monazite dating is currently considered as a reliable and acceptable tool to decipher the time of geological events. The purpose of the present study isto establish the quantification conditions of monazite chronology using SXFive tactis EPMA, recently installed at the National Centre for Earth Science Studies, Thiruvananthapuram, India. Consistency in the chemical-chronological data of the monazites starting from the chronologically well-constrained Maocyr monazite data followed by the analysis of monazite from the garnet-cordierite gneiss of the Kerala Khondalite Belt confirms the reliability of the NCESS-EPMA facility for the U–Th–total Pb chemical age dating of monazite. By applying the same analytical setup of chemical dating, the monazites from metapelites of Madurai Block of Southern Granulite Terrain, India yield two peak ages in probability density diagram of ca. 505 Ma and ca. 590 Ma (23 spots) which is similar to the ${}^{206}$Pb/${}^{238}$U age (ca. 506 Ma and ca. 585 Ma; 34 spots) obtained by LA-ICPMS.

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