• SANTANU BHATTACHARJEE

      Articles written in Journal of Earth System Science

    • Geology and tectonic implications of tourmaline bearing leucogranite of Bastipadu, Kurnool, Andhra Pradesh, India

      Kiran Jyoti Mishra Santanu Bhattacharjee Reddy M S Praveen M N Bhimte A D Mahanta N

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      Tourmaline bearing leucogranite occurs as a pluton with pegmatitic veins intruding the Archaean granodiorite in the Bastipadu area, Kurnool district of Andhra Pradesh. We present field and petrographic relations, mineral chemistry and geochemical data for the leucogranite. It is essentially a two-mica granite, composed of quartz, perthite, microcline, albite, tourmaline and muscovite alongwith minor biotite and titanite. The euhedral tourmalines are regularly distributed in the rock. The geochemical studies show that the leucogranite is calc-alkaline, peraluminous to metaluminous which formed in a syn-collisional to volcanic arc-related setting. It displays strong ‘S’ type signatures with high K/Na ratios, moderately fractionated light rare earth elements, relatively flat heavy rare earth elements with $\rm{[Ce/Yb]_{N}} \leq 27.8$ and a strong negative Eu anomaly. The geochemical characteristics indicate that the leucogranite melt might have been generated from partial melting of metasediments. Electron probe microanalyser data show the presence of alkali group tourmaline in leucogranite represented by schorl and dravite. Tourmaline compositions plot in the Li-poor granitoids and associated pegmatites and aplites and metapelites/metasammites fields. Partial melting of boron-enriched source rocks is linked with the development of tourmalines in the leucogranite.

    • Carbonate hosted intermetallic compounds in Paleoproterozoic Salumber Ghatol metallogenic belt, Aravalli Craton, Rajasthan, India

      SURESH CHANDER AUSAF RAZA SANTANU BHATTACHARJEE SANJAY DAS

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      Carbonate hosted intermetallic compound in the Umarvaniyan area is localized within the intensively sheared (mylonitised) dolomite in a NW–SE shear zone ($\sim$15 km), belongs to Salumber Ghatol metallogenic belt, in Debari Group of Aravalli Craton, Rajasthan, India. It is characterized by extensive silicification and ferruginisation with hematite, goethite, magnetite and native gold specks. The intermetallic compound within the dolomite is composed of varying proportion of Cu–Zn–Ni–Os–Fe which has been detected by electron probe microanalysis (EPMA) study. The EMPA (WDS) results of the intermetallic compounds also reveal occurrences of intermetallic compounds of Cu–Zn–Ni–Os–Fe and native Au. The occurrence of these non-separable compounds is probably because these metals were formed at very high temperatures and in reducing condition during the evolving shear with low oxygen and low sulfur fugacity. The fast cooling effect thereafter probably made the geochemical environment least conducive for reaction between Cu/Zn/Ni and sulphur or oxygen.

    • Characterisation of Kalalikhera felsic volcanics, Pur-Banera belt, Rajasthan: Insights from monazite–xenotime geochemistry and chemical ages

      SURESH CHANDHER SANTANU BHATTACHARJEE MANIDEEPA ROY CHOUDHURY NIKHIL AGARWAL

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      Geological and geochemical characteristics of the litho units exposed in and around Kalalikhera area of Pur-Banera belt have confirmed the presence of felsic volcanic rock unit named Kalalikhera felsic volcanic, with characteristic features such as (i) abundance of lapilli composed of polygonal quartz and feldspar and (ii) presence of relict bipyramidal quartz. These volcanics are associated with thin bands of chert. Geochemically, the volcanics are found to be of rhyolitic composition. Development of garnet porphyroblasts along with preferred orientation of the silicate minerals of rhyolite indicates a low to medium grade metamorphism and deformation of the units. Monazite geochemistry of the volcanics indicated towards the metamorphic origin of monazites, with REE pattern show steep fractionation trend from La to Lu. The in-situ chemical age of 2192 $\pm$ 57 Ma recorded from xenotime is interpreted as indicative of the opening of the Aravalli basin with the onset of rifting leading to the formation of Kalalikhera volcanics. The estimated ages of 1784 $\pm$  92, 1351 $\pm$ 45 and 1026  $\pm$  57 Ma from monazite analyses are interpreted as different metamorphic events associated with (i) closure of the basin and the onset of Aravalli orogeny, (ii) further imprints of Delhi orogeny, and (iii) with late Grenvillian age imprints.

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