http://20.198.91.3:8080/jspui/handle/123456789/137 2026-04-05T22:12:30Z 2026-04-05T22:12:30Z Mandal, Sumana http://20.198.91.3:8080/jspui/handle/123456789/8551 2025-09-12T08:04:11Z 2019-01-01T00:00:00Z

Title: Petrography and stable isotope geochemistry of graphite bearing coarse grained calcitic marble: a case study from parts of eastern ghats province Authors: Mandal, Sumana Abstract: The calcitic marble rock in Araku vally of Eastern Ghats province is poly-metamorphosed and poly-deformed associated with metapelites have suffered granulite facies metamorphism. The stable assemblage of forsterite + spinel + calcite represent peak metamorphic condition. Graphite are present mainly on white coloured band of cakcitic marble rock. Graphite is present at the boundary of calcite, apatite, biotite and along the fracture of olivine and spinel. Textural study indictes formation of graphite after the formation of calcite and silicates. Graphite grains show deformational structure. Carbon isotope thermometry has been applied to coexisting calcite and graphite in calcitic marble rock. Δ13C (Cc-Gr) is useful to estimate the temperature of formation of graphite from mathematical formula. Obtained temperature from the formula ranges between 855⁰C to 952⁰C. Carbon isotope ratio of a fluid deposited graphite is an important tool for identify the source of carbon (organic matter, mantle, or carbonates). δ13C value for our sample ranges betwenn(-0.7—1.2) which indicate an inorganic carbon source. δ13C and δ18O value of calcite is also an important tool to indicate the source of carbon. Precipitation on graphite can occure from a CO2 bearing fluid form due to decarbonation reaction at the prodrade path. From this fluid graphite can be precipited by cooling in retrograde path under low fO2 condition.

2019-01-01T00:00:00Z Majumder, Prakrity http://20.198.91.3:8080/jspui/handle/123456789/8550 2025-09-12T07:45:23Z 2019-01-01T00:00:00Z

Title: Petrology of coarse calcitic marble from parts of eastern ghats province, India Authors: Majumder, Prakrity Abstract: The coarse grained calcitic marble rocks from part of Eastern Ghats Province have been studied to decipher the petrological evolution. The white coloured calcitic marble consists of grey coloured band(s). The white coloured part (association (a)) is rich in carbonate phases containing abundant coarse calcite crystals and minor dolomite with biotite, olivine, spinel, amphibole, apatite, graphite and iron sulphide. The grey coloured band (association (b)) has modally higher abundance of silicate phases over carbonates. Association (b) contains calcite, biotite, clinopyroxene, plagioclase and apatite (± graphite). Overall granoblastic texture and crystal plastic deformation reveal that the rocks are deformed and metamorphosed. Calcite contains minor amount of Mg, which decreases from core to rim (Xmg = 0.002–0.06). Silicate phases are compositionally close to the Mg end member. Reaction textures and modelling in C-space suggest that Mg-bearing calcite + biotite ± silica developed the peak metamorphic assemblages of (i) forsterite, calcite, spinel and (ii) diopside, anorthite (+ calcite) respectively for association (a) and (b). Dolomite exsolution in Mg-bearing calcite and formation of secondary amphibole, biotite and serpentine after olive and pyroxene document the retrograde history of metamorphism. Solvus thermometry using reintegrated composition of exsolved dolomite and host calcite records peak metamorphic temperature above 850°C. However, matrix calcite composition estimates down temperature of ~500OC, which suggests a retrograde cooling event. Peak pressure could not be estimated due to absence of any suitable geobarometry. Therefore, this study shows that the coarse grained marble rock suffered deformation – metamorphism in granulite facies condition above 850°C followed by a cooling event with drop in temperature of at least 350OC.

2019-01-01T00:00:00Z Bhattacharjee, Sandipan http://20.198.91.3:8080/jspui/handle/123456789/8549 2025-09-12T07:37:57Z 2019-01-01T00:00:00Z

Title: Petrographic evolution of metagabbro from south Delhi fold belt Authors: Bhattacharjee, Sandipan Abstract: In north-western Indian shield South Delhi Fold Belt (SDFB) is a northeast southwest trending, multiply folded and poly-metamorphosed rock of Proterozoic age. The western margin of the SDFB is demarcated by Phulad Shear Zone (PSZ) of mid-Proterozoic age (~810 Ma). The PSZ is characterized by north-easterly striking ductile shear zone with a well-developed mylonitic foliation and a down-dip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with top-to-the-west reverse sense of movement. The present study deals with petrological evolution of a meta-gabbro that occur parallel to this shear zone. The meta-gabbros are coarsed grained and are variably deformed. The gabbro shows strong development of dominant foliation with attitude 38/87˚E and prominent down dip lineation. Systematic study of mesoscopic structures of the meta-gabbro and the shear zone rocks demonstrate a similarity in geometry and style. This indicates that the deformation in the meta-gabbro and the shear zone is broadly synchronous. The meta-gabbro contains clinopyroxene, plagioclase, ± orthopyroxene, amphibole with ilmenite, sphene in minor amounts. In the least altered meta-gabbro, the rock preserves prominent evidence of igneous texture. In the altered variety, the clinopyroxene grains are rimmed by amphibole grains with relict of clinopyroxene at the center. In more deformed variety the amphibole grains are completely replaced the clinopyroxene grains. Electron microprobe analysis data show the amphibole composition varies from actinolite to hornblende and edenite. Textural relation suggests actinolite formed earlier and hornblende and edenite formed later. Mylonitic gabbro comprised of amphibole minerals which exhibit well defined foliation appearance along with dynamically recrystallised plagioclase grains. Textural relations show formation of coronal sphene over ilmenite grains. Integrating the mesoscopic and textural relation it is suggested that all the metamorphic reactions are fluid driven reactions that further facilitate the exhumation of the present suite of gabbro.

2019-01-01T00:00:00Z Asgar Hossain http://20.198.91.3:8080/jspui/handle/123456789/8548 2025-09-12T07:28:14Z 2019-01-01T00:00:00Z

Title: Systematics of benthic foraminifera in Sundarban marshes, West Bengal Authors: Asgar Hossain Abstract: The marsh zones of Sunderban coast were examined for modern benthic foraminiferal assemblages. A total of 10 genera of foraminifera were recorded from the region. Ammonia is the most abundant genus among all other types. Agglutinated foraminifera like Trochammina spp., Miliammina spp.and Haphlophragmoides spp.indicate the high marsh environments. Calcareous foraminifera like Haynesina spp., Cribroelphidium spp., Ammonia spp., and Quinqueloculina sp., Nonionella spp., characterize low marsh conditions.

2019-01-01T00:00:00Z