Nilanjan Dasgupta

Bio: Nilanjan Dasgupta is an academic researcher from Presidency University, Kolkata. The author has contributed to research in topics: Metamorphism & Basement (geology). The author has an hindex of 6, co-authored 12 publications receiving 64 citations.

Meso-Neoproterozoic mid-crustal metamorphic record from the Ajmer–Shrinagar section, Rajasthan, India and its implication to the assembly of the Greater Indian Landmass during the Grenvillian-age orogenesis

Abstract: The Shrinagar–Ajmer section of the South Delhi Fold Belt exposes a package of medium-grade metasedimentary rocks intruded by synkinematic granite, and the entire package was thrust on top of the basement gneisses occurring further east. The metamorphic history is best developed in the staurolite schist that shows an overall increase in modal abundance of staurolite towards the east. Textural analyses, garnet zoning profiles, thermobarometric data and phase equilibria analyses show an increase in metamorphic pressure and temperature, reaching peak conditions of 592±12°C and 7.7±0.11 kbar. In situ monazite dating of a staurolite schist sample yields a pooled age of 980±22 Ma, which is assumed to be close to the age of the peak metamorphism. The Shrinagar granite was possibly emplaced close to the orogeny occurring at approximately 980 Ma and deformed by later events. The style and timing of metamorphism in the Shrinagar–Ajmer section match with the granulite-facies reworking of the basement rocks of the Aravalli–Delhi Mobile Belt. We envisage that the Grenvillian-age orogeny with its characteristic collisional style involved deep- to mid-crustal sections of the Aravalli–Delhi Mobile Belt. Our results further indicate that the Greater Indian Landmass was assembled during the formation of the supercontinent Rodinia.

Zircon U–Pb (SHRIMP) Ages of the Jahazpur Granite and Mangalwar Gneiss from the Deoli-Jahazpur Sector, Rajasthan, NW India: A Preliminary Reappraisal of Stratigraphic Correlation and Implications to Crustal Growth

Abstract: We present high precision geochronological data from the Jahazpur granite and the associated Mangalwar gneiss from Deoli-Jahazpur-Hindoli region of the Aravalli Craton, northwestern India. These data are useful to understand the stratigraphic correlation between the basement gneiss and the low-grade supracrustal rocks of the Hindoli-Jahazpur Group. U–Pb (SHRIMP-IIe) data from zircon suggest emplacement age of 2538 ± 5 Ma for the Jahazpur granite, whereas a similar age of 2520 ± 37 Ma is the timing of the high-grade metamorphism and anatexis of the Mangalwar gneiss. Combining these with whole rock geochemical data, we argue that the Neoarchean Jahazpur granite underwent crustal contamination and emplaced at the same time frame of the Berach granite. Concomitant metamorphism and granitic magmatism imply that overlying Hindoli-Jahazpur Group is younger than c. 2520 Ma. Thus, the Neoarchean Jahazpur granite and Mangalwar gneiss are constituents of the Banded Gneissic Complex which forms the basement of the Hindoli-Jahazpur supracrustal sequence.

Polygonal Impact Craters in the Thaumasia Minor, Mars: Role of Pre-existing Faults in Their Formation

Abstract: Terrestrial planets, dwarf planets and moons (natural satellites) in the solar system have undergone meteoric impacts since their formation. The craters formed due to such impacts may show various geometric shapes. Formation of impact craters that are polygonal in shape is controlled by the presence of pre-existing tectonic features in the area of impact. Thaumasia Minor, the easternmost part of Thaumasia Planum of Mars, has ~ E–W-trending grabens and ~ N–S-trending wrinkle ridges, similar to the rest of Thaumasia Planum. The massive weight of the Tharsis Montes, lying to the northwest of Thaumasia, is considered as the primary cause for the extensional and compressional fractures developed in multiple temporal phases throughout the geological history of Mars. Five such polygonal impact craters in the southern Thaumasia Minor were compared with the visible expressions of tectonic planes in the region. The straight segments of the craters are also used as a proxy to reveal the presence and possible orientations of buried weak planes in the region.

Water on Mars

Abstract: Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.

Thermal history of a Late Mesoproterozoic paired metamorphic belt (?) during Rodinia assembly: New insight from medium-pressure granulites from the Aravalli-Delhi Mobile Belt, Northwestern India

Abstract: In this study, we investigate the possible record of a Late Mesoproterozoic paired metamorphic belt in the Aravalli-Delhi Mobile Belt (ADMB), NW India using a suite of supracrustal and metaigneous granulites from the Pilwa-Chinwali granulite terrain at the north-western margin of the ADMB. Using metamorphic reaction textures, mineral chemistry, metamorphic reaction history, geothermobarometric computations and electron microprobe dating of monazite in 5 samples of pelitic granulite, leptynite gneiss, enderbite and charnockite, we have deduced a medium-pressure granulite facies metamorphism (P between 4.9 and 6.8 kbar, T > 760–815 °C) along a heating-cooling, counterclockwise P-T path between 1.09 and 1.01 Ga. When collated with published metamorphic and chronological constraints and geological settings of the adjoining crustal domains of the ADMB, these findings provide new insights into the developments of two tectonic domains of contrasting thermal gradients at ca. 1.0 Ga, consistent with metamorphic transformations in tectonically thickened middle-lower crustal sections during continental collision to continental subduction and in the root zones of spatially adjacent island arc, as part of the Rodinia supercontinent assembly event.