Piyali Sengupta

Bio: Piyali Sengupta is an academic researcher from Presidency University, Kolkata. The author has contributed to research in topics: Mafic & Colonnade. The author has an hindex of 3, co-authored 3 publications receiving 22 citations.

Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting

Abstract: The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.

Newer Dolerite dykes, Jharkhand, India: a case study of magma generation, differentiation and metasomatism in a subduction zone setting

Abstract: Copyright © 2012 by The Geochemical Society of Japan. belong to different generations (Saha et al., 1973). The geochemical characters of these dykes are strikingly uniform over a long period of time (Bose, 2008; Mallick and Sarkar, 1994). Bose (2008) suggested that Newer Dolerite dykes generated through partial melting of subcontinental mantle which in turn was metasomatised. Mir et al. (2010) documented geochemical characteristics of these dykes similar to those of back arc extension basalts (BABB). In the studied area shear fractures which appears to act as pathways of these mafic intrusives have two dominant trends NE-SW and E-W and a subsidiary NW-SE trends. This might suggest that stress system have not an uniform direction over a long period, but it changed orientation with time. The geochemical classification of these dykes and their linking to possible tectonic settings have not yet been reported by earlier workers. In the present work, attempts have been made to classify these dykes according to their trace and REE composition. The genesis of different chemical types of Newer Dolerite dykes has been discussed in the perspective of possible tectonic setting.

Primary volcanic structures from a type section of Deccan Trap flows around Narsingpur-Harrai-Amarwara, central India: Implications for cooling history

Abstract: Field investigations of the Deccan Trap lava sequence along a 70 km traverse in the Narsingpur-Harrai-Amarwara area of central India indicate twenty lava flows comprising a total thickness of around 480 m. Primary volcanic structures like vesicles and cooling joints are conspicuous in this volcanic succession and are used to divide individual flows into three well-defined zones namely the lower colonnade zone, entablature zone, and the upper colonnade zone. The variable nature of these structural zones is used for identification and correlation of lava flows in the field. For twenty lava flows, the thicknesses of upper colonnade zones of eight flows are ∼5 m while those of eight other flows are ∼8 m each. The thicknesses of upper colonnade zones of remaining four flows could not be measured in the field. Using the thicknesses of these upper colonnade zones and standard temperature-flow thickness-cooling time profiles for lava pile, the total cooling time of these sixteen Deccan Trap lava flows has been estimated at 12 to 15 years.

The emplacement of pahoehoe lavas on Kilauea and in the Deccan Traps

Abstract: There is a growing interest in deciphering the emplacement and environmental impact of flood basalt provinces such as the Deccan, India. Observations of active volcanism lead to meaningful interpretations of now-extinct volcanic systems. Here, I illustrate and discuss the morphology and emplacement of the modern and active lava flows of Kilauea volcano in Hawaii, and based on them, interpret the compound pahoehoe lavas of the Deccan Traps. The latter are vastly larger (areally extensive and voluminous) than Kilauea flows, and yet, their internal architecture is the same as that of Kilauea flows, and even the sizes of individual flow units often identical. Many or most compound flows of the Deccan Traps were emplaced in a gentle, effusive, Kilauea-like fashion. Bulk eruption rates for the Deccan province are unknown, and were probably high, but the local eruption rates of the compound flows were no larger than Kilauea’s. Large (≥ 1000 km3) individual compound pahoehoe flows in the Deccan could have been emplaced at Kilauea-like local eruption rates (1 m3/sec per metre length of fissure) in a decade or less, given fissures of sufficient length (tens of kilometres), now exposed as dyke swarms in the province.