Tushar Mouli Chakraborti

Bio: Tushar Mouli Chakraborti is an academic researcher from Presidency University, Kolkata. The author has contributed to research in topics: Gabbro & Craton. The author has an hindex of 5, co-authored 6 publications receiving 53 citations.

Crystal size distribution analysis of plagioclase from gabbro‐anorthosite suite of Kuliana, Orissa, eastern India: implications for textural coarsening in a static magma chamber

Abstract: The layered gabbro-anorthosite suite in the eastern Indian shield is ideal for a texture based study of the crystallization history of a mafic magma in a static magma chamber. The magmatic suite comprises 40–150 m thick persistent layers of different lithounits, which have been divided into two cycles. The lower cycle (I) is represented from bottom to top by gabbro, gabbronorite, leucogabbronorite, anorthositic gabbronorite and anorthositic gabbro. The upper cycle (II) is similar to cycle I, except that the anorthositic gabbronorite and anorthositic gabbro units are not present there. The characteristic textures of different lithounits in each cycle repeats with repetition in lithology. Distinctive textures observed in the suite have been classified into three categories, Types I, II and III. Adcumulus growth was the principle crystallization mechanism for Types I and III textures, which are characteristically present in the lower layers of cycle I and cycle II. The upper layers of cycle I show Type II texture, typically with bimodal size distribution of plagioclase, and pyroxene oikocrysts. Thus, Type II texture indicates a possible interplay between adcumulus growth and either polybaric crystallization or textural coarsening processes. Electron microprobe analysis (EPMA) data indicate uniform composition of plagioclase (An76–85), both from inclusions in pyroxene oikocrysts and from groundmass grains, hence ruling out the possibility of involvement of the polybaric crystallization in the layers with Type II texture. Crystal size distribution (CSD) analysis of plagioclase grains stands for textural coarsening process, and the graphical plots have been utilized to quantify the process. P-T calculation using EPMA data from selected pyroxene grains suggests that the textural coarsening took place at about 13.3 kb pressure and 990 °C temperature. We propose that adcumulus growth operating in a static magma chamber for a long period of time might have created conditions conducive for textural coarsening process to take place. Copyright © 2015 John Wiley & Sons, Ltd.

Geochemical characterisation of the Neoarchaean newer dolerite dykes of the Bahalda region, Singhbhum craton, Odisha, India: Implication for petrogenesis

Abstract: The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE–SSW to NE–SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5–25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75–2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.

Evidence of melt/rock interaction in the Cr-spinel bearing wehrlite rocks of Bangriposi, India: Implications for nature of the metasomatic agent

Abstract: Cr-spinel bearing wehrlite rocks of Bangriposi are found within the multiply deformed metasedimentary rocks of Singhbhum Group belonging to North Singhbhum Mobile Belt of eastern India. Detailed mineralogical and geochemical studies reveal that these rocks have suffered a two-stage alteration involving a deeper level modal and cryptic metasomatism and a subsequent shallower depth pervasive hydrothermal alteration. Cryptic metasomatism is defined by elevated LREE contents of the wehrlite and its clinopyroxne grains. Metasomatism induced changes in the modal mineralogy of the rocks include the absence of primary orthopyroxene grains, presence of secondary diopside-phlogopite (now present as vermiculite) defining disequilibrium reaction textures and secondary orthopyroxene rims around serpentinized olivine. The mineralogical and geochemical changes due to the metasomatic event present a contrasting picture in regard to the metasomatic history of the rocks. Possible scenarios involving a single stage or multiple stage metasomatism events have been discussed while explaining the metasomatic reactions that took place. An attempt has been made to estimate the REE concentrations of the final equilibrating melt from REE contents of clinopyroxene grains of the wehrlite. The possibility of the LREE-enriched equilibrating melt of the wehrlite rocks (the deeper level metasomatic agent) being similar to residual melts from the E-MORB type parental melts of nearby gabbro suite has been ruled out by geochemical modeling. REE abundance patterns of several natural enriched melts have been compared with REE pattern of calculated LREE-enriched equilibrating melt of the wehrlite and most resemblance has been observed with calcic and potassic melts. It is therefore suggested that the Cr-spinel bearing wehrlite rocks of Bangriposi has been affected by a calcio-potassic melt in deeper level, prior to the shallow level serpentinization event.

Computation of Parent Magma Compositions of a Layered Gabbro Suite around Kuliana, Orissa, Eastern India: Implications for Magmatic Evolution and Paleotectonic Setting

Abstract: A layered gabbro suite was emplaced around Kuliana (lat 22°3ʹN and long 86°38ʹE), Orissa, eastern India, within deformed metasedimentary rocks of the north Singhbhum mobile belt. This magmatic suite does not have any exposures of feeder dikes, chilled margins, or other evidence for an intrusive character. Because the cumulate layers do not provide information about the parent magma of this suite, the equilibrium distribution method has been utilized in this study to estimate trace element concentrations of melts in equilibrium with the cumulate solid products. The mineralogical and chemical evolution of the layered suite has been carried out on the basis of both calculated parent magmas and chemical data of cumulate layers. The magmatic differentiation of the layered suite was guided by fractional crystallization and punctuated by an event of magma chamber replenishment. The calculated parent melts exhibit enriched light rare earth elements and large ion lithophile elements, marked depletion of Ti...