Research Focus
Our group’s main research areas are (1) Composition of the Earth’s inner core, (2) Shock metamorphism in meteorite, (3) Olivine in cratonic lamproite, (4) Genesis of mantle xenoliths, (5) Water content in the source magma
Calculated compressional and shear velocities of Ni-doped bcc and hcp Fe equivalents at inner core conditions as a function of density and compared with hcp-Fe and the experimental results from 300 K to 1000 K and PREM and shock wave Hugonoit measurements at high temperatures. (Chatterjee et al., 2021 - Minerals)
Unlocking Earth's Inner Core Mystery: Fe-Ni Alloy Behavior and Composition
Earth’s inner core is comprised primarily of iron (Fe), often with 5-15% nickel (Ni), the inner core's role in Earth's dynamics is vital. While previous studies predominantly explore pure Fe's phase diagram under diverse temperature and pressure conditions, growing evidence suggests Ni inclusion's substantial impact on Fe's characteristics. Experimental and theoretical investigations indicate that even small Ni concentrations might stabilize a face-centered cubic (fcc) structure, diverging from the conventional hexagonal closed-packed (hcp) inner core assumption. Seismic data revealing the inner core's elastic anisotropy adds urgency to understanding alternative phases, particularly the body-centered cubic (bcc) structure, under inner core conditions. Our recent computational study, leveraging first-principles calculations, meticulously assesses bcc, hcp, and fcc structures within Fe-Ni alloys under extreme pressures and temperatures (200-364 GPa). Ni-doped bcc Fe's stability hinges on Ni's distribution within the Fe matrix, providing compelling theoretical evidence challenging prevailing inner core composition assumptions (Chatterjee et al., 2021, Minerals). Our research bridges experimental and theoretical realms, enhancing comprehension of Fe-Ni alloy behavior under extreme conditions and its impact on Earth's inner core. Through rigorous computational analysis, we contribute significantly to Earth sciences and seismic anisotropy research.
Composition of the Earth’s Inner Core
Ever since the discovery of the Earth's solid inner core 80 years ago, its composition has been a subject of significant debate. Deciphering the composition of the Earth’s solid inner core has been a scientific puzzle for decades. While it is now established that iron dominates this region, seismic observations indicate an unexpected lower density than pure iron and Fe-Ni alloys, hinting at the presence of a lighter element. Our research employs advanced computational studies, using first-principles calculations, to explore the possibility of silicon-doped iron carbide compounds as a key component of the Earth’s inner core. These simulations demonstrate that introducing small amounts of silicon impurities into specific carbon sites in Fe7C3 carbide phases can harmonize seismic parameters with observational data. This research opens a new avenue in our quest to understand the Earth's innermost composition, offering insights into the intriguing complexities of the inner core's composition and behavior.
Backscattered electron image of the Kamargaon chondrite and shock melt vein passing through the middle of the sample. The scale bar is 1 mm. (Tiwari et al., 2022 - JGR Planets)
High-pressure phases in shocked meteorites
Impact events played a vital role in the formation, evolution, and shaping of planetoids and planets. Such impact events result from collision among asteroids that are responsible for the formation and delivery of shocked meteorites and their fragments to the Earth. Shocked meteorites contain high-pressure phases in and around shock melt veins. Their textural and compositional analyses, as well as a mode of occurrence, reveal their transformation mechanisms and pressure and temperature conditions at which they formed, that is directly applicable to processes undergoing at mantle depth. Numerous high-pressure minerals have been discovered in shocked meteorites that have helped in comprehending their transformation mechanism and constrain the P-T-t path experienced by the meteorite.
Formation of natural Bridgmanite in shocked meteorite: Understanding Earth's mantle
Bridgmanite, the most abundant mineral in Earth's lower mantle, plays a pivotal role in deciphering the inner workings of our planet's interior. This enigmatic mineral has predominantly been studied in laboratory settings, but its natural occurrences remain rare and crucial for understanding its formation mechanisms.
Our research explores the discovery of a unique natural analog of bridgmanite within the Katol chondrite, an ordinary meteorite that fell near the town of Katol in the Nagpur district of India following a substantial meteor shower on May 22, 2012. This naturally occurring bridgmanite closely mirrors the composition of its terrestrial counterpart found in Earth's lower mantle. Notably, the Fe-bearing aluminous bridgmanite uncovered in the Katol chondrite exhibits a substantially higher Fe3+/ΣFe ratio than coexisting majorite, aligning with experimental predictions.
The Katol chondrite stands as an invaluable natural analog, shedding light on the crystallization processes of bridgmanite during Earth's early history, particularly during the final stages of magma ocean crystallization. Our research contributes to a deeper understanding of planetary interiors and advances our ongoing quest to unveil the enigmatic mysteries of Earth's formation and evolution.
TEM image shows Fe-bearing aluminous bridgmanite, majorite, and FeNi-FeS melt in the Katol L6 chondrite. High-angle annular dark-field (HAADF) image of an aggregate of submicrometer-sized crystals of bridgmanite enclosed in vitrified bridgmanite glass within a shock-melt vein from the Katol L6 chondrite. Majorite is found in the vein matrix together with a small metal-sulfide melt. (Ghosh et al., 2021 - PNAS)
Back-scattered electron image of olivine phenocryst from P2–2 sample with diffuse contacts between different zones (core, internal zone 1, rim) and Mg-chromite inclusions. (Sarkar et al., 2021 - Lithos)
Olivine in cratonic lamproites: A window to understanding lithospheric mantle and the petrogenetic relation with kimberlites
Olivine is one of the most abundant phases in cratonic lamproites and kimberlites, where it occurs as mantle-derived xenocrysts and magmatic phenocrysts or rims overgrowing xenocrystic cores, indicating its prevalence throughout most of the crystallization sequence of these magmas. Thus, olivine can provide valuable insights into lamproite and kimberlite petrogenesis and magma evolution through the lithospheric mantle to surface. The goal of our research is to understand and model olivine chemistry in lamproites worldwide and explain the petrogenetic relation between lamproites and kimberlites. It is a key step of a broader goal to link between lamproite petrogenesis, different mantle sources residing in the lithosphere and asthenosphere, and metasomatism in the cratonic mantle. This work is a collaboration between IIT Kharagpur and the University of Melbourne via the MIPA program.
Mantle xenoliths: A glimpse into Earth's mantle
Mantle xenoliths, fragments from Earth's mantle brought to the surface during volcanic eruptions, offer a unique opportunity to explore the composition and conditions of the Earth's upper mantle. Our investigations encompass the petrography, mineralogy, and chemical compositions of these xenoliths, predominantly collected from the Mesoproterozoic Wajrakarur kimberlites in the Eastern Dharwar craton (EDC), India. This research provides unprecedented insights, revealing depths exceeding 160 km and shedding light on the enigmatic base of the Dharwar cratonic lithospheric mantle. The distinct characteristics of garnet and clinopyroxenes within these xenoliths hint at metasomatism processes driven by fluids in the continental lithospheric mantle. Employing advanced modeling techniques, we strive to unravel the intricate formation mechanisms of olivine-rich peridotites, contributing to a deeper understanding of lithospheric evolution beneath the Dharwar craton.
A schematic model (not to scale) for the formation of the two earliest cratonic nuclei of the Eastern Dharwar craton and the Western Dharwar craton. (Pattnaik et al., 2020 - Lithos)
Representative unpolarized infrared spectra for anhydrous nominally mineral (olivine) from Wajrakarur kimberlite. (Pattnaik et al., 2021 - Precambrian Research)
Low hydrogen concentrations in Dharwar craton Inferred from mantle xenoliths
Hydrogen (H) subtly nestled within the lattice of mantle minerals can significantly influence their physical and chemical characteristics. Even in minute quantities, H can increase electrical conductivity, augment ionic diffusion, and weaken mineral strength, making its distribution in the upper mantle a crucial parameter in geodynamic models. Although natural mantle minerals contain variable H levels, a comprehensive global database remains lacking. In this study, we reported the first detailed measurements of H concentrations in nominally anhydrous minerals NAMs (olivine, orthopyroxene, clinopyroxene and garnet) from spinel- and garnet-bearing peridotite xenoliths and olivine grains embedded in kimberlites from the Wajrakarur kimberlite field in the Eastern Dharwar craton, India. We presented the inaugural quantification of hydrogen concentrations in nominally anhydrous minerals from rare ultramafic rocks within Mesoproterozoic Wajrakarur kimberlites (Eastern Dharwar craton, India). Our findings reveal remarkably low H levels in olivine, orthopyroxene, and clinopyroxene, providing essential insights into the hydrogen content of mantle minerals. These observations challenge prior assumptions about hydrogen-rich lithospheric characteristics, highlighting the importance of understanding mantle mineral hydrogen concentrations for geodynamic models.