Dr. Rahul Das Gupta
Research Scientist, ICP-MS Lab Manager
Room 221, Building B
Current project: Measurement of radiogenic Cr isotopic ratios using Thermo-Finnigan Triton and their implications in understanding nucleosynthetic anomalies in carbonaceous chondrites
Chromium has four naturally occurring isotopes in Earth materials - 50Cr, 52Cr, 53Cr and 54Cr - with respective relatives abundances of 4.35%, 83.79%, 9.50% and 2.36% (Meija et al., 2016). 50Cr, 52Cr and 53Cr are primarily produced by quasi-equilibrium processes during explosive nucleosynthesis in supernovae (Hartmann et al., 1985; Woosley et al., 2002). Additional contribution to the abundance of 53Cr comes from the decay of the short-lived 53Mn, which is also produced during explosive nucleosynthesis in supernovae (Wasserburg et al., 2006; Woosley et al., 2002). On the other hand, 54Cr is produced through neutron-rich statistical equilibrium or quasi-equilibrium processes in type 1a supernovae (Hartmann et al., 1985; Meyer et al., 1996; Woosley et al., 2002).
Nucleosynthetic isotopic anomalies with respect to Earth are present in a number of early solar system material and are generally thought to reflect residual heterogeneities stemming from a variety of stellar sources and processes (Dauphas et al., 2010; Rotaru et al., 1992; Trinquier et al., 2007).
Carbonaceous chondrites (CC) are known as carriers of various isotopic anomalies which are most pronounced in the neutron-rich isotopes 48Ca, 50Ti, 54Cr (Shukolyukov and Lugmair, 2006) and are fundamentally distinct from non-carbonaceous (NC) meteorites (Nanne et al., 2019). This dichotomy was first recognized by Warren (2011), who observed that the Cr, Ti and O isotopic composition of meteorites define two distinct cluster (Nanne et al., 2019). These differences are too great to be the result of by mass-fractionation processes. Thus, understanding variations in the Cr isotope abundances in meteorites and their components may provide significant constraints on the early Solar System history (A. Trinquier et al., 2008).
Apr 2023 – present
Post-doctoral research scientist at Department of Earth Sciences, Geochemistry group, Freie Universität Berlin
July 2022 – Feb 2023
Post-doctoral researcher at Centre for Earth Sciences (CEaS), Indian Institute of Science (IISc)
(mentor: Prof. Ramananda Chakrabarti) https://sites.google.com/site/ramanandachakrabarti/members-1
July 2021 – June 2022
Post-doctoral research associate at NanoSIMS laboratory, Physical Research Laboratory (mentor: Prof. Kuljeet Kaur Marhas https://www.prl.res.in/~plas/team.html
October 2020 – July 2021
Post-doctoral research associate at School of Earth and Planetary Sciences (SEPS), National Institute of Science Education and Research (NISER) (mentor: Dr. Guneshwar Thangjam) https://www.niser.ac.in/users/thangjam
2014 – 2020
Ph.D. at Centre for Earth Sciences (CEaS), Indian Institute of Science (IISc), Bangalore, India (supervisor: Prof. Ramananda Chakrabarti), https://ceas.iisc.ac.in/author/ramananda-chakrabarti/
2012 – 2014
Masters in Geology (M.Sc) at Department of Geology and Geophysics, Indian Institute of Technology (IIT), Kharagpur, India Master thesis supervisor: Prof. Dewashish Upadhyay (previous guest scientist at FUB), https://www.iitkgp.ac.in/department/GG/faculty/gg-dewashish
2009 – 2012
Bachelors in Geology at Department of Geology, Presidency College (Calcutta University), Kolkata, India, https://www.presiuniv.ac.in/web/geology.php
SS 2023 'Data Interpretation and Geochemical Modelling' (lecture & exercise 4h/week)
Petrographic and geochemical study of Calcium-Aluminum Inclusions, along with their relative chronology using Al-Mg isotopic decay system
Calcium-Aluminum Inclusions (CAIs) represent the earliest formed refractory condensates in the Solar System. These were formed at high temperature (>1500⁰C) near the proto-Sun and were blown out to the outer Solar System by solar wind. The mineralogy of CAIs reflect condensation from the proto-solar nebula and their isotopic compositions are used to understand the formation of the Solar System. Correlated variations of the short-lived radionuclides 26Al, 41Ca and 60Fe suggest a common source for these nuclides, which is likely to be a AGB star. These were incorporated into the Solar System during a supernova collapse of a nearby AGB star. This supernova, in turn, triggered the collapse of the Solar System. In contrast to this hypothesis, the proto-solar nebula could have also collapsed and contracted under its own gravitation. The isotopic composition of 10Be in CAIs was used to infer that short-lived radionuclides can also be formed by solar irradiation in the early Solar System. In this case, it is possible that there is an additional source of the short-lived radionuclides apart from the supernova collapse of a AGB star.
Photograph of a CAI with a pyroxene-anorthite core and a double layer of pyroxene rim
The objective of this study was to measure 26Al and 41Ca abundances in primitive CAIs and understand whether they were derived from a AGB star or formed within the Solar System. The condensation sequence of minerals within CAIs, starting from the earliest condensates at the highest temperature, is as follows: corundum, hibonite, perovskite, spinel, melilite (gehlenite-akermanite), Ca-pyroxene, anorthite. Based on their mineralogy, CAIs are divided into Type A, B and C. Among these the Type A CAIs are the most primitive and comprise of perovskite, spinel and melilite. Hence, these minerals in the Type A CAIs are ideal for understanding the sources of 26Al and 41Ca in the early Solar System. Calcium-bearing pyroxene and Anorthite represent later formed phases due to melting and recrystallization and are either present in the rims of CAIs or in the interior part of Type B and Type C CAIs. As part of this study, two CAIs were studied in detail using EPMA data. One of them shows a perovskite core, surrounded by spinel, in a melilite matrix, suggesting that this is a Type A CAI. In contrast, the other CAI shows pyroxene and anorthite as major phases and hence is a Type B CAI. The measurement of Mg isotopic ratios using NanoSIMS in the Type A CAI was used to infer the initial 26Al/27Al ratio. The calculated initial ratio is close to 5 x 10-5, which is accepted as the canonical value for this ratio. Hence, this Type A CAI is a primitive CAI and represents an ideal sample to understand the source of the short-lived radionuclides.
Mineralogy of the CM2 chondrite Jbilet Winselwan using SEM and XRD results, with particular emphasis on finding phyllosilicates and carbonates
Ceres is the largest planetary body in the asteroid belt between Mars and Jupiter. This asteroid is characterized by the presence of Na2CO3 and NH4 ions on its surface. Even though Ceres shows an absorption feature corresponding to OH ions similar to carbonaceous chondrites, the presence of Na2CO3 and NH4 ions are unique to Ceres. This is particularly important since NH4 ions are unstable at the present-day location of Ceres. Hence, it is suggested that Ceres has migrated from the outer Solar System, similar to carbonaceous chondrite parent bodies. Since Ceres has similarities with carbonaceous chondrites, these meteorites, particularly CM chondrites, could be used as analogues of surface processes on Ceres. The CM chondrites show prominent evidences of aqueous alteration and also show presence of N- bearing amino acids.
Geochemical and XRD data of the Jbilet Winselwan CM2 chondrite
The objective of this study was to look for products of aqueous alteration, which could be related to similar features on Ceres. As part of this study, I did a detailed mineralogic and petrographic study of the CM2 chondrite, Jbilet Winselwan. The analysis of XRD peaks of the Jbilet chondrite suggest that the CM chondrite parent body was affected by thermal metamorphism, in addition to aqueous alteration. The compositions of chondrules and matrix in this chondrite is complementary with respect to concentrations of Fe, Mg. The chondrules are Mg-rich and are surrounded by Fe-rich rims. Such complementary composition is also observed in other CM chondrites and this reflects secondary processes after accretion of the CM chondrite parent body. The FeO/SiO2 of the matrix in Jbilet CM2 chondrite is consistent with the compositions of CM 2.4 – 2.5 chondrites. In addition, sulfur-rich parts were also observed in the form of Tochilinite-Cronstendite intergrowths. Previous studies have found N-bearing compounds within such sulfur-rich areas. Hence these intergrowths are relevant for understanding formation of NH4 ions on Ceres.
Geochemical and isotopic study of the Lonar and Dhala impact craters and jarosites from Kutch, India as analogues to understand planetary surface processes
Photographs of the Lonar crater and spherules formed during the cratering event
During Ph.D., I used the measurement of elemental concentrations using solution-ICPMS and measurements of radiogenic isotopic ratios of Nd, Sr and Ca using TIMS to understand impact-related processes at the Lonar and Dhala impact craters as well as to understand the formation of jarosite at Kutch. The geochemical and Nd-Sr isotopic compositions of impact spherules and impact melt samples from Lonar show evidence of a chondritic impactor, melting of the Precambrian basement below the target basalt, and also evaporation-condensation processes during impact cratering. My research outcomes on the Lonar crater have been published in Geochimica et Cosmochimica Acta (Vol 215, pp. 51-75) in 2017.
I have also analyzed the morphology, mineralogy, and chemical compositions of impact spherules at Lonar to understand the physical processes in the impact ejecta plume at Lonar. This study has been submitted for publication and is under review. In contrast to the Lonar crater, which formed within the Deccan basalt about 0.5 Ma ago; the Dhala crater represents an eroded remnant of a Paleoproterozoic impact crater in the Bundelkhand granitoid rocks. I used combined analyses of K-Ca, Rb-Sr, and Sm-Nd radioactive decay systematics to infer the ages of the crater and a post-impact alteration event. In addition to my research on the Lonar and Dhala impact craters, I used the radiogenic Nd-Sr isotopic compositions and stable S isotopic ratios of hydroxy-sulfate samples from Kutch to understand that their formation of the hydroxy-sulfates at Kutch is due to oxidative weathering of pyrites in lignite at Kutch by a fluid derived from seawater. The publications on the Dhala crater and jarosites are under preparation.
1. Das Gupta R. and Chakrabarti R., 2022. Understanding ejecta plume dynamics based on morphology, mineralogy, and chemistry of impact glasses from the Lonar Crater, India. (under review)
2. Das Gupta R., Banerjee A., Goderis S., Claeys P., Vanhaecke F. and Chakrabarti R., 2017. Evidence for a chondritic impactor, evaporation-condensation effects and melting of the Precambrian basement beneath the ‘target’ Deccan basalts at Lonar crater, India. Geochimica et Cosmochimica Acta, 215, pp.51-75.
3. Geochemical and Sr, Nd and Ca isotopic study of the Dhala Impact Crater, India: implications for the type of impactor, ages of crater formation and post-impact alteration, source of sediments in the Central Elevated Area (under preparation for Meteoritics and Planetary Science)
Conference abstracts and papers
1. Das Gupta R. and Chakrabarti R., 2023, Estimates of the ages of the Dhala impact crater and a post-impact alteration event at Dhala based on K-Ca, Rb-Sr, and Sm-Nd radiogenic isotope systematics “Frontiers in Geoscience Research Conference" (FGRC - 2023) (Oral presentation at Physical Research Laboratory, Navrangpura, Ahmedabad, India)
2. Das Gupta R., Sarbadhikari A.B., Marhas K.K., 2021, Formation of carbonate-sulfide association in the martian meteorite ALH84001 and implications for the nature of water-rock interactions on the martian surface in the Noachian Era. ‘Meteoroids, Meteors and Meteorites: Messengers from Space’ (MetMeSS) (Oral presentation in online conference)
3. Das Gupta R. and Chakrabarti R., 2021, Constraints on the age and diameter of the Dhala crater based on the provenance of the sedimentary rocks on the Central Elevated Area and the morphological characteristics of the crater. ‘Meteoroids, Meteors and Meteorites: Messengers from Space’ (MetMeSS) (Oral presentation in online conference)
4. Das Gupta R. and Thangjam G., 2021, Aqueous alteration in CM2 chondrite Jbilet Winselwan as analog of alteration processes on asteroid Ceres. Indian Planetary Science Conference, 2021 (Oral presentation in online conference)
5. Das Gupta R. and Chakrabarti R., 2018, Micro-CT Imaging for Understanding the Formation of Impact Spherules and Their Compositional Heterogeneity: A Case Study from Lonar Impact Crater, India. Microsc. Microanal. 24 (Suppl 1), 2112. (Poster presentation at Baltimore Convention Center. Baltimore, USA)
6. Das Gupta R. and Chakrabarti R., 2018, Geochemical and Nd-Sr isotopic Study of Jarosite and Associated Rocks at Kutch, India. Goldschmidt Meeting abstract. (Poster presentation at Hynes Convention Center, Boston, USA)
7. Das Gupta R. and Chakrabarti R., 2018, Neodymium and Strontium isotopic compositions of jarosite and associated rocks at Kutch: implications for the source of Fe and role of seawater. National Seminar on Dynamics on Surface and Sub-Surface Geological Processes (Oral presentation at Pondicherry University, Pondicherry, India)
8. Chakrabarti R., Goderis S., Banerjee A., Das Gupta R., Claeys P. and Vanhaecke F., 2016. Geochemical and isotopic study of impact melts and spherules from the Lonar impact crater, India, indicate melting of the Precambrian basement beneath the ‘target’ Deccan basalts. In AGU Fall Meeting Abstracts.
9. Banerjee Y., Das Gupta R., Ghosh P., Chakrabarti R. and Hergt J., 2015, Evidence of decarbonation process in a skarn deposit from Matanumadh formation, Kachchh Basin, India. Goldschmidt Meeting abstract.