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Highlights in the last decade!
Crustal growth and tectonics during the Archaean
Research projects: 7
Completed Ph.D.s.: 4
Completed U.G. projects: 2
Completed M.S. projects: 2
Ongoing Ph.D.s: 2
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Development of a basic structural map with overlayed information of known geological and geochronological datasets was a preliminary step in understanding southern India's Archaean tectonics. Our new map of southern India helps to re-define the Precambrian crustal blocks. The PhD and post-doctoral projects focused on regional-scale geology and tectonics of several high-grade Archaean granulite blocks i.e. Karwar[Ishwar Kumar], Coorg[Ishwar Kumar], Nilgiri[Samuel], Namakkal[George], BR Hills[Ishwar Kumar, Ratheesh-Kumar], Madras[Thanooja], and Madurai[Shazia] (Fig. 1). The cumulative output shows that subduction and arc accretion were the significant processes responsible for crustal formation at ~ 2.9-2.5 Ga, including high-pressure granulite-grade metamorphism at ~2.5-2.4 Ga[30,34]. The Hf and Nd isotope results also provide evidence of crustal recycling, supported by the presence of inherited 2.7-3.0 Ga zircons[28]. Another key Archaean process was sediment recycling, evident from metamorphosed tuffs, shales, cherts and iron formations[28,36]. Most crustal blocks around the Dharwar Craton were amalgamated during the Archean-Proterozoic period.
Ishwar-Kumar discovered a new Mesoproterozoic suture (Kumta-Mercara) between the Karwar-Coorg blocks and the Dharwar Craton along the western margin of India[29,41]. We also examined the geological and geophysical relationships between eastern Madagascar (Antongil and Masora blocks) and western India (Coorg and Karwar blocks) [33, 35, 41]. Based on our new datasets we proposed for the first time that the Kumta-Mercara suture in India is the easterly continuation of the Betsimisaraka suture in Madagascar[25,29,41].
The Neoarchean Madras Block in south-eastern India and its geological and isotopic connection with North China Craton is a recent research focus. Based on our geological, petrological, geochronological, and isotopic datasets of rocks from India, South Korea, and China we proposed possible mutual correlations[A9].
The southern Archean margin of India experienced ultrahigh-temperature reworking in the Neoproterozoic (ca. 550 Ma)[32, 37]. Similar rocks in Sri Lanka[31] and Antarctica[A5, A11, A14] also show evidence of this unique high-temperature metamorphism.
Heavy mineral concentrates in rivers and beach placers are an efficient tool to better understand ambient crustal processes. Age, REE, and Hf isotopic compositions of zircons and monazites from beach placers from SW India, Sri Lanka, and Madagascar provide a key link between available information/datasets from the relevant source regions[A6].
Genesis and evolution of mineral resources
Research projects: 5
Completed Ph.D.: 1
Ongoing PhDs: 1
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Two of our principal geological activities are concerned with mineral resources and their magmatic and hydrothermal processes. Understanding the evolution of chromitite deposits from many geological settings worldwide is one of our principal projects[Veni]. Chromite chemistry can help us understand Archaean mantle and crustal tectonic processes. The abundant Indian chromite deposits will be compared with similar deposits worldwide (Archean to Phanerozoic) in order to help understand their influence on Earth evolution in the Archean [A1, A2] (Fig. 2). By examining the temporal changes in chromitites during Earth history, we can evaluate the ambient magmatic processes and Cr budgets in the mantle across geological time.
The case study on hydrothermal processes is focused on the largest hydrothermal tin deposit in Rwanda[Nambaje]. The results so far demonstrate that the formation of ~1.0 Ga tin deposits was associated with ~1.0 Ga granites that intruded an Archaean basement (~2.6 Ga) )[7,9]. Direct dating of the Sn-ore cassiterites will be crucial in this study using SIMS in our SPARC research project[UR2]. Attempts to develop platinum-osmium dating of the chromites are in progress as part of this project.
Neotectonics and Himalayan-Andaman subduction zone
Ongoing PhDs: 2
Ongoing MTech: 1
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To understand early Earth (Archaean) tectonics and subduction processes, it is very important to investigate equivalent present-day active subduction zones. The Himalayan subduction system is the best example to understand the Neotectonic scenario of continent-continent (Kumaun Himalaya)[Arya], and continent-microcontinent collisions (Nagaland)[Kiso], and is complemented by the still-active subduction zone in the Andaman Islands. Recent Ph.D. and MTech projects have focused on these regions with spectacular results.
