Significant Contributions

The chemical make-up of the mantle, particularly below the continents, and the nature of mantle fluids are areas that are presently demanding a great deal of attention. Carbonatites form one group of rocks that have much to reveal about the chemical and physical evolution of the sub-continental upper mantle. Cabonatitic magmas as source of fluids, and carbonatites as repository of Nb, Sr, and REE, make them especially topical and relevant. Not only do such rocks provide a very interesting way of sampling the mantle but they also hold many clues to understand fluid migration and its evolution at both mantle and crustal levels. Geochemical investigations on alkaline and carbonatite igneous complexes from Gujarat, Assam, Meghalaya, and Tamil Nadu have been the main focus of my research. Recent work on the Early Cretaceous ultramafic-alkaline-carbonatite complexes of remote areas of Assam and Meghalaya has gained lots of attraction. The data generated on these complexes enabled to develop new concept about the origin of these rocks. Many scholars have worked on these complexes, particularly on Sung Valley complex, but all have suggested liquid immiscibility origin for carbonatite and associated rocks. New petrological, geochemical, and isotopic data uggest their origin from a primary carbonatite magma generated by the low-degree partial melting of a metasomatized mantle peridotite. We have also dated these complexes very precisely by U-Pb method using igneous minerals like zircon, baddeleyite, and perovskite, which suggest that these alkaline-carbonatite complexes are spatially and temporally associated to the Kerguelen plume activity.

Geochemical and petrological investigations of Precambrian mafic igneous rocks that are important component in establishing crustal evolution of Archaean craton have gained global significance in recent years. Detailed study of mafic dyke swarms also provides valuable information on the evolution of mantle. My self and my team have extensively studied Precambrian mafic dykes from the central Indian Bastar craton, particularly to get better insight of the composition of sub-continental lithosphere and correlating continental fragments of coeval age. We have identified distinctly three generations of mafic dyke swarms throughout the Precambrian time; two sub-alkaline tholeiites and one boninitic-like mafic rocks. Verities of Neoarchaean mafic volcanics, which includes siliceous high-Mg basalts (SHMB) and boninites, are also recognized. Both SHMB and boninites are reported for the first time from the Indian subcontinent but the discovery of boninite rocks from the Central India is certainly an important contribution to Indian Geology. This is because the majority of boninites occur in supra subduction zones and common in Phanerozoic but their possible occurrence in rift or continental environments and their emplacement in Precambrian terrain cannot be discounted. Considering these distinctive petrogenetic characteristics these rocks are considered to be of great importance to Archaean granite-greenstone terrains in identifying successions that might be analogous to modern successions developed in subduction setting. Recently, I have published a paper in Geochemical Journal in which it is suggeated that such boninitic magma are responsible for the genesis of Neoarchaean noritic intrusion reported world-wide. This is an important study in respect as it denotes magmatic event at Neoarchaean-Paleoproterozoic boundary (~2.5 Ga). It is suggested that all the three dyke swarms are derived from different magmas generated from deep heterogeneous mantle source.

I have also initiated work on the Andaman ophiolite suite (AOS) and Jungel alkali lamprophyres from Mahakoshal greenstone belt. These suites of rocks also provide valuable information on the mantle composition.