Abstract The Indo-Myanmar Ranges (IMR) of NE India are host to various ophiolitic rocks, including metamorphosed Alpine-type harzburgite and lherzolite. Compared to abyssal peridotites of normal oceanic lithosphere, these ultramafic rocks are enriched in trace and rare earth elements. Spilitic pillow lavas along with mafic dykes and sills locally intruded into the serpentinized ultramafic rocks and associated pelagic sediments exhibit alkaline compositional affinities. Ophiolite formation and emplacement were by a process analogous to that described for mantle exhumation in hyper-extended continental margin settings and ophiolites in parts of the European Alps, involving very slow passive continental margin rifting accompanied by slow upwelling or extensional unroofing of the subcontinental upper mantle up to the seafloor. Preliminary palaeomagnetic measurements conducted on ultramafic rocks within the IMR ophiolite belt give a virtual geomagnetic pole (VGP) at 47° N, 045° E for thermal demagnetization (TDM) measurements and 33° N, 013° E for the alternating field demagnetization (AfD) measurements, requiring an anticlockwise rotation of the ultramafic bodies by 14° during the subduction process. The original trend of the spreading axis of the ophiolites was probably NE–SW, with spreading directed NW–SE. Computation of palaeolatitude of the ultramafic rocks gives an average value of 24.67°. Comparison between the palaeolatitude and the present latitude of the sample sites provides a mere latitudinal shift of less than 1°. Field studies, combined with an analysis of structural and tectonic features in the IMR, suggest a generalized WNW–ESE (east–west) compression and NNE–SSW (north–south) extension contradictory to the NNE–SSW contraction indicated by seismic data. Area balancing techniques employed along sections orientated perpendicular to regional tectonic strike in the IMR reveal systematic variations in the amount of crustal shortening, with a maximum of approximately 60% recorded in the Nagaland–Manipur segment along 25.644° N, 93.826° E–25.076° N, 95.897° E. The amount of shortening gradually decreases away from the axis of maximum shortening and on both sides. Calculations of relative plate motion based on rotation vectors given by different workers for various plate pairs represented in the region reveal that the interaction between the Indian and Myanmar plates can ideally produce the structural and tectonic features of this range. Dextral shear coupled to oblique subduction of the Indian Plate below the Myanmar Plate can best explain all of the structural and tectonic features present in the IMR.

Abstract Chromite is commonly used for deciphering the petrogenesis and geodynamic setting of ultramafic rocks. Chrome-spinels from the Indo-Myanmar ophiolite belt occurring in the form of podiform chromitites associated with the mantle sequence and associated volcanic rocks are studied to characterise their geochemical composition. We have measured major and trace element concentrations of the chrome-spinels. Cr/(Cr+Al) (Cr #) and Mg/(Mg+Fe 2+) (Mg #) range from 66 to 70 and 66 to 69 respectively in the chromitite and 47 to 56 and 67 to 70 in volcanic spinel. The computed crystallization conditions show that the studied samples crystallized in an upper mantle environment. Using the chrome spinel compositions, parental magma for the chromitite rock is calculated as boninite, and a MORB for the volcanic sample. Minor and trace element (Ga, Ni, Zn, Co, Mn, V, Sc) concentrations in the analysed spinels are comparable to other podiform chromitites hosted in the mantle section of the ophiolite complexes. Chrome-spinel compositions of the two rocks are used to recognize the probable crystallization condition and nature of the parental magma.

Abstract The topographical and geographical locations of North-Eastern region of India, consisting of eight states is unique with the hydro-meteorological situations making it one of the highest rainfall zones of the world. The region is characterized by low population density, difficult topography, different habitation pattern and social culture, rich forestry and biodiversity with changing climatic conditions. Rainfall of the region being high, varies with space and time in the scale 1000-11000mm. The major river basins of the region are Brahmaputra basin, Barak basin, Gumti basin and Imphal basin. Thus, the variability in rainfall causes some parts of the region water deficient affecting the people’s lives in general and agriculture in particular. Whereas the excess rainfall in some other regions, especially in the Brahmaputra valley causes the floods,drainage congestion, sedimentation and soil erosion problems. The region accounts for about 35% of total water resources of the country though its geographical area (26.23 Mha) is only 8% of the country. Ultimate Irrigation Potential (UIP) of the region is 43.16 Mha. Irrigation Potential Created (IPC) through major, medium and minor irrigation schemes of NE are less than one fifth of UIP. Percentage of net irrigated area (NIA) over net sown area of the region is 18.89 as compared to the national average of 44.88 %. Hydropower potential of this region is 63257 MW, of which only 1911 MW has been harnessed so far (3.02%). Per capita availability of water in the region is highest in the country. However, its harnessing is very limited, which is even less than 5% of the existing potential. In spite of such huge water resources potential of the region, harnessing and development of the water resources potential for irrigation and hydropower is very nominal. Thus, to assist the optimal and sustainable use of water resources in the North Eastern Region, there is a need to plan effectively by applying the management tools, and through institutional collaborations, and accordingly initiate actions for control, conservation and utilization of water throughout the region. This paper is a review on the status of development of water resources in NER. Some views and suggestions are also presented in terms of proper planning and management of water resources in the region.