Crustal structure across Sikkim, NE Himalaya from new gravity and magnetic data

Abstract

The new gravity and magnetic data recorded along a profile in the Sikkim, NE Himalaya are combined with the existing data from Tibet, Bangladesh and India, to delineate the crustal structure in this part of Himalaya. Modelling of gravity data, constrained from seismic results suggests that long wavelength gravity anomalies arise due to variations in the depth of Moho (36 to 74 km), which are caused by flexed lithosphere of effective elastic thickness of ∼ 50 ± 10 km. Simultaneous modelling of magnetic anomalies and short wave-length gravity anomalies reveals that (a) the magnetic anomalies observed over the Lesser Himalaya and the Higher Himalaya Crystalline rocks might be caused by remnant magnetisation with inclination I = − 18° ± 8° and declination D = 147° ± 10°, which is in conformity with the palaeomagnetic results. These magnetic parameters correspond to ~ 35 ± 10 Ma age of magnetic direction and suggest that the rocks might have acquired magnetisation during cooling period of metamorphism, (b) low grade meta-sediments of the Lesser Himalaya extend up to 12 km depth and thins on either sides forming a bowl shaped geometry and (c) relative gravity high in the Bengal basin might be caused by intrusion of the Rajmahal volcanics. Modelling has also provided constraint on the geometry of the north dipping thrusts.