Magnetometer array studies in India: present status, data interpretation and assessment of numerical modelling results

Abstract

Significant results from several array of magnetometers deployed in India to probe deep geoelectrical structures of the crust and the upper mantle are reviewed in this paper. Emphasis is on critical appraisal of earlier results so that the article summarizes what has been done so far and what caution is to be taken on future work. Two large-scale arrays over northwest and peninsular India during 1979-80, have been followed up with six more linear or two-dimensional arrays over different parts of the country. "Trans-Himalayan" conductor aligned along the strike of Aravalli range, delineated by arrays over northwest India, essentially represents one of the major continental induction anomalies mapped by electromagnetic methods. Efforts for quantifying the induction effects through numerical models are shown to be constrained due to the large inter-station spacing, lack of information on the regional background conductivity distribution and the non-inclusion of the frequency dependence of induction effects. A more comprehensive modelling, not biased by these factors, enables approximating the Trans-Himalayan conductor as an asymmetric domal upwarp in the middle and lower crust located between Delhi-Hardwar ridge and Moradabad fault. Numerical modelling results for southern peninsular, despite the constraints, indicate that the strong and complex induction pattern can be adequately attributed to the combination of conductors connected with triple junction between Indo-Ceylon Graben, Comorin ridge and the west coast rifting. Induction features derived from the Valsad array, operated over basalt-covered region of western India, demarcate an enhanced conducting zone beneath Plume-associated triple junction in the Gulf of Cambay, apart from characterizing the presently active seismic zone as a resistive block.