Magnetometer Array Studies in India and the Lithosphere

Srivastava. B.J.. Singh, B.P. and Lilley. F.E.M.. 1984. Magnetometer array studies in lndia and the lithosphere. In: S.M. Naqvi. H.K. Gupta and S. Balakrishna (Editors). Lithosphere: Structure. Dynamics and Evolution. Tectono&sics. 105: 355-371. Two magnetometer array experiments were conducted in India during 1978-1980, under an IndoAustralian collaboration project, using 21 Australian three-component magnetometers of the GoughReitzel type. The first array study was made in the northwestern region covering the Aravallis. the Punjab, and the lesser Himalaya, while the second experiment was carried out in the southern peninsular shield area. Both these sets of geomagnetic deep sounding (CDS) observations yielded valuable results on the crustal and upper mantle structure in the two geologically and geophysically important regions of India. Geomagnetic induction patterns observed in northwest India have revealed a variety of electrical conductivity structures. The primary conductivity structure providing paths for induced currents is found to be striking at right-angles to the Himalayan Mountains. The conductivity structure is indicated to be a northward continuation of the Aravalli belt and, thus, suggesting the continuation of the Indian shield at depth into the base of the Himalayan foothills under the Ganga basin. The induction effects observed in the southern tip of peninsular India are by far the most complex geophysical phenomenon due to the simultaneous occurrence of the sea coast, the crustal and upper mantle conductivity anomalies between India and Sri Lanka under the sea, and the day-time equatorial electrojet as part of the external heterogeneous inducing field. It is further complicated by the existence of a conductive step, structure along the coastline at the Moho boundary and a “graben” structure in the Palk Strait, as revealed by the array observations.