Geomagnetic results from Sabhawala,Yangi-Bazar and Alma-Ata in relation to the asthenosphere beneath the Pamir-Himalaya

An attempt is made to study the properties of the Mohorovi?i? discontinuity and the asthenosphere beneath the Pamir-Himalaya from the geomagnetic results obtained at Sabhawala (Dehra Dun), Yangi-Bazar (Tashkent) and Alma-Ata observatories, situated on its southern and northern flanks, in a narrow longitude zone.Medium-sized induction arrows (Wiese vectors) for night-time “bay” events at all the three stations are found to point northward. The northward orientation at Sabhawala indicates a subsurface concentration of induced currents in a step structure at the Moho to the south of Sabhawala and higher electrical conductivity in the Aravalli-Cambay region, where high heat flow and gravity values have also been reported, supporting an elevated asthenosphere, as against the one beneath the western Himalaya. The arrows at Yangi-Bazar and Alma-Ata also show an east-west current channelling in another step structure at the Moho to the south of these stations and north of the Pamir and the Tien Shan mountains.The Sq variations of the H, D and Z components at the three stations, lying close to the northern Sq ionospherics current focus, reveal the characteristic features, without reflecting any unusual asthenospheric conditions in the region.It is concluded that the orogenesis of the Pamir-Himalaya mountain system in terms of plate tectonics or block uplift is different from that of the Cordilleran and Andean mountains in North and South America respectively, where subsurface conductive structures have been delineated from geomagnetic observations by earlier workers.