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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Poster presentation 2148
Origin and evolution of Northwest indian conductor derived from
geomagnetic deep sounding and thermo-geodynamical processes
Dr. S N Prasad
Geophysics National Geophysical Research Institute (NGRI) IASPEI
Aravalli cratonic province situated in the northwestern part of Indian shield, forms one of the most
unusual late Archean Proterozoic terrain consisting of complex geotectonic elements and geophysical
features. This region has been associated with long sustained rejuvenation since late Archeans which
continued till the end of Mesozoic period. Geomagnetic deep sounding studies, which were conducted to
study the deeper structures of this region, led to discovery of a major conductivity structure having a
conductivity of 1 ohm. m (termed here as northwest Indian conductor), which strikes across the
western part of Ganga basin and extends into foot hills of Himalaya. Modeling result indicates the depth
to the top of this conductor at 32 km, which extends at least to the depth of 82 km, while lateral extent
is about 110 km. This conductor is stated to be the northward continuation of Aravalli belt which was
formed much before the collision of India with Eurasia. However, even after several investigations, the
cause of the conductivity anomaly still remains a subject of considerable debate. Present study suggests
the cause of high conductivity to be the presence of serpentinized olivine basalt peridotite at subcrustal
depths and its consequent dehydration, which conforms with the prevailing thermal regime of the
underlying lithosphere. Our calculations indicate melting conditions between the depths of 70 and 100
km beneath Aravalli belt, which would correspond to insitu temperatures of about 600 to 800oC ,
required for serpentinisation between the depths where conductive structure is located. However, if the
conductivity anomaly is influenced solely by the melting, then in all likelihood it would be related in
some way or other to the rise of isotherms caused by upwarped and molten asthenosphere sitting at a
very shallow depth of 40 50 km beneath a prominent thermal anomaly zone situated around western
margin of India. In this zone, temperature gradients and heat flow are high reaching to about 78oC/km
and 97 mW/m2 respectively and Moho is thinned to about 17-22 km. It is felt that the currents induced
in the adjoining areas are channeled through the delineated zone of high heat flow which provides a
passage to the anomalous flow of induced currents.
Keywords: conductivity anomaly, geodynamic evolution