Proposed relation between anomalous geomagnetic variations and the tectonic history of South India

  • Nityananda N
  • Jayakumar D
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Abstract

Anomalous geomagnetic variations have been observed at all geomagnetic stations in South India and they have earlier been attributed to ocean and crustal conductors. The spectral character of induced variations indicate that, in addition to coastal effects and channelling of currents through the Palk Straits, there is a concentration of currents in a conducting body at deeper levels in the crust or mantle. Current thinking on crustal evolution and the influence of Precambrian lineaments on tectonism and mineralisation up to recent times, provides support for the conjecture that zones of high electrical conductivity exist in the crust, which are related to tectonic and mineral influences. The Eastern Ghats and granulite terrain of South India and Sri Lanka are probably associated with such a zone of fundamental weakness in the crust. Extended graphite mineralisation along the Eastern Ghats, occurrence of economic graphite deposits near Trivandrum and in Sri Lanka and the association of alkaline and ultrabasic metallic minerals with deep faults in South India are indications of the possible chemical causes of high electrical conductivity in some regions of the crust. Similar relations between induced anomalous variations and tectonism and mineralisation in the Precambrian crystalline crust have been found in North America and Scotland. However, the regions of high electrical conductivity have not yet been mapped in detail in South India to confirm such a relationship. © 1981.

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Authors

  • N. Nityananda

  • D. Jayakumar

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