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Himalayan Geology, Vol. 30 (2), 2009, pp.187-192 Printed in India
Geoid and the regional density
anomaly field in the Indian Plate
RAJESH S.
Wadia Institute of Himalayan Geology,
Dehra Dun -248001, India
Abstract:
The distribution of deeper density anomaly structures in a tectonically
active region like the Himalaya-Tibet and its contiguous peninsular and
oceanic regions have been studied through satellite based geo-potential
methods. The basics of satellite geopotential method have been discussed. A
theoretical relationship has been developed to relate earth's major interior
processes and the associated density changes observed at various harmonics,
depth and anomaly wavelength in the geoid undulation spectrum. Analysis of
regional geoid undulation explains how the earlier Tethys oceanic subduction
defined the present distribution, polarity and the character of deeper
density anomaly structures beneath the Himalaya-Tibet. This has been studied
specifically in conjunction with the dominantly observed Indian Ocean geoid
anomaly low. Regional geoid analysis over the Himalaya-Tibet and the
adjoining oceanic regions of the peninsular India, suggest the existence of
a strong and contrasting deeper density anomaly field in the Indian plate.
This contrasting density anomaly or dipolar field is plausibly constituted
by the combined density effects of (1) major oceanic lower mantle density
void situated at roughly1800 km depth beneath the southern Indian Ocean
lithosphere, and (2) due to earlier subducted high density Tethys oceanic
slab beneath the Himalaya-Tibet. The observed geopotential gradient of
approximately +3m/100 km significantly controls the regional gravitational
potential energy gradient and hence creates a lateral north to south deeper
flow of lower mantle material with in the Indian plate. |
