Magnetic Evidence for Volcanism at Eastern Continental Margin of India: Juxtaposition with Elan Bank (Southern Indian Ocean) |
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| Authors: | B S P Sarma |
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| Institution: | (1) National Geophysical Research Institute, Uppal Road, Hyderabad, 500606, India |
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| Abstract: | The rifted Eastern Continental Margin of India (ECMI) has evolved as a result of breakup of East Gondwanaland. Previous geophysical
studies of the continental margin have not elucidated upon its volcanic nature. Magnetics plays a useful role in the study
of continental margins, particularly in identifying the volcanic units. The aeromagnetic map of the offshore Mahanadi basin
of ECMI displays a conspicuous linear anomaly along the continental shelf. A comprehensive study of the published aeromagnetic,
marine magnetic and gravity data of the offshore Mahanadi basin reveals the existence of a seaward dipping volcanic unit in
the offshore Mahanadi basin bordering the Hinge zone. This inference suggests that the ECMI is a volcanic rifted margin. The
study further indicates the deepening of the basement towards the sea. In addition, the existing geological studies on the
ECMI demarcated the probable limit of the continental crust by studying the basement detached tectonic style of the sedimentation
in sub-surface configuration of the East coast basins of India. The probable continental crustal limit, the Hinge zone, and
the inner edge of the presently inferred volcanic unit conform to one another spatially in the offshore Mahanadi region. These
features characterize the inferred volcanic body as seaward dipping reflectors (SDRs) that usually occur at the rifted continental
margins. The deepening of the basement towards the sea and the presence of the volcanic body on the continental margin are
indicative of the transitional nature of the crust. It is generally accepted that Antarctica and India were juxtaposed before
the breakup of Gondwanaland. But the microcontinents in the southern Indian Ocean are neglected in the reconstruction of Gondwanaland
continents. The recent studies of the discovery of continental crust within the Elan Bank (EB) microcontinent show that the
EB was contiguous with the East coast of India before the breakup of Gondwanaland. Moreover, it is reported that the upper
igneous crust of the EB consists of a 2–3 km thick layer of accumulated lava flows originating from the Kerguelen hotspot.
An estimate shows that the total volume of volcanic and plutonic component of the Elan Bank is about 0.3 million cubic kilometers.
The present inference of a volcanic body from the offshore Mahanadi basin is in agreement with the above observations of the
juxtaposition of EB with ECMI. |
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| Keywords: | Magnetic anomaly Volcanic body Volcanic rifted margin ECMI Juxtaposition Elan Bank |
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