Paleomagnetic constraints on the structure of the Deccan traps

Details Paleomagnetic constraints on the structure of the Deccan traps Paleomagnetic constraints on the structure of the Deccan traps

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pepi...74..241v&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 74, Issue 3-4, p. 241-261.

Physics

15

Scientific paper

New paleomagnetic results from two widely separated areas of the Deccan traps allow one to test the simple normal-reversed-normal (NRN) magnetostratigraphic model previously proposed. The new data from the Mandla region (to the northeast of the main outcrop of the Deccan traps), together with earlier apparently conflicting results, are all compatible with the NRN stratigraphy, provided the flows are not strictly horizontal but have a synform-antiform structure with 500 m amplitude and 150 km wavelength. The structure parallels the Paleozoic Narmada-Son rift system, with slopes never exceeding 0.5°. Sampling in Rajahmundry, a remote southeastern outlier of the Deccan with well-constrained age, allowed identification of the RN boundary in an area where only normal polarities had been reported. It has also been possible to correlate the detailed geochemical stratigraphy in the Western Ghats with the NRN magnetic stratigraphy. A compilation of 35 magnetic studies, together with the above findings, confirms the general applicability of the NRN model and reveals the large-scale topography of the RN boundary, which is an isochron, over most of the Deccan. The RN isochron surface displays a boomerang shape, with topography ranging from sea-level to above 1600 m. This observed topography is consistent with a simple model in which doming and renewed rifting and dyke intrusion resulted from impingement, 70-65 Ma ago, of the Reunion plume under the Indian lithosphere. The Narmada-Son rift was rejuvenated, and a continental rift system with minor extension with a triple junction in the Cambay Graben resulted and was subsequently covered by the Deccan flows, although in places tectonic faulting and volcanism continued to interfere. The Rajahmundry outcrops constrain the original extent and southeastward dip away from the triple junction of much of the traps, a significant part of which has now been removed by erosion and rifting away of the Seychelles.

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