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Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK
A geological map of an area of over 125 000 km2 within the southern Deccan Traps, India is presented, which is based upon variations in the basalt geochemistry. It represents a synthesis of new data and earlier work. The use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before. The geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the Ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense. However, the stratigraphy defines a pronounced coastward-dipping monoclinal flexure across the Western Ghats ridge between 16°N and 18°N.
The data are consistent with two models of eruption. The first considers the Deccan eruptive focus to have been fixed throughout the volcanic episode, producing an essentially annular flow pattern. The second considers the flow pattern to have been generated from a southerly migrating eruptive centre, resulting from the northerly drift of India over a fixed hotspot. Both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume-generated thermal 'highs'. Until a causal link between established plume/hotspot trails and impact sites can be satisfactorily demonstrated, we find it unnecessary to invoke a cataclysmic impact event as an explanation for the Deccan eruptions.
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