Implications for the Emplacement of the Deccan Traps (India) From Isotopic and Elemental Signatures of Dikes
Abstract
A large swarm of dikes with no preferred orientation in the western Deccan Traps of India, termed the Nasik-Pune swarm, has been interpreted by previous workers (Beane et al., 1986, Bull. Volcanol. 48, p. 61; Hooper, 1990, Nature 345, p. 246) to be the principal locus of feeders for the massive lava pile, and the lack of preferred orientation has been interpreted as strong evidence that the main phase of eruptive activity was not accompanied by significant directed extension of the regional lithosphere. Large dike swarms along the western coast and in the Narmada-Tapti graben in the northern Deccan show strong preferred orientations but have generally been discounted as major feeder systems. An isotopic, major element, and trace element study of dikes of the Nasik-Pune and coastal swarms demonstrates that the situation is more complex. About half of our samples display isotopic compositions that are not observed in the western Deccan lava pile, despite having major and trace element similarities to some of the lavas. The other half show isotopic and elemental compositions matching those of the upper formations of the lava pile (i.e. the Poladpur, Ambenali and Mahabaleshwar formations). Both categories of dikes are present in both the Nasik-Pune and coastal swarms. Thus far, only a single dike can be correlated unambiguously with the stratigraphically lowest formation, the Igatpuri-Jawhar; this dike is in the Nasik-Pune swarm. The combined results suggest that the coastal and Nasik-Pune swarms were both feeder zones for the Deccan Traps. The dikes having strong affinities with the Ambenali and Poladpur formations (two of the most extensive formations in the lava pile) appear to be preferentially, although only weakly, N-S oriented. The implication is that east-west extension may have begun by the time of the upper-formation eruptions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.V51B0561V
- Keywords:
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- 8109 Continental tectonics: extensional (0905);
- 3655 Major element composition;
- 3670 Minor and trace element composition;
- 1040 Isotopic composition/chemistry