Location and Geometry of the Deccan Traps Feeder System Inferred from Dike Geochemistry
Abstract
Three large dike swarms are exposed in the 500,000 km2 Deccan Traps of India: the Konkan swarm, where the majority of dikes run roughly N-S, sub-parallel to the west coast; the Narmada-Tapi swarm in the north-central Deccan, where dikes dominantly trend ENE-WSW, sub-parallel to the Narmada and Tapi river valleys; and the Nasik-Pune swarm in the central western Deccan, comprising dikes that lack any strongly preferred trends. Following Hooper (Nature, 349, 246, 1990), previous workers have commonly interpreted the Nasik-Pune swarm as the principal locus of feeder dikes for the immense lava pile. The lack of a preferred trend, in turn, has been used as key evidence that the main phase of volcanism was not accompanied by significant lithospheric extension. Our study of the major and trace element and Pb, Sr, and Nd isotope characteristics of samples from all three dike swarms reveals rare dikes in the Nasik-Pune and coastal swarms with signatures matching those of the Igatpuri and Jawhar lava formations in the lowermost part of the lava sequence, and the Bushe Formation in the middle part of the sequence. The scarcity of such dikes suggests these two swarms were not the main feeder systems for the middle and lower portions of the lava pile (or that most feeders for the lower and middle formations are not exposed and lie buried by later flows). Major and trace element data for dikes of the Narmada-Tapi swarm instead suggest that feeders for the lower and middle formations may be located in this swarm. In contrast, dikes with isotopic and chemical signatures matching those of the upper group of lava formations (i.e. the Poladpur, Ambenali and Mahabaleshwar formations) are abundant in the Konkan and Nasik-Pune swarms. As a group, these feeder-like dikes do not display any obvious dominant trend. Dikes compositionally similar to those three formations have also been identified as far north as the Narmada River and as far south as Goa, some 50 km south of the southernmost exposures of flood basalt flows.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.V13B0681V
- Keywords:
-
- 1033 Intra-plate processes (3615;
- 8415);
- 1040 Radiogenic isotope geochemistry;
- 1065 Major and trace element geochemistry;
- 1090 Field relationships (3690;
- 8486);
- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism