Physics
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pepi...76..189n&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 76, Issue 3-4, p. 189-197.
Physics
6
Scientific paper
The temporal coincidence of a major biological mass extinction (including dinosaurs), the well-known iridium excess anomaly at the Cretaceous-Tertiary (K-T) boundary and the eruption of Deccan flood basalts at about 65 Ma has aroused global interest among geologists and biologists. It is widely debated whether the mass extinction and iridium anomaly are due to an asteroid impact or the massive outpouring of extensive Deccan volcanism. An oval shaped unusual positive gravity anomaly (10 000 km2 in area) near Bombay has attracted our attention during a search for an impact site near Deccan basalts. A detailed gravity interpretation indicates the presence of a fossil conduit structure of 12 km height extending from a shallow crust-mantle boundary (at 18 km) to an approximate depth of 6 km from the surface. The conduit structure, with a maximum diameter of about 35 km at its base, may originate from cracking of a weak pre-Deccan trap shallow upwarped mantle. The structure may have been caused by a bolide impact which triggered the eruption of massive flood basalts (Deccan traps) on the western margin of the fast-moving Indian plate. An impact in this locality can explain the sudden detachment of the arcuate Seychelles block from India as well as the large-scale reorganisation of plate boundaries in the Indian Ocean. Our hypothesis of impact-triggered volcanism at 65 Ma advocates a bimodal cause for the mass extinction at the K-T boundary. Extraordinary geothermal and structural conditions of the nearby region are also discussed as circumstantial evidence to support the twin-cause mechanism by weakened features and the presence of partial melt at subcrustal depth.
Agrawal P. K.
Negi Janardan G.
Pandey Om Prakash
Singh Ajit P.
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