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Deccan Traps

Coordinates: 18°51′N 73°43′E / 18.850°N 73.717°E / 18.850; 73.717
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The Deccan Traps as seen from Matheran, MH, India
The Deccan Traps shown as dark purple spot on the geologic map of India
Deccan Traps near Matheran, east of Mumbai
The Deccan Traps near Pune

The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India (between 17°–24°N, 73°–74°E) and one of the largest volcanic features on Earth. They consist of multiple layers of solidified flood basalt that together are more than 2,000 m (6,562 ft) thick and cover an area of 500,000 km2 (193,051 sq mi) and a volume of 512,000 km3 (123,000 cu mi). The term "trap", used in geology for such rock formations, is derived from the Swedish word for stairs[1] and refers to the step-like hills forming the landscape of the region.

History

The Deccan Traps formed between 60 and 68 million years ago,[2] at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 65 million years ago. This series of eruptions may have lasted less than 30,000 years in total.[3]

The original area covered by the lava flows is estimated to have been as large as 1.5 million km², approximately half the size of modern India. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 512,000 km2 (197,684 sq mi).

Effect on climate and contemporary life

The release of volcanic gases, particularly sulfur dioxide, during the formation of the traps contributed to contemporary climate change. Data points to an average fall in temperature of 2 °C in this period.[4]

Because of its magnitude, scientists formerly speculated that the gases released during the formation of the Deccan Traps played a role in the Cretaceous–Paleogene extinction event (also known as the K-Pg extinction), which included the extinction of the non-avian dinosaurs. Sudden cooling due to sulfurous volcanic gases released by the formation of the traps and localised gas concentrations may have contributed significantly to mass extinctions. However, the current consensus among the scientific community is that the extinction was triggered by the Chicxulub impact event in Central America (which would have produced a sunlight-blocking dust cloud that killed much of the plant life and reduced global temperature, called an impact winter).[5]

Chemical composition

Within the Deccan Traps at least 95% of the lavas are tholeiitic basalts, however other rock types do occur:

Mantle xenoliths have been described from Kachchh (northwestern India) and elsewhere in the western Deccan.

Fossils

The Deccan Traps are famous for the beds of fossils that have been found between layers of traps lava. Particularly well known species include the frog Oxyglossus pusillus (Owen) of the Eocene of India and the toothed frog Indobatrachus, an early lineage of modern frogs, which is now placed in the Australian family Myobatrachidae.[6][7] The infratrappean and intertrappean beds also contain fossil freshwater mollusks. [8]

Theories of formation

It is postulated that the Deccan Traps eruption was associated with a deep mantle plume. The area of long-term eruption (the hotspot), known as the Réunion hotspot, is suspected of both causing the Deccan Traps eruption and opening the rift that once separated the Seychelles plateau from India. Seafloor spreading at the boundary between the Indian and African Plates subsequently pushed India north over the plume, which now lies under Réunion island in the Indian Ocean, southwest of India. The mantle plume model has, however, been challenged.[2]

Data continues to emerge which supports the plume model. The motion of the Indian tectonic plate and the eruptive history of the Deccan traps show strong correlations. Based on data from marine magnetic profiles, a pulse of unusually rapid plate motion begins at the same time as the first pulse of Deccan flood basalts, which is dated at 67 Myr ago. The spreading rate rapidly increased and reached a maximum at the same time as the peak basaltic eruptions. The spreading rate then dropped off, with the decrease occurring around 63 Myr ago, by which time the main phase of Deccan volcanism ended. This correlation is seen as driven by plume dynamics.[9]

The Indian and African plates motions have also been shown to be coupled, with the common element being the position of these plates relative to the location of the Réunion plume head. The onset of accelerated motion of India coincides with a large slowing of the rate of counterclockwise rotation of Africa. The close correlations between the plate motions suggest that they were both driven by the force of the Réunion plume.[9]

A geological structure exists in the sea floor off the west coast of India that has been suggested as a possible impact crater, in this context called the Shiva crater. It has also been dated at approximately sixty-five million years ago, potentially matching the Deccan traps. The researchers claiming that this feature is an impact crater suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early Paleogene.[10] However, the current consensus in the Earth science community is that this feature is unlikely to be an actual impact crater.[11][12]

See also

References

  1. ^ Trap at dictionary.reference.com
  2. ^ a b Sheth, Hetu C. "The Deccan Beyond the Plume Hypothesis." MantlePlumes.org, 2006.
  3. ^ "India's Smoking Gun: Dino-killing Eruptions." ScienceDaily, 10 August 2005.
  4. ^ Royer, D. L., Berner, R. A., Montañez, I. P., Tabor, N. J., Beerling, D. J., 2004, "CO2 as a primary driver of Phanerozoic climate", GSA Today, v. 14, pp.4-10, ISSN: 1052-5173
  5. ^ Schulte, Peter (5 March 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary". Science. 327 (5970). AAAS: 1214–1218. Bibcode:2010Sci...327.1214S. doi:10.1126/science.1177265. ISSN 1095-9203. PMID 20203042. Retrieved 5 March 2010. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ Noble, Gladwyn Kingsley, "The Fossil Frogs of the Intertrappean Beds of Bombay, India." American Museum of Natural History, Volume 401, 1930.
  7. ^ http://tolweb.org/Myobatrachinae/16946
  8. ^ Hartman, J.H., Mohabey, D.M., Bingle, M., Scholz, H., Bajpai, S., and Sharma, R., 2006, Initial survivorship of nonmarine molluscan faunas in end-Cretaceous Deccan intertrappean strata, India: Geological Society of America (annual meeting, Philadelphia) Abstracts with Programs, v. 38, no. 7, p. 143.
  9. ^ a b S.C. Cande & D.R. Stegman; Indian and African plate motions driven by the push force of the Réunion plume head; Nature; Volume 475; pp. 47–52; (07 July 2011) doi:10.1038/nature10174
  10. ^ Chatterjee, Sankar. "The Shiva Crater: Implications for Deccan Volcanism, India-Seychelles Rifting, Dinosaur Extinction, and Petroleum Entrapment at the KT Boundary." Paper No. 60-8, Seattle Annual Meeting, November 2003.
  11. ^ Mullen, Leslie (2004-11-02). "Shiva: Another K-Pg Impact?". SpaceDaily. Retrieved 2008-02-20. - original article at source
  12. ^ Moskowitz, Clara (18 October 2009). "New Dino-destroying Theory Fuels Hot Debate". space.com.

18°51′N 73°43′E / 18.850°N 73.717°E / 18.850; 73.717

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