Deccan Traps

Coordinates: 18°51′N 73°43′E / 18.850°N 73.717°E / 18.850; 73.717
Source: Wikipedia, the free encyclopedia.
Deccan Traps
Deccan Traps is located in India
Deccan Traps
Deccan Traps
Location in India

The Western Ghats at Matheran in Maharashtra
Oblique satellite view of the Deccan Traps
Map of the Deccan Traps[1]

The Deccan Traps is a large igneous province of west-central India (17–24°N, 73–74°E). It is one of the largest volcanic features on Earth, taking the form of a large shield volcano.[2] It consists of numerous layers of solidified flood basalt that together are more than about 2,000 metres (6,600 ft) thick, cover an area of about 500,000 square kilometres (200,000 sq mi),[3] and have a volume of about 1,000,000 cubic kilometres (200,000 cu mi).[4] Originally, the Deccan Traps may have covered about 1,500,000 square kilometres (600,000 sq mi),[5] with a correspondingly larger original volume. This volume overlies the Archean age Indian Shield, which is likely the lithology the province passed through during eruption. The province is commonly divided into four subprovinces: the main Deccan, the Malwa Plateau, the Mandla Lobe, and the Saurashtran Plateau.[6]

Etymology

The term

rock formations. It is derived from the Swedish word for stairs (trapp) and refers to the step-like hills forming the landscape of the region.[7] The name Deccan has Sanskrit origins meaning "southern".[6]

History

Deccan Traps at Ajanta Caves

The Deccan Traps began forming 66.25 million years ago,[5] at the end of the Cretaceous period, although it is possible that some of the oldest material may underlie younger material.[2][6] The bulk of the volcanic eruption occurred at the Western Ghats between 66 and 65 million years ago when lava began to extrude through fissures in the crust known as fissure eruptions.[8] Determining the exact age for Deccan rock is difficult due to a number of limitations, one being that the transition between eruption events may be separated by only a few thousand years and the resolution of dating methods used is not able to pinpoint these events. In this way, determining the rate of magma emplacement is also difficult to constrain.[2] This series of eruptions may have lasted for less than 30,000 years.[9]

The original area covered by the

lava flows is estimated to have been as large as 1.5 million km2 (0.58 million sq mi), 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 500,000 km2 (200,000 sq mi).

The Deccan Traps are segmented into three stratigraphic units: the Upper, Middle, and Lower traps. While it was previously interpreted that these groups represented their own key points in the sequence of events in Deccan extrusion, it is now more widely accepted that these horizons relate more closely to paleo topography and distance from the eruption site.[6]

Effect on mass extinctions and climate

The release of volcanic gases, particularly sulfur dioxide, during the formation of the traps may have contributed to climate change. An average drop in temperature of about 2 °C (3.6 °F) was recorded during this period.[10]

Because of its magnitude, scientists have speculated that the gases released during the formation of the Deccan Traps played a major role in the Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary or K–T extinction).[11] It has been theorized that sudden cooling due to sulfurous volcanic gases released by the formation of the traps and toxic gas emissions may have contributed significantly to the K–Pg mass extinction.[12] However, the current consensus among the scientific community is that the extinction was primarily triggered by the Chicxulub impact event in North America, which would have produced a sunlight-blocking dust cloud that killed much of the plant life and reduced global temperature (this cooling is called an impact winter).[13]

Work published in 2014 by geologist Gerta Keller and others on the timing of the Deccan volcanism suggests the extinction may have been caused by both the volcanism and the impact event.[14][15] This was followed by a similar study in 2015, both of which consider the hypothesis that the impact exacerbated or induced the Deccan volcanism, since the events occurred approximately at antipodes.[16][17]

However, the impact theory is still the best supported and has been determined by various reviews to be the consensus view.[18]

A more recent discovery appears to demonstrate the scope of the destruction from the impact alone, however. In a March 2019 article in the

tektites bearing "the unique chemical signature of other tektites associated with the Chicxulub event" found in the gills of fish fossils and embedded in amber, an iridium-rich top layer that is considered another signature of the event, and an atypical lack of evidence for scavenging perhaps suggesting that there were few survivors. The exact mechanism of the site's destruction has been debated as either an impact-caused tsunami or lake and river seiche activity triggered by post-impact earthquakes, though there has yet been no firm conclusion upon which researchers have settled.[19][20]

However, a recent computation involving more than 100 processors dedicated to algorithmic intelligence show that the Deccan Traps had been erupting for 300,000 years prior to the impact, and likely kept erupting for nearly 700,000 years, which would have greatly contributed to global extinction.[21]

Petrology

The Deccan Traps shown as a dark purple spot on the geologic map of India
tholeiitic basalts.[22] Major mineral constituents are olivine, pyroxenes, and plagioclase, as well as certain Fe-Ti-rich oxides. These magmas are <7% MgO. Many of these minerals are observed however, as highly altered forms.[2] Other rock types present include: alkali basalt, nephelinite, lamprophyre, and carbonatite
.

Mantle

Kachchh (northwestern India) and elsewhere in the western Deccan and contain spinel lherzolite and pyroxenite constituents.[2][23]

While the Deccan traps have been categorized in many different ways including the three different stratigraphic groups, geochemically the province can be split into as many as eleven different formations. Many of the petrologic differences in these units are a product of varying degrees of crustal contamination.[2]

Fossils

Life restoration
of the Deccan trap during the Late Cretaceous

The Deccan Traps are famous for the beds of fossils that have been found between layers of lava. Particularly well known species include the frog

molluscs.[26]

Theories of formation

It is postulated that the Deccan Traps eruption was associated with a deep

crustal thinning supports the theory of this rifting event and likely encouraged the rise of the plume in this area.[6] 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.[28]

Data continues to emerge that 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 began at the same time as the first pulse of Deccan flood basalts, which is dated at 67 million years 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 million years ago, by which time the main phase of Deccan volcanism ended. This correlation is seen as driven by plume dynamics.[29]

The motions of the Indian and African plates have also been shown to be coupled, 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.[29]

When comparing the Na8, Fe8, and Si8 contents of the Deccan to other major igneous provinces, the Deccan appears to have undergone the greatest degree of melting suggesting a deep plume origin. Olivine appears to have fractionated at near-

faulting, frequent diking events, high heat flux, and positive gravity anomalies suggest that the extrusive phase of the Deccan Traps is associated with the existence of a triple junction which may have existed during the Late Cretaceous, having been caused by a deep mantle plume. Not all of these diking events are attributed to large-scale contributions to the overall flow volume. It can be difficult, however, to locate the largest dikes as they are often located towards the west coast and are therefore believed to currently reside under water.[6]

Suggested link to impact events

The illustration of The Deccan Trap eruption that may have caused the extinction of the dinosaurs

Chicxulub crater

Although the Deccan Traps began erupting well before

K–Pg boundary.[31][32] However this proposal has been questioned by other authors, who describe the suggestion as being "convenient interpretations based on superficial and cursory observations."[33]

Shiva crater

A geological structure that exists in the sea floor off the west coast of India has been suggested as a possible impact crater, in this context called the Shiva crater. It was also dated approximately 66 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.[34] However, the current consensus in the Earth science community is that this feature is unlikely to be an actual impact crater.[35][36]

See also

References

  1. .
  2. ^ .
  3. .
  4. .
  5. ^ a b "What really killed the dinosaurs?" Jennifer Chu, MIT News Office, 11 December 2014
  6. ^
    OCLC 851375252
    .
  7. ^ Trap at dictionary.reference.com
  8. OCLC 778055464
    .
  9. ^ "India's Smoking Gun: Dino-killing Eruptions." ScienceDaily, 10 August 2005.
  10. ISSN 1052-5173
    .
  11. .
  12. .
  13. (PDF) from the original on 21 September 2017.
  14. ^ Keller, G., Deccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?, in Volcanism, Impacts, and Mass Extinctions: Causes and Effects, GSA Special Paper 505, pp. 29–55, 2014 abstract Archived 18 June 2017 at the Wayback Machine
  15. S2CID 206632431
    .
  16. .
  17. ^ "Asteroid that killed dinosaurs also intensified volcanic eruptions - study". The Guardian. 2 October 2015. Retrieved 2 October 2015.
  18. ^ "Dinosaur extinction: 'Asteroid strike was real culprit'". BBC News. 17 January 2020.
  19. ^ "Stunning discovery offers glimpse of minutes following 'dinosaur-killer' Chicxulub impact". 29 March 2019. Retrieved 10 April 2019.
  20. ^ Broad, William J.; Chang, Kenneth (29 March 2019). "Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs". The New York Times. Archived from the original on 1 January 2022.
  21. ^ "Volcanoes or Asteroid? AI Ends Debate over Dinosaur Extinction Event". 26 November 2023.
  22. ISSN 0022-3530
    .
  23. (PDF) from the original on 15 December 2016.
  24. .
  25. ^ "Myobatrachinae". Archived from the original on 22 September 2017. Retrieved 19 June 2011.
  26. ^ 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.
  27. S2CID 23709446
    .
  28. ^ Sheth, Hetu C. "The Deccan Beyond the Plume Hypothesis." MantlePlumes.org, 2006.
  29. ^
    S2CID 205225348
    .
  30. (PDF) from the original on 19 February 2018.
  31. .
  32. .
  33. .
  34. ^ Chatterjee, Sankar. "The Shiva Crater: Implications for Deccan Volcanism, India-Seychelles Rifting, Dinosaur Extinction, and Petroleum Entrapment at the KT Boundary Archived 2 December 2016 at the Wayback Machine." Paper No. 60-8, Seattle Annual Meeting, November 2003.
  35. ^ Mullen, Leslie (2 November 2004). "Shiva: Another K–Pg Impact?". Spacedaily.com. Retrieved 20 February 2008. - original article at source
  36. ^ Moskowitz, Clara (18 October 2009). "New Dino-destroying Theory Fuels Hot Debate". space.com.

External links

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