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The 'Deccan Traps' is a large igneous province located on the Deccan Plateau of west-central India and is one of the largest volcanic features on Earth. It consists of multiple layers of solidified flood basalt that together are more than 2,000 m thick and cover an area of 500,000 km². The term 'traps' is derived from the Swedish word for stairs (''trappa'', or sometimes ''trapp''), referring to the step-like hills forming the landscape of the region.

Contents

History

Chemical composition

Theories of formation

Link to Shiva Crater

Analogues to Venus flood eruptions

Formation's effects on life

See also

References

History

The Deccan Traps formed between 60 and 68 million years ago,^[1][2] at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 66 million years ago. This series of eruptions may have lasted fewer than 30,000 years in total. The gases released in the process may have played a role in the Cretaceous–Tertiary extinction event, which included the extinction of the dinosaurs.
Before the Deccan Traps region was reduced to its current size by erosion and continental drift, it is estimated that the original area covered by the lava flows was as large as 1.5 million km², approximately half the size of modern India. The present volume of directly observable lava flows is estimated to be around 512,000 km³.
The release of volcanic gasses during the formation of the traps "contributed to an apparently massive global warming. Some data point to an average rise in temperature of 8 °C (18.4 °F) in the last half million years before the impact [at Chicxulub]."^[3]

Chemical composition

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

★ Alkali basalts

★ Nephelinites

★ Lamprophyre

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

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.

Link to Shiva Crater

A large impact crater has been recently reported in the sea floor off the west coast of India. Called the Shiva crater, it has also been dated at sixty-five million years, right at the Cretaceous-Tertiary (K/T) boundary. The researchers 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 Tertiary.^[4] However, opinion in the geologic community is not unanimous that this feature is actually an impact crater.^[5] Also, the reported age is in the middle of the ages given for the Deccan rocks.

Analogues to Venus flood eruptions

The planet Venus is also thought to undergo vast basaltic flood eruptions, but on an even greater scale than those at Deccan Traps. It is not known whether the mechanisms are similar; Venus appears to lack Earth's plate tectonics and its internal structure may differ in other ways as well.

Formation's effects on life

Due to the volcanic gasses causing a drastic climate change the formation of the traps is seen as a major stressor on all life at the time. Dr. Norman Macleod, of the Natural History Museum in London, points out “We're talking about catastrophic effects in terms of changes in habitat, changes in rain fall patterns, changes in climate, all of these you can think of all of the things that are going on in the modern world magnified many many times, many many orders of magnitude indeed.” While the fossil records of dinosaurs at this time is hard to interpret, those of other types of life are more conclusive, as Macleod states “Six million years prior to the KT boundary there were about twenty species of ammonites in the world's oceans. Three million years before the KT boundary there were only fifteen or so and one million years prior to the KT boundary we have less than half of what we started out with, we have less than ten species so the extinction event has already been going on for millions of years. The amazing thing is that we see the same pattern in the fish record, we see the same pattern in the terrestrial reptile record, we even see the same pattern in the mammal record. All of these groups were undergoing an extinction event for millions of years and it would be absolutely amazing to me if dinosaurs weren't undergoing the same sort of extinction and indeed I think they were undergoing the same sort of long term extinction.” Many scientist conjecture that due to the global warming caused by the volcanic formation of the traps the dinosaurs were already doomed, but the impact of the meteoroid that formed the Chicxulub Crater (which made a sunlight blocking dust cloud that killed much of the plants) pushed them over the edge into extinction.

See also

★ Siberian Traps

★ Geology of Venus

★ Geology of India

References

1. The Deccan beyond the plume hypothesis
2. Geochronological Study of the Deccan Volcanism
3. What Really Killed the Dinosaurs Production Manager: Yolanda Ayres
4. 2003 GSA
5. Space daily Deep Impact