Deccan Traps

The Deccan Traps are a huge area of volcanic rock in west-central India. They are one of the largest volcanic features on Earth. These traps are made from many layers of hardened lava called flood basalt. They are more than 2 kilometers thick and cover about 500,000 square kilometers.

The volcanic eruptions that formed the Deccan Traps happened between about 66.3 and 65.6 million years ago. At this time, a big event happened called the Cretaceous–Paleogene boundary . Some scientists thought these eruptions caused a major change on Earth, but most now believe that a space impact called the Chicxulub impact was the main cause.

These volcanic eruptions are thought to have been caused by a place deep in the Earth called the Réunion hotspot . This same hotspot also helped create the Mascarene Islands in the Indian Ocean today.

Etymology

The word trap comes from geology. It has been used since 1785–1795. The word comes from the Swedish word for stairs, trapp, because the hills in this area look like steps. The name Deccan is from Sanskrit and means "southern".

History

See also: Gondwana and opening of western Indian Ocean and Geology of India

The Deccan Traps started forming 66.25 million years ago, near the end of the Cretaceous period. Most of the volcanic eruptions happened along the Western Ghats between 66 and 65 million years ago. Lava flowed from cracks in the earth.

At first, the lava covered an area about half the size of modern India. But erosion and movement of the Earth's plates have made it smaller. Today, the Deccan Traps are split into three layers: the Upper, Middle, and Lower traps. These layers are thought to relate to the shape of the land and how far the lava traveled.

Effect on mass extinctions and climate

The release of volcanic gases, especially sulfur dioxide, during the formation of the Deccan Traps may have changed the climate. Scientists have wondered if these gases helped cause the end of the dinosaurs. However, most scientists now believe the main cause was a big impact from space in North America called the Chicxulub impact. This impact blocked sunlight and made temperatures drop sharply.

Some studies suggest that both the volcanic activity of the Deccan Traps and the Chicxulub impact might have worked together. But recent research shows that the Deccan Traps likely only caused short-term climate changes and were not the main reason for the mass extinction.

Petrology

The Deccan Traps are mostly made of a type of rock called tholeiitic basalt. These rocks contain minerals like olivine, pyroxenes, and plagioclase, along with some iron and titanium-rich oxides.

Scientists have found many fossils between the layers of lava in the Deccan Traps. These include ancient frogs like Oxyglossus pusillus and Indobatrachus, as well as freshwater molluscs in the Infratrappean and Intertrappean Beds.

Theories of formation

Scientists think the Deccan Traps were formed by a deep mantle plume. Special ratios in the lava support this idea. The area where the eruptions happened for a long time, called the Réunion hotspot, may have caused both the eruptions and the opening of a rift that moved parts of the Earth’s surface apart.

The movement of the Indian tectonic plate and the timing of the eruptions match closely. When the eruptions began, the plate moved faster, and when they stopped, the speed slowed down. This suggests the plume had a big effect on how these plates moved. The Deccan Traps show signs of deep melting and changes in the Earth’s crust, which also support the idea of a mantle plume.

Suggested link to impact events

The Deccan Traps began erupting before a big event, an impact. Some scientists believe this impact may have caused more lava to flow, helping create most of the Deccan Traps. They also think this event, along with the impact, might have helped many plants and animals to die out at the end of the Cretaceous period.

There is another possible impact spot deep under the ocean near India's west coast, called the Shiva crater. Some scientists once thought it might be linked to the Deccan Traps, but most now believe it is probably not an impact spot.