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 and are more than 2 kilometers thick. They cover about 500,000 square kilometers and were even larger in the past.

The volcanic eruptions that formed the Deccan Traps happened between about 66.3 and 65.6 million years ago, around the time of a big event called the Cretaceous–Paleogene boundary . At first, some scientists thought these eruptions caused a major extinction event at the same time. But now, most believe that a space impact called the Chicxulub impact was the main cause, with the Deccan eruptions playing only a small role, if any.

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

Etymology

The word trap comes from geology and has been used since 1785–1795. It 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 began 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, with lava flowing from cracks in the earth.

Originally, the lava covered an area about half the size of modern India, but erosion and movement of the Earth's plates have reduced it to its current size. Today, the Deccan Traps are divided into three layers: the Upper, Middle, and Lower traps, which are believed to relate to the shape of the land and distance from where the lava came.

Effect on mass extinctions and climate

The release of volcanic gases, especially sulfur dioxide, during the formation of the Deccan Traps may have contributed to climate change. Scientists have wondered if these gases played a major role in the Cretaceous–Paleogene extinction event, which marked the end of the dinosaurs. However, most scientists now believe that the main cause of this extinction was the Chicxulub impact event in North America. This impact would have blocked sunlight, causing a sharp drop in temperatures.

Some studies suggest that both the volcanic activity of the Deccan Traps and the Chicxulub impact might have worked together. However, recent research indicates that the Deccan Traps likely caused only short-term climate changes and were not the primary 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. This is supported by special ratios found in the lava, which are common when a plume is involved. The area where the eruptions happened for a long time, called the Réunion hotspot, may have caused both the Deccan Traps 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 being involved.

Suggested link to impact events

The Deccan Traps started erupting before a big event happened, called an impact. Some scientists think this impact might have made more lava come out, creating most of the Deccan Traps. They also think this event, together with the impact, may have helped cause many plants and animals to die out at the end of the time called the Cretaceous period.

There is another possible impact spot far under the ocean near India's west coast, called the Shiva crater. Some scientists thought it might be linked to the Deccan Traps too, but most scientists now think it probably isn’t an impact spot.