Mascarene Plateau

The Mascarene Plateau is an undersea plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2000 km, from the Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km² of shallow water, with depths ranging from 8 to 150 meters, plunging to 4000 m to the abyssal plain at its edges. It is the largest undersea plateau in the Indian Ocean.

The northern part of the plateau, including the Seychelles, is formed of granite, and is a fragment of the ancient supercontinent of Gondwana. The granite is topped with deposits of limestone and basalt. The basalt deposits in the Seychelles are from the Deccan Traps eruption, which occurred in central India 65 million years ago. The Seychelles formerly lay next to the west coast of India, but seafloor spreading later moved India to its current position, causing it to collide with Asia.

The southern part of the plateau, including the Saya de Malha Bank, Nazareth Bank, the Cargados Carajos Shoals (Saint Brandon), and the mountainous islands of Mauritius, Réunion, and Rodrigues, were formed by the Réunion hotspot. The banks and shoals were once volcanic islands much like Mauritius and Réunion, which have now sunk or eroded to below sea level, or, in the case of the Cargados Carajos, to low coral islands. The Saya de Malha Bank formed 35 million years ago, and the Nazareth Bank and the Cargados Carajos shoals after that. Limestone banks found on the plateau are the remnants of coral reefs, indicating that the plateau was a succession of islands. Some of the banks may have been islands as recently as 18,000 - 6,000 years ago, when sea levels were up to 130 meters lower during the most recent ice age. Mauritius formed 8-10 million years ago, and Rodrigues and Réunion beginning two million years ago; Piton de la Fournaise volcano on Réunion is one of the most active volcanoes in the world.