The Mascarene Plateau is an submarine 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 – 150 meters, plunging to 4000 meters to the abyssal plain at its edges. It is the largest undersea plateau in the Indian Ocean.[1]
The northern part of the Mascarene plateau includes the Seychelles and Agalega Islands. The southern part of the Mascarene plateau includes the Mascarene Islands, Saya de Malha Bank, Nazareth Bank, Soudan Banks, and Hawkins Bank. The Mascarene Islands are the mountainous islands of Mauritius, Réunion, Rodrigues, and the Cargados Carajos Shoals.
The Indian subcontinent was at one time next to the east coast of the Seychelles, but seafloor spreading has moved the landmass to its current position, where it has collided and fused with the continent of Asia.
The northern part of the Mascarene plateau 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 the central part of the Indian subcontinent 65 million years ago, at the end of the Cretaceous period.
The southern part of the Mascarene plateau, also known as Southern Mascarene plateau (SMP), was formed by the Réunion volcanic hotspot along with the Chagos-Laccadive Ridge.[2] The banks and shoals of the southern part of the Mascarene plateau 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 formed later. Limestone banks found on the plateau are the remnants of coral reefs, indicating that the plateau was once 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 formed around two million years ago. Piton de la Fournaise volcano on Réunion is one of the most active volcanoes in the world.