The granite outcrops of the Seychelles Islands in the central Indian Ocean were amongst the earliest examples cited by Alfred Wegener as evidence for his continental drift theory. Ridge–plume interactions have been responsible for separating a thinned continental sliver from a large continent (i.e. India).
The granites of the Seychelles microcontinent were emplaced 750 Ma, during the late Precambrian. Thermally-induced rifting in the Somali Basin and transform rifting along the Davie fracture zone began in the late Permian 225 million years ago, with Gondwana supercontinent beginning to break up in the mid-Jurassic (about 167 million years ago) when East Gondwana, comprising Antarctica, Madagascar, India, and Australia, began to separate from Africa; East Gondwana then began to separate about 115–120 million years ago when India began to move northward.
The Seychelles then underwent two more stages of rifting to isolate it from Madagascar and India. Between 84–95 million years ago rifting separated Seychelles/India from Madagascar. An initial period of transform rifting moved the Seychelles/India block northward. At 84 million years ago oceanic crust started to form in the Mascarene basin, causing a rotation of the Seychelles/India land mass. This continued until 66 million years ago when new rifting severed the Seychelles from India forming the currently active Carlsberg Ridge. The rift jump coincided with the maximum output of the Deccan traps, and volcanics found on the Seychelles Plateau have also been linked with this event. This has led to suggestions that the initiation of the Reunion plume caused rifting to jump to its current location.
The geology of the Seychelles is an example of a felsic granite microcontinent that broke off from the supercontinent Gondwana within the past 145 million years and become isolated in the Indian Ocean. The islands are primarily granite rock, with some sequences of sedimentary rocks formed during rift basin periods or times when the islands were submerged in shallow water.Indian Plate
The Indian Plate or India Plate is a major tectonic plate straddling the equator in the eastern hemisphere. Originally a part of the ancient continent of Gondwana, India broke away from the other fragments of Gondwana 100 million years ago and began moving north. Once fused with the adjacent Australia to form a single Indo-Australian Plate, recent studies suggest that India and Australia have been separate plates for at least 3 million years and likely longer. The Indian Plate includes most of South Asia—i.e. the Indian subcontinent—and a portion of the basin under the Indian Ocean, including parts of South China and western Indonesia, and extending up to but not including Ladakh, Kohistan and Balochistan.List of tectonic plates
This is a list of tectonic plates on the Earth's surface. Tectonic plates are pieces of Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium). The composition of the two types of crust differs markedly, with mafic basaltic rocks dominating oceanic crust, while continental crust consists principally of lower-density felsic granitic rocks.Madagascar Plate
The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.
Rifting in the Somali Basin began at the end of the Carboniferous 300 million years ago, as a part of the Karoo rift system. The initiation of Gondwana breakup, and transform faulting along the Davie Fracture Zone, occurred in the Toarcian (about 182 million years ago) following the eruption of the Bouvet (Karoo) mantle plume. At this time East Gondwana, comprising the Antarctic, Madagascar, Indian, and Australian plates, began to separate from the African Plate. East Gondwana then began to break apart about 115–120 million years ago when India began to move northward. Between 84–95 million years ago rifting separated Seychelles and India from Madagascar.
Since its formation the Madagascar block has moved roughly in conjunction with Africa, and thus there are questions as to whether the Madagascar Plate should be still considered a separate plate.Mascarene Plateau
The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2,000 km (1,200 mi), from the Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km2 (44,000 sq mi) of shallow water, with depths ranging from 8–150 m (30–490 ft), plunging to 4,000 m (13,000 ft) to the abyssal plain at its edges. It is the second largest undersea plateau in the Indian Ocean after the Kerguelen Plateau.Rodrigues Triple Junction
The Rodrigues Triple Junction (RTJ), also known as the Central Indian [Ocean] Triple Junction (CITJ) is a geologic triple junction in the southern Indian Ocean where three tectonic plates meet: the African Plate, the Indo-Australian Plate, and the Antarctic Plate. The triple junction is named for the island of Rodrigues which lies 1,000 km (620 mi) north-west of it.
The RTJ was first recognized in 1971, then described as a stable R-R-R (ridge-ridge-ridge) triple junction based on coarse ship data.Submerged continent
A submerged continent or sunken continent is a continental mass, extensive in size, but mainly undersea. The terminology is used by some paleogeologists and geographers in reference to some land masses.
The main examples in this class are the Kerguelen Plateau, Seychelles microcontinent, Mauritia, and Zealandia. There's also the hypothesis that the Rio Grande Rise is another sunken continent.
Submerged continents have been sought and speculated about in regard to a possible "lost continent" underwater in the Atlantic Ocean. There was also a search in the 1930s for Lemuria, believed to have possibly been a submerged continent between the Indian and African coasts.
Major African geological formations
|Cratons and shields|