Extending from c. 10°S to 15°N, the CLR includes the Laccadive, Maldives, and Chagos archipelagos and can be divided into three corresponding blocks, of which the first is continental and the two latter are oceanic. The CLR is asymmetrical with a steeper eastern slope and has an average depth of less than 1,000 m (3,300 ft). It formed south of or near the Equator together with the remaining western continental margin of India, when India separated first from Madagascar in the Mid-Cretaceous and then from the Seychelles in the Late Cretaceous.
The CLR extends northward for c. 2,550 km (1,580 mi) from 10°S at the southern end of the Chagos Archipelago to 14°N around the Adas Bank. The second element of the name is for the Laccadive Islands, among the islands of Lakshadweep. ("Laccadive" is a form of the name "Lakshadweep".) The islands of Chagos, the Maldives and Lakshadweep are the above-water parts of the Chagos-Laccadive Ridge.
The Laccadive Ridge, the northern part of the CLR, parallels the Indian west coast (8°N–16°N) and has an average width of 270 km (170 mi). It is separated from the flanking basins by fault scarps made of thick, high-density crust. It is made of thinned continental crust marked by the volcanism that occurred near the KT-boundary c. 66 Ma. This caused by the passage over the Rėunion hotspot and the resulting India–Madagascar breakup.
The western coastal margin of the Indian subcontinent was affected by two large igneous provinces at 85 Ma and 65 Ma associated with the Marion and Réunion hotspots, respectively. This has left a complex of ridges that run parallel to the west coast of which the Laccadive Ridge is the larger. A complex of considerably smaller ridges constitutes a northern extension to the CLR. The Laxmi Ridge, the larger of these, is made of continental crust and formed during the Seychelles-India breakup. East of the Laxmi Ridge in the Laxmi Basin, the Panikkar Ridge is made of stretched continental crust and has a similar tectonic history. In contrast, the Palitana Ridge north of the Panikkar Ridge probably represents an extinct spreading centre and on the nearby shelf and slope a lineament, known as the Prathap Ridge Complex, is similarly made of oceanic crust and both are probably leftovers from the India–Madagascar breakup.
The vast Chagos-Laccadive Ridge was formed by the Réunion volcanic hotspot along with the southern part of the Mascarene Plateau. Both plateaux are volcanic traces of the Réunion hotspot.[failed verification] Although the Chagos-Laccadive Ridge is an aseismic ridge, between 1965 and 1970 an unusual, isolated swarm of earthquakes occurred on the west side of the Great Chagos Bank at approximately .
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- Hydrographic Description (Indian Ocean Pilot)
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