The Central Indian Ridge (CIR) is a north–south-trending

mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a div ...

in the western

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by ...

Geological setting

The morphology of the CIR is characteristic of slow to intermediate ridges. The axial valley is 500–1000 m deep; 50–100 km-long ridge segments are separated by 30 km-long transform faults and 10 km-long non-transform discontinuities. Melt supply comes from axial volcanic ridges that are 15 km-long, 1–2 km wide, and reaches 100–200 m above the axial floor. With a spreading rate of 30 mm/yr near the Equator and 49 mm/yr near the

Rodrigues Triple Junction The Rodrigues Triple Junction (RTJ), also known as the Central Indian ceanTriple 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 An ...

(RTJ) at its southern end, the CIR is an intermediately fast spreading ridge characterised by moderate obliquity and few large offsets, the obvious exception being the almost 300 km-long Mary Celeste Fracture Zone at 18°S. Between 21°S and the Mary Celeste Fracture Zone (18°S) the CIR deviates westward. Along this section the larger offsets switch from right-lateral to left-lateral but return to right-lateral north of 18°S. Otherwise, the southern section (RTJ-Argo Fracture Zone, 25°S-13°S) of the CIR is near-orthogonal relative to the spreading direction. North of the Argo FZ it is highly oblique and dominated by numerous small ridge segments. The northern section of the CIR, including the

Carlsberg Ridge The Carlsberg Ridge is the northern section of the Central Indian Ridge, a divergent tectonic plate boundary between the African Plate and the Indo-Australian Plate, traversing the western regions of the Indian Ocean. The ridge of which the Carl ...

, trends NNW and lacks fracture zones. The axial depth of the CIR increases from 3200 m at 20°S to 4000 m at the RTJ.

Boundaries

The CIR is traditionally said to separate the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...

from the

Indo-Australian Plate The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...

. Likewise, the

Owen Fracture Zone The Owen Fracture Zone (OFZ), though misnamed a fracture zone, is a transform fault in the northwest Indian Ocean that separates the Arabian and African Plates from the Indian Plate. Extending north-northeast from where the Carlsberg Ridge meets ...

in the northern end of the CIR is traditionally said to separate the Indian-Australian plate from the

Arabian Plate The Arabian Plate is a minor tectonic plate in the Northern and Eastern Hemispheres. It is one of the three continental plates (along with the African and the Indian Plates) that have been moving northward in geological history and colliding ...

. Movements in the Owen Fracture Zone are, however, negligible and Arabia and India are moving as a single plate. This plate, in turn, is separated from the Australian Plate by a diffuse boundary, the India– Capricorn boundary, which stretches east from the CIR near Chagos Bank to the

Ninety East Ridge The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approxima ...

and north along the Ninety East Ridge to the northern end of the

Sunda Trench The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian- Capricorn plates subduct under a part of the Eurasian Plate. It is ...

. This diffuse boundary was probably initiated in the Late Miocene and is probably related to opening of

Gulf of Aden The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Chann ...

and the uplift of the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...

Tectonic history and hotspot interaction

The CIR was opened during the separation of the

Mascarene Plateau The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately , from Seychelles in the north to Réunion in the south. The plateau covers an area of over of shallow water, wi ...

and the Chagos-Laccadive Ridge about 38 Ma, both of which are the products of the

Réunion hotspot The Réunion hotspot is a volcanic hotspot which currently lies under the island of Réunion in the Indian Ocean. The Chagos-Laccadive Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Réunion hotspot. The hotsp ...

, the only hotspot known to have interacted with the CIR. Now located 1100 km from the CIR, hotspot crossed the CIR near 18-20°S, from the Indian to the African plate, at 47 Ma. The Réunion hotspot track includes the Chagos-Laccadive Ridge on the Indian Plate which leads to the Indian west-coast where the newborn hotspot produced the

Deccan Traps The Deccan Traps is a large igneous province of west-central India (17–24°N, 73–74°E). It is one of the largest volcanic features on Earth, taking the form of a large shield volcano. It consists of numerous layers of solidified flo ...

in north-west India at 66 Ma. The only above-water structure near the CIR is the

Rodrigues Island Rodrigues (french: Île Rodrigues, link=yes ; Creole: ) is a autonomous outer island of the Republic of Mauritius in the Indian Ocean, about east of Mauritius. It is part of the Mascarene Islands, which include Mauritius and Réunion. Rod ...

, the top of the enigmatic Rodrigues Triple Junction between

Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label= Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It ...

and the CIR. The Rodrigues Ridge reaches the CIR at 19°S via a series of en echelon ridges known as the Three Magi. Volcanic rocks from the Rodrigues Island are, however, similar to 1,58-1,30 Ma-old rocks from

Réunion Réunion (; french: La Réunion, ; previously ''Île Bourbon''; rcf, label= Reunionese Creole, La Rényon) is an island in the Indian Ocean that is an overseas department and region of France. It is located approximately east of the island o ...

and Mauritius and the Rodrigues Ridge can't therefore have originated on the CIR leaving the Réunion hotspot the most likely candidate.

References

Notes

Sources

* * *

External links

* {{Coord, 34.6555, S, 54.4828, E, source:wikidata, display=title Underwater ridges of the Indian Ocean