The Central Indian Ridge ( CIR ) is a north–south-trending mid-ocean ridge in the western Indian Ocean .
23-450: 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
46-789: 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 and north along the Ninety East Ridge to the northern end of the Sunda Trench . This diffuse boundary was probably initiated in the Late Miocene and is probably related to opening of Gulf of Aden and
69-626: A spreading rate of 30 mm/yr near the Equator and 49 mm/yr near the Rodrigues triple junction (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
92-667: A stable R-R-R (ridge-ridge-ridge) triple junction based on coarse ship data. The boundaries of the three plates that meet at the Rodrigues triple junction are all oceanic spreading centers, making it an R-R-R type triple junction. They are: the Central Indian Ridge (CIR, between the African and Indo-Australian plates) with a spreading rate of 50 mm/yr; the Southwest Indian Ridge (SWIR, between
115-610: Is a configuration similar to that of the Galápagos triple junction in the east Pacific. Each time the RTJ offset eastward a new segment is added to CIR. resulting in a constant length for the SEIR while CIR constantly lengthens. Spreading rates in the SWIR, in contrast, is intermittent and very slow, but the extension of the plates in the SEIR and CIR causes constant lengthening of the SWIR near
138-556: The Arabian plate . 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 and north along the Ninety East Ridge to the northern end of the Sunda Trench . This diffuse boundary
161-617: The East African Rift divides Africa into the Nubian and Somalian plates. These plates converge in the southern part of the rift valley (2 mm/yr) but diverge in the northern part (6 mm/yr) and a very slight difference in spreading rates across the central part of the ultra-slow SWIR indicates there is a vague triple junction somewhere south of Madagascar. The RTJ was born when the Seychelles microcontinent drifted off
184-559: The Indian plate at 64 Ma and the Carlsberg Ridge opened. Since then the RTJ has moved eastward from south of Madagascar (modern coordinates) to its current location. Since 65 Ma the RTJ has been migrating north-east at a decreasing rate: originally the velocity was 10 cm/yr, at 43 Ma 2.6 cm/yr, and since 41 Ma around 3.6–3.8 cm/yr. The stability in migration rate around 41 Ma coincides with
207-577: 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
230-549: The African and Antarctic plates) 16 mm/yr; and the Southeast Indian Ridge (SEIR, between the Indo-Australian and Antarctic plates) 60 mm/yr. The SEIR has the highest spreading rates at the RTJ, and, while now considered an intermediate spreading centre, it was a fast spreading ridge between anomalies 31 and 22, with a rate of 110 km/myr at anomaly 28. The spreading rate is similar in
253-538: The CIR but slower and the ridge has a more complex geometry. The SWIR has ultra-slow spreading rates, a rough topography, and great number of large offset fracture zones. All three boundaries are themselves intersected by diffuse boundaries: the CIR is intersected by the Indian – Capricorn boundary; the SEIR by the Capricorn– Australian boundary; and the SWIR by the Nubian – Somalian boundary. For example,
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#1732765421340276-459: 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
299-555: The CIR increases from 3200 m at 20°S to 4000 m at the RTJ. The CIR is traditionally said to separate the African plate from the Indo-Australian plate . Likewise, the Owen Fracture Zone in the northern end of the CIR is traditionally said to separate the Indian-Australian plate from the Arabian plate . Movements in the Owen Fracture Zone are, however, negligible and Arabia and India are moving as
322-687: 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 in north-west India at 66 Ma. The only above-water structure near the CIR is the Rodrigues Island , the top of the enigmatic Rodrigues triple junction between Mauritius and
345-401: The CIR, including the Carlsberg Ridge , 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. The CIR is traditionally said to separate the African plate from the Indo-Australian plate . Likewise, the Owen Fracture Zone in the northern end of the CIR is traditionally said to separate the Indian-Australian plate from
368-416: The Chagos-Laccadive Ridge on the Indian plate which leads to the Indian west-coast where the newborn hotspot produced the Deccan Traps in north-west India at 66 Ma. The only above-water structure near the CIR is the Rodrigues Island , the top of the enigmatic Rodrigues triple junction between Mauritius and the CIR. The Rodrigues Ridge reaches the CIR at 19°S via a series of en echelon ridges known as
391-631: The RTJ. 25°30′S 70°00′E / 25.500°S 70.000°E / -25.500; 70.000 Central Indian Ridge The Central Indian Ridge ( CIR ) is a north–south-trending mid-ocean ridge in the western Indian Ocean . 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
414-709: The Three Magi. Volcanic rocks from the Rodrigues Island are, however, similar to 1,58-1,30 Ma-old rocks from Réunion and Mauritius and the Rodrigues Ridge can't therefore have originated on the CIR leaving the Réunion hotspot the most likely candidate. 34°39′20″S 54°28′58″E / 34.6555°S 54.4828°E / -34.6555; 54.4828 Rodrigues triple junction The Rodrigues triple junction ( RTJ ), also known as
437-414: The axial floor. With a spreading rate of 30 mm/yr near the Equator and 49 mm/yr near the Rodrigues triple junction (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)
460-479: The bend in the Hawaiian–Emperor seamount chain — hinting at a global reorganisation of tectonic plates at this time. Originally considered a stable RRR (ridge–ridge–ridge) triple junction, the RTJ is now believed to be an unstable RRF (ridge–ridge–fault) triple junction in which the axis of the CIR is offset eastward by 14 km/myr because of differences in spreading rates between the SEIR and CIR. This
483-455: 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 , trends NNW and lacks fracture zones. The axial depth of
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#1732765421340506-682: The uplift of the Himalayas . The CIR was opened during the separation of the Mascarene Plateau and the Chagos-Laccadive Ridge about 38 Ma, both of which are the products of the Réunion hotspot , 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
529-421: Was probably initiated in the Late Miocene and is probably related to opening of Gulf of Aden and the uplift of the Himalayas . The CIR was opened during the separation of the Mascarene Plateau and the Chagos-Laccadive Ridge about 38 Ma, both of which are the products of the Réunion hotspot , the only hotspot known to have interacted with the CIR. Now located 1100 km from the CIR, hotspot crossed
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