The Rodrigues triple junction (RTJ), also known as the central Indian ceantriple junction (CITJ) is a geologic triple junction in the southern

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

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 Rodrigues ( ; Mauritian Creole, Creole: ) is a Autonomous administrative division, autonomous Outer islands of Mauritius, outer island of the Republic of Mauritius in the Indian Ocean, about east of Mauritius. It is part of the Mascarene Isl ...

which lies 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.

Boundaries

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 The Central Indian Ridge (CIR) is a north–south-trending mid-ocean ridge in the western Indian Ocean. Geological setting The morphology of the CIR is characteristic of slow to intermediate ridges. The axial valley is 500–1000 m deep; ...

(CIR, between the African and Indo-Australian plates) with a spreading rate of 50 mm/yr; the Southwest Indian Ridge (SWIR, between the African and Antarctic plates) 16 mm/yr; and the

Southeast Indian Ridge The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost between the Rodrigues triple junction () in the Indian Ocean and the Macquarie triple junction () in the ...

(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 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 Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal Aus ...

boundary; and the SWIR by the Nubian– Somalian boundary. For example, the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. It was formerly considered to be part of a l ...

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.

Tectonic evolution

The RTJ was born when the Seychelles microcontinent drifted off the

Indian plate The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...

at 64 Ma and 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 Carls ...

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 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 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 the RTJ.

References

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Sources

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