The Rodrigues Triple Junction (RTJ), also known as the Central Indian ceanTriple Junction (CITJ) is a geologic

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can b ...

in the southern

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 th ...

where three tectonic plates meet: 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 Plat ...

, 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 ...

, and the

Antarctic Plate The Antarctic Plate is a tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and some remote islands in the Southern Ocean and other surrounding oceans. After breakup from Gondwana (the southern part of the superconti ...

. The triple junction is named for the island of

Rodrigues 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. Rodr ...

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 which 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 The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...

(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 Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...

– 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 Au ...

boundary; and the SWIR by the

Nubian Nubian may refer to: *Something of, from, or related to Nubia, a region along the Nile river in Southern Egypt and northern Sudan. *Nubian people *Nubian languages *Anglo-Nubian goat, a breed of goat * Nubian ibex * , several ships of the Britis ...

– 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. In the past it was considered to be part of a ...

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 The Seychelles Microcontinent is a microcontinent underlying Seychelles in the western Indian Ocean made of Late Precambrian rock. The granite outcrops of the Seychelles Islands in the central Indian Ocean were amongst the earliest examples cit ...

drifted off the

Indian Plate The Indian Plate (or India Plate) is 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 , began mov ...

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 the bend in the

Hawaiian–Emperor seamount chain The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, ...

— 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 Galapagos 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

Notes

Sources

* * * * * * * * * * {{coord, 25, 30, S, 70, 00, E, type:waterbody_source:kolossus-jawiki, display=title Triple junctions Plate tectonics