Series of en echelon normal faults mark the trace of the Rodriquez triple junction on Antarctica

What is it about?

The Indian Ocean Triple Junction, otherwise known as the Rodriguez Triple Junction, is the point where the African, Indo-Australian and Antarctic plates meet. It is also where the Central Indian Ridge (CIR), Southwest Indian Ridge (SWIR) and Southeast Indian Ridge (SEIR) meet. From earlier work, the triple junction was expected to be a ridge-ridge-ridge type (three ridges meeting at a point). In this article, the structures originally produced at or near the triple junction and now left on the three tectonic plates were studied with a reconnaissance sonar, bathymetry, gravity and magnetic anomalies. On the Antarctic plate, we found a series of en échelon faults representing the easterly end of the paleo-SWIR. These suggest that the rift valley of the easterly SWIR continually propagated eastwards and then became abandoned by subsequent ridge jumps. Rift shoulders appear to follow simple flexural displacements (flexure of the lithosphere as a result of unloading by the rift normal faults) with modest plate elastic thicknesses of 2-5 km. Matching features on the different plates, in particular, across the SWIR (Africa-Antarctica), provided an assessment of finite plate rotations in the literature and intraplate deformation.

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Why is it important?

The Rodriguez is arguably the simplest of the triple junctions that are at large-scale ridge-ridge-ridge. Even here, however, the triple junction appears to have evolved in a series of rift jumps of the slow-extending SWIR. The unusual geometry here allows us to assess the flexural rigidity of the lithosphere from unloading by normal faulting, suggesting an elastic plate thickness of only 2-5 km for young lithosphere created at the SEIR.