Aden–Owen–Carlsberg triple junction
The Aden–Owen–Carlsberg triple junction (AOC) is where three tectonic plates meet in the northwest Indian Ocean: the Arabian, Indian, and Somali (Somalia) plates. It connects the Aden Ridge, the Owen fracture zone, and the Carlsberg Ridge.
Originally, it was described as one of only a few ridge–ridge–fault junctions on Earth, but such unstable setups soon evolve into junctions where all three arms are ridges. Since about 10 million years ago, the AOC has moved westward in steps along the Aden Ridge.
West of the southern end of the Owen fracture zone lies the Beautemps-Beaupré Basin, a budding plate boundary that is expected to shift from the Arabian plate to the Indian plate in the near future.
The Carlsberg Ridge opened between the Seychelles and India in the early Cenozoic and has gone through three spreading phases: a fast early stage about 61–51 million years ago, with relatively rapid spreading; a long ultra-slow stage about 39–23 million years ago during the India–Eurasia collision; and the present slow spreading, fastest toward its northern end. The current phase began with the Gulf of Aden opening, as the Aden Ridge began to spread westward quickly, at roughly 200 kilometers per million years.
The Owen fracture zone, with the Dalrymple Trough to the north, acts as a transform boundary that links the spreading at Carlsberg with the Himalayan subduction to the north. North of the triple junction, the fracture zone shows mostly right-lateral slip, indicating Arabia moving north faster than India.
Reconstructing past motions shows that before about 11 million years ago, the relative motion between Nubia and Somalia was faster and had a significant sideways component, a detail geologists infer from studying the AOC.
This page was last edited on 3 February 2026, at 16:47 (CET).