The Azores triple junction (ATJ) 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 be ...

where the boundaries of three tectonic plates intersect: the North American plate, the Eurasian plate and the African plate. This triple junction is located along the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a Divergent boundary, divergent or constructive Plate tectonics, plate boundary) located along the floor of the Atlantic Ocean, and part of the List of longest mountain chains on Earth, longest mountai ...

(MAR) amidst the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

islands, nearly due west of the

Strait of Gibraltar The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Europe from Africa. The two continents are separated by 7.7 nautical miles (14.2 kilometers, 8.9 miles) at its narrowest point. Fe ...

. It is classified as an R-R-R triple junction of the T type (for its shape), as it is an intersection of the Mid-Atlantic Ridge running north–south and the

Terceira Rift The Terceira Rift is a geological rift located amidst the Azores islands in the Atlantic Ocean. It runs between the Azores triple junction to the west and the Azores–Gibraltar transform fault to the southeast. It separates the Eurasian pla ...

which runs east-southeast. The spreading rate along the MAR does not change abruptly at the ATJ, instead decreasing from 22.9±0.1 mm/yr at 40°N to 19.8±0.2 mm/yr at 38°N. This means the ATJ is not a simple triple junction where three tectonic plates meet at a point. The transitional range of spreading rates instead indicates the presence of a

microplate A microplate, also known as a microtiter plate, microwell plate or multiwell, is a flat plate with multiple "wells" used as small test tubes. The microplate has become a standard tool in analytical research and clinical diagnostic testing lab ...

, commonly referred to as the Azores Microplate, although the observed behaviour can also be explained in terms of a diffuse boundary. Its northern boundary intersects the MAR between 39.4°N and 40.0°N and its southern between 38.2°N and 38.5°N. The microplate moves about 2 mm/yr east-northeast along its Nubian (African plate) boundary.

References

Notes

Sources

* *
Tectonics of the Azores

External links

Main tectonic structures that can be defined in the area of the Azores triple junction
Triple junctions Mid-Atlantic Ridge {{tectonics-stub