The Chile triple junction (or Chile margin triple junction) is a geologic triple junction located on the seafloor of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

off Taitao and

Tres Montes Peninsula The Tres Montes Peninsula (, English: ''Three Hills Peninsula'') is a southwestward projection of Taitao Peninsula which in turn connects to the mainland of Chile by the narrow Isthmus of Ofqui. The peninsula is situated in Aysén del General ...

on the southern coast of

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

. Here three

tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

plates meet: the

South American plate The South American plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African plate, with which it forms the southern part of the Mid ...

, the

Nazca plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

and the Antarctic plate. This triple junction is unusual in that it consists of a

mid-oceanic ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a ...

, the Chile Rise, being subducted under the South American plate at the Peru–Chile Trench. The Chile triple junction is the boundary between the Chilean Rise and the Chilean margin, where the Nazca, Antarctic, and South American plates meet at the trench.

Tectonic plate movement

The Antarctic plate started to subduct beneath South America 14 million years ago in the Miocene epoch forming the Chile triple junction. At first the Antarctic plate subducted only in the southernmost tip of

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

, meaning that the Chile triple junction lay near the

Strait of Magellan The Strait of Magellan (), also called the Straits of Magellan, is a navigable sea route in southern Chile separating mainland South America to the north and the Tierra del Fuego archipelago to the south. Considered the most important natura ...

. As the southern part of Nazca plate and the Chile Rise became consumed by

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

and the more northerly regions of the Antarctic plate begun to subduct beneath Patagonia so that the Chile triple junction advanced gradually to its present position in front of

Taitao Peninsula The Taitao Peninsula ( Spanish: ''Península de Taitao'') is a westward-facing landmass on the south-central Pacific west coast of Chile. The peninsula is connected to the mainland via the narrow Isthmus of Ofqui, over which tribal peoples and ea ...

at 46°15'. The South American plate is moving away from the Nazca plate and moving in a direction to the north of the Chile ridge spreading center, while the Nazca plate is subducting under the South American plate at a rate of about 80–90 mm/a north of the triple junction. The triple junction of the Chile Ridge, the Chile Trench and the Antarctic plate collided about 14 Ma ago near the latitude of

Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South America, South American mainland, across the Strait of Magellan. The archipelago consists of the main is ...

. Since then it has migrated north, with the actual triple junction now located at 46°12'S.The Chilean margin consists of the Nazca-Antarctic spreading center, the Chile Rise or Chile Ridge, and the Chile Ridge, with the Nazca-Antarctic spreading center being at 46.5° S, the Chile Rise or Chile Ridge being more prominent in the south. Additionally around 14 Ma, the Chile Rise collided with the South American continental plate. The high relief

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

caused the trench to be devoid of sediment at the Chile-South America junction.

Subduction

Subduction accretion is an important process that leads to mountain building and the growth of continents, but it is also associated with the destruction of forearc material. The impact of topographic features, such as topographic features of mountain ranges and faulting, is one important mechanism. An impact between a

spreading ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a d ...

and a continental forearc can result in a thermal pulse within the forearc. This thermal pulse can be quantified using apatite fission track data and the thermal maturity of organic carbon in the forearc sediment. Several authors have suggested that subduction erosion or slip during earthquakes may be responsible for the uplift of the Coastal Cordillera, a trench-parallel morphostructural system in north Chile.

Geologic characteristics

The Juan Fernández Ridge (JFR) is a prominent feature on the oceanic Nazca

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

located west of the Chile Trench. The O'Higgins seamount group, surrounded by a topographic swell, acts as a barrier between the north and south half of the Chile Trench.

Sedimentary compositions

The continental basement of southern Chile is mainly formed of metasedimentary and metavolcanic rocks of Paleozoic age intruded by Cretaceous and Tertiary, acidic, I-type plutonic rocks of the Patagonian Batholith. In the southern-central Chilean margin, the sediment in the Chile trench is confined to the Chile Rise. The trench is unusually poor in sediments north of the JFR, but is heavily sedimented south of the Chile triple junction. The accretionary prism is confined between the two large topographic features, the Chile Rise and the JFR. The northern Chilean margin is poor in sediments due to low sediment supplies from the

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

and the presence of the JFR, which acts as a barrier to the transport of trench sediments from the southern Chile trench to the north.

Ophiolites

lies near the triple junction and various geological features, such as the Taitao ophiolite, are related to the dynamics of the triple junction. Ridge and trench collisions are clear indications of the

history around the

and are likely a dominant mechanism of ophiolite positioning. This results in a rapid sinking and spreading along with magmatic activity near the

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

References

Tectonics of South America: Chile Triple Junction
{{Triple Junctions Plate tectonics Triple junctions Geology of Aysén Region