The Chile Triple Junction (or Chile Margin Triple Junction) 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 ...

located on the seafloor of the

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

off Taitao and

Tres Montes Peninsula The Tres Montes Peninsula ( es, Península Tres Montes, 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 situa ...

on the southern coast of

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

. Here three

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

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 tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the N ...

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 ...

. 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 dive ...

, the

Chile Rise The Chile Ridge, also known as the Chile Rise, is a submarine oceanic ridge formed by the divergent plate boundary between the Nazca Plate and the Antarctic Plate. It extends from the triple junction of the Nazca, Pacific, and Antarctic plates ...

, being subducted under the South American Plate at the

Peru–Chile Trench The Peru–Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about off the coast of Peru and Chile. It reaches a maximum depth of below sea level in Richards Deep () and is approximately long; ...

. 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 The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

forming the Chile Triple Junction. At first the Antarctic Plate subducted only in the southernmost tip of

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

, 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 Tierra del Fuego to the south. The strait is considered the most important natural ...

. 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 is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

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 projection of the mainland of Chile, with which it is connected by the narrow Isthmus of Ofqui, over which the natives and early missionaries were accustomed to carry their bo ...

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 the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...

. 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 Continental may refer to: Places * Continent, the major landmasses of Earth * Continental, Arizona, a small community in Pima County, Arizona, US * Continental, Ohio, a small town in Putnam County, US Arts and entertainment * ''Continental'' (a ...

. 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 land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...

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 dive ...

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 The Juan Fernández Ridge is a volcanic island and seamount chain on the Nazca Plate. It runs in a west–east direction from the Juan Fernández hotspot to the Peru–Chile Trench at a latitude of 33° S near Valparaíso. The Juan Fernández I ...

(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 portion of the upper mantle that behaves elastically on time scales of up to thousands of years ...

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 In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment Sediment is a naturally occurring material that is broken down by processes of weathering and e ...

and

metavolcanic Metavolcanic rock is volcanic rock that shows signs of having experienced metamorphism. In other words, the rock was originally produced by a volcano, either as lava or tephra. The rock was then subjected to high pressure, high temperature or both ...

rocks of Paleozoic age intruded by Cretaceous and Tertiary, acidic, I-type

plutonic rocks Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...

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 Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

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 Taitao ophiolite ( es, Ofiolita de Taitao) is an ophiolite in Taitao Peninsula of western Patagonia, Chile. The ophiolite crops out about 10 km w to the east of the Peru-Chile trench and 50 km to the south of Chile Triple Junction —two features ...

, 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 topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...

References

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