Chile Ridge

It extends from the triple junction of the Nazca, Pacific, and Antarctic plates to the Southern coast of Chile.

[1][2] The ridge-collision has generated a slab window beneath the overlying South America Plate, with smaller volume of upper mantle magma melt, proven by an abrupt low velocity of magma flow rate below the separating Chile ridge.

This is because the Chile ridge subducts beneath the Taitao Peninsula, which give rise to unique lithologies there.

[2] Due to the subduction of the Chile Ridge beneath the South American plate, there were intrusive magmatism which generates granite.

[2][8] Taitao ophiolite lithosphere forms a special sequence from the top to bottom: pillow lavas, sheeted dike complex, gabbros and ultramafic rock units.

[2][9] The thermal configuration and the structure of the subduction zone affects the interactions of the oceanic lithosphere, seafloor sediments, the eroded rock from the overlying South American plate, and the sub-arc mantle wedge as well as the chemical composition of the magma, that melts from the mantle.

[2] Due to the subduction of oceanic ridges (Chile Ridge) beneath the South American plate which has occurred since 16 Ma, this caused the alteration in the thermal configuration and the geometry of the sub-arc mantle wedge, creating a distinct chemical composition of magma generations.

[2] This has found that the slab window produced by the subduction of the ridge causes the generation of alkali basalt.

[2][6] (5.19 Ma) Bathymetry of the Chile ridge is inspected, which is the submarine topography that studies the depths of landforms under the water level.

[1] The experimental results from the magnetic anomalies within the oceanic crust suggest that about in 14–10 Ma (late-Miocene), some of the Chile Ridge segments were subducted beneath the Southern Patagonian Peninsula (located between 48° and 54°S) subsequently.

[13] A slab window is formed as the Nazca and Antarctica Plate continues to diverge when colliding with Chile trench, a gap is created as new lithosphere production is becomes very slow.

[14][3][15] Moderate to high offshore seismicities for magnitude higher than 4 is detected in the segmented Chile Ridge as well as the transform faults.

Furthermore, intraplate seismicity in the overriding South American plate is more likely resulted from the deformation of the Liquiñe-Ofqui fault system.

It is proved that Chiloe microplate (Fig-5, 6) is migrated northwards relative to the South American plate which is rather immobile.

[13] The northward migration of Chiloe Microplate along the Liquiñe-Ofqui fault creates the Golfo de Penas basin in the late Miocene period.

Nevertheless, in 2007, the Liquiñe-Ofqui fault system releases the accumulated stress brought by the subduction of Nazca underneath the South America Plate with seismicity magnitude reaching 7 in an earthquake.

The reason behind this is that the Antarctica Plate undergoes shallow subduction which causes very limited seismic deformation.

It is formed when the segments of separating Chile Ridge subducts under the southern South America Plate.

[15][1][2][17] The ridge segment between Taitao and Darwin transform faults are currently located near the Chile Trench and collide with the South American plate.

The presence of slab window underneath southern South America Plate has been proven by the research which aims at determining the lithosphere and upper mantle structure proximate to the Chile Ridge.

[14][8] The experimental results of the P wave travel-time tomography show there is low-velocity zone in the predicted slab window location, migrating eastward with increasing depth.

Same bathymetry data also discovered the Fault zones in East Pacific Rise as well as the low-velocity-spreading Mid-Atlantic ridge.

[4] The Valdivia Fault Zone has caused the offset of the north and south Chile ridge for more than 600 km in the E-W direction.

[1] Ridge-parallel abyssal hills present on both sides of the axial valley Geophysical and geothermal analysis in the southern Chile triple junction has been examined.

[8] Chile Ridge segment within the Taitao fracture zone collides with the southern end of the trench.

[8] Furthermore, by the application of bottom-simulating reflectors (BSR), more convincing evidence of the existence of high heat flow underneath the trench slope, as a wider range of heat flow observations grid is shown from the north to the south of the triple junction.

[4] In addition, due to the presence of the Patagonian slab window and the obduction of the Nazca plate, the geological process that happened historically are not the same.

[4] Therefore, the Chile Ridge subduction is not conformable with the uniformitarian principle (geological process happened now is the same with that in the past).

[19] The subduction of Kula-Farallon/Resurrection ridge started during Late Cretaceous-Paleocene, this is currently located at the Chugach complex, Alaska where mafic-ultramafic high grade metamorphism is found nowadays.

Relationship of the Chile Ridge (Chile Rise) and other plate boundaries (CTJ=Chile triple junction; Yellow arrows show direction of relative motion of plates)
Fig-1 Map of the Chile ridge in the Pacific Ocean. The red line and red letters 'CR' represents Chile ridge. The ridge is divided into numerous segments of the fault line indicated by black lines. 'FZ' means fracture zone . The pink arrows indicate the direction of the Nazca plate and Antarctic plate movements as well as their rate of migration. They show that the Nazca plate is moving in an ENE direction, which is oblique to the boundary with the South American plate , while the Antarctica Plate is moving in an E-W direction, which is almost perpendicular to the plate boundary. In addition, the Nazca plate migrates over four times faster than the Antarctica Plate. The dark purple circle shows the Taitao Peninsula where the Chile ridge collides to the South American plate. The yellow line shows the plate boundary . [ 1 ]
Fig-2 shows the geology of the Taitao Peninsula . Taitao granites and Taitao ophiolites would be mainly focused on in this part. Chile ridge is located west of the Taitao Peninsula, and the geology of Chile Ridge is closely associated with that of Taitao Peninsula. [ 5 ] [ 6 ] [ 4 ]
Fig-3 shows a close up view of the spreading Chile Ridge . With difference relative plane motion of Nazca plate and Antarctica plate, this creates an extensional force for sea floor spreading to carry out. [ 11 ]
Fig-4 shows the Evolutionary diagram of the Chile Ridge Movement. The magmatism of under Taitao Peninsula from about 6 Ma to 5.7–5.1 Ma is shown. CTJ stands for Chile triple junction. A) The ridge is located at the edge of the Chile Trench. the Magma chambers developed and cause the upwelling of the ophiolite onto the surface of the spreading ridge. Cabo Raper pluton is also shown in the diagram. B) The old magma chamber is pushed away by the new magma chamber. Some ophiolite was also formed when the Nazca plate obducted and uplift. A new magma chamber was generated. The Chile Ridge segment subducts beneath the South American plate. [ 5 ] [ 4 ]
Fig-5 This sketch shows the cross-section of the slab window. The Nazca plate and Antarctic plate is colliding with South American plate. [ 3 ]
Fig-6 This figure shows the slab window caused by the subduction of Chile ridge , slab window also brings about a seismic gap . The black lines are fault zones (FZ) and the red lines are Chile ridge segments. The dark blue spot is the Chile triple junction (CTJ). [ 16 ] [ 14 ] The purple area reveals the Chiloe Microplate and Liquine-Ofqui fault zone is located between the Chiloe Microplate and the main South American plate. [ 14 ] [ 16 ]
Fig-7 This picture shows the several segments of Chile ridge which is divided by numerous transform fault zones . The segment numbers are shown in red words next to the ridge segments. The Chiloe Microplate is located at the east of the Chile ridge and the Liquine-Ofqui fault zone is located between the Chiloe Microplate and the main South American plate. [ 9 ] Figure made with GeoMapApp (www.geomapapp.org)
Fig-8 The contour lines show the hourglass morphology of one of the segments of the Chile Ridge. Below is the cross-section of the Chile Ridge topography. [ 9 ]