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 to the Southern coast of Chile. [1] [2] The Chile Ridge is easy to recognize on the map, as the ridge is divided into several segmented fracture zones which are perpendicular to the ridge segments, showing an orthogonal shape toward the spreading direction. The total length of the ridge segments is about 550–600 km. [1]
The continuously spreading Chile Ridge collides with the southern South America Plate to the east, and the ridge has been subducting underneath the Taitao Peninsula since 14 million years ago (Ma). [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. [2] [1] [3] The subduction generates a special type of igneous rocks, represented by the Taitao ophiolites, which is an ultramafic rock composed of olivine and pyroxene, usually found in oceanic plates. [4] [2] In addition, the subduction of the Chile Ridge also creates Taitao granite in Taitao Peninsula which appeared as plutons. [2] [5]
The Chile Ridge involves spreading ridge subduction which is worth studying because it explains how the Archean continental crust initiation formed from deep oceanic crust. [4]
From approximately 14 to 3 million years ago, a series of trenches collided the Chile Trench, forming what is part of the Chile Ridge.[ citation needed ]
In the 2010 Concepcion earthquake (magnitude 8.8) struck the ridge.[ citation needed ]
The geology of the Chile ridge is closely related to the geology of the Taitao Peninsula (East of the Chile ridge). This is because the Chile ridge subducts beneath the Taitao Peninsula, which give rise to unique lithologies there. [4] [5] The lithological units would be discussed from youngest to oldest, and Taitao Granites and Taitao Ophiolite would be our main focus.
Adakite magmatism is formed by the melting of the Nazca Plate’s trailing edge. [2] Due to the subduction of the Chile Ridge beneath the South American Plate, there were intrusive magmatism which generates granite. [4] This is also formed by the partial melting of the subducted oceanic crust. [4] [5] The young Nazca crust (less than 18 Myr old) are warmer so that the metamorphosed subducted basalts are melted. [5] [4] In normal mid-oceanic ridge, the presence of volatiles like water also reduces the solidus temperature. [4] However, in Chile Ridge, there is relatively low-extent (20%) of partial melting of the lithosphere, the pressure and the temperature of the partial melting is less than 10 kbar and higher than 650° respectively. [4] This is because the warm young Nazca Plate has hindered high rate of cooling and dehydration. The partial melting of the Taitao granite creates plutons like the Cabo Raper adakitic pluton. [4]
Adakite is a felsic to intermediate rock and are usually calc-alkaline in composition. It is also silica-rich. [2] The partial melting causes the alteration of the subducted basalts into eclogite and amphibolite which contains garnet. [4]
Along the axis in the Chile ridge, magmatic rocks which are mafic to ultramafic are emplaced. [4] For instance, the Taitao ophiolite complex is discovered in the westernmost of the Taitao Peninsula (east of the Chile Ridge), about 50 km southeast of the Chile Triple Junction. This is contributed by the obduction of the Nazca Plate produced due to the convergence of the overriding South America Plate and the Chile ridge Tres Montes segment. [2] [7] The obduction and the thrusting causes low-pressure metamorphism and forms the ophiolite complex. This metamorphism indicates the onset of hydrothermal alteration in a spreading ridge environment. [4] [7] There are also recent activities of acidic magmas in the Taitao Peninsula which allows the comparison between the past composition and current composition, history of the magma can be determined. [2] [8]
Taitao ophiolite lithosphere forms a special sequence from the top to bottom: pillow lavas, sheeted dike complex, gabbros and ultramafic rock units. For the ultramafic rock units, it proved that there are at least two melting events that happened before. [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] That means by understanding the composition of the magma, specific conditions of subduction systems can be known. [2] This has found that the slab window produced by the subduction of the ridge causes the generation of alkali basalt. The ridge-trench convergence and slab window generation aids the emplacement of the alkaline basalts. [2] [6]
Age of the rocks | Kinds of magmatism | Rock type | Subduction settings | Composition |
---|---|---|---|---|
Holocene | / | Conglomerate | / | Variable compositions: rock fragments from Taitao granites, ophiolite, |
Late-Miocene (3.92 Ma, 5.12 Ma) | Arc magmatism | Taitao Granites | low-extent partial melting of the altered basalt (from the trailing edge of Nazca Plate) in a hot subduction event beneath the volcanic arc | intermediate to felsic, calc-alkaline, adakites: high Sr/Y and La/Yb ratio |
Late-Miocene (5.19 Ma) | Arc magmatism | Taitao Ophiolite | obduction and uplift of the Nazca Plate produced due to the convergence of the overriding South America Plate and the Chile ridge, causing low-pressure metamorphism | mafic to ultramafic, olivine and pyroxene |
Pre-Jurassic | / | Meta-sedimenary basement | / | / |
Bathymetry of the Chile ridge is inspected, which is the submarine topography that studies the depths of landforms under the water level. [10] It is discovered that there are large abyssal hills extend along two sides of the ridge. The abyssal hills grow cyclically which is caused by the cyclic fault growth. During faulting cycles, the extension of the Chile ridge brought about 'diffusion' tectonic deformation which forms numerous tiny faults. The continuous divergence of the ridge causes the extensional strain to concentrate, the tiny faults to link together to generate tall and long abyssal-hill-scale faults. The huge faults push the old and inactive faults away from the ridge axis by extensional force. This process would repeat again. Therefore, the further the abyssal hill to the ridge axis, the older the age it is. [9]
The Chile Ridge is formed by the divergence of the Nazca and Antarctica plates. [4] It is spreading actively at the rate of about 6.4 – 7.0 cm/year since 5 Ma to present. [4] The Late Miocene Nazca-Antarctic spreading ridge formation creates about 550 km-long Chile Ridge as there are differences in the convergence rates between Nazca and Antarctica plates. [2] According to the results from space geodetic observations, Nazca-South America converges four times faster than that of Antarctica-South America. [1] [9]
In addition, the direction of the Nazca Plate migration is different from the Antarctica plate migration since 3 Ma. The direction that Nazca plate moves is ENE, while the Antarctic plate is ESE. The net diverging movement of the two plates contributes to the spreading of the Chile Ridge. [4]
Name of the Plate | Direction of movement | Rate of movement |
---|---|---|
Nazca plate | N77°E (ENE) | 6.6–8.5 cm/year |
Antarctica plate | N100°E (ESE) | 1.85 cm/year |
The subduction of the ridge started is an oblique subduction with 10° – 12° oblique to the Chile trench since 14 Ma, [4] which subducts beneath the southeastern Southern Patagonia. [1] [4] Thus it is found that both the Nazca-South American Plate collision and Antarctic-South American Plate collision have been taken place at the same time when the Chile ridge is separating, i.e. segments of Chile Ridge have been subducting beneath the South American Plate. [1] Due to the difference in the convergence rate, the formation of a slab window is favoured. [1] Slab window is a gap underneath the South America Plate, where the overriding South America Plate has only little lithospheric mantle supporting it and is directly exposed to the hot asthenospheric mantle. [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. [2] From 10 Ma to the present, Chile Ridge was separated into several short segments by the fracture zones, and the segments of the ridge are subducted between 46° and 48° S. [2] [1] The above findings have proven that Chile Ridge has been encountered a northward migration. [2] [9] [4] Thus it has been found that the spreading rate of Chile Ridge from 23 Ma to the present has slowed down. While the spreading rate of the ridge is correlated to time of the collisions of ridge and trench. [1] Some studies have different discoveries in the rate of spreading which shows that the ridge may have spread uniformly for about 31 km/Myr half spreading rate starting from 5.9 Ma. [9]
In the Chile Ridge Subduction Project (CRSP), seismic stations are deployed in the Chile Triple Junction (CTJ). [12] The tectonic activity and seismicity are mainly driven by the subduction of Chile Ridge. [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. [12] It is predicted that the subduction of the spreading Chile Ridge under South America to the north of the Chile Triple Junction give rise to the seismic event. Furthermore, intraplate seismicity in the overriding South American Plate is more likely resulted from the deformation of the Liquiñe-Ofqui fault system. [14] [13] [16]
This is a tiny plate between Nazca Plate and South American Plate, it locates east of the Chile ridge. It is proved that Chiloe Microplate (Fig-5, 6) is migrated northwards relative to the South American Plate which is rather immobile. The Golfo de Penas basin is formed because of the northward movement of Chiloe Microplate. [16]
The Liquiñe-Ofqui fault system is a right-lateral strike-slip fault separating Chiloe Microplate and the South America Plate. [13] The northward migration of Chiloe Microplate along the Liquiñe-Ofqui fault creates the Golfo de Penas basin in the late Miocene period. [16]
The Liquiñe-Ofqui fault is a fast-slipping fault (with a geodetic rate of 6.8–28 mm/yr). [16] Intraplate seismicity has mainly been taken place in this fault system. Also, enormous stress from the Nazca Plates and South America Plate collision has accumulated along the fault system. [16] [13] Throughout history, only limited seismic studies have been conducted in the Aysén Region, southern Chile. There is only an event of seismic magnitude higher than 7 happening in 1927. [13] This hinders the finding in seismicity near the Chile Ridge. 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. [16] Recently, 274 seismic events have been detected in 2004–2005. [16]
There is an intraplate seismicity gap between 47° and 50°S (area with abnormal high heat flow), which coincides with the Patagonian slab window, disrupting most seismic events. The local seismic data only reveals a low-magnitude (magnitude lower than 3.4) seismic event, which is not related to tectonic process. The reason behind this is that the Antarctica Plate undergoes shallow subduction which causes very limited seismic deformation. [16] [14] (Fig-5)
Regions | where the seismicity is concentrated | depth of focus (km) | magnitude of seismic event | Orientation of the maximum compressional stress |
---|---|---|---|---|
North of the Chile Triple Junction | intraplate seismic events concentrated along Liquiñe-Ofqui fault system | 4–21 | 1.5–6 | ENE-WSW (oblique to the continental margin of South American Plate of N10°) |
South of the Chile Triple Junction (between 46.5°-50°S) | seismic events sparsely populated in Southern Patagon | 12–15 | 5 | ESE-WNW |
The most obvious impact of the subduction of the Chile ridge is the formation of slab window. It is formed when the segments of separating Chile Ridge subducts under the southern South America Plate. The trailing edge of the Nazca plate is completely melted in the subduction zone, and the leading edge of the Antarctic Plate diverges, a widening gap is created between the two plates as very little crust is melted after subduction. In this case, only a very little amount of magma is produced underneath the slab window. [3] The mantle in the slab window is rather hotter than the mantle that melts from the lithospheric crust, and the generation of magma is very slow. This is due to low-extent of hydration to the subduction zone, decreasing mantle convection velocity, as the production of magma in the subduction zone is mainly driven by the hydration that lowers the partial melting of the crust. A volcanic arc gap is formed above the slab window as the magma melted from the crust convects slowly which hampers the volcanism. [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. [1] [3]
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. [3] An intraplate seismic gap is recorded which coincides with the Patagonian slab window location. [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. [3]
Other than the generation of the slab window, the Chile Ridge subduction into the Chile Triple Junction also influences the Taitao Peninsula. First of all is the tectonic erosion, Neogene basaltic volcanism and tectonic uplift in Late Cretaceous. [2] Obduction and thrusting of Nazca plate produced due to the convergence of the overriding South America Plate and the Chile ridge, causing low-pressure metamorphism, facilitated the emplacement of ophiolite complex. [13] [4]
The Chile Triple Junction is the intersection of Nazca, Antarctica and South American Plate. The position of the junction shifts over time, and depends whether the spreading ridge subducts or the transform fault subducts beneath the South American Plate. When the spreading ridge subducts, the Triple junction shifts northwards; but if the fracture zone subducts, the Triple junction shifts southwards. [1] The junction has shifted to the north starting from the onset of Chile Ridge subduction since 17 Ma after the rupture of the Nazca-Antarctic-Phoenix triple junction. [2] Since then, the Chile Triple Junction has arrived to its current position in the western Taitao Peninsula. [14] Prior to 10 Ma, Chile Triple Junction reaches the southern Taitao peninsula. Currently, the temperature of Chile Triple Junction below the depth of 10 – 20 km is predicted to be 800 – 900 °C. [18] [13]
The ridge axes are the middle part of the ridge where newer crusts are formed. The central ridge axis of Chile Ridge is trending in the direction of north-northwest (NNE). Ridge axes are also known as topographic axial rift valleys. With the help of satellite altimetry data and magnetic data, gravity lows are discovered near the ridge axes. [1]
It is also named as fault zones. They are the transform faults and separate the Chile Ridge into segments, , causing the entire ridge axis to trend southeastward. [9] [1] Fracture zones are trending east-northeast (ENE). The total length of the Chile ridge axis offset is 1380 km caused by the 18 fault zones, among the fault zones, there are also 2 complex fault systems. The longest fault zones are Chiloe fault with 234 km long, and Guafo fault being the shortest (39 km). [9] Through various research on the magnetic and bathymetry data, fracture zones’ locations are located. While major fault zones are surveyed by the bathymetry method and defined as troughs. Same bathymetry data also discovered the Fault zones in East Pacific Rise as well as the low-velocity-spreading Mid-Atlantic ridge. [1] [8] [9]
Chile Ridge is divided into a wide range of several short spreading segments which have different lengths and offset distances, in the following section, 7 segments will be discussed. [9] [1] From the table below, it reveals that the spreading ridge segments range in length from about 20 to 200 km, the offsets within segments are about 10 to 1100 km. There are actually a total of 10 first-order ridge segments in the northern ridge (N1-N10), 5 first-order ridge segments (V1-V5) in Valdivia Fracture Zone, 5 first-order ridge segments (S1-S5) are in the southern ridge. Moreover, both segments N9 and S5 are divided into two parts by non-transform offsets. The table above summarized the longer, more regular and less complicated faults: N1, N5, N8, N9N, N9S, N10, V4, S5N, and S5S.
Deep contours are located along the segment ends while shallow contours are located at the segment center. The segment center is narrower as the while the axial valley located at the segment ends are wider. This forms an hourglass morphology. (Fig-8) [9]
It is located in the middle of the Chile ridge (Fig-1, 2, 7), and separates the ridge into northern and southern sections, discovered by the bathymetry and magnetic profiles study, as well as the gravity anomaly detection. [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. There are six fault zones between the Valdivia Fault Zone. [1]
Name of the segment | Length (km) | Number of orders (No. of hourglass) | Location relative to the Chile Ridge | Morphology |
---|---|---|---|---|
N1 | 70 | First-order | Northernmost; Bounded by 1000 km-long transform fault zones in both north and south | Asymmetric hourglass, Ridge-parallel abyssal hills present on both sides of the axial valley |
N5 | 95 | First-order | Offset east of N1 for 250 km; Bounded by 'pseudofaults' between the southern end of N5 and the northern end of N6, which offset 20 km east | Asymmetric hourglass (located in short volcanic chains) |
N8 | 65 | First-order | Offset east of N9 for 80 km, bounded by a transform fault in N7 in the north, and a transform fault with offset N9 80 km | More obvious hourglass (deeper segment center, local minimum is at the shallowest part of the segment) |
N9 | 140 | Second-order (N9N and N9S) | Offset east of N8 for 80 km, and offset east of N10 for 25 km, N9 are broken into two parts by a non-transform offset (N9N and N9S), bound by the transform offset in the north and a transform offset N9 by 80 km in the south | |
N9N | 110 | Bound in the south by NTO which offset east of N9S 8 km | Two obvious hourglasses (deep, wide axial valley) | |
N9S | 30 | Semi-hourglass (shallow hourglass structure) | ||
N10 | 95 | First-order | Offset west of N9 for 25 km, bounded by a transform fault that offsets west of N9 in the north, and Valdivia fracture Zone in the south which offset 600 km in E-W direction | Hourglass (decrease in relief towards the spreading center, i.e. middle of the ridge segment) |
V4 | 20 | First-order | In the Valdivia Fracture zone, bounded by N10 and S5 transform fault segments in the north and south, segment lengths are very short | / |
S5 | 115 | Second-order (S5N and S5S) | Bounded by Valdivia Fracture Zone transform fault in the north, and a transform fault in the south that offset next segment 60 km eastward | Hourglass |
S5N | 70 | Hourglass | ||
S5S | 45 | More obvious hourglass (inside corner of southern section is more shallow than the outside corner) |
Geophysical and geothermal analysis in the southern Chile Triple junction has been examined. Magnetic and bathymetric data have been recorded across the Chile Ridge which recognizes a slight transformation in the configuration of the spreading ridge when the ridge converges with the trench. [13] [8] [14]
The overriding South America Plate is dominantly impacted by the ridge collision. The Chile-Peru Trench becomes steeper and narrower when the Chile Ridge is subducting. [8] Chile Ridge segment within the Taitao Fracture Zone collides with the southern end of the trench. The collision of the ridge may also be associated with the obduction process onto the landward trench slope. Geothermal data along the southern Triple Junction are measured. The heat flow analysis in the collision zone of the trench indicated a high value of heat pulse (345 mW/m2) related to the Chile ridge subduction in the lower part 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. [8] Also, the hypothesized conductive heat flow is consistent with the heat flow data from BSR. [8] [12]
Understanding the spreading ridge subduction is crucial as it controls the evolution of continental crust. The subduction of the Chile Ridge beneath the Chile Trench provides a suitable analog for the initiation of the Archean continental crust via the melting of deep oceanic crust. [4] This is because the Chile Ridge subduction is the only example in the world that the overriding plate is a continental one. The correlations between the rocks in the past can also be examined. The ridge trench interaction can also be studied. [4]
In addition, due to the presence of Patagonian slab window and the obduction of the Nazca plate, the geological process that happened in different period 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. [4] The ridge subduction controls the magmatism of the North American boundary. [4]
Subduction is a geological process in which the oceanic lithosphere and some continental 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, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
Obduction is a geological process whereby denser oceanic crust is scraped off a descending ocean plate at a convergent plate boundary and thrust on top of an adjacent plate. When oceanic and continental plates converge, normally the denser oceanic crust sinks under the continental crust in the process of subduction. Obduction, which is less common, normally occurs in plate collisions at orogenic belts or back-arc basins.
A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Izanagi Plate and the Phoenix Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart and after the formation of the Pacific Plate at the centre of the triple junction during the Early Jurassic. It is named for the Farallon Islands, which are located just west of San Francisco, California.
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 Nazca Plate under the South American Plate is largely responsible for the Andean orogeny. The Nazca Plate is bounded on the west by the Pacific Plate and to the south by the Antarctic Plate through the East Pacific Rise and the Chile Rise respectively. The movement of the Nazca Plate over several hotspots has created some volcanic islands as well as east–west running seamount chains that subduct under South America. Nazca is a relatively young plate both in terms of the age of its rocks and its existence as an independent plate having been formed from the break-up of the Farallon Plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.
Forearc is a plate tectonic term referring to a region in a subduction zone between an oceanic trench and the associated volcanic arc. Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergent plate margins. A back-arc region is the companion region behind the volcanic arc.
The Mendocino Triple Junction (MTJ) is the point where the Gorda plate, the North American plate, and the Pacific plate meet, in the Pacific Ocean near Cape Mendocino in northern California. This triple junction is the location of a change in the broad plate motions which dominate the west coast of North America, linking convergence of the northern Cascadia subduction zone and translation of the southern San Andreas Fault system. This region can be characterized by transform fault movement, the San Andreas also by transform strike slip movement, and the Cascadia subduction zone by a convergent plate boundary subduction movement. The Gorda plate is subducting, towards N50ºE, under the North American plate at 2.5 – 3 cm/yr, and is simultaneously converging obliquely against the Pacific plate at a rate of 5 cm/yr in the direction N115ºE. The accommodation of this plate configuration results in a transform boundary along the Mendocino Fracture Zone, and a divergent boundary at the Gorda Ridge. This area is tectonically active historically and today. The Cascadia subduction zone is known to be capable of producing megathrust earthquakes on the order of MW 9.0.
The Gorda Ridge, aka Gorda Ridges tectonic spreading center, is located roughly 200 kilometres (120 mi) off the northern coast of California and southern Oregon. Running NE – SW it is roughly 300 kilometres (190 mi) in length. The ridge is broken into three segments; the northern ridge, central ridge, and the southern ridge, which contains the Escanaba Trough.
The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca Plate and Antarctic Plate underneath the South American Plate. The belt is subdivided into four main volcanic zones which are separated by volcanic gaps. The volcanoes of the belt are diverse in terms of activity style, products, and morphology. While some differences can be explained by which volcanic zone a volcano belongs to, there are significant differences within volcanic zones and even between neighboring volcanoes. Despite being a type location for calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a broad range of volcano-tectonic settings, as it has rift systems and extensional zones, transpressional faults, subduction of mid-ocean ridges and seamount chains as well as a large range of crustal thicknesses and magma ascent paths and different amounts of crustal assimilations.
The Chile Triple Junction is a geologic triple junction located on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula on the southern coast of Chile. Here three tectonic plates meet: the South American Plate, the Nazca Plate and the Antarctic Plate. This triple junction is unusual in that it consists of a mid-oceanic ridge, 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.
The Nazca Ridge is a submarine ridge, located on the Nazca Plate off the west coast of South America. This plate and ridge are currently subducting under the South American Plate at a convergent boundary known as the Peru-Chile Trench at approximately 7.7 cm (3.0 in) per year. The Nazca Ridge began subducting obliquely to the collision margin at 11°S, approximately 11.2 Ma, and the current subduction location is 15°S. The ridge is composed of abnormally thick basaltic ocean crust, averaging 18 ±3 km thick. This crust is buoyant, resulting in flat slab subduction under Peru. This flat slab subduction has been associated with the uplift of Pisco Basin and the cessation of Andes volcanism and the uplift of the Fitzcarrald Arch on the South American continent approximately 4 Ma.
This is a list of articles related to plate tectonics and tectonic plates.
In geology, a slab window is a gap that forms in a subducted oceanic plate when a mid-ocean ridge meets with a subduction zone and plate divergence at the ridge and convergence at the subduction zone continue, causing the ridge to be subducted. Formation of a slab window produces an area where the crust of the over-riding plate is lacking a rigid lithospheric mantle component and thus is exposed to hot asthenospheric mantle. This produces anomalous thermal, chemical and physical effects in the mantle that can dramatically change the over-riding plate by interrupting the established tectonic and magmatic regimes. In general, the data used to identify possible slab windows comes from seismic tomography and heat flow studies.
The Lau Basin is a back-arc basin at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colville Ridge, a remnant arc, sit to the eastern and western sides of the basin, respectively. The basin has a raised transition area to the south where it joins the Havre Trough.
The Troodos Ophiolite on the island of Cyprus represents a Late Cretaceous spreading axis that has since been uplifted due to its positioning on the overriding Anatolian plate at the Cyprus arc and ongoing subduction to the south of the Eratosthenes Seamount.
Flat slab subduction is characterized by a low subduction angle beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. A broader definition of flat slab subduction includes any shallowly dipping lower plate, as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism, and an eventual cessation of arc magmatism. The coupling of the flat slab to the upper plate is thought to change the style of deformation occurring on the upper plate's surface and form basement-cored uplifts like the Rocky Mountains. The flat slab also may hydrate the lower continental lithosphere and be involved in the formation of economically important ore deposits. During the subduction, a flat slab itself may deform or buckle, causing sedimentary hiatus in marine sediments on the slab. The failure of a flat slab is associated with ignimbritic volcanism and the reverse migration of arc volcanism. Multiple working hypotheses about the cause of flat slabs are subduction of thick, buoyant oceanic crust (15–20 km) and trench rollback accompanying a rapidly overriding upper plate and enhanced trench suction. The west coast of South America has two of the largest flat slab subduction zones. Flat slab subduction is occurring at 10% of subduction zones.
Cachet Fault is a dextral strike-slip fault in Aysén Region, Chile. The fault runs in north–south direction right to the east of the Northern Patagonian Ice Field. Various west-east glacial valleys have been displaced the movement of the fault. The existence of the fault and its movement has been linked to the Chile Triple Junction and the oblique subduction of Nazca Plate. The fault exhibits present-day seismicity. Together, Exploradores Fault Zone and Liquiñe-Ofqui Fault Zone and Cachet Fault makes up the boundaries of a crustal block that has been uplifted hosting at present the Northern Patagonian Ice Field.
Taitao ophiolite 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 to which it is related.
Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.