The Chile Ridge, also known as the Chile Rise, is a submarine

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 diverg ...

formed by the

divergent plate boundary In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent b ...

between the Nazca Plate 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 ...

. It extends from the triple junction of the Nazca,

Pacific 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 contine ...

, and Antarctic plates to 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 east a ...

. The Chile Ridge is easy to recognize on the map, as the ridge is divided into several segmented

fracture zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

s 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. The continuously spreading Chile Ridge collides with the southern

South America 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-A ...

to the east, and the ridge has been

subducting 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, the ...

underneath the

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 ...

since 14 million years ago (Ma). The ridge-collision has generated a

slab window 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 ...

beneath the overlying South America Plate, with smaller volume of

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from appr ...

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

melt, proven by an abrupt low

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of magma flow rate below the separating Chile ridge. The subduction generates a special type of igneous rocks, represented by the Taitao ophiolites, which is an

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rock composed of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

and pyroxene, usually found in oceanic plates. In addition, the subduction of the Chile Ridge also creates Taitao

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

in Taitao Peninsula which appeared as

plutons In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

. The Chile Ridge involves

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 diver ...

subduction which is worth studying because it explains how the Archean continental crust initiation formed from deep oceanic crust.

History

From approximately 3-14 million years ago, a series of trenches collided the Chile Trench, forming what is part of the Chile Ridge. In the

2010 Concepcion earthquake The 2010 Chile earthquake and tsunami ( es, Terremoto del 27F) occurred off the coast of central Chile on Saturday, 27 February at 03:34 local time (06:34 UTC), having a magnitude of 8.8 on the moment magnitude scale, with intense shaking la ...

, an 8.8 magnitude struck the ridge.

Regional geology

Geology of the Chile ridge

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. The lithological units would be discussed from youngest to oldest, and Taitao Granites and Taitao Ophiolite would be our main focus.

Taitao Granites (Adakite-like rocks in Late-Miocene)

Adakite Adakites are volcanic rocks of intermediate to felsic composition that have geochemical characteristics of magma originally thought to have formed by partial melting of altered basalt that is subducted below volcanic arcs. Most magmas derived ...

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

is formed by the melting of the Nazca Plate’s trailing edge. Due to the subduction of the Chile Ridge beneath the South American Plate, there were intrusive magmatism which generates granite. This is also formed by the

partial melting Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different minerals or a mineral that displays solid solution, this melt can be different from the bulk composition of the soli ...

of the subducted oceanic crust. The young Nazca crust (less than 18 Myr old) are warmer so that the

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

subducted basalts are melted. In normal

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 presence of volitiles like water also reduces the

solidus Solidus (Latin for "solid") may refer to: * Solidus (coin), a Roman coin of nearly solid gold * Solidus (punctuation), or slash, a punctuation mark * Solidus (chemistry), the line on a phase diagram below which a substance is completely solid * ...

temperature. 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. This is because the warm young Nazca Plate has hindered high rate of cooling and

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

. The partial melting of the Taitao granite creates plutons like the Cabo Raper adakitic pluton.

= Characteristics of Taitao Granites

Adakite is a felsic to intermediate rock and are usually

Calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

in composition. It is also silica-rich. The partial melting causes the alteration of the subducted basalts into

eclogite Eclogite () is a metamorphic rock containing garnet (almandine- pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, ...

and amphibolite which contains

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

Taitao Ophiolite (pillow lava, sheeted dikes, gabbro, ultramafic rocks in Late-Miocene)

Along the axis in the Chile ridge, magmatic rocks which are mafic to ultramafic are emplaced. For instance, 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 ...

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 Obduction is a geological process whereby denser oceanic crust (and even upper mantle) 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 ...

of the Nazca Plate produced due to the

convergence Convergence may refer to: Arts and media Literature *''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-part crossover storyline that ...

of the overriding South America Plate and the Chile ridge Tres Montes segment. The obduction and the thrusting causes low-pressure metamorphism and forms the ophiolite complex. This metamorphism indicates the onset of

hydrothermal alteration Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical co ...

in a spreading ridge environment. 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.

= Characteristics of Taitao Ophiolite

= Taitao

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found ...

lithosphere forms a special sequence from the top to bottom:

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of discont ...

s, sheeted dike complex,

gabbros Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

and

rock units. For the ultramafic rock units, it proved that there are at least two melting events that happened before. The thermal configuration and the structure of the subduction zone affects the interactions of the

oceanic 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 or ...

, 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. 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 Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is ...

of the sub-arc mantle wedge, creating a distinct chemical composition of magma generations. That means by understanding the composition of the magma, specific conditions of subduction systems can be known. This has found that the

produced by the subduction of the ridge causes the generation of Alkaline basalts. The ridge-trench convergence and slab window generation aids the

emplacement Emplacement may refer to: * A place where something is located * Fortification ** Artillery battery ** Casemate, fortified gun emplacement ** Redoubt, enclosed defense emplacement * The geological process of pluton emplacement See also * * * P ...

of the Alkaline basalts.

Bathymetry

Bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...

of the Chile ridge is inspected, which is the submarine topography that studies the depths of landforms under the water level. 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 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 ...

deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defor ...

which forms numerous tiny faults. The continuous

divergence In vector calculus, divergence is a vector operator that operates on a vector field, producing a scalar field giving the quantity of the vector field's source at each point. More technically, the divergence represents the volume density of t ...

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.

The Chile Ridge movement

The spreading of the Chile Ridge

The Chile Ridge is formed by the divergence of the Nazca and Antarctica plates. It is spreading actively at the rate of about 6.4 – 7.0 cm/year since 5 Ma to present. 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. According to the results from space geodetic observations, Nazca-South America converges four times faster than that of Antarctica-South America. 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.

Migration and subduction of the Chile ridge

The subduction of the ridge started is an oblique subduction with 10° – 12° oblique to the Chile trench since 14 Ma, which subducts beneath the southeastern Southern Patagonia. 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. Due to the difference in the convergence rate, the formation of a

is favoured. Slab window is a gap underneath the South America Plate, where the overriding South America Plate has only little

lithospheric mantle The lithospheric mantle is the uppermost solid part of Earth's mantle. The lithospheric mantle is subdivided into the subcontinental lithospheric mantle associated with the continental lithosphere and oceanic lithospheric mantle, associated with ...

supporting it and is directly exposed to the hot asthenospheric mantle. The experimental results from the

magnetic anomalies In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

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° to 54°S) subsequently. From 10 Ma to the present, Chile Ridge was separated into several short segments by the

s, and the segments of the ridge are subducted between 46° to 48° S. The above findings have proven that Chile Ridge has been encountered a northward migration. 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. 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.

Associated seismicity

In the Chile Ridge Subduction Project (CRSP), seismic stations are deployed in the Chile Triple Junction (CTJ). The

activity and

seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 19 ...

are mainly driven by the subduction of Chile Ridge. 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. Moderate to high offshore seismicities for

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

higher than 4 is detected in the segmented Chile Ridge as well as the transform faults. 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

of the Liquiñe-Ofqui fault system.

Chiloe Microplate

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.

Seismicity of Liquiñe-Ofqui fault system in the Aysén Region

The

Liquiñe-Ofqui fault The Liquiñe-Ofqui Fault is major geological fault that runs a length of roughly in a NNE-SSW orientation and exhibits current seismicity. It is located in the Chilean Northern Patagonian Andes. It is a dextral intra-arc strike-slip fault. Most ...

system is a right-lateral strike-slip fault separating Chiloe Microplate and the South America Plate. The northward migration of Chiloe Microplate along the Liquiñe-Ofqui fault creates the Golfo de Penas basin in the late Miocene period. The Liquiñe-Ofqui fault is a fast-slipping fault (with a geodetic rate of 6.8–28 mm/yr). 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. Throughout history, only limited seismic studies have been conducted in the

Aysén Region The Aysén del General Carlos Ibáñez del Campo Region ( es, Región de Aysén, , '), often shortened to Aysén Region or Aisén,Examples of name usage1, official regional government site refers to the region as "Región de Aysén"., Chile's of ...

, southern Chile. There is only an event of seismic magnitude higher than 7 happening in 1927. 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. Recently, 274 seismic events have been detected in 2004–2005.

Seismicity of the Patagonian Slab Window

There is an intraplate seismicity gap between 47° to 50°S (area with abnormal high heat flow), which coincides with the

Patagonian 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 ...

, 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. (Fig-5)

Geological Formation related to the Chile Ridge Movement

Consequence of the Subduction of the Chile Ridge

Patagonia Slab Window

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. 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 Mantle convection is the very slow creeping motion of Earth's solid silicate mantle as convection currents carrying heat from the interior to the planet's surface. The Earth's surface lithosphere rides atop the asthenosphere and the two for ...

velocity, as the production of magma in the subduction zone is mainly driven by the hydration that lowers the

of the crust. A

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc lo ...

gap is formed above the slab window as the magma melted from the crust convects slowly which hampers the

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a ...

. 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. An intraplate

seismic gap A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long ...

is recorded which coincides with the Patagonian slab window location. The experimental results of the P-wave travel-time

tomography Tomography is imaging by sections or sectioning that uses any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, astrophysics, ...

show there is low-velocity zone in the predicted slab window location, migrating eastward with increasing depth. Slabwindowmapviewver

Tectonic Erosion and Emplacement of Ophiolite

Other than the generation of the slab window, the Chile Ridge subduction into the Chile Triple Junction also influences the

. First of all is the tectonic erosion, Neogene

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

volcanism and

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal th ...

in Late Cretaceous. 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

of ophiolite complex.

Chile Triple Junction

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.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. Since then, the Chile Triple Junction has arrived to its current position in the western

. 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.

Ridge Axes

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 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 scien ...

axial rift valleys. With the help of

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...

altimetry data and magnetic data, gravity lows are discovered near the ridge axes.

Fracture Zones

It is also named as fault zones. They are the

transform faults A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...

and separate the Chile Ridge into segments, , causing the entire ridge axis to trend southeastward.

Fracture zones Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...

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). Through various research on the magnetic and

bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...

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 The East Pacific Rise is a mid-ocean rise (termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), a divergent tectonic plate boundary located alon ...

as well as the low-velocity-spreading

Mid-Atlantic ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North ...

Segmentation of Chile Ridge

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. 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. Bathymetry (1)

= Hourglass morphology

= Deep

contours Contour may refer to: * Contour (linguistics), a phonetic sound * Pitch contour * Contour (camera system), a 3D digital camera system * Contour, the KDE Plasma 4 interface for tablet devices * Contour line, a curve along which the function has a ...

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)

= Valdivia Fault Zone

= 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. 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.

Interaction between Chile Ridge and Chile Trench

Geophysical Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' some ...

and geothermal analysis in the southern Chile Triple junction has been examined. Magnetic and

bathymetric Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water d ...

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. 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. Chile Ridge segment within the Taitao

Fracture Zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on eit ...

collides with the southern end of the trench. The collision of the ridge may also be associated with the

process onto the landward trench slope. Geothermal data along the southern Triple Junction are measured. The

heat flow Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

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. 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. Also, the hypothesized conductive heat flow is consistent with the heat flow data from BSR.

Importance of the spreading ridge subduction

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

Other example of spreading ridge subduction

The Kula-Farallon/Resurrection ridge subduction

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. The ridge subduction controls the magmatism of the North American boundary.

References

{{coord missing Geology of Chile Underwater ridges of the Pacific Ocean