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Landforms · Marine Geology
Oceanic plateaus are broad submarine regions where oceanic crust is much thicker than normal, usually because unusually large volumes of magma entered and erupted through the lithosphere.
An oceanic plateau is more than a broad high on the seafloor. Beneath its sediment and volcanic surface lies an enlarged crustal body built from lava flows, dikes, sills, gabbroic intrusions, and other igneous material. Some plateaus formed during short periods of very high magma output, while others developed through several volcanic stages linked with spreading ridges, rifting, or changing plate boundaries.
The term describes a class of submarine landforms rather than one formation history. Oceanic plateaus can differ greatly in age, crustal thickness, shape, degree of rifting, sediment cover, and later interaction with subduction zones.
Landform Note
The word plateau refers to regional relief. An oceanic plateau does not need a perfectly flat top. It may contain volcanic massifs, faulted blocks, ridges, troughs, sedimentary basins, escarpments, and later seamounts.
What Qualifies as an Oceanic Plateau?
Geologists identify oceanic plateaus through a combination of bathymetry, crustal structure, rock composition, geochemistry, and tectonic setting. A broad submarine rise alone is not enough.
Normal oceanic crust is commonly about 6–7 kilometres thick. Oceanic plateau crust can be far thicker, often reaching roughly 15–30 kilometres in strongly developed provinces and locally more in their thickest interiors. Much of this added material may lie below the erupted lava sequence.
| Feature | Typical Form | Crustal Character | Difference from an Oceanic Plateau |
|---|---|---|---|
| Oceanic plateau | Broad elevated submarine province, sometimes made of several massifs or blocks | Thickened, mainly basaltic and gabbroic oceanic crust | The comparison landform |
| Seamount | Individual submarine mountain or volcanic cone | Volcanic edifice built on oceanic crust | Usually narrower, steeper, and smaller in regional extent |
| Mid-ocean ridge | Long linear ridge along a divergent plate boundary | Zone where new oceanic crust is produced | Part of an active spreading system rather than a discrete thick-crust province |
| Aseismic ridge | Long ridge or volcanic track away from an active spreading axis | Variable crust, often linked with hotspot or plate-motion history | Usually more linear and may form progressively as a plate moves |
| Submerged continental plateau | Broad underwater high associated with continental crust | Thinned or modified continental crust | Its deep crust is continental rather than mainly basaltic oceanic crust |
| Microcontinent | Isolated block separated from a larger continent | Continental crust | Represents rifted continental material rather than an enlarged oceanic magmatic province |
Common Mix-Up: Names such as rise, ridge, bank, and plateau do not by themselves identify crustal type. Seismic velocity, gravity, magnetic mapping, drilling, and rock chemistry help determine what lies beneath the seafloor.
Why Many Oceanic Plateaus Are Large Igneous Provinces
Many oceanic plateaus belong to the broader geological group called large igneous provinces. These regions formed when magma production rose far above the amount normally associated with ordinary seafloor spreading or isolated volcanoes.
On a continent, such an event may leave widespread flood-basalt sheets. In an ocean basin, large volumes of magma can thicken the crust over hundreds or thousands of kilometres and build a broad submarine plateau.
The visible lava is only part of the magmatic system. Magma can remain below the seafloor as dikes, sills, plutonic bodies, gabbroic layers, and additions near the base of the crust. A plateau may therefore contain far more igneous material than its surface relief suggests.
Oceanic plateau formation also does not require every eruption to occur at the same time. Some provinces record one dominant volcanic pulse followed by smaller episodes. Others contain sectors formed at different times as plate boundaries shifted or magma production moved.
How Plateau-Scale Magmatism Builds Thick Oceanic Crust
The common process begins when mantle material rises and undergoes partial melting as pressure falls. Large amounts of melt can then move into oceanic lithosphere and eventually reach the seafloor. The amount and distribution of magma depend on mantle temperature and composition, lithospheric thickness, fractures, and nearby spreading systems.
Mantle Material Rises
Hot or easily melted mantle moves upward. Lower pressure allows part of it to melt before reaching the base of the crust.
Large Melt Volumes Collect
Melt separates from mantle rock and gathers beneath the lithosphere. Thin crust or existing fractures can focus magma toward particular areas.
Dikes and Sills Move Magma
Steep dikes carry magma upward, while sills spread laterally through weaknesses in the crust. Much of this magma may cool before erupting.
Submarine Lava Builds the Upper Surface
Pillow lava, sheet flows, massive basalt, and volcanic debris accumulate across the seafloor. Repeated eruptions can cover older oceanic crust.
Cooling, Faulting, and Sediment Reshape the Plateau
After the main volcanic phase, the crust cools and subsides. Sediment covers the volcanic surface while faults, rifting, and later volcanism alter its original relief.
Mantle Heat and Mantle Composition
Hotter mantle can produce more melt during decompression, but temperature is not the only control. Mantle composition also matters. Material containing components that melt more readily can generate unusually large magma volumes without requiring the same temperature anomaly everywhere.
Geochemical data from oceanic plateau basalts are therefore used to examine both temperature and source composition. Isotope ratios and trace elements can also indicate whether more than one mantle source contributed to the same province.
Why Spreading Ridges Can Change Plateau Growth
Oceanic lithosphere is thin and fractured near a spreading centre. Magma can use these weaknesses to rise more easily than through an older, colder plate. If an unusually productive mantle source lies close to a ridge, magma may spread along ridge segments instead of building one circular volcanic centre.
This helps explain why some oceanic plateaus contain chains of massifs, elongated highs, or structures aligned with former spreading axes.
Triple Junctions Can Redirect Magma
A triple junction is a place where three plate boundaries meet. Where the boundaries are spreading ridges, three fracture systems can influence where magma enters the crust. Changing ridge geometry may move the main volcanic centre through time and leave several large volcanic units rather than one central edifice.
Shatsky Rise is a well-known example of an oceanic plateau whose development is closely tied to an ancient spreading triple junction, but the detailed reconstruction of that plateau belongs to its individual geological history.
Submarine Eruptions Produce Several Lava Forms
Water depth, eruption rate, magma supply, and local slope influence the shape of submarine lava. Pillow lavas form when lava chills rapidly in seawater. More sustained eruptions can produce sheet-like or massive flows capable of covering much larger areas.
If a growing plateau reaches shallow water, its rocks may also preserve wave-worked deposits, shallow-marine sediment, erosion surfaces, or evidence that individual volcanic highs briefly stood above sea level.
Much of the Added Crust Can Form Below the Seafloor
The erupted basalt layer may represent only a fraction of the entire igneous body. Magma that does not reach the seafloor can crystallize within the crust as dolerite, gabbro, layered intrusions, and other dense igneous material.
Large additions near the base of the crust can push the crust–mantle boundary deeper. This is one reason the depth of the Mohorovičić discontinuity, or Moho, is useful when studying oceanic plateaus.
Field Note
Ocean drilling samples narrow vertical sections. Drill cores can reveal lava and sediment directly, while seismic surveys are needed to estimate crustal thickness and trace deeper structures across the wider plateau.
The Layered Structure Beneath an Oceanic Plateau
An oceanic plateau is not a single mass of basalt. Its structure usually changes from the seafloor downward and from the thick interior toward thinner margins.
| Structural Level | Common Materials or Features | What It Can Record |
|---|---|---|
| Sedimentary cover | Pelagic clay, carbonate sediment, siliceous sediment, volcanic ash, shallow-water beds | Subsidence, water depth, ocean productivity, currents, and pauses in volcanism |
| Extrusive upper crust | Pillow lava, sheet flows, massive basalt, volcanic rubble | Eruption style, lava chemistry, water depth, and separate volcanic pulses |
| Dike and sill zones | Steep feeder dikes and horizontal intrusions | Magma pathways and crustal stress directions |
| Middle crust | Basalt, dolerite, gabbro, and intrusive complexes | Magma storage and crystallization inside the crust |
| Lower crust | Gabbroic cumulates and high-velocity igneous material | Deep crystallization and addition of magma below the upper volcanic section |
| Moho and upper mantle | Crust–mantle boundary and modified mantle rock | Total crustal thickness and changes caused by large-scale magma movement |
Sediment Can Hide the Volcanic Surface
Once eruption rates fall, marine sediment begins to accumulate across the plateau. Carbonate-rich sediment may cover higher surfaces, while depressions and basins can collect much thicker sequences.
Millions of years of burial can smooth the modern bathymetric appearance even where the volcanic basement below remains irregular. Faults, buried massifs, lava escarpments, and old channels may therefore be clearer on seismic profiles than on present-day seafloor maps.
The Thickest Material May Lie in the Middle and Lower Crust
Seismic waves move at different speeds through sediment, basalt, gabbro, and mantle rock. These changes allow geophysicists to estimate crustal layering even where drilling reaches only the upper few kilometres.
Many oceanic plateaus contain thick middle- and lower-crustal layers. This shows why crustal thickness cannot be estimated from the visible lava pile alone.
The Plateau Margin Usually Thins
Crustal thickness commonly changes across a plateau. An interior massif may contain a deep magmatic root, while outer sectors grade toward ordinary oceanic crust. Faulting and later rifting can make the transition even more uneven.
For this reason, a single crustal-thickness figure rarely represents an entire oceanic plateau.
Formation Models for Oceanic Plateaus
Oceanic plateaus do not all require the same geological mechanism. Several formation models are used, and more than one process may operate during the growth of a single province.
Mantle Plume Head Model
In the classic plume model, a broad body of unusually hot rising mantle reaches the base of the lithosphere. As the mantle rises, decompression produces large quantities of basaltic melt over a wide area.
A strong early pulse may build most of the plateau in a relatively short geological interval. Later, a narrower zone of mantle upwelling may continue to feed smaller volcanic features as the plate moves.
Evidence considered when testing this model can include high magma volume, geochemical signals linked with deep mantle sources, patterns of uplift and subsidence, age progression, and possible younger volcanic tracks.
Plume and Spreading-Ridge Interaction
A mantle melting anomaly positioned near a spreading ridge can interact with thin lithosphere and existing fractures. Magma may then be distributed along the plate boundary rather than remaining concentrated directly above one source.
This type of setting can produce broad crustal thickening together with ridge-aligned volcanic structures. Magnetic lineations are especially useful because they can show whether ordinary seafloor spreading continued while the plateau was being built.
Triple-Junction Interaction
Where several spreading arms meet, magma pathways can be influenced by changing plate geometry. Ridge jumps, plate rotations, and shifts in spreading direction may leave a plateau made of several age-progressive volcanic units.
This process is especially relevant where bathymetry and magnetic lineations show that plateau construction occurred directly across a former plate junction.
Rifted Magmatic Plateau Development
Some thick magmatic provinces form during continental breakup or early ocean opening. As extension continues, the growing volcanic region may split into separate blocks. New oceanic crust can then form between the fragments.
The surviving highs may later appear to be unrelated plateaus even though plate reconstruction, rock ages, and geochemistry suggest that they once belonged to a wider magmatic system.
Geology Note
Labels such as plume-related, ridge-related, and rifted magmatic plateau describe geological interpretations. They should not be treated as rigid categories when several processes operated in the same province.
Why Oceanic Plateaus Are Rarely Uniform
Large oceanic plateaus can cover areas comparable with major land regions, but their internal structure may change sharply across relatively short distances.
- Magma output changes through time. Some sectors receive far more lava and intrusive material than others.
- Older fractures guide magma. Weak zones in existing oceanic crust can focus dikes and volcanic centres.
- Spreading systems move. Ridge migration can shift the main area of crustal growth.
- Rifting thins the plateau. Extension can divide one magmatic province into fault-bounded blocks.
- Later volcanism modifies older crust. Seamount chains and younger volcanic centres may grow on top of the plateau.
- Subduction removes margins. Parts of the original province may be carried into the mantle.
- Sediment hides basement relief. Thick marine deposits can conceal volcanic structures below a smooth modern surface.
Major Oceanic Plateaus
The examples below show the range of geological settings found among oceanic plateaus. Formation ages and crustal measurements are approximate because boundaries and seismic interpretations differ between studies.
| Plateau or Plateau System | Ocean Region | General Age | Main Geological Trait |
|---|---|---|---|
| Ontong Java Plateau | Western equatorial Pacific | Early Cretaceous main construction | Extremely thick oceanic crust produced by very large magma volumes |
| Kerguelen Plateau–Broken Ridge | Southern Indian Ocean | Cretaceous to Cenozoic development | Long magmatic history with rifting and local continental material |
| Shatsky Rise | Northwest Pacific | Late Jurassic–Early Cretaceous | Several volcanic massifs formed near a spreading triple junction |
| Manihiki Plateau | Southwest Pacific | Early Cretaceous | Rifted and internally variable oceanic plateau crust |
| Hikurangi Plateau | Southwest Pacific near New Zealand | Early Cretaceous | Plateau crust later carried toward an active subduction margin |
| Caribbean–Colombian Oceanic Plateau | Caribbean region | Mainly Cretaceous | Thickened oceanic crust later fragmented by collision and subduction |
| Alpha–Mendeleev Ridge Complex | Arctic Ocean | Mainly Cretaceous magmatism | Broad volcanic submarine high whose exact classification and boundaries remain debated |
Geography Note
Oceanic plateau boundaries are geological rather than political or coastal. Some disappear beneath thick sediment, cross modern plate boundaries, enter trenches, or survive partly as faulted rock bodies exposed around island arcs and continental margins.
Western Pacific
Ontong Java Plateau
The Ontong Java Plateau north of the Solomon Islands is the largest commonly recognized oceanic plateau. Its central areas contain oceanic crust several times thicker than normal, while its margins become thinner and interact with surrounding basins and plate boundaries. Most of its construction occurred during an Early Cretaceous episode of very high magma production. Its scale makes it an important example of how large igneous provinces can build thick crust without creating a continent.
Southern Indian Ocean
Kerguelen Plateau–Broken Ridge
The Kerguelen Plateau is a long submarine volcanic province between Australia and Antarctica. Its geology records several stages of magmatism rather than one short eruption period. Parts of the system also contain evidence of older continental material associated with Gondwana breakup. Broken Ridge was once connected with the larger province before later spreading separated it. The system shows how volcanic construction, continental fragments, shifting ridges, rifting, and long subsidence can occur within the history of one plateau complex.
Northwest Pacific
Shatsky Rise
Shatsky Rise is a large volcanic plateau composed of several major massifs arranged across the northwest Pacific. It developed near an ancient spreading triple junction, making it useful for studying how unusually large magma supplies interact with active seafloor spreading. Magnetic lineations and drilled basalt help connect plateau construction with changing ridge geometry. Its southwest-to-northeast arrangement also records a shift in volcanic activity through time rather than growth around one fixed central cone.
Southwest Pacific
Manihiki Plateau
The Manihiki Plateau is an Early Cretaceous oceanic plateau marked by rifted blocks, deep troughs, and large changes in crustal structure across the province. Geological reconstructions have examined whether it once formed part of a wider Pacific magmatic region together with other Early Cretaceous plateaus. Its present form is useful for showing how an initially broad volcanic province can be stretched and divided after its main period of crustal growth.
Southwest Pacific
Hikurangi Plateau
The Hikurangi Plateau lies east of New Zealand and represents thickened oceanic crust that has travelled far from its formation setting. Its structure varies across the plateau, and its western margin now interacts with the Hikurangi subduction zone. The plateau is often considered in reconstructions of Early Cretaceous Pacific magmatism, but its later movement and partial subduction have altered the shape that existed when the crust first formed.
Caribbean Region
Caribbean–Colombian Oceanic Plateau
The Caribbean–Colombian Oceanic Plateau forms part of the thickened Cretaceous crust preserved beneath the Caribbean region and in tectonic fragments around its margins. Plate motion carried the province into subduction zones and continental boundaries, so it no longer appears as one simple submarine high. Parts of its volcanic record are now preserved beneath the sea and in accreted rocks around Central America, Caribbean islands, Colombia, and the northern Andes.
Arctic Ocean
Alpha–Mendeleev Ridge Complex
The Alpha–Mendeleev Ridge complex forms a large submarine high in the Amerasia Basin of the Arctic Ocean and is widely linked with Cretaceous magmatism. Thick sediment, sparse direct sampling, and difficult survey conditions make its deep structure harder to define than many Pacific examples. It also shows why surface names alone can be misleading: a feature called a ridge can contain broad volcanic crust that shares several traits with oceanic plateaus.
How Scientists Identify Plateaus Hidden Beneath the Ocean
Most oceanic plateaus cannot be studied directly across their full area. Their surfaces lie under kilometres of seawater, while their deeper crust may extend tens of kilometres below the seafloor. Geologists therefore combine several types of measurements.
Surface Form
Multibeam Bathymetry
Maps massifs, faults, escarpments, troughs, seamounts, and sedimented surfaces in detail.
Shallow Structure
Seismic Reflection
Images sedimentary layers, buried volcanic surfaces, faults, and reflectors within the upper crust.
Deep Structure
Seismic Refraction
Measures seismic velocities through the crust and helps estimate internal layering and Moho depth.
Plate History
Magnetic Mapping
Traces seafloor-spreading lineations, volcanic boundaries, dike orientations, and later magnetic overprinting.
Rock Record
Ocean Drilling
Recovers lava and sediment for age dating, geochemistry, alteration studies, and reconstruction of past water depth.
Deep Earth
Seismic Tomography
Maps broad differences in seismic velocity that may reflect mantle temperature, composition, or altered lithosphere.
Gravity Reveals Buried Crustal Changes
Variations in crustal thickness and density affect the gravity field. Ship measurements and satellite-derived gravity can trace large structures between seismic survey lines and help identify buried plateau margins where sediment has softened the bathymetric relief.
Gravity cannot identify rock composition by itself. It works best when models are compared with seismic data and geological samples.
Magnetic Lineations Record Seafloor Spreading
Oceanic crust records changes in Earth’s magnetic field as basalt cools. Alternating magnetic bands can reveal the direction and age pattern of ancient spreading.
Where lineations continue through or around a plateau, they may show whether the province formed on pre-existing crust, directly at a spreading centre, or while ridge geometry was changing.
Paleomagnetism Helps Restore Plate Motion
Magnetic minerals locked into cooled lava can preserve information about the latitude and orientation of the plate when the rock formed. These measurements help test whether widely separated plateau fragments could once have occupied nearby positions.
Age, paleolatitude, geochemistry, and plate-motion models must agree before two separated features can reasonably be reconstructed as parts of one former province.
How Oceanic Plateaus Rift and Break Apart
Thick magmatic crust can later be stretched by tectonic extension. Faults divide the plateau into blocks, crust thins within rift zones, and continued spreading may create ordinary oceanic crust between the separated pieces.
A Broad Magmatic Province Forms
Large magma volumes build thick crust across a wide part of the ocean basin.
Extension Opens Troughs and Fault Zones
The plateau stretches. Normal faults create basins and separate volcanic blocks.
New Seafloor Forms Between Fragments
Continued extension develops into seafloor spreading, placing younger oceanic crust between plateau remnants.
Later Plate Motion Alters the Match
Rotation, sediment burial, younger volcanism, and subduction make the original edges harder to reconstruct.
Rifting is one reason present-day plateau size may differ greatly from the original magmatic province. A large early plateau can survive as several separated highs on different plates.
What Happens When an Oceanic Plateau Reaches a Subduction Zone?
Normal old oceanic lithosphere can descend into the mantle at a subduction zone. An oceanic plateau brings thicker and usually more buoyant crust to the plate boundary, changing the mechanical conditions at the trench.
The result varies from one margin to another. Plateau crust may descend, become partly attached to the overriding plate, flatten the descending slab, or alter the position of subduction.
| Possible Response | What May Happen |
|---|---|
| Plateau is mainly subducted | Much of the thickened crust descends, while upper fragments may be scraped off or faulted onto the margin. |
| Slab angle changes | Buoyant plateau crust can promote a shallower section of the descending slab. |
| Collision deforms the upper plate | Compression and faulting may increase where the plateau reaches an arc or continental margin. |
| Crust is accreted | Fragments can remain attached to an island arc or continent as tectonic terranes. |
| Subduction reorganizes | A trench segment may migrate, weaken, shut down, or be replaced by another plate-boundary configuration. |
Why Thick Crust Does Not Always Stop Subduction
Plateau crust is more buoyant than normal oceanic crust, but this does not make every plateau impossible to subduct. Age, temperature, width, crustal density, plate strength, convergence rate, and the angle at which the plateau reaches the trench all influence the outcome.
A broad, relatively buoyant province may disturb a subduction system more strongly than a narrow, old, or heavily fractured plateau.
Plateau Fragments Can Become Tectonic Terranes
Sections that avoid complete subduction may become attached to an island arc or continental margin. Later faulting, metamorphism, folding, intrusion, and erosion can alter them so strongly that their original submarine form is no longer visible.
Geologists can still identify an oceanic origin through basalt chemistry, deep-water sediment, intrusive rocks, age relationships, and structural position.
How Oceanic Plateaus Affect Marine Geography
An oceanic plateau continues to shape its surroundings long after active volcanism ends. Its elevated seafloor can separate deep basins, redirect bottom currents, influence sediment pathways, and create different marine environments across its slopes and summit areas.
Plateau Relief Changes Deep-Ocean Circulation
Large submarine highs can block or redirect deep-water flow. Currents may accelerate around escarpments, follow plateau margins, or enter gaps between massifs.
These circulation patterns affect where fine sediment accumulates and where stronger currents remove it. They can also help create sediment drifts and erosion surfaces far from the original volcanic structures.
Sediment Collects Unevenly
Broad summit areas, internal basins, and faulted troughs can preserve very different sediment records. Some sectors receive continuous pelagic sediment, while others experience erosion by bottom currents or repeated mass wasting from steep slopes.
As a result, two drill sites on the same plateau may preserve different parts of its volcanic and environmental history.
Plateau Topography Changes Ocean-Basin Depth
Thick crust raises parts of the seafloor relative to ordinary abyssal plains. At the scale of a large province, this reduces the volume available to hold seawater compared with an ocean basin made entirely of thinner crust.
Changes in ocean-basin capacity can contribute to long-term sea-level variation, although ridge volume, thermal expansion, continental ice, and other processes also influence global sea level.
Oceanic Plateau Volcanism and Environmental Change
Very large submarine eruptions can release carbon dioxide, sulfur compounds, metals, and heat into the ocean–atmosphere system. Hydrothermal circulation through hot young crust can also move chemical elements between basalt and seawater.
Some large marine magmatic events overlap in age with major changes in ocean chemistry and marine ecosystems. Establishing a direct connection requires close agreement between eruption timing, gas release, hydrothermal activity, carbon-cycle records, and marine sediment data.
Evidence Limit: The presence of a large igneous province at the same geological time as an oceanic environmental event does not by itself prove cause. Individual provinces require separate age and geochemical evidence.
Water Depth Changes the Environmental Effect
Gas released during an eruption several kilometres below the ocean surface does not behave in exactly the same way as gas released from subaerial lava. Water pressure, dissolution, seawater chemistry, eruption rate, and hydrothermal circulation all affect how volcanic material reaches the atmosphere or remains dissolved in the ocean.
Plateau summits that reached shallow water or emerged above sea level may therefore have produced different environmental effects from eruptions on the deeper flanks.
Why Oceanic Plateau Size and Thickness Values Differ
Oceanic plateaus have no shoreline that provides a simple outer boundary. Researchers may define their limits using bathymetry, crustal thickness, gravity anomalies, magnetic boundaries, or reconstructed volcanic provinces.
Different methods can produce different values without describing different landforms.
- Bathymetric boundary: follows the visible rise above surrounding abyssal seafloor.
- Crustal boundary: follows the area where oceanic crust remains thicker than background crust.
- Igneous province boundary: may include related volcanic crust beyond the obvious bathymetric plateau.
- Rifted fragments: may be counted separately or restored to the parent plateau.
- Subducted sectors: can no longer be measured directly at the seafloor.
- Sediment burial: can hide basement slopes and reduce the apparent surface area.
- Survey spacing: seismic measurements represent individual lines through a much wider three-dimensional structure.
Measurement Note
Area, water depth, relief, crustal thickness, and magma volume are different measurements. A plateau may cover an enormous area without having equally thick crust everywhere, while one central massif may contain a much deeper crustal root than the surrounding plateau.
Oceanic Plateaus Compared with Continental Plateaus
The word plateau is used for both terrestrial and submarine features, but the measurements used to identify them are different.
| Trait | Oceanic Plateau | Continental Plateau |
|---|---|---|
| Main setting | Ocean basin | Continental landmass |
| Main elevation reference | Height above surrounding seafloor and water depth | Height above sea level and surrounding land |
| Typical crust | Thickened mafic oceanic crust | Continental crust of varied composition |
| Common rocks | Basalt, dolerite, gabbro | May include sedimentary, igneous, and metamorphic rocks |
| Main evidence | Bathymetry, seismic surveys, gravity, magnetics, drilling | Topography, field geology, mapping, geochronology, seismic data |
| Surface processes | Marine sedimentation, submarine erosion, bottom currents, mass wasting | Rivers, weathering, glaciers, wind, soil development, slope erosion |
A submerged continental fragment can resemble an oceanic plateau in bathymetry. The distinction depends on the nature of the underlying crust. Thick basaltic and gabbroic crust points toward an oceanic magmatic province, while granitic or other continental crust points toward a rifted continental block.
How Oceanic Plateaus Change Through Geological Time
The appearance of an oceanic plateau at formation may differ sharply from its modern bathymetry. Construction is only the first stage of its history.
- Magmatic growth: large volumes of magma thicken oceanic crust and build broad volcanic relief.
- Cooling and subsidence: hot crust cools, contracts, and generally sinks deeper below sea level.
- Sediment burial: marine sediment covers lava surfaces, fills depressions, and softens relief.
- Faulting and rifting: tectonic extension may divide the plateau or create deep internal basins.
- Later volcanism: younger seamounts, ridges, or volcanic islands may overprint older plateau crust.
- Plate transport: plate motion carries the plateau away from its original mantle and ridge setting.
- Subduction or collision: margins may enter trenches, become faulted, or attach to other crustal blocks.
This history explains why the present outline of a plateau may preserve only part of the original magmatic province.
Terms Used in Oceanic Plateau Geology
| Term | Meaning |
|---|---|
| Large Igneous Province | A region created by magma output far above ordinary background volcanism. It may form on continents or in ocean basins. |
| Oceanic Basement | The solid volcanic and intrusive crust beneath marine sediment. |
| Bathymetry | Measurement and mapping of seafloor depth and underwater relief. |
| Dike | A steep sheet of igneous rock formed when magma fills a fracture and solidifies. |
| Sill | A sheet-like intrusion that spreads mainly parallel to existing rock layers or structural surfaces. |
| Dike Swarm | A large group of related dikes recording repeated magma movement through the crust. |
| Magmatic Underplating | Addition and cooling of magma near the base of the crust, increasing lower-crustal thickness. |
| Moho | The seismic boundary between the crust and mantle. |
| Pillow Lava | Rounded lava forms created when basalt erupts and cools rapidly under water. |
| Pelagic Sediment | Fine sediment that accumulates in the open ocean away from major land-derived sediment sources. |
| Terrane | A fault-bounded crustal fragment whose geological history differs from surrounding rocks. |
| Triple Junction | A place where three tectonic plate boundaries meet. |
Questions That Remain Open in Oceanic Plateau Geology
Do All Large Oceanic Plateaus Require a Deep Mantle Plume?
Deep mantle upwelling remains an important explanation for many large magmatic provinces, but the relative roles of mantle temperature, mantle composition, spreading ridges, and lithospheric fractures differ between plateaus. Some provinces may record strong interaction between deep magma supply and shallow plate-boundary structure.
How Quickly Can Plateau Crust Form?
Rock dating can identify broad volcanic intervals, but the highest magma-output phase may be much shorter than the total age range represented by a plateau. Distinguishing a rapid main pulse from long later activity affects estimates of magma production and environmental effects.
How Much Magma Remains Below the Erupted Lava?
Drilling mainly samples the upper crust, while seismic models infer deeper material. The proportion of erupted lava compared with intrusive and lower-crustal magma remains uncertain for many provinces.
How Often Did Oceanic Plateaus Reach Sea Level?
Shallow-water sediment, erosion surfaces, and terrestrial deposits show that parts of some plateaus once stood near or above sea level. The full extent and duration of emergence are harder to determine because many summit regions were later eroded, submerged, or buried by sediment.
How Much Ancient Plateau Crust Has Been Lost to Subduction?
Oceanic crust is continually recycled into the mantle. Plateaus older than the surviving ocean basins may have disappeared almost completely, with only fragments preserved as accreted volcanic terranes on continents or island arcs.
Where Does an Oceanic Plateau End and an Oceanic Ridge Begin?
Some submarine provinces combine broad plateau-like crust with elongated ridge geometry. Classification is clearest when surface shape is considered together with crustal thickness, rock composition, magnetic structure, and plate history rather than relying on the geographic name alone.